Oscillations of flow past perforated and slotted plates: attenuation via a leading-edge ramp

The present investigation aims to attenuate purely hydrodynamic, long-wavelength, self-excited oscillations of flow past a perforated or slotted plate by deflection of the inflow with a small ramp located at the leading-edge of the plate. Digital particle image velocimetry is complemented by unsteady pressure measurements to determine the underlying physics associated with attenuation of the oscillations. Irrespective of whether a perforated or slotted plate is employed, complete attenuation of the pressure fluctuations associated with the oscillation can be achieved for dimensionless deflection ratios of h/L >= 0.035, in which h is the height of the ramp and L is the effective plate length. The attenuation of the self-excited oscillation involves: a steady jet at the trailing-edge of the plate directed into the cavity; a lower magnitude upstream-oriented counterflow along the backside of the plate; and jet-like flows through the plate openings to satisfy the entrainment demands of the separating shear layer.