GACLIT 75
Fall 2003

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Celebrating 75 Years of Experimental, Theoretical, and Computational Innovation

On the occasion of the 75th Anniversary of the founding of the Graduate Aeronautical Laboratories of the California Institute of Technology—GALCIT, that is—we took the liberty of talking with each of the faculty members about the current direction of this world-renowned research group and the factors that have led to its unique—some say unparalleled—position in the world of fluid mechanics, solid mechanics, and combustion research. It is well known in the scientific community that GALCIT is the birthplace of a large number of ideas, new theories, innovations, and scientific discoveries. It has established a long tradition of leadership in its chosen fields. However, GALCIT’s ongoing obsession with the scientific foundations of fluid and solid mechanics has ensured that this75-year old intellectual powerhouse shows no signs of advanced age.

As Professor Mory Gharib deftly explains, “the same principle that guided GALCIT’s early research efforts still governs today—find the most challenging unsolved problems, the show stoppers, and attack them before the rest of the scientific community even has them on their radar screen.” Each generation has its own mix of show stoppers, and the original areas in which GALCIT worked revolved around aeronautical applications. The lab was founded in 1926 as the Guggenheim Aeronautical Laboratories with a $300,000 grant from the Daniel Guggenheim Fund for the Promotion of Aeronautics (Caltech was one of seven schools that were so funded). Hans Liepmann, the third Director of GALCIT, speaking at GALCIT’s 50th Anniversary celebration, noted:

[Daniel] Guggenheim stated clearly that his endowment was not intended to be permanent, but that he thought aeronautics, then in its infancy,would be raised to a state where support would be guaranteed from both private and government sources. […] it would have been absolutely out of the question to raise that money for that purpose at thattime from the government. Congress would have never permitted such a strange venture. The legislators would have just laughed, because at that time, flying was often barnstorming and the accident rate on the few existing airlines was something like one fatality for 1,300 miles, a number that has only been reached at times by private automobiles.

Its first director, Theodore von Kármán, a pioneer in both fluid and solid mechanics, began visiting Caltech in 1926, but made a firm landing in 1930 to direct GALCIT full time. As recorded by Clark Millikan, the second Director of GALCIT, von Kármán spent the fall of 1926 at the California institute advising its staff regarding the educational policies and experimental facilities of the new graduate school and laboratory. During this visit the essential features that characterized their subsequent development were largely worked out under von Kármán’s leadership.

The initial focus on the applications of fluid and solid mechanics to aeronautics blossomed, and by the end of the Second World War, observed Liepmann, “GALCIT was the only school in the nation equipped to tackle the problems arising from the explosive development of aircraft and missiles to transonic and supersonic speeds and finally into spaceflight.” In fact, the burgeoning aerospace industry in Southern California was catalyzed, supported, populated, and maintained by GALCIT (and Caltech) with cutting-edge research, unique testing facilities, and top-notch graduates. Aerospace companies were founded by Caltech and GALCIT alumni, led by our alumni, and served as home to creative thinkers, inventors, and engineers who succeeded in transforming society by breathtaking advances in communications and transportation. A particularly unique institution “spun-off ” from GALCIT is the Jet Propulsion Laboratory ( JPL), which put the first U.S. satellite into space and continues to this day leading the country’s unmanned space program. Von Kármán was JPL’s first director.

Even as early as the ’30s, ’40s, and ’50s, the pioneering research undertaken by GALCIT faculty and colleagues spanned a wide range of interests outside of the aeronautical envelope.

