《湍流研究的黄金时代》

aspen · 发表于 2005-6-21 22:34

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<a href="http://www.chalmers.se/HyperText/Prof-E/George-E.html" target="_blank" >http://www.chalmers.se/HyperText/Prof-E/George-E.html</A> 转贴前沿：这是我读过的关于湍流研究最honest，也最ambitious的文章。原文较 长，不过先摘录文中最后一段中的一句话让大家听听什么叫真正的牛气冲天： I have been a full professor for 20 years in the USA, so I did not come to Sweden to BECOME a professor. I came to Sweden because I thought I could be a better professor. -------------------------------- Turbulence William K. George has been appointed Professor of Turbulence at Chalmers University of Technology from September 5, 2000. He was born in Camp Shelby, Mississippi in 1945. He graduated from Cambridge, Maryland High School, in 1963 as valedictorian. He received his BES and PhD degrees in 1967 and 1971 respectively from the Johns Hopkins University in Baltimore, Maryland. He joined the faculty of the Pennsylvania State University in 1968 and left in 1974 for the State University of New York at Buffalo, where he has been a Chair Professor since 1980. He has authored several hundred papers, mostly on turbulence and its applications, and is a fellow of the American Physical Society/Division of Fluid Dynamics. He is known for his work on both theoretical and experimental turbulence. His contributions range from measurements in gas turbines and automotive components, to fundamental studies of turbulent shear and wall-bounded flows. He has supervised 16 PhD students and an equal number of MScEng students. //////////////////////////////////////// The golden age of turbulence // //////////////////////////////////////// The turbulent motion of fluids has captured the fancy of observers of nature for most of recorded history. The patterns of blowing snow and torrential streams fascinate adult and child alike. Turbulence marked by billowing clouds and falling leaves, cigarette plumes and even the swirling cream in our coffee cups, constantly competes for our attention. From our almost subconscious winter observation of the moisture jets condensing before our mouths to our lazy, dreamy summer-day musings under the contrails high overhead, turbulence makes us conscious of our pace as well as the pace of our lives. And who has not been willingly hypnotised by the licking flames of an open fire? The handiwork of turbulence enriches the lives of everyone. Yet no-one can comprehend its mysteries. Even so, the distinction between art and research is often difficult - especially for those like me who try. But even as the omnipresent turbulence delights us with its unending variety of artistic forms, it also challenges our quest for authority over the world around us. This is why turbulence is near the top of any list of the major unresolved problems for science and engineering. And this is also why it has been the focus of my own research for the past 30 years. As a graduate student I was fascinated by the sheer impossibility of the problem. And I was totally captivated by the fact that I not only think about it, I see it all around me. Whether I am driving my car, riding in a plane, or making an ocean passage, the turbulence problem is inescapable. And because it is, I am driven by both scientific curiosity and engineering need. Let us consider the engineering problem. While it may be difficult to place a price tag on the cost of our limited understanding of turbulence, it requires no imagination at all to realise that it must be enormous. Try to estimate, for example, the aggregate cost to society of our limited turbulence prediction abilities that result in inadequate weather forecasts alone. Or try to place a value on the increased cost to the consumer of the need to design virtually every fluid-thermal system - from heat exchangers for automobiles to wings for hypersonic planes - from empiricism, crude engineering models and experimentation. Add to this the resulting need for abundant safety factors and non-optimal performance, and also factors in the sometimes prohibitive cost of innovation. One of the curious characteristics of turbulence researchers is that we often wear two hats - scientist and engineer. On the one hand we can perform seemingly useless experiments to elucidate some hidden feature of turbulence that has no foreseeable engineering application. On the other, we can tinker with the constants of turbulence "models" to improve "engineering prediction", even though the models can be connected with the physics of the flow in only the most primitive manner. On the one hand, like all scientists, we seek to understand; on the other, like all engineers, we try to enable design and construction. Unfortunately, this dual mission is sometimes poorly understood even by us, since the two parts are not necessarily complementary - at least in this generation! A scientist or mathematician could certainly make a case that we do not know enough about turbulence to even start to consider engineering problems. To begin with, we have fewer equations than