Optimisation of solid rocket motor blast tube and nozzle assemblies using computational fluid dynamics

Abstract

A framework for optimising a tactical solid rocket motor nozzle is established and investigated within the ANSYS Workbench environment. Simulated results are validated against thrust measurements from the static bench firing of a full-scale rocket. Grid independence is checked and achieved using inflation based meshing. A rocket nozzle contour is parametrized using multiple control points along a spline contour. The design of experiments table is populated by a central composite design method and the resulting response surfaces are used to find a thrust optimised rocket nozzle geometry. CFD results are based on Favre-mass averaged Navier-Stokes equations with turbulence closure implemented with the Menter SST model. Two optimisation algorithms (Shifted Hammersley Sampling and Nonlinear Programming by Quadratic Lagrangian) are used to establish viable candidates for maximum thrust. Comparisons are made with a circular arc, Rao parabolic approximation and conical nozzle geometries including the CFD simulation there-off. The effect of nozzle length on thrust is simulated and optimised within the framework. Results generally show increased thrust as well as demonstrating the framework's potential for further investigations into nozzle geometry optimisation and off-design point characterisation.