A. Rosakis: As a matter of fact I have been told that von Kármán himself was arguing about calling GALCIT basically a center of applied mechanics—the Graduate Applied Mechanics Laboratory. But at that time, the biggest applications of mechanics, theory, and experimentation in both solids and fluids were in aeronautics. That was the star application, so it made sense to emphasize the aeronauticspart. Today, one may be surprised to find out that investigation of the blood flow in hearts of embryonic zebrafish is one line of research in GALCIT. Mory Gharib is carrying out this extraordinary work with colleagues Scott Fraser, who is Rosen Professor of Biology, senior research fellow Jay Hove, and post-doctoral scholar Reinhardt Köster. By surgically blocking the flow of blood through the hearts—these tiny beating hearts are less than the diameter of a human hair— the researchers were able todemonstrate that a reduction in “shear stress,” or the friction imposed by a flowing fluid on adjacent cells, caused the growing heart to develop abnormally. The results demonstrate for the first time that the very action of high-velocity blood flowing over cardiac tissue is an important factor in the proper development of the heart. Because the early development of an embryonic heart is thought to proceed through several nearly identical stages for all vertebrates, Gharib and his colleagues say the effect should also hold true for human embryos. Also, the studies of embryonic zebrafish hearts offered Gharib’s team a unique opportunity to learn from nature how to develop a proper strategy for the design of an optimal artificial valveless vascular pump for medical applications. One may similarly be surprised to learn that an active line of inquiry in GALCIT is directed toward exploring dynamic crack formation in geomaterials such as the Earth’s crust—otherwise known as earthquakes—and that this research has shown that cracks can propagate at supersonic speeds.

A. Rosakis: I remember my second year in GALCIT. I was asked to give a talk in geophysics by Professor Hiroo Kanamori [John E. and Hazel S. Smits Professor of Geophysics], and I spoke about dynamic fracture ofengineering materials. He said to me: have you ever thought about applying these same principles to different problems with different length scales, that is, earthquakes? It took me about ten years to follow his suggestion, but I finally did. And it has been a very, very interesting ride. During this same period, engineers starting working very closely with new composite materials. In order to be light and efficient and strong, the materials had to be made of composites.While they vary from application to application, the efficient new structures have interfaces everywhere. That situation is very similar to what happens in geophysics. The San Andreas fault is an interface between two plates that are sliding against each other. The engineering application is mimicking part of the geophysical application. Also the San Andreas fault separates two pieces of material that have been sliding for centuries. So they are not exactly the same material anymore to the right and left. All mature faults, for example, are composed of different properties on one sidecompared to the other, like a composite is. So here are applications that are very similar.

The high-speed cameras used in Rosakis’s lab show that shear cracks in interfaces propagate as fast as 7 kilometers per second. One of these cameras operates at 50 million frames per second, which is necessary since these shear cracks are faster than the fastest supersonic jet planes. This work has practical applications not only for materials engineering, but also for geophysics, because there is reason to believe that certain large earthquakes feature rupture that propagates intersonically along the geological fault.

Considering even larger scales, one may think that the dynamics of galaxies, giant whorls of matter, and other cosmological flows may be a concern only to those in Caltech’s astrophysics corridors. Think again. The computational theoretical fluid dynamics work of Tony Leonard and Dale Pullin has application here, as well as in more down-to-earth applications such as climate studies and ocean dynamics problems.

D. Pullin: I am presently interested in turbulence, and although fluid dynamical flows can be simulated on a computer, there are limitations. One limitation is that turbulence involves a very vast range of eddies. Turbulence is about eddies. And there is not just one eddy in a turbulent flow, there are billions of them, and they’re all of different length scales. Further, turbulence occurs everywhere: in the intergalactic medium, in the interior of stars, probably in star formation processes; it occurs in environmental fluid mechanics, on the scale of climatology; it occurs locally in environmental flows over mountains, it occurs at the interface between the ocean and the waves, it occurs inside the ocean; it occurs in turbulent combustion, inside a jet engine, in the boundary layers on 747s. It’s a very important problem.

It would be nice to have a simulation tool thatcould deal with these problems, for obvious reasons.But unfortunately, because of the huge range oflength scales, even with the world’s biggest computers,we can’t really do it in a faithful way. So one of theareas that I am interested in is called large-eddy simulation.This is an attempt to try and compute turbulentflows without resolving all of the length cales. Maybein 20 years, because Moore’s Law is working out prettywell,we will have the computational capability.

Dealing with turbulence in the presence of a wall has turned out to be a very, very difficult problem. It’s actually a bit of a bottleneck at the moment. Take the computation of a very simple flow, the flow past a sphere, at large Reynolds numbers. The very best we can do at the moment, resolvingall the scales, is probably flow at a Reynolds number of 10,000. And that’s pushing it a bit.

