Throat diameter influence on the flow characteristics of a critical Venturi sonic nozzle

The discharge coefficients of 21 normally machined sonic nozzles with throat diameters (1.921-12.444) mm were measured for stagnation pressures of (100-2500) kPa. The 518 experimental data points show that the sonic nozzle throat diameter strongly influences the flow characteristics of sonic nozzles, including the discharge coefficient and the boundary layer transition. The results were used to correlate the discharge coefficient with the (2.39 × 104~2.89 × 106) Reynolds number with deviation of less than ± 0.20% for 95% of the experimental data. The Reynolds number for the boundary layer transition was also correlated with the throat diameter, with good agreement with previous results for larger throat diameter.