Hi, and welcome to the Neil Ashton Podcast.
In each episode, we explain some of the fascinating ways
that science and engineering are changing the world around us.
We talk to leading engineers from elite level sports like
cycling and Formula One to some of the world's top academics to
understand how fluid dynamics, machine learning and
supercomputing are bringing in a new era of discovery.
We also hear some of their life stories, their career advice,
the lessons they've learned on the way that I hope will be
helpful to you too. So sit back and enjoy this
episode. Hi, and welcome back to the Neil
Ashton Podcast. I just finished recording
today's episode with Professor Brian Launder, the incredible
person who has truly been one of The Pioneers and legends of
computational fluid dynamics and fluid dynamics more broadly.
He is most well known for the k-epsilon model, for the LRR
Reynolds-stress model. And I would argue, and I didn't
fully appreciate it until after actually speaking to him, just
the number of people that he supervised, mentored and
brought, you know, these people like Bill Jones and Kemal
Hanjalić and Michael Leschziner and Tim Craft and Hector
Iacovides, who are people that themselves have gone on to
supervise people. You know, this is the thing with
academia. One of the core roles I believe
of of as a professor is research, of course, but the
people that they nurture and then bring on to go into
industry, go into academia is the real credit.
And so many people have benefited from from what he's
done. It's hard to believe that most
of this stuff was done in the 1970s, fifty years ago.
Today we are still using the K epsilon model.
If you're doing a CFD simulation of many different objects,
whether you know heat transfer cars, engines, you're probably
using what the k-epsilon or some variant of it or, or Reynolds
stress model. And the fact that that was done
in the 70s when computers, you know, he was telling us that you
have to walk up to the building.
There was no SSH remote access punch cards, you know, the codes
were just being written. It was incredible.
I genuinely in awe of the development that happened back
then and it we we went through essentially his life story from
his undergraduate years moving across to the US from Imperial
to then MIT coming back to Imperial, the role of Brian
Spalding, a key interesting one that we reflect on at the
beginning and the end, you know, incredible at that time, the
turbulent time of how the CHAM code came about and some of the
tensions around that. His ultimate move to UMIST now
the University of Manchester. And as I said, the the key
developments around the eddy viscosity model, second moment
closure models, but also things like the wall functions that I
mentioned to him is now even more relevant in the context of
wall-modelled LES etcetera. And just yeah, an incredible
person. And I think some of the advice
and lessons you get from it, it reminds you even the greatest
people have some of the challenges that that we have.
And, and they don't realize at the time the amazing work that
they're doing. But yeah, really, really special
person. And someone I really liked
speaking to, you know, he's a fellow with the Royal Society.
He's he's done so many things. He's you know, how many good
citations, you know, 10s of thousands, super high h-index,
all of all of the things, of course, that a top professor
would have. So if you're looking for the
pinnacle of people in the simulation world, quite a few of
his people he supervised and worked with have now gone off
into some of these major multibillion dollar companies.
In fact, if you use these big simulation codes, many of them
are the foundations are on the work that the professor Brian
Launder was part of or, or or leading.
And so, yeah, really interesting story as as we've ever.
There was lots of things that I could have asked him.
We did talk a little bit about some of the rivalry with
Spalart, Menter and Wilcox and, of course, you know, Professor
Launder is a gentleman. And then I genuinely think his
focus was more on the research. But it's always interesting to
us who used turbulence models to understand, you know, what was
the difference between these these key figures, I guess at
the time. But so I hope you enjoy this
episode. I genuinely really did.
I, I mentioned that I studied the University of Manchester.
I was taught by Professor Launder's.
So it was one of my good friends, Alastair West, who was
also his last PhD student. And yeah, it's it was an honor
to speak to him. And I hope you enjoyed this as
much as I did speaking to him. So sit back and enjoy this
episode with Professor Brian Launder.
Thank you very much for agreeing to do this.
I really appreciate you taking the time to speak to me today.
And I thought maybe it would be good for the people listening
to, you know, hear about your early days, where it all began
and you starting off, you know, what did you do at university?
What was your undergraduate studies?
OK, well that doesn't sound a bad place to start.
Let's let's begin with early 1961.
I was in the final year of my bachelor's program at Imperial
College. I found a topic that really
interested me, convective heat transfer, and I was doing a
final year project on flows related to boiling.
When I heard that the new professor of heat transfer was
going to talk about postgraduate opportunities, I was quite
excited. I made sure to attend because I
knew by then that I would like to do postgraduate work.
So I went along to the meeting that he was to address, and he
probably did talk about the range of opportunities that
there might be. But what I remembered were a
particular sentence or two that he presented us with.
He said, you well know that the college is being rebuilt, and
they're rebuilding it on the same site as the present
building. This will inevitably mean
interruptions and delays. So if you're looking for a fast
PhD, you ought to go elsewhere. This was a very deflating
statement from him. A day or two later, I asked my
closest friend in the course guy called Hugh Kendrick what he
planned to do. He chuckled, looked at me and
said I'll probably go to America.
I fancy doing a master's program at Yale or Princeton.
Which time I interrupted him and said, you're talking rubbish.
What would a top American university do, having a thicko
like you? We both chuckled at that point
and moved on to other things. But you know, when I was alone
reflecting on this in the evening, I thought that's,
that's a pretty neat idea. So I wrote to a half dozen
universities in the USA seeking graduate or postgraduate
engagement there, together with funding.
Nothing happened for several weeks, of course, but then
responses started to come in and I was absolutely delighted.
Princeton offered me a name scholarship that would cover my
tuition fees, my living costs to do research on whatever I
wanted to do. There was a second offer from
MIT that was specifically to work in boiling heat transfer,
which was a subject that I I was really interested in.
However, the downsize was that I had to earn my keep as a
teaching assistant, that I'd spend maybe 15, 20 even 20 hours
a week tutoring students probably brighter than me on on
the various courses they'd be taking.
So I knew where my preference was, but I thought I'd go back
and ask her for an appointment with Brian Spalding to confirm
my choice. His secretary graciously gave me
a 5 minute interview slot. I went in and took perhaps a
minute describing my fortunate pair of choices and he said
Princeton. Huh.
Well, Princeton's Princeton. Bob Drake, who's just
co-authored a heat transfer textbook with Professor Eckert.
But you know, from my meetings
with him, Drake hasn't had an original idea in his life.
Go to MIT with Rohsenow and do boiling heat transfer.
This response somewhat deflated me again, but equally I felt I
had to take take his advice and reluctantly declined the
Princeton scholarship. But before I got to write to
MIT, a counter offer came in from their gas turbine
laboratory and the important difference was that they offered
me not a teaching assistantship, but a research assistantship.
This meant that I would do research on one of their
projects, which would also become my thesis.
This was a no brainer for me at any rate.
