On the Absence of Self-Sustained Flow–Acoustic Coupling Between the Slat and Flap Coves of High-Lift Devices

The present study investigates the flow-acoustic interactions within the slat and flap coves of a 30P30N high-lift configuration. Velocity fluctuations in the slat cove exhibit a dominant tonal feature at a Strouhal number based on the slat chord (cs), Sts=fcs/U∞=1.75 (f≈ 1500 Hz), corresponding to the second acoustic mode predicted by the feedback model. Strong coherence between wall-pressure sensors in the slat cove and shear layer velocity fluctuations confirms this coupling. The same tonal signature appears in the flap cove wall-pressure spectra, with high coherence between slat and flap surface-pressure signals, indicating propagation of acoustic waves from the slat to the flap. However, no tonal content is observed in the flap cove velocity spectra, suggesting that while acoustic waves propagate between coves, they do not excite shear-layer unsteadiness within the flap cove.