In an effort to improve the validated understanding of aerodynamic losses across orifices, this publication describes discharge coefficient measurements, derived from a specially designed test rig. This rig contains a straight, square section main channel (20 × 20 mm~2) with exchangeable orifice plates at one side wall with 7 mm hole diameters. The channel was supplied with compressed air at between about zero velocity and nearly the speed of sound. Static pressure ratios across orifices were varied between 1.05 and 2 in addition. Test orifices had inclinations of 0°, 30° and 60° in and against inlet cross-flow. Further, orifice length-to-diameter ratios were varied to 0.5, 1 and 2. Orifice inlet and outlet corners were sharp. The main channel velocity was determined using a pitot tube, a thermocouple and flush-mounted static pressure off-takes. Orifice downstream pressure was measured by a flush mounted static pressure off-take. Orifice through flow was determined by a calibrated hot film measurement device with constant temperature difference control, equipped with an additional thermocouple to determine fluid properties.
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