So I accepted that offer. I declined the heat transfer
offer, and I'm afraid that from there on in my life, boiling
heat transfer had sunk beneath my horizon.
OK, Well, before I talk about my research at MIT and
thereafter, let me just switch back for a minute to Hugh
Kendrick. We were talking one day and I
said to him, hey, I have accepted a postgraduate position
at MIT, where are you going? You'd talked about going to
Princeton or Yale. I suddenly realized I was
talking that someone with the blood draining from his face.
He was literally dumbfounded at what I told him.
Eventually he muttered that he had a he had a graduate
apprenticeship, signed up with Vickers, that he hadn't even
been looking at other opportunities.
He'd go and complete his postgraduate apprenticeship with
them. But then I could almost see the
wheels turning around in his brain.
He said with you could see growing confidence, he said, But
I was under 21 when I signed that contract.
It's not enforceable. And I'm sure MIT will take in a
thicko like you. They'll, they'll find a place
for me. Well, he was right.
They did find a place for him, but by then it was two or three
months after I'd been in touch with them.
They'd allocated all their funding for the year.
However, not to be deterred, he applied to Caltech on the other
side of America and was offered a teaching assistantship.
And that was in August 1961. He and I sailed across in a very
tiny cabin on the Queen Mary together.
Thereafter I caught the train up to MIT, or rather to Boston.
But then Boston is just across the Charles River in Cambridge
and not a just a short distance.
He flew out to Los Angeles and indeed made the rest of his life
in America that. That's that's amazing.
And I I'm more interested and I don't know if other people
hearing this is the comment about sailing across from the
Queen Mary, mainly because now if I go to America and it'll
probably the same for you, you know, it's a flight.
How long did it take on the boat?
It was it was a five-day voyage. It was convenient because we
worked on 25 hour days so that so that we are on the right
time. When we finally arrived in New
York, it was fine, fine sea journeys, a bit boring, you
know, try to amuse oneself. We had a tiny cabin, but we
would sneak through into the, I'm not sure if it was first
class or second class areas and were able to watch films and and
and so on in their luxury, luxury cinemas.
And so that they had on. It was an interesting experience
to do once. The other thing I remember was
that as we got close to New York, you close to?
Yeah, the final destination, the air became more and more humid.
So now I remember a site sailing
past the Statue of Liberty. Of course.
But it was absolutely 9090% humidity by then it it was
difficult. Anyway, that must have been a
moment, though, to see the Statue of Liberty coming to
America with your friend. Yeah, that's a that's a great
point. So what happened then when you
got to to MIT? How did you decide what research
projects to welcome? Well, I was simply checked in
there and they gave me a folder with perhaps 15 research
projects summarized in there, the sufficient amount of
background that one could make a decision, and I knew pretty
much straight away what my choice would be.
At Imperial I'd learned the rudiments of boundary layer
transition. That is to say, a boundary layer
developed initially was laminar, but then when the Reynolds
number got high enough, conditions were right for a
transition to a turbulent boundary layer and there and
turbulent it remained. But this this outline
description that I was reading said that couple of Soviet
scientists had found that in supersonic flow, if a turbulent
boundary layer was passed around what is called a a
Prandtl–Meyer expansion, essentially that's a series of
waves that one might go through in turning a corner and the
flow is through that expansion greatly accelerated.
They found that downstream they had a laminar boundary layer
growing again. So this project outlines said
you will determine whether in subsonic flow a boundary layer
that's strongly accelerated also can revert back to
turbulent—sorry, to laminar and I knew I had to take that it, it
just seemed very a very interesting topic and it
occupied the next three years of my life doing doing research
there. And the outcome was that yes,
you could make a turbulent boundary layer go back to
laminar or at least towards laminar.
I established the acceleration parameter, dimensionless
acceleration parameter that would determine when that would
take place and how roughly how big the parameter was.
I even developed what would be called a simple integral profile
method of predicting the phenomenon based on the idea
that whilst the viscous stresses were greatly increased by the
acceleration, that happened too quickly for the turbulent
stresses to respond. So I just left those as they
were and doing calculations based on that idea pretty much
imitate mimic the experiments that I'd.
OK, so now having finished my work at MIT, what next?
There were there were jobs available for PhD graduates from
MIT offering $14,000 or so a year, but I wasn't eligible to
apply for those. I'd taken a a Fulbright travel
grant to come across to the US, but remember that at the end of
it, I had to go back. So finding a job back in
England, I'd had one or two offers came in for postgraduate
research studentships. Not studentships, postgraduate
employment at government laboratories like the National
Gas Turbine Establishment, central electricity research
labs, and so on. They were.
They weren't uninteresting, but they didn't quite tick all the
boxes. So I decided to write to Brian
Spalding again and wondering whether there was a post and he
said send a CV. So I sent a CV of what I'd
accomplished and I just was working on proofs of the 1st
paper that I'd written and I decided to send those along too
for good measure. It may sound a long time.
Everything was roughly 2 weeks between writing and getting.
I was just. Going to say yeah.
It wasn't. E-mail.
Yeah, yeah, there wasn't the e-mail response.
So anyway, 2 weeks later I I got a note from Spalding saying I
could expect the offer of a lectureship shortly, and sure
enough, two or three days later there was a formal note from
the Registrar's department offering me a position as a
lecturer at the bottom of the lecturer scale, which at the
time was 1400 lbs a year. It didn't compare very well with
what I could have earned in the USA if I'd been eligible, but I
forget this was Imperial College in London.
I was also awarded London Allowance and this was an extra
£60 a year. So I, I accepted like a shot and
my early years at Imperial College were, were were just
delightful. I'd really a very light teaching
load, but an interesting teaching load.
It was a master's level course.
I was asked to take in fluid mechanics.
I had plenty of time free to try and get research students.
Sorry, research funding, but then I mentioned research
students. There was also an important
element there, Brian Spalding said.
Would I take over as my administrative load the process
of research student admissions? It meant that I, I looked at all
the proposals that came in, collected further references if
these weren't provided, distributed the applications to
members of staff that I thought might be interested in taking
them and so on. But naturally I got first sight
of all of the students, and it was from that site that I was
able to recruit both Bill Jones and Kemal Hanjalić the projects
as my first PhD students. Now, viewers may well have heard
of these names because they've they've both gone on to very
successful academic careers and published extensively in
Turbulence Modelling. Can I just ask you a question at
that point? Sure.
How? How did it feel to go back to
London? Because you've gone to Boston,
you've gone to MIT. Was it almost a nice feeling to
come back now as a lecturer, not as a student be teaching?
You know, how did it feel to come back there?
Did it feel like progression with Spalding now as a fellow
member of the academic staff? I don't think I I felt was
terribly conscious of a change of status.
What I was aware of didn't, doesn't relate directly to your
question, but was that some of the research students whom I got
to know a bit while I was doing my final undergraduate
year experimental special tasks, they were still there
working on their pitch. So it very much brought home to
me Spalding his comment that if you want a quick PhD, go
elsewhere. Yeah.