unknowns in any attempt to predict anything other than the instantaneous motions of the simplest kinds of fluids. Moreover, we will not be able to perform even these calculations for real engineering problems until many more generations of computers have come and gone. And even if we could perform a simulation of real flows, we would still be overwhelmed by the amount of data, especially in the absence of real criteria for selecting from it in a single lifetime what is important. Furthermore, even the things we think we understand about turbulence have never really been tested in controlled experiments because we have never had the large-scale facilities required to do so. In fact, most of what turbulence researchers agree on is perhaps more due to the time that has elapsed since the ideas were proposed than that they were ever subjected to experimental tests over the range of their assumed validity. The engineer would counter that planes must fly, weather must be forecast, sewage and water management systems must be built and society needs ever more energy-efficient hardware and gadgets, not to mention better ways to transform energy itself. Thus, regardless of the inadequate state of our knowledge, we have the responsibility as engineers to do the best we can with what we have. In fact, the engineer might continue to argue that we have done so well with so little for so long that perhaps there is no need for further research at all, especially if he is asked to pay for it. The famous British aerodynamicist B. Melville Jones wonderfully captured the essence of the problem when he said: Successful research enables problems which once seemed hopelessly complicated to be expressed so simply that we soon forget that they ever were problems. Thus the more successful a research, the more difficult does it become for those who use the result to appreciate the labour which has been put into it. This perhaps is why the very people who live on the results of past researches are so often the most critical of the labour and effort which, in their time, is being expended to simplify the problems of the future. But I am scientist and engineer. And my own personal assault on the turbulence problem has always been as both. Together, my students and co-workers and I have explored the very nature of turbulence. We have not hesitated to challenge the old ideas, or to offer new ones. But most of all we tried to be honest about what we knew, what we only believed to be true and what we used for the lack of better alternatives. And we tried especially to keep in mind that the ultimate goal was not just to expand the state of our understanding but to help provide engineering solutions to real problems.1 Not surprisingly, this dual approach to the turbulence problem, science and engineering also characterises the Turbulence Research Laboratory we are building at Chalmers. The staff have been carefully chosen from within the university and from industry, both for their expertise and for their breadth of experience and knowledge. The experiments and facilities that are being assembled have been designed to reveal new physics and test existing hypotheses but yet at the same time provide important new data for engineering model development. The equipment and tools we will install offer the potential to understand flows that were almost unimaginable even a decade ago. At a recent American Physical Society meeting Professor Franz Durst of Erlangen suggested that because of this we are entering the golden age of turbulence and fluid mechanics. Our goal at TRL is make Chalmers a major participant in this golden age. I have been a full professor for 20 years in the USA, so I did not come to Sweden to become a professor. I came to Sweden because I thought I could be a better professor. The rich tradition of Chalmers, especially the close interaction with industry and the commitment to excellence on the part of both faculty and leaders - all help create an environment in which I and my co-workers can be creative and productive. Hopefully by doing so we will not only make substantial contributions to turbulence but to the community as a whole. It is a joy to have this opportunity to join the Chalmers faculty and to be able to share it with my co-workers in the new Turbulence Research Laboratory and the Department of Thermo and Fluid Dynamics. 1 Information about this work is available from the website of the Turbulence Research Laboratory at <a href="http://www.tfd.chalmers.se/trl/" target="_blank" >http://www.tfd.chalmers.se/trl/.</A> -------------------------------------------------------------------------------- Updated: November 22, 2000 To the menu of the Research profiles at Chalmers To Chalmers Home-page About <a href="http://www.chalmers.se/" target="_blank" >www.chalmers.se</A>

cora · 发表于 2005-10-17 15:54

虽然上个世纪湍流统计理论取得了很大的成就，但是个人总还觉得研究湍流是一个苦海[em03]

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[基础理论] 《湍流研究的黄金时代》

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