Let’s take an example. A golf ball flies at a Reynolds number of 50,000 – 100,000. So we are not even close. The roughness of a golf ball means that the turbulent boundary layer near the surface of the golf ball is very complicated. And it is also spinning, which is a further significant complication.You can’t hit a smooth golf ball much more than about 100 yards. Tiger Woods couldn’t hit a smooth golf ball out of the backyard. But he can hit a dimpled one 300 yards. That’s an example of how the behavior of the turbulent boundary layer profoundly affects behavior. If, in the next 10 years, I can do a faithful numerical simulation of the flow past a sphere, even a smooth sphere at a Reynolds number of 100,000 or a million, I’d be reasonably happy.

Professor Dimotakis, who also considers turbulence in his work, concurs and adds more to the mix:

P. Dimotakis: What is different about what is coming? There are two things. To “solve” the turbulence problem, we must appreciate what it is that makes it a problem, and a difficult one at that. And in the case of turbulence and turbulent mixing, what makes it difficult is that this is an unsteady, three-dimensional, nonlinear phenomenon. And I need to add one more element: it is all those things but it also encompasses an enormous range of space and time scales. If it weren’t for the latter,we would just put it on a computer since we understand the equations. The combination puts it out of reach of traditional analysis.

What is new and different is that we have computers that are getting larger and will eventually be large enough to handle this problem, with some help from gray matter. In addition, experiments are getting better.We are now able to measure in three and four dimensions in the laboratory. That is one of the things I’ve been involved in: developing the methods and technology for doing this. So that’s the other component: experimental tools, diagnostics, coupled with computers that
are actually getting powerful enough to permit recording of the kinds of data required to describe and analyze turbulence
and mixing.

There is joint project with Caltech’s Center for Advanced Computing Research (CACR) that we have been working on for three years.We will soon have the means of acquiring up to twenty terabytes of data in a short time. This will allow recording of three-dimensional data from flow that occupies about one cubic foot.We will be recording up to 109 measurements per second. And that is roughly what it takes to capture such phenomena. If you have not been able to see what the phenomenon is that you are trying to describe,well, you are not likely to do a good job describing it. So this is what is changing and what will be different in the next few years.

The breadth of GALCIT’s work has been only hinted at.We look at a couple more examples that hearken back to the “aero” in GALCIT.

F. Culick: I am working principally on unsteady chemically reacting internal flows, or combustion instabilities as this area is known. Understanding and controlling unwanted unsteady motions in liquid rockets, gas turbines, solid rockets, afterburners, and ramjets have been my areas of research, really beginning with my thesis work. The crux of the problem is that a great deal of energy is being released in a relatively small volume,with almost no losses, and this energy is being converted into unwanted, nonlinear motions of fluid. It’s a tough problem.My group attacks it with both theoretical and experimental investigations. I also work in other areas, notably propulsion systems.

M. Ortiz: My particular interest is in space structures. The two main challenges there are surveillance and energy. By surveillance, I refer broadly to large-aperture optics.We want to build structures, lenses in space, which have sizes in the kilometer range. It is very difficult to deploy those structures, stabilize them in space, and then get them to work as desired. These requirements really challenge traditional concepts in structures.We are used to thinking of structures as working in gravity here on Earth and they’re typically designed to withstand gravity. Now we’re thinking of very large structures in the absence of gravity. These structures cannot be tested on Earth because they’re too large.We cannot achieve zero gravity conditions on Earth anyway.You have to have confidence in the design and that the deployment sequence is going to work, because launching these things is very expensive. I see an important role there for modeling and simulations. It’s a very exciting area. I am also interested in ideas that might allow us to capture solar energy and beam it down to Earth. This is an area where GALCIT in particular is going to play a very significant role. And there are very obvious connections to JPL with both of these projects.

J. Shepherd: We are working with companies who are building new propulsion devices based on explosions— pulse detonation engines (PDEs). It is a very interesting idea, but like many new ideas, it’s not really clear how well this is going to work. So we are carrying out very basic research on several aspects of this concept so that we can give them some guidance. Should they be spending millions of dollars on this? We are doing the same thing for our government.We are working with the Office of Naval Research to determine if PDEs are something we should be investing the R&D budget of the country in. Should more funding and effort be directed here? We have a large number of students working on this and quite a number of publications related to this area in the last 5 years.

Shepherd and his students have been active in many areas concerned with explosions and detonations, and much of their work has centered on hazard mitigation. Shepherd’s investigations were instrumental in determining the cause of the TWA800 explosion. Lesser known, however, is his work on improved safety of nuclear waste facilities.