OK. OK.
So you sort of skipped ahead a little bit, almost, yeah.
Yeah. So how so how about, you know,
the research sort of project? How about with with Bill?
Jones, Bill Jones I basically continued PhD research, only we
arranged that he would simply look at one particular
configuration of acceleration and that was flow between
converging planes. What I mean by converging planes
is we measured the boundary layer developing on that surface
and the and the other wall just sloped like this.
It's a very special geometry so far as accelerating boundary
layers is concerned because the thickness of the boundary layer
goes down strictly in proportion to the velocity going
up. So the Reynolds number of the
flow reaches an equilibrium in which it stays constant
thereafter and also the acceleration parameter
determining the reversion to laminar flow that also stays
constant. And what we discovered there
that there wasn't just a single point first of all for various
levels of the acceleration parameter, you actually got a
frozen boundary layer was dissimilar from a turbulent
boundary layer. And this the viscous sub layer
was getting progressively thicker and thicker in what was
still a turbulent flow, a self preserving turbulent flow until
you reached a critical acceleration.
And at that level it you had a complete collapsed to turbulent
flow. So a a lot more came out from
from Bill Jones's study than I had I had achieved.
As for Kemal, we actually looked at a project sponsored by the
Berkeley Nuclear Laboratories. They asked us to determine
whether for flying a duct, whether the position where the
velocity reached its maximum would coincide with where the
turbulent shear stress fell to 0.
They'd been doing tests themselves in flow through an
annulus with a rough inner core tube and a smooth outer
containing tube and had assumed that there was this coincidence
and it gave them very hard to understand values for the
respective shear stresses on the rough and the smooth surface.
Could we sort it out, Judy? We did we he didn't look at an
annulus, we looked at parallel flow between parallel plates and
found there was a huge difference.
That was a thesis very well, very well completed by Kimo.
Now I think the next point I should mention was research that
Brian Spalding and his brilliant student Suhas Patankar had
done. They produced a very efficient,
very easy to use boundary layer code.
The only thing that it was weak on was its model of turbulence.
It it had the mixing length
hypothesis. Prandtl's 1925 paper.
In there, Spalding realised that what he needed was a much more
sophisticated model, one that had individual velocity and
length scales of turbulence available, and not only the
these scales would be affected by diffusion, convection and
various source and sink terms. So he'd obviously chosen the
turbulence energy as one of them.
But then there was the issue of what would you use to get the
turbulent length scale didn't have to be the length scale
itself because you already were solving a transport equation
for the kinetic energy K. So any combination of K with L
would be a possibility. Indeed.
Wolfgang Rodi, Spalding's student adopted the product of
K * L where whereas Brian Spalding himself had an
individual project underway and he chose something he called
W, which basically amounted to K divided by the square of
length scale. OK, well one day Spalding said
to me, hey, would you like to join our group?
I put it to Bill and Kimmo and they thought that sounded a neat
idea. By then we'd started to explore
elaborations of the mixing length hypothesis, but although
we've published several papers on the topic, it clearly wasn't
going to get anywhere. So one thing I should say
though, is that Kemal Hanjalić came from Yugoslavia and
Yugoslavia was a communist country at the time.
Naturally then he had learned Russian in school and that meant
he could, he could have ready access to the Russian literature
and came across a paper by somebody called Davidov, which
advocated in an otherwise totally unusable turbulence
model, but it advocated the use of epsilon, the energy
dissipation rate, OK, of, of turbulence that appealed to us
just physically. It was something that one could
put one's hand on and hopefully one day be able to measure
accurately. And thus that was what we chose.
We produced that, I say we, but
I was sitting back, it was my research students that that were
doing the computation. We produced the version of that
and we're delighted to discover that precisely the same model
enabled us to compute both the free flows, that is to say of of
mixing layer or a plane jet, but with the same model that we
used to compute flow along a flat plate.
Neither of the options that Spalding and Rodi were using
achieved that. So it it was indeed real
progress. And fairly soon thereafter,
Brian Spalding advocated that the group's work should focus on
what he called the k-epsilon model rather than either of the
alternatives. Of course, this model that we
arrived at, the k-epsilon eddy viscosity model, wasn't any good
as it stood for either Bill or Kimo's research.
It needed great extension. For example, in Bill's case, he
had to deal with situations where one started with a
turbulent boundary layer and it went back to or towards lamina.
And so with the inner boundary condition that was being used
next to the wall wasn't strictly a wall boundary condition.
It assumed that across the viscous sub layer there was a
universal velocity profile. And so we didn't need to go
actually to the wall. We'd make our boundary condition
out in the fully turbulent region just a millimetre or so
from the wall. That meant that he had to
develop and extend his model and it it was a major task so that
it included all semi viscous effects that would modify both
kinetic energy that that wasn't that difficult, but also also
energy dissipation rate. And this one was flying blind.
There was no experience in this.
So he, he did a very good job and I'm glad to say that the
paper he and I produced describing it as being cited a
large number of times over 6000. I think likewise for chemo, he
had been asked by sponsors to explain or indeed provide a
model for situations where the position of maximum velocity did
not coincide with the position of 0 shear stress.
But of course with an eddy viscosity model, you can't do
that. They're linked by the definitive
link interlinkage between the mean field velocity gradient and
the turbulent shear stress. So there what we did was provide
an additional independent transport equation for the
turbulent stress. Again, that paper has been
reasonably widely cited. I think both Kimmo and Bill and
I felt at the times, though, that eddy viscosity modelling
wasn't the way to go for most cases.
We felt that you really needed to solve transport equations for
all the Reynolds stresses independently of the velocity
field. And curiously enough, Brian
Spalding was the agent enabling me to pursue that work.
Wolfgang Rodi by then had completed all his computations,
but he was in the throes of trying to write a thesis that
met his supervisors very exacting standards in English.
His scholarship had run out by then and so I was able to hire
him as a a quasi postdoctoral fellow and together we worked on
developing a full stress transport model.
And in the time available that also went very, very well.
We produced a solver that nowadays known as the LRR model:
Launder, Reece and Rodi in alphabetical order.
I'd I didn't so, and that too has been quite widely cited.
I think that's a little bit of an understatement.
I think they're quite widely used.
And maybe you just forward maybe getting on to the next point,
just on this chapter, I guess would it be fair to say for
people to realize that all of the work prior to Spalding's
finite volume code was essentially experimental and you
were mainly deriving relationships from the
experimental data, There wasn't as much coding or numerical
simulation work. Is that correct?
It was I'd say 80 to 90% correct there.
There was work on developing solvers people in the in the the
USA was were on to on to that a group at Los Alamos.
There were others in England. You mustn't forget Peter
Bradshaw also, although he was out and out an experimentalist.
