A COMPLETE PROCESS FOR SONIC BOOM ASSESSMENT WITH ATMOSPHERIC AND MANOEUVRES EFFECTS.

Dassault Aviation as a civil aircraft manufacturer is studying the feasibility of a supersonic business jet with the target of an “acceptable ” sonic boom at ground. A sonic boom prediction process has been developed involving three main steps that can be summarized as follows. 1) First, pressure nearfield around the aircraft is obtained from CFD; however, compared to usual CFD for aerodynamic performances (lift and drag), computation with good precision has to be performed at relatively large distances from aircraft. 2) Then midfield pressure variations can be extrapolated from the following rules: • Propagation code is valid as soon as the pressure variations can be considered as locally axisymmetric; • Pressure variations around the aircraft can be rebuilt as a modal distribution which ratisfies the assumptions of the propagation code. This method allows to take into account automatically all the pressure disturbances around the aircraft (shape, lift effect, engines integration,..) that contribute to the sonic boom signal propagated down to the ground. 3) Finally, a propagation code based on geometrical acoustics in an heterogeneous, moving medium takes into account meteorological effects, nonlinear distorsion and aircraft manoeuvres (acceleration and turns). For this later case, caustics due to sonic boom focussing are yet only located at the ground level