Experimental investigation of pressure-reducing instabilities in perforated plates for compressible and cavitating flows

The pressure losses through sharp-edged, multi-orifice circular perforated plates with two different ratios of plate thickness to orifices' diameter are experimentally investigated using both water and dry air as working fluids. The choice of a thickness for which fluid-dynamic instabilities related to flow reattachment are known to occur allows to investigate the effects of cavitation and compressibility on such instabilities. It is found that both cavitation and compressibility may be the cause of an early reattachment of the flow within the plate's perforation, modifying the pressure loss characteristics of the device. Wall pipe pressure fluctuations measurements for subsonic air flows allow linking changes in whistling frequencies to changes in the pressure loss regime of the plate.