He worked with a group at the
National Physical Laboratory that included some numerical
fluid mechanicians and they developed a scheme usually
called Bradshaw's method that indeed at the 1968 Stanford
conference was rather more successful than Spalding and
Patankar scheme with that had used the mixing length
hypothesis, of course. OK, So the this bringing
together, how did it work in practice at that point?
Was Spalding still essentially running the department?
And and so in some ways was that the slight you still had your
individual research groups, but you were sort of merging in
one, you know, what was that? Because I can imagine he is the
senior professor here. You you're the How did that
relationship at that point? Well, well, Spalding was never a
head of department. He was happy to be head of the
heat transfer section, OK, really the next, and he was
happy doing that. The next major change in my own
career also arose indirectly from Brian Spalding with the
success of this new boundary layer code.
And he had another code that handled recirculating flows too.
There was a lot of interest outside of the university in
getting consultancy help on applying these new schemes to
flows that were of interest to the people in question.
Spalding initially tried handling that internally by
sharing tasks with trusted members of staff and they're
research students. But after a year or so, he he
just felt that wasn't working. He'd find somewhere outside of
the university. So he established an independent
company, Concentration, Heat and Momentum, or CHAM for short.
It established headquarters in Wimbledon and then he had the
enormous task of recruiting staff, completing the various
consultancy requests that were coming in.
And inevitably, even for someone as able as him, the activity
within the university itself, his academic role, they'd they
very much were on hold and this this produced unhappiness with
within the department. Now, as it happened, one of the
Spalding's group had also been made a professor by then.
His name was Jim Whitelaw. He was an experimentalist in
fluid mechanics mainly, but the idea developed that since he
was a professor, he was eligible to basically to lead a group
of staff. Maybe the head of department
would form something called the fluid section, and those who
wanted would transfer their affinity from the heat transfer
section to the fluid section. What was the outcome of that?
You can guess absolute turmoil.
I won't go into the details of the battling, but essentially it
brought research to a halt. Then one day I had a telephone
call from the USA. It was from the head of
department at the University of California, Davis.
He'd been on sabbatical leave within Spalding's Group A couple
of years before. He and I had got to know each
other somewhat. So he called and he said
something like, hey, Brian, I really sorry to hear about the
problems that you guys have got in the department at the moment.
I've been talking with the Dean
and he said to me that if I wanted to offer you a full
professorship to come here to Davis, that was that.
Would you be interested? I heard these words and just
just seemed like someone had I was drowning and that someone
had dropped a lifeline from a helicopter to pull me out of the
So we I said yes without hesitation.
It took maybe well, we didn't get, didn't arrive in Davis
until, well, I think it was 96, the summer of 1976, but we were
very pleased to get there at the time.
What was it, what was it like though with your family,
children? Was that and that was a big
move, you know, big thing to move to the US, to leave London.
Was it an excitement to do it in a way?
Was it a challenge to convince your wife and family to to go
with you? With my, my wife, she's Danish
and moving away from moving away from Europe was a big thing
for her. And I softened that by buying,
buying a property in France. My contract at Davis was for
nine months, that is to say just just just until June and then
you were free completely over the summer.
And I'd have to say also that unlike, unlike Imperial College
that I just come out of staff didn't have administrative work
to do. There was other other workers
that handled all the administration academics were
there just to teach and do research.
So it did make sense having this nine month contract.
So what I agreed we do was in in the summer months, we, we come
to Europe entirely, which would give her more opportunity to
interact with friends and and so on.
Yes, we bought a rundown. We bought a rundown farmhouse
just north of Lyon and in the in the summer I would would drop
in two or three times a week to the École Centrale de Lyon in
enjoying doing research with new colleagues there.
My wife was happy at our our rather dilapidated farmhouse,
but that was that was a different life.
So, so yes, we will make that. But what about UC Davis then?
What was it like there? Well, the department was about
half the size of Imperial College.
Colleges staff did a lot more teaching.
They didn't have administration to do, but they certainly did a
lot more teaching. And some of them treated
research really like a hobby, something that they'd squeeze in
when time allowed. Luckily I struck up a very good
working relationship with two staff there that really they
were experimentalists in various aspects of heat transfer and
they they invited me to join them to add a computational side
to their activity. Probably the main thing though
that I should should mention is that ONERA, which is the French
equivalent of NASA ONERA, sent a post doc who had done his
doctorate in in turbulence modelling to work with me for a
year. I guess they thought that the
interaction of the two of us might be useful.
What he had done was produce an equation, sorry, a turbulence
model not with one length scale, but two effectively length
scale equations that are used in different ways in his model.
I didn't find the model as presented in his thesis exactly
coherent. But we work together and agreed
that what we do would be to develop what's known as a multi
scale model. That is to say, we'd effectively
cut the turbulent spectrum in half with a large scale part in
which eddies would capture mean energy from the from the flow
and a medium and fine scale part that received energy from the
large scale turbulence and finally dissipated it.
That is so we had separate transport equations for the two
parts of turbulence. Davis didn't have a great
computing system. We could only look at simple
flows, which also suited very well the background of the
French visitor. So we looked at sudden
contractions, sudden distortions.
They were just, these were just one-dimensional flows.
You could almost calculate them by hand rather than using the
computer. Well anyway, the outcome of this
was I felt quite spectacular. The simple flows which we did a
so so job on with previous models were now much better
predicted. You got a delayed response when
you put new energy in. You didn't get the dissipation
rate occurring straight away. There was a delayed response and
that mimicked very well the experiments that more or less
brought us to the end of his year.
But I wanted to continue the research to include really the
sorts of flows that in engineering 1 is dealing with
boundary layers, mixing layers, jets, wakes this, that and the
other. But in order to do that, the
Davis system wasn't really suitable.
That is to say, the computer gave too slow turn around for
model development. Also, well, I needed to get
funding if I was to get anyone else.
I couldn't easily recruit research students at Davis.
They didn't seem to want to do research in turbulence
modelling. But Kemal Hanjalić, I knew, was
struggling with the administration that had hit him.
And having got funding from NASA, I invited him to come over
for a year and join me. Now, as I say, the Davis
computing system wasn't up to it, but it wasn't difficult to
obtain computing resources at the the Lawrence Berkeley labs.
Now in those days, we're still talking about the 1970s.
You've you've got computing resources.
Laptops weren't invented and you sure didn't have anything
called remote access. In order to use these, one had
to get in one's car and drive the 60 miles or so down to the
Lawrence Berkeley labs, which had brilliant facilities at the
time. Well, Kimo mainly, but I, I in
joined in as well, worked on this problem for the best part
of a year. And I have to say the outcome
was disappointing. We made one or two improvements
that applied equally to single scale models.
But there was really in you, you're looking at flows like a
mixing layer where so much energy is captured from the mean
flow into the turbulence that the medium and fine scale part
of the spectrum hardly had a look in.
