Contribution to the definition of a simple focusing test case and ONERA results for the two test cases of the sonic boom focusing predictions special session

For usual cruise flight conditions, the prediction of the sonic boom on ground caused by an aircraft flying supersonically can be predicted numerically by ray tracing codes according to the geometrical acoustics hypotheses. Such codes account for the non-linear and dissipative (thermoviscous and molecular relaxation) effects that occur during the propagation from flight level down to the ground by solving dissipative Burgers' equations along the rays, accounting for the evolution of the ray tube area. Such an approach is not applicable to predict the pressure waveform in the neighbourhood of a caustics that can be generated by the cusp of the focussing pressure wave generated under specific unsteady flight conditions of the aircraft. For such focussing conditions, the pressure waveform can be modelled by the Tricomi equations. The BANGV code has been used to predict the pressure waveforms in focussing conditions of the sonic boom focusing predictions special session of the 182nd ASA meeting. The results obtained for the two test-cases will be presented in this paper to be compared to other participants' results and contribute to the validation of numerical simulation methods of focussing boom.