Aeroacoustics and vorticity assessment for a highly-heated, supersonic aerospike nozzle jet

Large Eddy Simulations (LES) are deployed to characterize the effect of temperature on the various terms of the time-averaged vorticity equation for a supersonic aerospike nozzle jet. It is known that convection of vortices through the shock-cell structure formed in a non-ideally expanded jet generates sound propagating into the far-field. In the meantime, higher jet temperature ratios are also strongly affecting sound generation. This study allows to describe the effects of jet temperature on the different vorticity equation terms and hence to shed new light on the underlying mechanisms for sound generation. It is found that the vorticity transport term is the strongest in the annular region of the jet indicating strong dynamic effects responsible for sound generation. In the cold case, the vorticity transport term is highest at the location of the separation bubble whereas at higher temperature ratios, it is stronger at the outer annular shear layer. A further distinction of the tilting and stretching terms due to compressibility and velocity gradients shows that stretching effects are dominating in the vicinity of the annular nozzle outlet. The tilting term is dominating the vorticity dynamics further downstream in the jet. Finally, the baroclinic term grows in intensity with increasing temperature ratio.