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Back in the late 1980s, a document went around the CFD group at General Dynamics (now Lockheed Martin) in Fort Worth that gave us all a pretty good chuckle. In the year 2096 researchers were wondering whether wind tunnels could be used to reproduce the flowfields computed by CFD. In case the humor is lost on you early-career professionals, CFD in the 1980s was still wet behind the ears and wind tunnel testing was how one got quality aerodynamic data.
Time passed and I lost the printed sheets of paper with the funny story. (No email, no word processing. This story reproduced by photocopier.) But I never forgot it. As luck would have it, when I casually asked a NASA CFD friend if he had ever seen it, he was able to dig up a PDF and share it with me. This tells me two things. At least one other person thought it funny enough to type it all in to a word processor and produce a PDF. And another person also liked it enough to save it.
Little is known of the original author. The byline names the author as Robert Coopersmith. A search on LinkedIn produced no likely leads. And the story's footer states "Appeared in AIAA Student Journal." If anyone knows the original author, please have them stand up and take a bow.
by Robert CoopersmithJanuary, 2096Lockheed Aeronautical Systems Company
We all know of the importance of computers in today’s aerospace engineering environment. The latest advances in cryogenically cooled semi-superconductor technology and microscopic germanium sub-wafer assembly has made desktop 100 MINS (Millions of Navier-Stokes solutions) machines commonplace in engineering use.
We are also aware, however, of the high cost of this aging technology. The most accurate aerodynamics prediction code available today, FLO-1234.5, is so complex and expensive that it has never been run. Many other codes, if run to completion, would require CPU time exceeding the average human lifespan. Most engineers attribute this situation to the time when the task of writing aerodynamic computer programs was automated and handed over to the computers. We now have codes too complex to be understood by any human being. The cost of computing has been rising exponentially over the years. Clearly, if these trends continue unabated, computational solutions will soon be beyond anyone’s means.
Fortunately, there is an exciting new technology on the horizon which may someday replace the computer for aerodynamic design and analysis. Two workers at UNCAF (United Nations Computational Aerodynamics Facility) have recently made a startling discovery. They found that by building a small wooden model of an airplane and then blowing air past it in an enclosed tunnel, reasonably accurate predictions may be made of what the flow codes would compute. They refer to the method they have discovered as a “wind tunnel”. At present, “wind tunnel” modeling is still in an early and relatively crude stage, and cannot be expected to precisely reproduce numerical results. For example, the continuous surface of a wood or metal airplane model will never exactly duplicate the discrete nature of a computational grid. Also, some factors, such as artificial viscosity, are neglected completely in wind tunnel modeling. It may be especially hard to accurately predict linearized potential flow in the tunnel. Nevertheless, in many cases, the wind tunnel agrees surprisingly well with the computer.
Constructing a wind tunnel model is much quicker and less labor-intensive than running all but the simplest computer programs. Shops such as Minicraft or Static Engineering complete even a highly detailed titanium model in a mere matter of months. Thus, many design iterations and trade-off studies can be conducted in a fraction of the time required via the computer. Advances in wind tunnel technology and model fabrication are expected to proceed at a rapid pace. Many promising techniques, such as the chiseling of facets in Plaster-of-Paris models to more closely resemble computational panelings and grids, are already being suggested by researchers around the world. The future prospects of this amazing new wind tunnel technology are bounded only by the imagination.
But what, you may ask, will be the fate of the millions of computational aerodynamicists presently employed in the aerospace industry? Is the wind tunnel a threat to their job security? While it is true that some may lose their jobs, a brand-new demand will be created for those well-versed in the state-of-the-art wind tunnel technology. Engineering graduate schools are already replacing courses in Finite Volume Methods and Grid Generation with curricula in woodworking and whittling. Clearly, engineers will be freed from the tyranny and drudgery of computational methods, giving them more time to concentrate on creative tasks. It is doubtful, however, that the computer will ever be completely eliminated: the thought of an airplane designed solely from wind tunnel data without the aid of the computer seems too incredible to believe. While the wind tunnel may never fully replace the computer, it is almost certain to become the most useful engineering tool of the future.
<end of original article>
For the record, I did fix two typos and changed one gender-specific pronoun. But otherwise, the article is as I received it in that PDF from my NASA friend. I cannot guarantee this is the exact version I first saw in the 1980s but it seems so familiar. Yet my re-reading did latch onto several interesting topics.
3D printed structured grid around an airfoil, c. 2012. STL file produced with the Print3D plugin for Pointwise. Printing by Shapeways.
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