Large-eddy simulations of supersonic rectangular jets including screech

Abstract

Large-eddy simulations (LES) are used to study supersonic jet screech, an aeroacoustic resonance phenomenon found in non-ideally expanded jets. This work specifically analyses screech generation for an under-expanded cold jet exhausted from a converging-diverging rectangular nozzle. With an aspect ratio of 4:1, the nozzle has a design Mach number of 1.44 and was previously tested at Florida State University. The simulations are performed with the compressible flow solver, “CharLES,” developed by Cascade Technologies. The meshes are generated based on the computation of Voronoi diagrams and contain around 40 to 120 × 106cells, targeting a few set points close to maximum screech. The far-field acoustics are obtained using a permeable Ffowcs Williams-Hawkings formulation in the frequency domain. In the noise spectra, screech tones are detected at various observer locations. At the specific tonal frequency, a spatially modulating standing wave pattern is observed in the near-field flow data, which possibly results from the partial interference between oppositely moving hydrodynamic and acoustic waves. Using the LES data, a modal form for the partial standing wave pattern can be obtained. Furthermore, a more in-depth stability analysis can provide insights on the origins and effects of these coherent features associated with screech.