Numerical analysis of the shock train in conical nozzles with straight-cut throats

Abstract

The overexpanded flow regime in supersonic rocket engine nozzles presents different shock wave structures due to the geometrical configurations of the internal walls. In the present investigation, the study of the shock train phenomenon is addressed for a group of convergentdivergent conical nozzles with straight-cut throats for the overexpanded flow condition for NPR=12. The viscous and compressible flow field under stationary conditions is simulated with the RANS model in the ANSYSFluent R16.2 code, which applies the finite volume method (FVM) to discretize the computational domain. The Spalart-Allmaras turbulence model is used, and Sutherland's law is used for the viscosity as a function of temperature. The results show that, in the straight-cut throat section, as its length increases, the flow accelerates and decelerates with the presence of oblique shocks, which forms a definite shock train structure, where the flow velocity fluctuations are within the estimated Mach number range of 0.6 to 1.8. Increasing the throat length significantly affects the flow development at the nozzle outlet, which decreases the thrust force.

Keywords

• conical nozzle
• oblique shock
• overexpanded flow
• straight-cut throat
• shock train
• velocity fluctuation