Abstract
Discharge coefficients and inner contour of 24 sonic Venturi nozzles, which had various shapes at their throats, were measured by a constant volume tank system developed as the primary standard in Japan and a coordinate measuring machine, respectively. The nozzles, diameters of which ranged from 6.7 to 18.9mm, had been made by a super-precise machine tool and the deviation of the inner contour from the designed dimensions complying with ISO 9300 were less than ±2μm between the inlet plane and the throat. The measured discharge coefficients of the nozzles, which had the toroidal throats complying with the ISO, coincided with the ISO within the specified uncertainty at the Reynolds number from 0.6 to 2.4×105, but their fitted curve had steeper gradient than that of the ISO. Those of the nozzles, which had lower projections than the boundary layer thickness at their throats and depressions of similar dimension of the thickness right after the projections, were larger by 0.2∼0.3% and had smaller dependency on the Reynolds number than the ordinary ISO nozzles.
