Noise radiated from free and impinging hot supersonic jets

Abstract

On behalf of CNES, ONERA studied the noise of high supersonic hot jets, in order to anticipate the acoustic loads of ARIANE 5 launcher at lift-off. The free jet acoustic model, deriving from NASA's studies, uses an empirical approach based on multiple experiments. For the extrapolation at the full scale, the model has been applied to firings of different sized rockets. With a constant Mach number of the fully expanded jet, the acoustic efficiency appears to be constant. An extension of the model, using simple assumptions (conservation of the acoustic power), allows us to calculate the acoustic field when the jet impinges on a full or open plate, which represents the launch pad. First tests with realistic conditions (exit Mach number greater than 3) were carried out in the MARTEL test stand of CEAT Poitiers. An appropriate measurement technique shows that the radiated acoustic power is practically independent of the shape of the obstacle and of its distance from the nozzle. The MARTHA computer code, using empirical improvements (acoustic reflections on the wall jet, strong upstream directivity of the acoustic sources of the impingement area), allows a satisfactory simulation of the measured sound pressure levels.