In a Nutshell,
How I Came to Write Flow Simulations

by Tom Benson

January 3, 2000

I'm an aeronautical engineer at NASA Glenn Research Center, in Cleveland,Oh. I've been an engineer for a long time ... almost 30 years now. I was in college in the 60's (which was a lot of fun !! .. especially the music.) I received my degrees from Ohio State University and then had to serve four years in the Air Force since I was drafted during the Vietnam war. I was stationed at Wright-Patterson Air Force Base during some pretty exciting times. I participated in wind tunnel testing and evaluation of the Air Combat Fighter (YF-16 and YF-17), the B1-A bomber, the EF-111, and the F5-E, specializing in installed engine performance. I also did a little flight testing with the AC-130 gunship.

It was during wind tunnel tests for the F-16 inlet that I first visited NASA Lewis (which has been re-named Glenn.) When my military service was finished, I returned to OSU to work on a PhD in aeronautical engineering, with an emphasis on Computational Fluid Dynamics (CFD) for biological flows. We used computers to model the flow of blood through the circulatory system. I passed my qualifier exams and had begun building a computer program for my dissertation work, but decided to leave school and take a job with NASA before I had finished. I've been here at NASA ever since.

I started here at Glenn in a group that was developing CFD programs for inlet design and analysis. The inlet is the part of a propulsion system which brings the outside air into the engine. A well-designed inlet can let you do some marvelous things, like cruise at Mach 3+ with the SR-71, or maneuver to high angles of attack in an F-16. But a poorly designed inlet can cause big problems .. engine stalls or flameouts, high fuel consumption, or limits on the maximum speed of a hypersonic air-breather.

Wind tunnel testing of inlets is very expensive and time consuming, because you have to check many different flight conditions; different angles of attack, and yaw, and speed, and engine airflow conditions for each inlet design. So we try to do as much of the design and evaluation as we can using CFD. Hopefully, we can uncover and solve some problems before going to wind tunnel test. One problem that occurs in high speed inlets is an interaction between the boundary layer on the surface of the inlet, and the shock waves generated to slow the flow down and increase the pressure of the flow. In hypersonic inlets, the interactions can be highly three-dimensional, with the low energy boundary layer flow being pushed by the shocks into the corners of the inlet causing flow separation and bad inlet performance. During the 1980's I was involved with the National Aerospaceplane (NASP) program here at Glenn where we studied shock- boundary layer interactions in hypersonic inlets using CFD.

When NASP was cancelled, I used some of the visualization tools which had been developed to study the flow that would occur in an experiment flown in the bay of the Space Shuttle. This experiment was looking at ways to move and stir fluids in microgravity using a small jet of fluid in a large tank. The experiment was flown twice and we made comparisons between the computer predictions and the results which were observed by video on the flight. I also used the computer programs which were developed to model this low speed flow to study the more fundamental unsteady flow past a circular and a rectangular cylinder. I produced some videos from these calculations which were made available to universities for students who were studying these types of flow problems.

My interactions with universities, plus my familiarity with interactive graphics packages, plus the increased speed, size, availability, and affordabililty of PC's and workstations led me to my current interests. For the last 5 years, I've been building and distributing small interactive programs which run on PC's or workstations which simulate flow problems which students encounter in undergraduate education. I have packages to solve shock wave problems, basic airfoil problems, and the thermodynamics (thrust and fuel flow) of jet engines. All of the programs are interactive ... you change an input using a slider or type-in box and you get a new answer instantly. This lets students explore the physics without getting bogged down in the math. I distribute the programs using the world wide web, so that anybody, anywhere in the world, who has a PC or workstation can get the programs for free. To support the distribution of the programs, I have also developed an extensive web site called the Beginner's Guide to Aeronautics which includes explanations of how airplanes and propulsion systems work including the mathematical equations. http://www.grc.nasa.gov/WWW/K-12/airplane/index.html

This site is a web-based text book with problems developed by high school and middle school teachers. Most recently, I have begun to include JAVA applets on the pages to allow students to interactively explore some of the ideas presented on the pages.
FoilSim download, FAQ, all kinds of other stuff is at: http://www.grc.nasa.gov/WWW/K-12/aerosim/index.html
EngineSim interactive Java applet is at: http://www.grc.nasa.gov/WWW/K-12/airplane/ngnsim.html

I have found the past five years to be the most rewarding of my long career and look forward to developing new educational programs for students.