Performance analysis of CD nozzle

Abstract

In engines, nozzles are used to convert pressure energy into kinetic energy. While converting, the velocity (momentum) of the flow increases. This process drives the engine to produce the required thrust force. Among the different nozzle shapes, only the convergent-divergent nozzle can convert a subsonic flow into a supersonic flow. Hence, it has a wide range of applications in Aeronautics. But it requires the correct pressure difference between entry and exit to get the optimum performance. This paper covers the performance analysis of the chosen rocket nozzle (convergent-divergent nozzle) under various operating conditions. Initially, an already existing rocket nozzle was chosen and its operating conditions were identified. Then, for the chosen geometry some hand calculations were made to predict the critical backpressure conditions. Then by keeping the same identified operating input condition (80 bar at the inlet), a two-dimensional Computational Fluid Dynamics (CFD) analysis was performed for various backpressure conditions. From the analysis, the nozzle flow characteristics under various back pressures were plotted in a graph and identified the impact of backpressure variations on the performance of the chosen rocket nozzle. A normal shock will appear in the chosen nozzle over the range of back-pressures 13.21 to 79.64 bar. To get a perfect expansion, the back-pressure should be 0.864 bar. However, the chosen nozzle will deliver supersonic flow for all back pressures below 13.21 bar.