Investigation of integral surface formulations for acoustic post-processing of unsteady aerodynamic jet simulations

The acoustic post-processing of unsteady aerodynamic jet simulations using Kirchhoff or Ffowcs Williams and Hawkings (FW–H) surface integral methods is investigated from the theoretical and practical points of view. This analysis is carried out for a supersonic hot jet, starting from the flow fields provided by an unsteady aerodynamic simulation whose characteristics are recalled. Both acoustic integral methods are first compared from a theoretical point of view. In particular, the role of the ‘entropic’ sources on the control surface is pointed out. Various acoustic calculations are then carried out for this hot jet to assess the influence of the type of method and of the position, extent and nature (open or closed) of the control surfaces on the noise predictions. This parametric study shows that the Kirchhoff method using density as input data is poorly suited for acoustic predictions of hot jets. The Kirchhoff method using pressure as input data provides results similar to those obtained with the FW–H surface integral but the latter appears to be more reliable. The study also shows that the use of a downstream closed control surface does not present a real interest, whatever the acoustic method is.