Effect of Nozzle-exit Flow Conditions on the Flow and Acoustic Properties of Imperfectly Expanded Supersonic Jets

Abstract

§** †† The impact of the turbulence level at the nozzle exit on the jet flow and far-field noise level has been investigated using large-eddy simulations (LES) and the Ffowcs Williams & Hawkings (FW-H) surface integral method. The jet exit flow condition is slightly underexpanded. Both the random perturbations inside the nozzle and the nozzle surface roughness are used to increase the turbulence level. Increasing the turbulence level at the nozzle exit increases the shear-layer spreading, reduces the screech intensity and also decreases slightly the far-field noise level. The LES predictions of the shock-cell structures and the jet core lengths agree well with the measurement data. In addition, the impact of grid resolution used in both the jet flow and the near-field acoustic propagation region has also been investigated. It is found that the grid resolution used in the shear layer impacts the numerical predictions more than those used in the other regions. Adding an adequate amount of turbulence level at the nozzle exit greatly improves the predictions using a coarser grid resolution in the shear layer. Furthermore, the far-field noise predictions agrees well with measurement data, and the contribution from the end cap is found small, but it is sensitive to the mesh size used in the integration.