The influence of gas-dynamic processes on acoustic radiation in the interaction of impinging jet with the flat plate

1Nikolin, SO, 1Sokol, GI
1Oles Honchar National University of Dnipropetrovsk, Dnipro, Ukraine
Space Sci. & Technol. 2020, 26 ;(3):20-31
Publication Language: Russian
The spacecraft launch is one of the most important phases of the flight missions since the complex gas-dynamic interactionprocesses of a high-temperature supersonic jet which is flowing from the nozzle of the propulsion system with the structural elements of the launchpad are typical for this phase of flight. These processes entail the occurrence of turbulent flows accompanied by shock waves, the waves’ discharge, and contact discontinuities. As a result, elements of the launch pad and the walls of the flame duct undergo intense gas-dynamic and thermal loads. Instabilities and transients generate acoustic and vibration fluctuations. The last ones affect the structural elements of ground structures, the state of the payload, and the ecosphere around the launch pad. Therefore, the correct prediction of these loads at the preliminary design phase of the rocket and launch facilities can significantly increase the strength and stability of the spacecraft elements, increase their reliability, as well as provide measures to reduce noise levels in the rocket launch area.
              The objective of the study is the impact of the distance between the nozzle exit and a flat obstacle on the gas-dynamic characteristics of the impinging jet and the resulting acoustic radiation. The gas-dynamic processes that occur when a supersonic jet flows onto a barrier are described using the Navier-Stokes system equations. The equations express the laws of conservation of mass, momentum, and energy for an ideal gas. Calculation of acoustic processes was performed in two stages using the Fox Williams-Hawkings integral method and Fourier series expansions. At the first stage, the gas-dynamic problem was solved in a steady-state mode using the SST k- turbulence model. The second
stage was acoustic in transient mode using the DES turbulence model. The results of calculations were some gas-dynamic and acoustic characteristics of the supersonic underexpanded jet flowing onto a flat plate presented in the form of diagrams and graphs.
            The results demonstrated that an increase in distance between the nozzle exit and the plate leads to the appearance of complex turbulent flows, which in turn cause the increase in acoustic radiation levels. This is due to the fact that oscillations of the turbulent sublayer and the presence of shock waves and rarefaction waves are the main sources of noise when a jet flows onto a flat plate. The intensity of noise sources also increases with increasing distance between the nozzle and the plate. However, if we consider the far acoustic field, changes in this distance weakly affect the overall sound pressure level possibly due to receivers are far outside the computational domain. In this case, the used FW-H method works worse.
Keywords: acoustic pressure, flat plate, Mach number, pressure coefficient, sound pressure level, underexpanded jet

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