Three-dimensional unsteady flow computations around a conventional slat of high-lift devices

Three dimensional unsteady flow structure inside a deployed slat of high-lift configuration is simulated numerically to investigate the cause of slat noise. Because the Reynolds number of the flow is high and the geometry is complex a zonal large eddy simulation/Reynolds-averaged Navier-Stokes hybrid method is used to reduce the overall computational cost. The power spectral density of the pressure coefficient is compared to the experiment, and some issues regarding grid resolution, order of numerical scheme, and number of subiterations for implicit time integration are discussed. Two different types of fluctuations (high-frequency narrowband and low-frequency broadband are observed, and the computational results are consistent with the experiment. Careful observation of the unsteady computational data reveals longitudinal vortical structures under the lower surface of the slat, which is consistent with the previous studies. The low-frequency broadband fluctuation becomes large around this region. Therefore, it is assumed that these longitudinal vortical structures are causing the broadband noise from the slat.