Slat Noise Trend Predictions Using CAA With Stochastic Sound Sources From A Random Particle-Mesh Method (RPM)

Abstract

Slat Noise simulations are carried out for a high-lift airfoil. The high-lift airfoil geometry is a two-element slat-airfoil configuration without deployed flap in order to avoid additional sound sources at the flap. A low-cost CAA approach is applied, which is based on acoustic perturbation equations (APE) in the time-domain that are forced by stochastic sound sources. The stochastic model was introduced in AIAA 2005-2862 and is based on the spatial convolution of white-noise with a filter kernel and can reproduce target distributions of turbulent kinetic energy and length scales, e.g., provided by a steady RANS computation of the turbulent flow problem. The Mach number scaling law of the broadband slat noise component is evaluated based on three different freestream velocities (M=0.088, 0.118, 0.165). The capability of the stochastic method to reproduce a target turbulence kinetic energy topology is studied. The effect of model parameter variations on the quality of the reproduced turbulent kinetic energy distribution and its effect on the predicted far-field spectrum is evaluated. Only a small dependence on the model parameter is found. The effect of slat gap variation on the broadband acoustic far-field is studied for three different slat configurations, which encompass beside the reference slat position one configuration with reduced, and one with increased slat gap. Previous experimental findings at a full three-element high-lift airfoil indicated an effective dependence of the slat gap width on the acoustic far-field with typically 5dB reduction for a slat gap reduction of about 15\% due to a decrease of the velocity of about 25\%. The current study investigates this effect for the two-element high-lift configuration.