Construction of a Toroidal-Throat Critical Nozzle Using 3D Printing and Flow Visualization

Toroidal-throat critical nozzles, first conceptualized in the 1960s, are widely utilized for high-precision flow rate measurement. Conventional straight nozzles present a problem: deviation from the theoretical value due to pressure loss. This study aimed to resolve this issue by constructing a toroidal-throat nozzle using 3D printing technology and examining its utility. The nozzle's performance was evaluated through a comparison of Schlieren flow visualization images of the underexpended jet and the predictions of an empirical correlation. The experimental results demonstrated favorable agreement with the empirical correlation, thereby suggesting the utility of the 3D-printed critical nozzle.