So the results that we got for these flows were only marginally
better than we had obtained with a single scale model.
End of story. I thought it worth mentioning
that because this brings home that what looked like very good
research directions sometimes don't don't work.
Which is, which is a good lesson for people, I guess.
Maybe you're well known for your successes with the k-epsilon
model and the LRR. But I guess if the point is not
all research comes out in success.
But maybe that's the point of research, isn't it?
Some stuff works. Indeed doesn't.
Yes. Well, there was something else
that arose from these trips down to Berkeley, because I got to
know the head of department at the University of California,
Berkeley. And one day he he said to me,
listen, I see you're down here quite regularly.
We need someone to teach turbulence modelling to our our
students here. And there are students asking to
do research in that area, but we really don't have anyone that
could provide that role. What if we, we're in the same
university system as Davis? What if we arrange to hire you
for, let's say, one day a week?
It would be very easy to arrange.
And then when you're down here at the LBL, you could also call
in here at the department, see students, give a lecture or two.
And it seemed to me that that
that would work well. Again, I was delighted at this
suggestion. Couldn't wait to get back to
Davis to break the good news to the head of department so he
could then just sign whatever forms were needed to bring the
change about. I told him and he said
absolutely not. If students know they can work
with you by going to Berkeley, they're not going to come to
Davis. I said to him, Alan, that that
doesn't make sense, it's because they won't come to Davis.
But I can. I can see great opportunities
from recruiting students in in Berkeley.
However, he was implacably opposed and I accepted it.
I liked life in California. It was was a bitter pill, but I
could swallow it. But then not very long later, I
got a phone call from England. It was the principle of UMIST,
that is to say Manchester's Institute of Science and
Technology. He said the head of thermofluids
here has died and we're looking to recruit his replacement.
A few people I've asked have suggested you might be
interested. I disabused him of of that idea.
I said listen, I've only been here for 2 1/2 years, I put in a
lot of effort. I haven't started reaping the
rewards of being here so it's it's too early for me to
consider coming. However, he kept persisting and
in the end I thought I'll take a short back trip back to
England, see my parents, haven't seen them for a while, then
I'll go up to Manchester, have the interview and I'll
politely decline if they offer me a position and life will
return to normal. And that was the plan that I put
into motion. Spent a pleasant weekend with my
parents, travelled to Manchester and had a whole day before the
interview to be exposed to what UMIST could offer.
And I have to say Neil, I was just blown away.
First of all, Thermofluids research had its own building
all through itself. It had 15 academic staff that I
would generally have responsibility for, but not just
academic staff. There must have been at least 30
technician staff and what are called experimental officers to
basically help push research along.
There were around computing staff, of course, at the end.
At this point in time everyone was using card decks and it
needed it, needed quite a lot of support.
But four or five full time positions, That was amazing.
Finally, at the end of the day, I had an interview with the
principal himself. It was a relaxed chat really
over a glass of Sherry I recall.
And he said, of course, if you do come here, there will be
administrative work you won't need to get involved in.
And to make it easier for you, you'll have a dowry appointment.
Meaning that I could choose
anyone that I thought was would going to be helpful to come and
work as a lecturer. No interview, no anything.
It was just me saying I want to have him.
It probably runs counter to to in nowadays, but it didn't at
that time. So at the end of that I had to
say I really wanted the interview the next day to go as
well. And it was a disaster.
I was taken into the room itself where the interview was
conducted. In front of me was a huge Oval
table. I was sat on one side of the
table and ranged all around the other side were the
questioners. There were about 10 or 12 there.
The principal was there.
He introduced me, welcomed me, introduced me to the other.
Other people on the panel think he maybe even asked me a couple
of soft questions which I dealt with.
But then he stepped back and turned me loose to these hyenas
that ravaged me for the next 50 minutes or so.
They were obsessed with something called the Finniston
Report, a report, a government produced report by Lord
Finniston or whoever that looked at potential changes in the
training and development of engineers.
I think by then it had been recognized that Britain didn't
recognize engineers to the extent that someone somewhere
like Germany or Japan did. And of course these these
countries, despite the set back of the Second World War, were
already very advanced and overtaking other European
countries. I honestly, I've been in America
for 2 1/2 years. I didn't have a clue about what
my reactions should be. Likewise, and I could have
anticipated this, there were a lot of questions related to what
management style I would apply if I had the post.
I hadn't been talking about management.
I'd I wanted to do research and do some creative teaching.
So again, my my questions were were very weak.
I felt at the end of an hour they released me to catch the
plane back to California. I remember my wife meeting me
and she was quite excited. She said, well, how was it?
Did it did it meet your hopes? We will we be going there?
And I held my hand up and said the job looked fantastic and I
made it a real terrible job of the interview.
That's the end. So I mentally got back to my
work in Davis. But you know, a week later the
principal phoned again and said the job was mine.
It may have been a a fine decision because usually they
don't take that long in reaching a decision.
But anyway, I did accept the position and well, by the time I
got loose from Davis, there were various entanglements that
slowed my departure. It was spring 1980.
After I'd accepted the appointment, the principal
pointed out that I wouldn't be really responsible for the
engine testing work that my predecessor had specialized in.
He had a right hand man for that work.
And if I was agreeable, he could be promoted to professor to
thus removing me from any responsibility.
And then that's what I very much agreed to and for my dowry
lectureship, I recruited Michael Leschziner.
Michael had been my final PhD student before I left Imperial
College. In interim, he'd gone to work
with Wolfgang Rodi in Karlsruhe.
But when I suggested that he might rejoin me as a lecturer at
Manchester, he was very happy to come.
So I was able to get off to a very good start there because I
could delegate to Mike Leschziner responsibility for
the developing software and generally looking after the
turbulence related work while I got experimental work going.
In fact, I was very lucky in that while I was in Davis I'd
negotiated a contract with the Office of Naval Research, ONR as
it's known. The person behind that was
someone who was very sceptical of CFD, of what CFD codes could
do at that time. In particular, he was interested
in flow through heat exchangers, in particular, flow through a
tube, but in a tube that went in a series of U bends as you get
in a heat exchanger. He said he didn't believe that
current CFD software could accurately predict what heat
transfer coefficients would arise from the complications
that the swirling flow that was generated by these U bends
would create. Fine, I accepted that there was
no problem transferring the contract to Manchester.
So we got under way and after we'd got a very nice set of
results, not just for a circular U bend, circular section U
bend, we actually also produced experimental results for a
square section U bend. Real heat exchangers don't have
a square section pipes, of course, but it was easier to do
the experiments using laser Doppler anemometry going through
a plain surface rather than a circular surface at a time.
It took us a little while to work out how to do that.
Anyway, when we went to apply software to that we've we found
very poor agreement. The contract monitor was
delighted he'd been proved correct.
We carried on as well as we could refining the model.
