Abstract
Venturi and quadrant nozzles of a total number of 27 were made by using super-accurate lathes, positions of the cutting heads of which were controlled with a resolution of 0.1μm. Their discharge coefficients were measured in the critical condition by using a constant volume tank system at the Reynolds number of 0.8-2.4×105. All the measured discharge coefficients on the Venturi nozzles distributed along a fitted curve as a function of the Reynolds number with a deviation of less than ±0.03%, which showed a feasibility of an accurate standardization on critical Venturi nozzles made by the super-accurate lathes. The measured discharge coefficients on the quadrant nozzles were larger than the fitted curve by 0.07%. The discharge coefficient of a critical Venturi nozzle was theoretically derived into an analytical form from theories of an axis-symmetric inviscid flow field and a laminar boundary layer at the throat of a critical nozzle. The calculated discharge coefficient agreed with the fitted curve with a deviation of less than 0.03% at the Reynolds number larger than the lower extreme of the measuring one.
