Re-definition of the discharge coefficient of throat-tapped flow nozzle and investigations on the influence of geometric parameters

Abstract The objective of this paper is to obtain a useful equation which gives a discharge coefficient of a throat-tapped flow nozzle. Experiments for throat-tapped flow nozzles with several different geometric parameters were performed using highly accurate flow facilities at the National Metrology Institute of Japan (NMIJ). The effects of some geometric parameters on the discharge coefficient were experimentally investigated. The parameters include the ratio of the diameter of the pressure taps located at the throat to the throat diameter, the diameter of the pressure taps located at upstream pipe and the roughness of the nozzle surface. Also, the effectiveness of a flow conditioner prescribed in ASME PTC 6 was examined. Although a limitation to the proposed equations was found, the discharge coefficient is affected by the geometric parameters smaller than the measurement uncertainty. Finally, new equations for the discharge coefficient, which cover all experimental results within 0.5%, have been proposed as a set of functions of the Reynolds number.