We found in that case that that taking the calculation all the
way to the wall was highly beneficial.
We at that point just put in the mixing length hypothesis
across the sub layer. Remember this, these were
three-dimensional flow calculations and although
computers were getting more and more capable, the calculation
like flow 3 dimensional flow through a a succession of U
bends stretch the resources available.
OK, well we then went experimentally on to rotating U
bends. Now rotating U bends.
Heat exchangers don't rotate, but this configuration also
arises in tubes 1 millimetre in diameter that are inside gas
turbine blades and because of the pressure there and other
other factors. So for Rolls Royce for several
years we continued looking at the impact that swirl has on in
that particular configuration. I think on the research
computing side rather we'd for my money, I'd more or less run
out of road. The there didn't seem to me much
scope within the stress transport models or algebraic
simplifications thereof that we could exploit.
And then one day in a reflective mode, I recalled a paper that
John Lumley had published in 1978.
He made what I then asserted was a absurd suggestion that
turbulence should comply with what he called the two component
limit. Turbulence, as you know, is 3
dimensional, John said. However, if you have a situation
where the fluctuations just lie in a plane, that is a state
that you should insist on your turbulence model agreeing with.
Indeed, he worked out a parameter that automatically
went to zero whenever you did have that two component state,
and thus it would be a useful parameter to use in one's
turbulence model. Well, in reflecting on this that
day, I suddenly realised that as you went closer and closer to
a wall, the presence of the wall damped out fluctuations normal
to the wall, so that then as you get close enough to the wall,
you indeed did have turbulence that was essentially 2
dimensional. At that instant I went from
being a critic to an enthusiastic supporter.
It was, it really was an overnight night thing.
I had two other students at the time but worked on this.
I'm happy to mention the My name 1 was Dimitri Tselepidakis and
the other was Song Fu. Anyway, they made important
first steps, but then their names aren't linked with the TCL
modelling simply because they were in at the development stage
at the exploiting level. Though Li Xiaoping, another
Chinese student who now works for Fluent in the USA, He
applied the scheme both to flows along a flat plate, but also
to riblet flows in order to reduce the drag.
The results from his computations came out well.
And then especially a little afterwards, Tim Craft looking at
a whole range of turbulent flows found that that this two
component limit, the TCL model as we called it, did a brilliant
job of imitating, mimicking the effects of buoyancy
stratification on the behaviour of the turbulent stresses much
better than the other the earlier LRR model that everyone
still uses. Maybe I can ask a quick
question. Actually on the TCL model, it
strikes me that from my understanding, that has probably
the most, that was the peak of the most sophistication, the
most complexity in a turbulence model in, in terms of the
number of equations, the completeness.
And yet if I look at fluent or, you know, other codes today,
it's probably still the case that people use their LR, you
know, LRR or SSG. Is there a reason you think that
the TCL wasn't adopted more widely?
Was it just too difficult to implement?
Do you have any? Yeah, thoughts.
On that, I think it may well be certainly what you suggest was a
contributor. Maybe maybe I didn't get
involved myself in trying to promote the model.
I don't know. Dave Wilcox I think has has done
a better job in in in advocacy.
Florian Menter's another name that is, is is an advocating
that approach. But well, I don't know.
It's a it's a thing of history.
My philosophy is often, and I just wonder whether that's why
the k-epsilon is still today one of the most widely used is there
is a simplicity is often preferred because it's it's
easier to implement, it's easier to debug, it's easier to get
right. And so sometimes I wonder
whether people are inherently favouring simpler models.
And so the k-epsilon, it's probably an easier model to
implement and test and use than the TCL model that is has more
places to make a mistake. I don't know if that's the
reason, it could be war. I I think as well you, you
touched on it, simplicity is a very key point.
But nowadays 1 is, is looking at a situation where computers have
developed so much that if the k-epsilon model isn't good
enough, perhaps you should use a hybrid k-epsilon-LES approach.
Yeah, and LES is conceptually
quite simple. The k-epsilon model is also
pretty simple. I think people can live with
that package, maybe more easily than solving rather obscure
looking models for the pressure strain hypothesis in the in the
TCL. Yeah, but how about, you know,
Tim Craft, somebody who actually taught me when I was at
university? He went further, right?
You went on to move to look at what I would consider I guess a
blend or a theoretical blend of trying to bring some of the
concepts of anisotropy into simpler models.
So this was the non linear cubic models, right?
That was this the next stage, I guess, of the turbulence
modelling work. Very much so.
Toyota had contacted me wanting to send one of their staff at
the time, Kazuhiko Suga, to work with me, and I'd figured that
they wouldn't be interested in TCL modelling.
It really would be a step too far for this car manufacturer.
But we did agree to look at non linear eddy viscosity models.
There had already been half a dozen schemes that brought in
quadratic terms in addition to the principal linear term of an
eddy viscosity model. We started off looking at those
five schemes that already come forward and what we concluded
was that because these five models were also very different,
different magnitudes of coefficients for different
terms, these models had been designed so that they cope with
one particular class of flow that a linearity viscosity model
didn't get right. We concluded that since the
models weren't anything like the same, we would be wasting our
time to continue research at the quadratic level.
So for the first time then, we we explored modelling at cubic
level. Cubic level of course brought in
many more potential terms, each with empirical coefficients
to tune. But Kazuhiko Suga very patiently
and very thoroughly looked at a whole wide range of flows that
were difficult or couldn't be predicted with a linear eddy
viscosity model, and we ended up with a version that perhaps
wasn't the final word in cubic eddy viscosity modelling at at
least did a hell of a lot better for a large number of flows than
than the quadratic models. So he was content.
I'd say after returning to Japan, he worked for a few years
with Toyota. But then this is interesting.
He got permission from Toyota to move to a university position.
Oh nice. You could you could see that as,
as you've just said Neil, a simplification from from the
pinnacle of TCL modelling. And I guess the next step I took
in research went a step further.
What really bugged me was that still in commercial CFD, people
so frequently use wall functions based on this old idea and
very limited, a very limited idea that the near wall
velocity profile was universal.
What could we do with that? Well, I worked on this with Tim
Craft, who had become a lecturer at the time, and Hector
Iacovides, an earlier student that had worked on flow around
bends with me, who was now a professor.
In fact, we decided we'd figure out a better way of building a
wall function. Indeed, we worked on 2 schemes.
There was a analytical approach.
We took the view that although the near wall velocity profile
wasn't universal in most of the flows that one would want to
look at, maybe the turbulent Eddy viscosity would be much
more nearly universal, Particularly as we agreed to
allow the viscous sub layer where there was 0 turbulent
mixing. According to our model, we could
vary that in thickness depending upon the gradient of shear
stress across the layer. Well, this we worked on with a
Russian student. My only Russian student, Aleksey
Gerasimov, was just fun to work with and I'm glad to say that
the model he came up with, what was called the analytical wall
function, did pretty well. It's widely used at Manchester
now and and is at least incorporated in some of the
commercial software. It's a lot, lot better than log
law wall functions. They should be made illegal, but
we also developed a second scheme in situations where you
have the velocity vector changing direction across the
viscous layer, such as a rises in those flow around U bends,
very tight U bends. We developed a numerical scheme.
