The compressible discharge of air through small thick plate orifices

Summary The choking of nozzles at pressure ratios below the critical has long been understood. Knife edge orifices however do not appear to choke. This can be explained and the variation of discharge coefficient with pressure ratio may be calculated. The present paper is an experimental investigation into the discharge through thick plate orifices when the pressure ratio is in the vicinity of its critical value. A comparison is made with the results of other workers and an attempt is made to explain the discharge characteristics of thick plate orifices.Notation C discharge coefficient - D orifice diameter - P absolute static pressure - T thickness of orifice plateSuffixes c critical pressure - d downstream conditions - i incompressible flow conditions - u upstream conditions