J. Shepherd: One of the projects that initially funded my laboratory was an interest in understanding the hazards in a nuclear waste storage facility in Hanford, Washington. Up in Hanford they have several hundred tanks that are each full of millions of gallons of toxic and radioactive waste. And it is sitting there cooking, chemically reacting.You can have releases of flammable gas, and there are mechanisms for ignition, so you can have explosions inside those tanks,which are partially full. And so one of the things we’ve studied is: what are the detonation and combustion properties of these gases? And then I do things like testify in front of committees about what we think the properties of these gases are. Is this something that should be of the greatest concern? Where does this rank? You have many, many types of concerns in these types of facilities.What about leakage of radioactive material into the ground? You are also worried about contamination of workers, long-term waste storage, explosions, and so on. There is a long list of issues that you have to evaluate, and we provide some input into that.We try to provide scientific input. Our goal is to give them data, and to analyze that data and apply it to their situation. The consequences of our experimentation are farreaching.

The people in GALCIT are constantly inventing new gadgets.
Measurement devices, shock tubes, image-capturing systems, the list is endless. The precision is daunting.

G. Ravichandran: One of the things we do is develop new, one-of-a-kind instruments. Recently we developed a camera that takes thermal pictures at a million frames per second. The need was related to basic experiments that we were doing to understand failure under dynamic conditions. That is,where the cracks or the shear failures propagated at very high speeds, on the order of one to several kilometers per second. In order to visualize the thermal events associated with those dynamic failure events, one cannot use ordinary thermal cameras. The breadth of the work in GALCIT continues to expand, and the professors at play are inventing on all fronts: from methods, to tools, algorithms, devices, and experiments. They are active in all the areas that the Division of Engineering and Applied Science has identified as core intellectual thrusts for the next decade: computational science and engineering, nanotechnology, global environmental science, bioengineering, and information science and technology.

The GALCIT tradition of bringing together the best theoreticians and experimentalists, and then letting them fly in their own directions of discovery has both left a legacyand created a playground for future players that is hard to find anywhere else in the world. GALCIT, like its sister epartments in the Division of Engineering and Applied Science, strives to do a few things extraordinarily well, attracts the very best people in each chosen area, and provides them with an unparalleled environment for research. This has lead to GALCIT having a visible impact out of proportion to its size, the best faculty, the best students, and a unique approach that has been emulated by others.

D. Pullin: Caltech is an unmatched research environment.
I’ve never seen, never come across, anything like it. GALCIT has a nice balance of experimentalists, computationalists, and theoreticians.You really have to have that. A group of theoreticians, by themselves, can go off on a tangent, for years. Having experimentalists around helps you keep your feet on the ground. And of course, the intellectual temperature here is very high. The students are very good, so good they keep us on our toes. Perhaps the best feature of the group is the Tuesday Research Conference. It’s somethingwe all contribute to, and it keeps us talking. It is intended to be a relatively informal forum for presenting unfinished work and ideas about future work. Everyone attends: students, post-docs, faculty, and visitors. And because we are generalists,we can all respond to each other’s interests. That contributes to the unique environment here. It really makes the environment. There is a community, a very stimulating one at that.

G. Ravichandran: When I first came to GALCIT, it was a new culture for me. What particularly struck me was the
camaraderie between students and the people here, the family atmosphere. People got along and people seemed to know everything about each other’s research. Ideas were flowing freely. People were not operating in an isolated manner. And what I found particularly interesting was that it was very easy to interact with people from other parts of campus. It still is.

F. Culick: I’ve been here a long time. I am probably the only one still here who knew both Millikan and von Kármán. The outstanding thing from the very beginning has been the quality of the students and the quality of the faculty. It’s important to realize that the entire faculty is good, not just two or three. That’s always been important for GALCIT.

The other crucial element is the relation between the research we do and its application. While my work in particular has always had a very practical bent—at one point I was consulting to all the rocket companies simultaneously—it is always done in the atmosphere and context of fundamental research and science, or “engineering science.”This is an important point. Engineering science is really where GALCIT and Caltech excel. The work may be motivated by applications, but we certainly are not like a commercial lab.Without the fundamental science that we discover, develop, and then disseminate out of academia, engineering per se would not go far.

