Prediction of acoustic resonance phenomena for weapon bays using detached eddy simulation

Abstract

AbstractIt is argued that acoustic resonance phenomena in open cavities such as weapons bays cannot be adequately predicted through numerical solution of Reynolds averaged Navier-Stokes (RANS) equations. The requirement to resolve the growth of the shear layer instability from the lip of the cavity inevitably implies that turbulence further downstream is resolved while also being modelled thus making RANS over dissipative. Large eddy simulation (LES) models only unresolved scales and a hybrid method combining RANS near walls with LES in the cavity appears a practical alternative to pure RANS. This paper compares computations of the M219 cavity configuration made with unsteady RANS and with the hybrid method known as detached eddy simulation (DES). It is shown that whilst unsteady RANS and DES give very similar predictions for the 1st and 3rd modes of the acoustic resonance the 2nd mode (which is dominant near the centre of the cavity) is absent in the RANS results but well predicted by DES. The 2nd mode is thought to arise from an interaction with vortical structures in the shear layer which are suppressed in the highly dissipative RANS method. The 4th mode, which is much weaker than the other three modes, is over-predicted by DES and under-predicted by a smaller amount in RANS.