Application d'un modèle de champ acoustique aléatoire à l'environnement sonore de la maquette Ariane 5

Abstract
The prediction of the acoustic environment of a launcher at take-off is an important problem to which jet noise theories do not give a satisfactory answer, because of the complex interactions between the jets of the boosters and the structures of the launch pad. Thus, a modelization of the acoustic field has been undertaken directly, using the measurements on the cylinder wall of a captive ARIANE 5 1/20 scale-model. The measurements were made for several firings of the launcher at various altitudes. The physical model, composed of a limited number of uncorrelated plane waves, takes into account the random character of the incident field and allows us to compute the acoustic field scattered by the wall of the launcher, represented by a portion of an infinite cylinder. The comparisons between computed and measured sound pressure levels and cross-correlation functions allow us to optimize the parameters of the model. This is the first step for determining the acoustic pressure on the payload of the launcher. These computation also give us information on the sound sources and on the efficiency of noise reduction devices.