W. Knauss: One of Caltech’s—and GALCIT’s— strengths is the high caliber of its students. While my colleagues don’t necessarily and uniformly want to admit it, Caltech wouldn’t be so excellent if we did not have this pool of outstanding students. We can do a much greater volume of high quality work here because we need to spend relatively little time with detailed guidance of graduate students. There is also a closeness, a camaraderie among the students and advisor which derives, in good part, from the fact that we are small and that makes GALCIT unique.

Embedded as it is in another unique institution, the California Institute of Technology, GALCIT benefits from collaborations with other academic disciplines. Professor Ortiz puts it quite clearly: “The fact of interdisciplinary collaboration at Caltech is not just ‘talk.’ It’s really true.We work on a daily basis across disciplines.” Ortiz works in computational solid mechanics. The direct impact of his work is improving our understanding of the behavior of materials. As a necessary intermediate goal, he is improving methodsin computational mechanics and computational sciencein general. His algorithms, for instance, seek to make more efficient uses of computers. His efforts in this regard have made some impact on mathematics, and
with respect to his collaborators in this area he mentions, “We shouldn’t forget, I’m a real fan of mathematics. I think it’s the grease that makes everything possible. So we interact very closely with card-carrying, hard-core mathematicians.”

The collaborations between GALCIT and various groups on campus are varied and endless. Another to note is that between Professor Ravichandran and his newest partners.

G. Ravichandran: Most recently, in collaboration with my colleagues in Mechanical Engineering, Applied Physics, and Materials Science, I have been working on active materials. Active materials are materials that respond to external electro/magneto mechanical or thermal mechanical loads and they can change shape. So they can be used for active control
of structures. For example, for a helicopter blade, you want to deform the surface during flight to adapt to the aerodynamic conditions. This is really a dream—but I believe it will happen.
So we study material behavior for actuators for novel applications. We apply an electrical voltage on a ferroelectric material, and at the same time we subject it to mechanical loading via stress. This causes the material to change shape;
as it generates strain, it is doing work against the stress, and you have work output, so it can be an active device. When we take off the voltage the material deforms again due to the stress and you can have a cycling actuator. There is a broad range of applications one can envision. It can be used in adaptive optics for use in astronomy, and so on. My role in this project is to demonstrate the principles in such an active device.

The interactions are not limited to projects between faculty members. As Professor Leonard explains, “If a student in another department happens to be interested in what you are doing, there are no barriers at all. I had a PhD student in physics; several in mechanical engineering, and one in applied mathematics. It’s great!”

One of the particularly unique aspects of GALCIT is its strong experimentalmode. No matterwhom you talk to in GALCIT, a pure theorist,or the pointedly experimental types,the message is the same. Gharib puts it succinctly: “GALCIT is the mecca of experimentalmechanics. There is no place in theworld that can come close. The quality andthe types of problems we investigate are atthe most challenging frontiers.”

A. Rosakis: At GALCIT, we arevery proud of our experimentalfacilities. They are unique,and they are extensive.Wehave managed to keepthem in an era where computationis taking over theworld. And although thedevelopment of computerfacilities is an excellentthing, in certain casesthis has been at theexpense of the observation of reality. Computationalanalysts like my colleagues Michael Ortiz and TonyLeonard are developing very advanced codes that arecapable of doing things that are unprecedented. However, as they would admit themselves, they are notobserving reality. So advanced experimental techniquesthat have high fidelity and use high-resolutiondiagnostics are absolutely necessary. It is true that inmechanics, both in solids and fluids, the trend is to gotowards theory and computation, rather than experiments,because experiments are expensive. It is a simpleexplanation. They are difficult, dirty, and expensive.However, at GALCIT,we have managed to preserveour experimental identity and that isone of the things that I would like to seecontinue. Our position is so unique in thecountry and the world that actually its losswould be a great crime.

