Investigation of the unsteady flow and noise sources generation in a slat cove: hybrid zonal RANS/LES simulation and dedicated experiment

Abstract

This study presents numerical simulations of the unsteady flow and noise generation phenomena in the slat cove of a highlift wing profile by mean of a zonal hybrid RANS/LES approach. These computations are part of a joint numerical/experimental aeroacoustics collaborative program, dedicated to slat flow analysis. For that purpose, a dedicated twoelement wing profile (slat+main body) has been designed in order to isolate the slat noise sources from other possible spurious sources (flap for instance), while minimizing mean flow deflection effects in order to improve the reliability of open-jet wind tunnel measurements. The design of this two-element airfoil has been done numerically using an optimization process based on steady RANS calculations. This airfoil has been investigated experimentally in Ecole Centrale de Lyon open jet facility, therefore providing unsteady wall-pressure measurements in the slat cove area and farfield acoustic measurements. Unsteady zonal hybrid RANS/LES simulations have been performed to provide a comprehensive description of the unsteady flow inside the slat cove, with focus being made on the noise generation processes. A fine physical unsteady analysis of the flow inside the slat cove is presented, as well as a comparison of numerical results with available experimental ones. The pressure spectra associated to the slat cove flow appear to be characterized by several tonal peaks emerging from a global broadband content. The existence of such peaks is discussed and attributed to a feedback loop involving the main shear layer inside the slat cove. A theoretical law is proposed and assessed at the end of the paper to predict the associated tonal frequencies.