Studies on Internal Ballistics of Dual-thrust Motors for Nozzleless Propulsion

Abstract

Theoretical studies have been carried out to examine the flow features of dual-thrust motors for nozzleless propulsion. Using a two-dimensional k-omega turbulence model, detailed parametric studies have been carried out to examine the aerodynamic choking and the possibility of the premature unchoking in motors of insufficient length to diameter ratios. This code solves standard k-omega turbulence equations with shear flow corrections using a coupled second order implicit unsteady formulation. In the numerical study, a fully implicit finite volume scheme of the compressible, Reynolds-Averaged, Navier-Stokes equations is employed. We observed that the possibility of the occurrence of choked flow condition at the transition region of the dual-thrust motor with narrow upstream port is very high and that might lead to the formation of shock waves. We have conjectured that the shock waves in dual-thrust motors can generate additional turbulence. The multiple choking phenomena and the new turbulence level will alter the location of the reattachment / secondary ignition point and also enhance the heat flux to the propellant surface, which in turn will enhance the local burn rate. Note that errors in predicting the recirculation bubble and the location of reattachment can lead to significant errors in burn rate mapping, which will add further complexity for the design of dual-thrust motors for nozzleless propulsion.