Influence of swirl on the discharge coefficients of sonic nozzles

Flow characteristics of a swirl generator are studied using an open circuit flow loop, and influence of upstream swirl on the discharge coefficients of sonic nozzles is investigated using a high pressure gas flow standard measurement system. The open circuit flow loop consists of swirl generator, testsection, sonic nozzle, suction fan and LDV system. The gas flow measurement system comprises two compressors, storage tank, temperature control loop, sonic nozzle testsection, weighing tank, gyroscopic scale and data acquisition system. Experiments are performed at various nozzle throat diameters, inlet pressures and angles of swirl generator. As the angle of swirl generator becomes larger, axial velocities decrease near the wall and rapidly increase in the pipe core, and swirl velocities increase to form swirl flow. Influence of upstream swirl on discharge coefficients becomes greater as the intensity of swirl increases and as the nozzle throat diameter is enlarged. Variation trend with Reynolds number, however, is very similar each other regardless of swirl intensity.