Noise Prediction for Increasingly Complex Jets. Part II: Applications

Abstract

The numerical system described in Part I (Ref. 1) is applied to a variety of cases which increase difficulty, and progress in the direction of the complete simulation of an airliner engine. The grids have on the order of 1 million points. In many cases, the system meets the 2–3 dB accuracy target both in terms of directivity and of spectrum, up to a Strouhal number of about 1.5. The jet Mach number is varied from 0.3 to slightly supersonic with under-expansion, generating shock cells and greatly increasing side-line noise. For heated jets, the cross-effect between the acoustic Mach number and the temperature is correctly reproduced. Jets placed in a co-flowing stream with velocity up to 60% of the jet's are studied and found to sustain natural transition without unsteady forcing; the noise trends are correct. Finally, “synthetic chevrons” are added by altering the inflow conditions, and found to reduce low-frequency noise while increasing mid-frequency noise. In total, about fifteen meaningfully different cases are presented, and subjected to quantitative comparisons over the direction/frequency space without major failure. The principal limitation of the large-eddy-simulation approach remains its upper limit on frequency.