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Solid Rocket Motors frequently experience unsteady gas motions and combustion instabilities. Pressure oscillations are a well-known problem of large solid rocket motors (e.g. those of the US Space Shuttle, Arianne 5 P230 and P80). Pressure oscillations lead to thrust oscillations which can generate unstable dynamic environments for the rest of the launcher up to the payload. This kind of instability is governed by the flow behavior of the combusted gas combined with pressure fluctuations and acoustic resonances within the combustion chamber. In the present investigation a computational analysis of the combusted gases passing through the chamber of such a solid rocket motor has been conducted, with particular attention to Corner and Parietal Vortex Shedding instabilities, inside the core section of the motor together with a study of the associated pressure oscillations. Nomenclature Downloaded by Mario Panelli on July 18, 2017 | http://arc.aiaa.org |

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This study details the reactive flow simulation of a single injector LOX/CH 4 rocket similar to a comparable device, the CIRA Sub Scale Bread Board (SSBB) planned within the context of the HYPROB program funded by the Italian Ministry of University and Research (MIUR). In order to identify a suitable numerical method for use in the design of the SSBB calculations have been performed on the NASA sponsored Penn State LOX/CH 4 uni-element rocket engine for which heat flux data are available. The main features of this rocket are discussed in a former article relating to the experimental setup, methodology and results. The current reactive flow model is based on a twostage injector-chamber and chamber-throat-nozzle approach. In the first stage the injector-chamber region is modelled using a pressure based solver approach. In the second stage the converged results for the chemical distribution at the outlet calculated in the first stage are used as upstream boundary conditions to model the chamber-throat and nozzle region using a density based solver. In the first stage reactive flow is modelled using the Peng-Robinson equation of state whereas the second stage assumes an ideal gas. The reason for this two-stage approach is to reduce CPU time and circumvent problems associated with numerical stability which occur when modelling the complete domain in a single stage and which is validated by direct comparison of predicted wall heat fluxes with experiment. Comparison is also made between the results of this two-stage method and calculations for the complete configuration using different chemistry models. These simulations are performed with a commercial CFD solver to solve the steady state axi-symmetric Navier-Stokes equations. The Laminar Finite Rate and the Eddy Dissipation Concept models are used for the turbulent chemical kinetic coupling and the Jones-Lindstedt model is used for the chemical reactions for liquid oxygenmethane combustion. The results presented indicate the qualitative effects of different turbulence and chemical kinetic models on flow structures as well as a quantitative comparison of wall heat fluxes for different model combinations which are compared with experimental data.

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