Investigation of effects of convergence and divergence half-angles on the performance of a nozzle for different operating conditions

Abstract

The effects of convergence and divergence half-angles on the performance of a nozzle at the different pressure ratios are investigated numerically. SST k − ω turbulence model is applied to simulate the compressible gas flow inside the nozzle and its exhaust plume. Exhaust nozzle performance parameters have been calculated and compared with available experimental data to show the validity of the simulations. For this purpose, different nozzle pressure ratios for various operating conditions including over-expanded, under-expanded and design condition are considered. The effects of the nozzle geometry (convergence and divergence half-angle) on the velocity coefficient (Cv), discharge coefficient (Cd), gross thrust coefficient (Cfg) and nozzle adiabatic efficiency (ηn) are investigated. Predicted results show that for a given nozzle pressure ratio, by increasing the divergence angle from 5 to 20, there is about 3% loss in the gross thrust coefficient and also by increasing this angle from 20° to 40°, the value of the Cv and ηn will decrease 5 and 10%, respectively. Increasing the convergence angle reduces the discharge coefficient about 6% and causes a 3% penalty in nozzle gross thrust coefficient.