Numerical Simulations of Overexpanded Jets at a Mach Number of 3.1 Impinging on a Plate with and without a Hole

International audienceFour initially highly-disturbed overexpanded round jets at an exit Mach number of 3.1 and a Reynolds number of 2&_times; 10<sup>5</sup> have been computed by Large-Eddy Simulation (LES). The static pressure and temperature at the nozzle exit are respectively equal to 0.63 &_times; 10<sup>5</sup> Pa and 738 K. One jet is free whereas the three other ones impinge on a plate located at a distance of L=30r<sub>0</sub>, where r<sub>0</sub> is the nozzle radius. Two of the plates have a hole of diameter d=2.6r<sub>0</sub> and 4r<sub>0</sub> while the last one has no hole, in order to study the effects of the hole on the jet flow and acoustic fields. For all jets, the acoustic field in the downstream direction is dominated by the radiation of Mach waves. However, the acoustic levels for the impinging jets in the upstream direction are significatively higher than for the free jet. They are caused by the sound waves generated by the impingement of the jet turbulent structures on the plate, namely the impingement noise, and the reflection of Mach waves on the plate. Furthermore, the upstream sound pressure levels are the highest for the plate with no hole and are reduced when the hole diameter increases, suggesting that the impingement noise is the main acoustic contribution