APPLICATION OF A RANDOM ACOUSTIC FIELD MO DEL TO THE NOISE OF AN ARIANE-5 SCALE-MODEL

The prediction of the acoustic environment of a launcher at take-off i s an important problem to which jet noise theories do not give a satis factory answer, because of the complex interactions between the jets o f the boosters and the structures of the launch pad. Thus, a modelizat ion of the acoustic field has been undertaken directly, using the meas urements on the cylinder wall of a captive ARIANE 5 1/20 scale-model. The measurements were made for several firings of the launcher at vari ous altitudes. The physical model, composed of a limited number of unc orrelated plane waves, takes into account the random character of the incident field and allows us to compute the acoustic field scattered b y the wall of the launcher, represented by a portion of an infinite cy linder. The comparisons between computed and measured sound pressure l evels and cross-correlation functions allow us to optimize the paramet ers of the model. This is the first step for determining the acoustic pressure on the payload of the launcher. These computation also give u s information on the sound sources and on the efficiency of noise redu ction devices.