Aeroacoustic Analysis of a Circulation-Controlled High-Lift Flap by Zonal Overset Large-Eddy Simulation

Abstract

Circulation-controlled wings using the Coanda effect over the high-lift device (i.e., the flap) potentially enhance the wing’s lift coefficient by delaying or avoiding separation of the strongly deflected flow on the flap. However, such a Coanda-jet-equipped flap contributes significantly to the airframe noise. Hence, identifying the sound sources on the flap in the aircraft landing conditions is of paramount importance. In this context, the current paper reports the outcomes of zonal overset–large-eddy-simulation (Overset-LES) computations carried out on such a Coanda-jet-equipped flap of a DLRF16 profile. The results show that the Overset-LES computation quantitatively corrects the Reynolds-averaged Navier–Stokes baseflow. The effect of Coanda jet scales on the noise generation is studied by stochastically reconstructing them. As a validation of the computations performed, the power spectral densities of surface pressure fluctuations show a good agreement with the experimental data. This validation further emphasizes the necessity of considering the Coanda jet scales in the Overset-LES. Furthermore, aeroacoustic source ranking is performed based on far-field overall sound pressure levels. Results show that the curvature noise arising from the flow acceleration over the flap’s curvature is dominant at all angles except between 180 and 280°, where the flap’s trailing-edge noise contribution is higher. The effect of the Coanda jet scales on the far-field noise can be ignored when the complete flap is considered. However, the fluctuating jet scales have the tendency to reduce the noise arising from the curvature in the low-frequency regime of the spectrum when individual sources are accounted for, due to enhanced mixing aided by the smaller turbulent scales. This suggests that ignoring the jet scales will result in overpredicting the curvature noise in the low-frequency regime. Including the Coanda jet scales results in a flow-straightening effect near the flap trailing edge and hence alters the magnitude and directivity pattern of the flap trailing-edge noise. The current investigation reveals an additional, previously not recognized sound source at play, resulting from the strong flow deceleration at the region between the curvature and the flap’s trailing edge.