Unstructured Large-Eddy Simulations of Rectangular Jet Screech: Assessment and Validation

Abstract

High-fidelity large-eddy simulations (LESs) of a 4:1-aspect-ratio rectangular screeching jet are conducted at two underexpanded nozzle pressure ratios and nonheated flow conditions. To identify key numerical requirements for obtaining physically realistic jet screech in rectangular nozzles, a detailed assessment of mesh resolution and the Ffowcs Williams–Hawkings (FW-H) surface design is performed. Sufficiently fine grids are required in the jet shear layers and jet potential core to obtain accurate shock cell positions and jet spreading. To save computational costs, the FW-H sampling surface can be placed fairly close to the jet turbulence. In the region containing the jet initial shear layers and the supersonic core, the sampling surface can be placed near the 5–10% contour levels with respect to the maximum turbulent kinetic energy; and in regions further downstream, the sampling surface can be placed near the 20–25% contour levels. The LES results match closely with experimental measurements in terms of flow velocity and near- and far-field acoustics. The broadband noise spectra calculated by LESs agree very well with the experiment between and . For the stronger screech case, LESs are able to capture the screech tones within 2–5 dB as microphone measurements; whereas for the weaker screech case, the screech tones from LESs are weaker than measured values.