I I won't attempt to go into any detail on that, but the key
thing was that just as in a boundary layer solver, if you
think of a but 2D boundary layer solver, you treat the static
pressure as though it is uniform across the layer.
We applied the same slight approximation, but only to the
very near wall region covered by the wall function.
And I won't go into the details.
Indeed I've forgotten some of the details by now.
It's a while ago. But that permitted us to very
much reduce the cost of using quite advanced models.
I mean, Bill Jones's low- Reynolds-number model could be
put in or or any any other other model and it reduced the
computing time by something between 80% and 90%.
So it represents a huge saving. I should just maybe add a point
and maybe you're not even aware of this, that I have seen a
resurgence of the interest in the work that you did with Tim
and Hector for advanced wall functions in the context
actually of LES. That now because there is a
resurgence of interest in the wall-modelled LES, there is a
realization that the model used to approximate the near wall
behaviour. Can we look at more advanced
ways of calculating that? And I I've seen now people
reference and look at that work not in the context of RANS, but
actually in the context of LES, which I thought is quite
interesting how work that was done, you know, 30 years ago is
now being re looked at in a in a different context, but still.
Yeah.
So anyway, just a. Thank you Neil.
I, I was not aware of this resurgence of interest.
Long may it continue, but I, I have to say that that having got
that far, what I found was that turbulence models was looked on
as what might be called a mature subject.
People weren't interested in looking for radical changes in
in modelling. It was applications that were
very much to the fore for I didn't feel that that was what I
was perhaps best at at doing, though I, I did, I did supervise
one PhD student by a friend of yours, Alastair, and that was
very successful. He was looking at in-line tube
banks and it was quite extraordinary.
We found the the sorts of deviations from from going
straight through an in-line tube-bank heat exchanger
tended to develop a diagonal path through that.
I should maybe just interrupt you slightly.
I, I was mean to say it before, but maybe this is a good time to
say it that almost as a, an observation or to people
listening that I studied at Manchester University with
Alastair as well. And we did our undergraduate
degrees and, and you taught us and so did Tim Craft and so did
Hector Iacovides and these folk.
Not Michael, I guess Michael, I think moved to Imperial then
and but we didn't know who you were.
We didn't know who Tim was. We didn't know.
And I, I know Alastair and I talk about this now that we feel
bad in a way. And I'm sure others are like
that. They see some professor come in,
teach a subject, second year something and you all, you don't
mean to be disrespectful, but you know, you don't know who
they are. And it's only later you look
back and think, oh wow, I was, you know, taught by this person
or supervised. And I, I wonder, I think you
mentioned to me this happens sometimes that people come or
want to take a selfie with you or something.
Because now with social media, I guess people know who people are
more. But at the time we had no clue.
And it was an honour to be
taught by you. But I feel guilty that we didn't
say it at the time. Well, I have no thoughts on
that. Indeed you mentioned people
coming in to have selfies with me.
I I was just amazed and thought they were slightly crazy but
complied with their request to to be photographed.
Well, I suppose the one of the reasons that slightly steered me
away from continuing too deeply in basically CFD applications.
Much as there were very interesting things to explore, I
would in fact mention another application case.
We were looking at trailing vortices behind a wing.
There was a good set of experimental data, and we
computed that with a Eddy viscosity model, and as we knew
it would, the swirl died out far too quickly.
Now the trailing vortices behind a wing in practice are known
to persist a long time, so that a big aircraft landing at an
airport would make it really dangerous for a plane coming in
a minute or so after them on the same track because the swirl
persisted and persisted. The Eddie Viscosity model said
don't worry folks, the swirl dies out very quickly.
But experiments that Peter Bradshaw had done said, no, it
doesn't die out. It hangs around an awful long
time. And I'm happy to say that one of
the applications that I did with Tim Craft at Manchester was to
look at this with the TCL model.
And the TCL model was the only one of four schemes that we
looked at that in any way mimicked the observed
experimental behavior. I will just add if you don't
mind a quick again interesting thing that you may or may not be
aware of and it's probably one of the reasons that Alastair
works where he does now at the Formula One team, is that use
case of RANS turbulence modelling for highly vortex
driven flows is a key use case in Formula One.
And actually from when I was working and even recently, I
still see people looking at nonlinear eddy- viscosity models
and Reynolds-stress models because the flow around a
Formula One car is driven by 10s or more of individual
vortices and they find that they need these non linear terms
to capture it more nicely. So even today, I think that's
one of the industries that still is very much into turbulence
modelling. So yeah, yeah, that's that, that
wing tip exact test case I've seen used internally at in F1
teams to investigate different turbulence models.
So. Gosh.
Well, thank you. I hadn't supposed that that
ground based object like a racing car would encounter the
same problems. Yeah, that's because all the
wings, they generate the tips and there's so many of those
individual wings, there's, there's probably 40 different
vortices I guess on the car all touching each other.
You need a pretty fine. It's a result, yes.
Well, yeah, there's like a billion grid points nowadays, so
things have moved on. But yes, sorry I interrupted
you. I think you were talking more
about the Osborne Reynolds and and some of that work.
Yeah, well, I've really reached the end of the end of the line.
I thought I was also getting a
bit old and so I was interested that the Royal Society
announced that they had the original copies of referees
reports from some of the early papers.
Now I was quite interested in Osborne Reynolds, of course.
He'd been a professor at Manchester, forerunner of
Manchester University, but also he his paper on Reynolds
averaging. Whilst it didn't actually get
into the problems of modelling the Reynolds stresses, at least
it marked a starting point for the subject that I'd been
involved in for most of my professional career.
So he asked whether they had copies of Reynolds papers.
Judy travelled down to London to see them.
And again was I was just blown away.
I was blown away in much the same way that first coming to
UMIST had had done for me. You got communications from
Horace Lamb, George Stokes, from Reynolds of course, really from
from all of these people that were involved in refereeing or
acting as editor of of the manuscripts that Reynolds had
submitted. So I said, well, can I have a
copy of these? Yes.
The Royal Society said no, I could not Xerox them.
They wouldn't allow me to Xerox them, but they could arrange for
their photographer to come in and copy them for me, which they
duly did. I was charged 75 lbs for the
privilege which I the other day I looked up as to what that
would be today. It was a little over £200 but I
happily paid that in order to get get the photographs and
subsequently then I wrote a paper on how despite crushing
referees reports, nevertheless Osborne Reynolds did publish his
paper on Reynolds averaging. Well that's a lesson on even the
famous and well known people like Osborne Reynolds can get
very harsh reviews, so maybe that's reassuring for everybody
else who probably also has had those.
