Exhaust Nozzle Plume Effects on Sonic Boom Test Results for Isolated Nozzles

Abstract

Reducing or eliminating the operational restrictions of supersonic aircraft over populated areas has led to extensive research at NASA. Restrictions were due to the disturbance of the sonic boom, caused by the coalescence of shock waves formed off the aircraft. Recent work has been performed to reduce the magnitude of the sonic boom N-wave generated by airplane components with focus on shock waves caused by the exhaust nozzle plume. Previous Computational Fluid Dynamics (CFD) analysis showed how the shock wave formed at the nozzle lip interacts with the nozzle boat-tail expansion wave. An experiment was conducted in the 1-by 1-ft Supersonic Wind Tunnel at the NASA Glenn Research Center to validate the computational study. Results demonstrated how the nozzle lip shock moved with increasing nozzle pressure ratio (NPR) and reduced the nozzle boat-tail expansion, causing a favorable change in the observed pressure signature. Experimental results were presented for comparison to the CFD results. The strong nozzle lip shock at high values of NPR intersected the nozzle boat-tail expansion and suppressed the expansion wave. Based on these results, it may be feasible to reduce the boat-tail expansion for a future supersonic aircraft with under-expanded nozzle exhaust flow by modifying nozzle pressure or nozzle divergent section geometry. Nomenclatureβ nozzle boat tail angle, ° D test nozzle diameter, in. NPR nozzle pressure ratio = P t /P ∞ P local static pressure, psia P t total pressure in nozzle, psia P ∞ free stream static pressure, psia ΔP/P (P -P ∞ )/P ∞ t time, sec x axial distance from jet simulator nosecone tip, in. y distance from nozzle centerline, in. IntroductionNASA has been conducting extensive research programs to reduce the sonic boom signature caused by supersonic flight speeds. Current aircraft flight restrictions, allowing supersonic flight over water only, are due to the disturbance caused by the sonic boom. The sonic boom is generated by coalescing shock waves formed by aircraft components, which generate an N-wave. A sample N-wave sonic boom signature is shown in Figure 1. The N-wave consists of a rise in pressure versus time as the aircraft 'bowwave' passes over an observer, followed by a reduction in pressure, and finally a return to atmospheric Complementary work is desired to reduce the sonic boom signature in the aft portion of the sonic boom N-wave, which in turn would decrease the peak-to-peak magnitude and result in a reduced sonic boom. This can be accomplished by aircraft shaping, and through study of how aft components, such as the tail, nacelles, and nozzles contribute to the right hand portion of the sonic boom N-wave.Previous work on exhaust nozzle contribution to sonic boom included a report by Putnam and Capone (Ref. 3), and another by Barger and Melson (Ref. 4). In the work by Putnam and Capone, nozzles were tested from a fully expanded Mach 1.7 nozzle to a fully expanded Mach 2.9 nozzle. Their study was conducted in a wind tunnel, where near-field pressure measurements we...

Exhaust Nozzle Plume Effects on Sonic Boom Test Results for Vectored Nozzles

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Computational and Experimental Study of Supersonic Nozzle Flow and Aft-Deck Interactions

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Computational and Experimental Study of Supersonic Nozzle Flow and Shock Interactions

“…Data were collected at this location due to space restrictions in a small wind tunnel, and is consistent with previous experiments. 15 The static pressure probe had a capability to travel axially up to 8.0 inches to capture pressure profiles, with an x=0 chosen as the nozzle exit plane. The actuator position and probe starting location were changed during the test, dependent upon where the shock interaction was located.…”