Time-Space POD Decomposition of the Slat Velocity Field of the 30P30N High-Lift Model

Highly unsteady flows in the slat vicinity of a high-lift airfoil have several features attributable to noise generation. Multiple tonal peaks in the pressure/velocity spectra are commonly observed in scaled wind-tunnel tests in the range of St_s (Strouhal number based on freestream speed and slat chord length) of 1 - 5. These tones are generated from the slat-cove shear layer and fluid-acoustic interaction associated with flow impingement on the cove surface. In the current study, we applied the spectral analysis modal method to non-time-resolved velocity data obtained from particle image velocimetry measurements with synchronized time-resolved surface pressure data on a two-dimensional 30P30N model at 0-deg angle-of-attack and chord-based Reynolds number of 1.71 million. The resulting velocity modes reveal the coherent flow structures at these frequencies. Specifically, bulk flow motion in the slat-cove recirculation region at St_s = 0.14 and vortex structures within the slat-cove shear layer at the tonal frequencies are observed. The temporal evolution of the vortex in the shear layer is also reconstructed, showing the vortex escaping from the cove into the trailing edge wake. A reduced-order model is provided to reconstruct the fluctuating flow field with selected dominant modes.