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News & Highlights NAS Engineers Design Innovative Sonic Boom Measurement Technology 07.05.12 Aeronautics experts in the NASA Advanced Supercomputing (NAS) Division and the NASA Ames Wind Tunnel Division, in collaboration with NASA Langley Research Center and Lockheed Martin, have designed an innovative apparatus to increase the accuracy of sonic boom measurements in future wind tunnel tests. Pressure rail instrumentation is used in sonic boom tests to measure the pressure signature of modeled supersonic aircraft in small-scale wind tunnel tests. The new design features a very thin, blade-like rail with a small, tapered tip (1.27 millimeter radius) near the sensors that measure the pressure caused by the boom. This design decreases shock reflections off the tunnel wall from contaminating the data by measuring upstream of the reflected shocks—ensuring a greater accuracy in the test results. Averaging the data with the model at multiple tunnel positions further reduces any other errors caused by ambient tunnel shocks and expansions. The pressure rail was designed and validated with NAS-operated supercomputers and computational fluid dynamics (CFD) codes such as CART3D, which produces high-fidelity analyses for conceptual and preliminary aerodynamic designs. The rail has been used in several experiments conducted in the 9x7-foot Supersonic Wind Tunnel at NASA Ames. A pair of unique wind tunnel tests on the effects of humidity on pressure measurements were performed using two Lockheed calibration models, a large Lockheed supersonic transport model, and a low-boom wing-tail model developed by NAS engineers. Test results showed that by injecting dry, high-pressure air into the wind tunnel, scientists could effectively control and stabilize humidity levels, thereby enabling more accurate measurements of sonic boom signatures. In the process of designing the new rail instrumentation, the NAS team also dramatically increased the accuracy of sonic boom prediction capabilities of tetrahedral-based flow codes such as AIRPLANE and USM3D, which solve complete aircraft configuration problems in supersonic flow regimes using CFD. Their new technique enables a simulation's computational grid to be extended much farther from the vehicle—without suffering signal dissipation—than was previously possible with AIRPLANE or USM3D. A sonic boom/aerodynamic drag prediction workshop for computational tool validation will use the new NAS-designed rail instrumentation to obtain experimental sonic boom data from Lockheed and Boeing low-boom test models. The workshop will be scheduled for sometime in 2013. For more information contact: Susan Cliff firstname.lastname@example.org