I'm sure it wouldn't have been published except that the
earlier paper that he'd published in which he discovered
that transition occurred at a particular of what we call today
a particular critical Reynolds number.
If he hadn't published that experimental paper first because
the referees were saying things like the previous work he
did was very good. Maybe there's something in this,
but I can't see it that that was probably the reason it got
published. Of course, having having
published one paper, you get a request from conference
organiser, could I give a paper just like that one?
And of course my response is I couldn't bear to give the same
paper twice. But what I discovered was that
at Manchester they had all of the archive material from
Reynolds applying for a his chair.
Retired colleague of mine had also been following up on
Reynolds's life, a person called Derek Jackson.
And so we collaborated in producing a much fuller paper on
Reynolds's life as a whole that was was published in a book
that I forget. Let me find the name of the book
here. It is A Voyage Through
Turbulence that was edited by Keith Moffatt and others from
Cambridge. Anyway, I don't know whether it
was connected with these papers when colleagues in the Royal
Society died. It's the practice of the Royal
Society to produce a 25 or 30 page memoir on their lives,
their achievements. So I was when my friend Jim
Whitelaw passed away, I was asked to write his.
And you know, that is, that is really an interesting branch of
research that was quite like looking at looking at Osborne
Reynolds's past life because Jim had produced a huge catalog of
what he'd done. And so as a matter of sifting
through that, pulling out the aspects that would be
particularly important to stress, plus any personal views
I might have. So that started following Brian
Spalding's death. I I also.
Contributed to his memoir and now most recently, Peter
Bradshaw, who died last year. I've written his article.
So life in my retirement hasn't, hasn't by any means been without
involvement with turbulence. Brian Spalding, When we started
off in the earlier discussions about the beginning of your
career, you had the initial chat about where to study, then the
offer of coming back to Imperial and obviously then there was a a
sort of falling out and then leaving to UC Davis.
What was your relationship like later on in in your career?
Did you stay in touch? Did you?
Yeah. How was your relationship when
you came back to UMIST? Well, when I came back to UMIST
it was. It was static.
Nothing had moved by then, but then when in 1994 received a
note notice that I was to be admitted to the Royal Society, I
got a warm, very brief but brief brevity is certainly
Spalding style. A brief note congratulating me.
I didn't respond to that.
I think in as generous a way as I could.
We, we might have developed much closer linkages again when he
was when he was reaching his 90th birthday, there was a, a
celebration for him and I, I was distantly involved in helping
to organize that. And of course we met there and
exchanged pleasantries between us.
I I guess there was still slightly a feeling of the
tension. I think the last time I saw him
was when I was giving, We were both giving, in fact invited
lectures at a meeting in Sarajevo.
I would by then had worked into the area of climate change and
that was the topic of my lecture, really suggesting how
engineers with their experience and now of being able to
predict turbulent swirling flows could actually contribute to
the modelling of hurricanes, perhaps devising methods to
diminish the intensity of a hurricane.
I think the paper went over the heads of those there.
There was, I think, no question at all from the floor except
from Brian Spalding. He was sat in the front row of
the audience. We did mend our fences between
us. I didn't do as much as I should
have done, and I'm sorry, but I hope in contributing to his bio
memoir, I'm forgiven. My other question, I'm kind of
see how you saw it from the outside.
Often the turbulent modelling, particularly in a RANS context,
it's often seen as a almost a competition between Philippe
Spalart, you know, Florian Menter yourself, Wilcox, how
much did you see it that way in the night?
And I guess you had done it a little bit before, but in the
Seventies, 80s and 90s, were you aware of this almost papers
always comparing the different turbulence modelling approaches
and which one was better? Was that something you aware of
or was it not? Yeah, part of your thinking.
I guess one could say I was dimly aware of, but I was so
interested, you might say obsessed with tackling the
problems in research that I felt I needed to deal with.
I I wasn't looking over my shoulder all the time.
Looking over one shoulder in implies people are behind me.
Maybe some some of. Do you think it's ultimately
though, just a matter of where you studied and what your
funding was, new use cases, If you're in at Stanford and you're
in the US, you have close links with NASA and the
aerospace industry, you're going to be solving airplane
cases. And so I wonder whether that
motivated the Spalart–Allmaras and those.
And if you had, instead of being funded by, you know, Boeing or
or Rolls Royce, sorry, or Airbus, or would you have
naturally pivoted and maybe come up with a slightly different
terms model? Is it ultimately that you were
driven a little bit by the problems you were trying to
solve? I haven't.
I haven't really thought of it that way, but I think I think
that's it's correct. Had I, had I been at Stanford,
say yes, NASA Ames would be the natural point of collaboration
in research. Who knows?
I don't. Well, I I say, I don't think I
would have gone for a one-equation model as Philippe
Spalart. Yeah.
And it's interesting, I think now if you look, even with the
Spalart–Allmaras, there's a lot of modifications to try and add
some of these non linear terms. So I, I think ultimately people
come from different directions and you know, I guess you can
argue which one's correct and which one's not.
But yeah, it, it's just a curiosity to us externally,
because if you open up Ansys Fluent or STAR-CCM+ or one of
these commercial packages, you are almost, you know, this, I
didn't tell you, but you have radio buttons on which
turbulence model to pick. Do I pick the k-epsilon?
Do I pick the k-omega? And in some ways, if you have no
context of the background, it is in some ways just which one
do you pick? And that's why people often find
it so interesting that there's these different options and how
did they come about and what was their motivation.
So that ends the question. So maybe to finish off, what if
you were to now, you know, you're speaking to your 20 year
old self, what advice would you give having all of what you've
learned through your amazing career?
What? What words of wisdom would you
impart? Gosh, it's hard to imagine a 20
year old who would sit and listen to somebody closer to 90
than 80I. I suppose looking back over my
life, what I can see is that changes have come about.
Really not of my own driving, but I've somehow been thrust
upon me. And I think I would say that
people should be ready to accept change, not be downcast by it
nor overly ill related, but to be inquisitive of of change.
And I think making changes constructively has, in a sense,
reflects my approach to modelling.
When we'd reached the stage where it was just a matter of
pushing a button to, as you had alluded to, to choose which
model is applicable, that's when I think it's time for me to say
thanks but no thanks, I'll do something else.
Great words of wisdom and thank you so much for sharing your
stories and your work. I'm sure I speak for everybody
to say that the impact of, you know, the k-epsilon, the LRR and
the wall-function work is today used by hundreds of thousands of
engineers across the globe to design the things that we and
you, the listener use it every day.
So the impact, even though some of that work was 50 years ago,
it is still impacting today, which is I think an incredible
testament to the work you've done.
So thank you for being on today and it was great to speak to
you. Well, thank you, Neil.
It's been fun. Bye bye.