Unsteady Flow Computations of a Slat with a Blunt Trailing Edge

Abstract

A detailed computational study of a high-lift configuration was conducted to understand the source mechanism behind a dominant acoustic tone observed in recent experiments on slat noise. The unsteady Reynolds-averaged Navier-Stokes computations focused on accurate simulation of the local flowfield of a slat with a blunt trailing edge. At a slat deflection angle of 30 deg relative to the main element, the simulations revealed the presence of strong vortex shedding behind the slat trailing edge. The resulting flow unsteadiness produced large-amplitude acoustic waves propagating away from the trailing-edge region. The local spatial resolution of the computed solution was sufficiently fine to capture both the near-field structure and propagation direction of the generated sound. The calculated shedding frequency is in good agreement with the measured acoustic frequencies obtained at NASA Langley Research Center's Low Turbulence Pressure Tunnel. In contrast, computational results at a slat deflection angle of 20 deg indicated that the shedding process was severely damped, and, therefore, in agreement with the corresponding acoustic measurements during the experiment. There was no evidence of a strong acoustic source near the trailing edge at this lower slat deflection.