Aeroacoustic Prediction of a Multi-Element Airfoil Using Wall-Modeled Large-Eddy Simulation

Wall-modeled large-eddy simulation is employed in combination with the Ffowcs Williams-Hawkings equation to predict and analyze the aeroacoustics of a 30P30N three-element airfoil. The results are compared with experimental measurements, and quantitative agreement is obtained in terms of flow statistics, frequency spectra of pressure fluctuations on the slat surface, and the far-field noise spectra, thus demonstrating the feasibility and accuracy of the wall-modeled large-eddy simulation approach. The slat cove is confirmed to be the primary sound source and emits narrowband tonal noise at several resonance frequencies in addition to broadband noise. The main element is the largest contributor to low-frequency noise, and the flap is a negligible noise source at all frequencies. Computational results for different freestream Mach numbers indicate that the resonance frequencies are well predicted by the semi-empirical models of Block (Noise Response of Cavities of Varying Dimensions at Subsonic Speeds, NASA Technical Note D-8351, 1976) and Terracol etal. (Investigation of the Unsteady Flow and Noise Generation in a Slat Cove, AIAA Journal, Vol.54, No.2, 2016). The intensity of flyover noise is shown to largely scale with the fifth-power of Mach number, as suggested by Guo and Joshi (Noise Characteristics of Aircraft High Lift Systems, AIAA Journal, Vol.41, No.7, 2003), but in most other directions, the Mach number scaling of sound intensity is higher than the fifth power.