Tag: Computational fluid dynamics modeling

Computational Fluid Dynamic Researchers and Experimental Fluid Dynamics Researchers Must Work Together

Panelists: Moderator James Heidmann, NASA’s Glenn Research Center; Keith Blodgett, GE Aviation; Michael Mastaler, NASA; Richard “Dick” Scharnhost, Boeing Co.; Roy Shultz, Mira Facilities 2 Inc.; Paul Van Slooten, United Technologies Research Center

By Duane Hyland, AIAA Communications (2008-2017)

Government and aerospace industry experts debated the merits of computational fluid dynamics modeling and experimental fluid dynamics modeling during “Integrated Roles of Experimental Fluid Dynamics and Computational Fluid Dynamics,” a panel at the 2015 AIAA Propulsion and Energy Forum in Orlando, Florida. The conclusion: CFD and EFD practitioners must find ways to work together rather than dividing into separate camps.

CFD is the computer-driven analysis of flows in and around structures, and EFD is the use of a wind tunnel to do the same analysis.

Panel moderator James Heidman, an aerospace engineer with NASA’s Glenn Research Center, told the audience that, in his opinion, “there is a strong need for a collaborative effort for CFD and EFD going forward; they both have a lot in common, and the communities should communicate better.”

Paul Van Slooten of the United Technologies Research Center said that in 1975 it was believed that CFD would replace wind tunnel testing within two decades. He then pointed out that the declared death of wind tunnel technology was premature, with NASA, NASCAR and Mercedes-Benz just some of the companies who have built wind tunnel facilities in recent years. Every panelist agreed that although CFD use is expanding throughout testing circles, there are still some things that it can’t do well, so researchers must still use EFD methods.

Among the things that CFD can’t do well, but EFD can, according to all the panelists, are accurately predicting separated flows; modeling compressor stalls; modeling transonic separation; and modeling high angles of attack. The panelists said that traditional EFD testing in wind tunnels is still the best way to obtain data in those instances.

The best paradigm, Van Slooten explained is for CFD and EFD to work “side-by-side, complementing each other.”

Another problem with relying exclusively on CFD can be the “garbage-in, garbage-out” problem, as several panelists pointed out. If the operators don’t know how to work the data sets properly, you could end up in a situation where you have a lot of data but nothing that really matters, or even worse, just bad data.

In the end, both sides of CFD and EFD methods must talk to one another and work side-by-side.

As Roy Shultz of Mira Facilities 2 Inc. explained: “It’s relevant and important, and the people who need big data should be very interested in talking to the people who produce big data so we understand what the big data we are getting is.”

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All 2015 AIAA Propulsion and Energy Forum Videos

Constraints on Wind Tunnel Testing Frustrate Engineers

Panelists: Doug Garrand, Aerospace Testing Alliance; Michael Mastaler, NASA; Michael Holden, CUBRC; Michael McWithey, Lockheed Martin Corp.; David Schuster, NASA’s Langley Research Center; Roger Simpson, NASA’s Stennis Space Flight Center

By Hannah Godofsky, AIAA Communications

Wind tunnels have been a key part of the testing and validation process in aerospace for a long time. However, the operational capacity of those systems is being threatened by several outside forces. Budget cuts and the use of computer simulations have made the use of wind tunnel facilities to conduct testing seem a luxury to engineers.

“In today’s budgetary climate, large, costly facilities naturally become a prime target for mothballing, closure or divestment to offload the financial burden,” explained David Schuster, a NASA technical fellow with the NASA Engineering and Safety Center at NASA’s Langley Research Center, during the 2015 AIAA Propulsion and Energy Forum panel “Evolution of our National Ground Test Capability,” which discussed the role and capabilities of wind tunnel testing in this new environment.

Doug Garrard of the Aerospace Testing Alliance expressed optimism about the state of wind tunnel testing in the U.S., saying several facilities operated by the military are the best in the world.

Michael McWithey, manager of Wind Tunnel Testing Labs with Lockheed Martin Corp., said many of the facilities in the U.S. are aging as they were built following World War II or during the Cold War to compete with Germany and Russia. He explained that in the absence of a similar threat, many U.S. wind tunnels have been closed or moved offshore as a result of budget constraints.

Computational fluid dynamics modeling of air flows using software programs also has reduced the need for some wind tunnel testing. Michael Mastaler, associate director of the Advanced Air Vehicle Program with NASA’s Aeronautics Research Mission Directorate, emphasized that wind tunnel testing should play a complementary role to the use of computer simulations. He said wind tunnels continue to have some unique capabilities that software programs do not and that it is those unique capabilities that must come into play before the cost can be justified.

“The primary reason we are here and our assets are here is to support the NASA programs,” elaborated Roger Simpson, program manager of the Rocket Propulsion Test Program Office with NASA’s Stennis Space Flight Center.

Michael Holden, vice president of aeronautics with CUBRC, a nonprofit wind tunnel testing facility, spoke about the advances that have been made on the technology side of ground testing. He said the CUBRC facility has some very advanced capabilities, including that missiles can be tested at Mach 20, a level that would duplicate a vehicle’s effects of actually flying the missile.

Component testing can run up to 30,000 feet per second, Holden said. He described some of the chemical and technological constraints on this type of testing, including the introduction of unknown variables at high speeds and the inconsistency of results.

According to the panelists, wind tunnel testing may continue to become rarer, but it will never go away entirely. Though companies and agencies have a responsibility to be prudent and ensure that resources are not being wasted, no software program can fully eliminate the need for lab experiments. Wind tunnels and the skilled employees that operate those facilities are still needed to develop new aerospace vehicles.

Video

All 2015 AIAA Propulsion and Energy Forum Videos