W. Knauss: A totally new field that GALCITis exploring is experimental nanomechanics.There are really very few directexperiments being performed inthe nano range. Instead,everything is done byinference from what ismeasured on a considerablylarger scale, and todeduce properties orbehavior with the aid ofthose inferences,assumptions are a necessaryevil. It has always seemed terribly dangerous to make these assumptionsand then apply the results without the direct experimentationbackground. Let me cite a recent experience as an example.One of my students performed measurements of the(frequency dependent) volumetric compliance of apolymer. This deformation process was then simulatedvia a molecular dynamical computational model. Uponcomparing experiment with the computations, the two differed very significantly—they were in the ballpark,but not close enough even for rough engineering purposes.Where GALCIT excels is in supplying both experimentsand computational capability to fine-tunenumerical codes and make them accurate. Asengineers,we are often asked to put faith incomputations because they all look fine oreven rational in the sense that what has togo up, goes up and what should go down,does go down. But how close we come tophysical reality by computational means canonly be ascertained via experiment. This is anexpensive proposition, and because computationalanalysis renders “results”more quicklythan experiments, the trend inresearch—and funding—is on aseemingly unstable slopetowards computation. Mybiggest worry is that theexperimentalists are beginningto disappear in solidmechanics. If GALCIT has amission it is the perpetuationof the proven synere gisms of experiment and analysis in both solid andfluid mechanics. As a final reminder in this context itneeds to be remembered that new physical phenomenaare only found in the laboratory.

G. Ravichandran: I am an experimentalist—sometimesI do computations, but I am primarily interestedin experiments. I always liked to build things and seethings work. I am interested in physical phenomenarather than doing things on the computer or withpaper and pencil. I am a hands-on person and that’swhat fascinates me. As part of our ferroelectrics work,we have experimentally validated a theoretical prediction.Kaushik Bhattacharya [Professor of Mechanicsand Materials Science] first made the prediction of how to achieve large strain in these materials. But hiswas a thought experiment, on paper. One has tounderstand what are the principles behind theconcept, and whether one can even make this ideawork.What can be imagined is not always possibleto implement. So we are doing a reality check onthese thought experiments. That is one role of theexperimentalist. The other role is to discover newphenomenon that have not yetbeen predicted bytheory. The theorythen catches up.This doesn’t happenoften, but thereare quite a fewexamples. It’s a veryimportant part ofthe mix.

Very striking is that the thing which is most attractive to the theorists is this practical, “downand dirty” work at which GALCIT excels.

A. Leonard: GALCIT is very strong experimentally. Thatis what makes it great. And that’s one thing I think thatwe all agree on; even the computational people agreethat we have to keep this going. In today’s climate it’shard to do that, but we’ve got to,we can’t just followthe crowd. The experiments that [Professor Emeritus]Don Coles was doing in the 1970s were the things thatreally attracted me to this place. He was doing experimentson turbulent spots in laminar boundary layers.They were really neat experiments, and I just appenedto be trying to compute these same things atthe time.

GALCIT’s experimental facilities aretucked into labs large and small, found byexploring the labyrinthine corridors of theFirestone, Kármán, and Guggenheimbuildings. Some are quite well known, asthe T5 shock tube is, others are absolutelyunique and a bit harder to find.

J. Shepherd: When I came,my idea was to set up alaboratory where wecould study explosionsin a universitysetting. There arepeople who dothat around theworld, but it’s afairly uniqueactivity. Mostpeople view explosions as something that is hazardous and theyare a little reluctant to think about setting up a labinside a building.We built this lab in order to look atproblems that are both of scientific interest, and ofinterest to industry.We have to pay the bills. So wehave always looked to practical problems—crashingairplanes, explosions in chemical plants, hazards insideof nuclear waste storage facilities. The goal,though, is to have a scientific understandingof these problems; there is avery large community of engineers,including those in the chemicalindustry, who study explosionsfrom a very pragmatic standpoint.They simply want to minimize oreliminate the problems and for themwhat’s interesting is not to have theexplosion; for us,what’s interestingis to have the explosion andstudy it.

New to GALCIT are theLucas Adaptive WallWind Tunnel (AWT)and the Ludwieg Tube.The Lucas AWT wasmade possible by agenerous gift from theRichard M. Lucas Foundation. It uses adaptive wall technology in the testsection to reduce and even eliminate the need for datacorrections required in straight-wall tunnel tests. Whilethe tunnel is operating, pressure measurements are takenalong the floor and ceiling of the test section; combinedwith the current displacement profiles, a one-step predictivealgorithm determines the required wall contourfor the current model configuration and adapts the wallsto match. The system effectively “tricks” the air intothinking it is in an infinite flowfield, rather than confinedby the walls of the tunnel.

The Ludwieg Tube is a Mach 2.3 facility that providesclean supersonic flow with relative ease and lowcost. It is ideal for universities as it allows students thepossibility to do experimental work at supersonicregimes without a complex facility to support. Thedevice is the ultimate in simplicity, consisting of a tubepressurized with air and an evacuated tank.When thethin aluminum diaphragm separating the tank fromthe tube is broken, the flow is accelerated to supersonicvelocities for about one-half second inside thecarefully machined nozzle at the end of the tube. Thenoisy boundary layer on the tube walls is divertedinto an annular slot at the end of the tube in order tokeep the flow quiet inside the nozzle. The LudwiegTube is being used not only for teaching, but like manyfacilities in GALCIT, as a research tool as well.
The most importantproduct thatGALCIT hasproduced, however,is its people. Approximately2,000 people have graduate degreesfrom GALCIT, and they havegone forth to all parts of theworld to make their mark. TheBrazilian, Indian, and Chinese space programs all beganwith significant leadership by GALCIT graduates. Youwill find many GALCIT graduates as professors in universitiesacross the U.S. and throughout the world, aswell as in the top echelons of government labs andindustry.

P. Dimotakis: And if you ask me what is differentabout GALCIT, I would say it is this philosophy thatwhat we strive to impart to the students is a very fundamentaland a very broad-based understanding inmathematics and physics, as well as engineering principlesand fluid mechanics and solid mechanics, and soon. There is a continuum of types of knowledge oneneeds so that one is productive not only at the timeone graduates, but also 10, 20 years later. That is a verysobering thought. In case it is difficult to imagine 20years out, I invite students to think back 20 or 30 yearsand to imagine that they had graduated then, andnow they are called upon to contribute to bioengineering,to space physics, to high-energy lasers, to failureanalysis—you name it.Would they have receivedthe tools and educational background to make suchcontributions? Did they receive them then, and arethey receiving them now? Well, GALCIT graduates did.The testimony to that is that if you look at many of thenew technologies and many of the new thrusts in scienceand engineering that were initiated in the last 10to 20 years, many of them have GALCIT graduatesbehind them. The development of the chemical laser,for instance. And, in some measure, GALCIT graduatescontributed to the development of inertial-confinementfusion and laser fusion. These could well be thepower sources of 50 years from now. Many of the challengesand limitations in how well one can hope toconvert hydrogen and deuterium into helium andenergy have to do with shockwaves and gasdynamics.The compression takes place by a converging shockthat is driven by umpteen lasers ablating an outershell. Not many people understood the gasdynamicsof how to do that—but GALCIT graduates helped dothat.You will find GALCIT graduates doing all kinds ofthings. Some of them are in the aerospace world, butprobably not the majority.

And so GALCIT is poised for the next 75 years, balanced on long-standing organizing principlesand unbounded imagination.

F. Culick: My thesis supervisor at MIT had been a GALCIT
student for a while, and he eventually earned hisPhD elsewhere with H.S. Tsien [PhD ’39]. So my connectionwith GALCIT in this respect stretches way back.When I arrived in the early 1960s, most of the then currentfaculty had been here a long time and constitutedreally the first generation of GALCIT. I have seen all theincarnations of GALCIT over the decades. In somerespects, the place is still the same, still guided by thesame aspirations and goals it was founded with. Butwe are suffering from the same problem most universitiesare suffering from these days—we are more andmore buffeted by external influences, and this usuallycomes down to funding. Time spent raising moneydetracts from cultivating the closeness that we havealways treasured.

G. Ravichandran: GALCIT has adapted in a uniqueway to the current and future universe of ideas in thesense that for 75 years it has evolved.You cannot bestationary and be successful.We have adapted to newideas and generated new ideas.We also look into thefuture and reach out. This is what keeps the place alive.This has been brought about by a culture based onfundamental science with an eye toward practicalapplications.

P. Dimotakis: The philosophy of von Kármán, still embraced today, guides us. If you want something thatis lasting, that will be at the forefront 20 years fromnow: don’t train people, educate them. There is a differencethere that is not so subtle. This is what setsGALCIT apart.

It’s important to capture people’s imagination. It’s important to work and contribute to frontier areas,because those capture the imagination of young peopleand ultimately that is what it’s all about.