Investigation Of Aft-End Internal Flows In Solid Rocket Motors With Submerged Nozzle

Submerged nozzles are commonly preferred in large solid rocket motors. The Aft-End internal flows are very complex because of submergence. The flow process and mechanism are not very clear yet. This paper described a cold gas simulation of solid rocket motor with submerged nozzle. A two-dimension model with rectangular channel was designed, which can simulate different flow conditions at three periods after ignition. For the first time the complex separated flow in the Aft-End zone was measured using PDPA technology. The whole mean and fluctuating flow field were obtained. It is showed that Aft-End internal flows vary obviously with the regression of the burning surface during the operation. At the preliminary stage of burning the gas flows along the back surface of the submerged nozzle and no recirculation forms in the Aft-End cavity. At the medium stage of burning a weak recirculation forms in the rear of Aft-End cavity by the force of injection flow. At the end stage of burning the flow separates at the combustion channel and a strong vortex forms in the Aft-End cavity. Under the influence of the submergence the turbulence intensity are quite high at the end stage of burning. However, the turbulence intensity decreases obviously at the medium stage and the preliminary stage of burning because the flow disturbance is eliminated by the mixture of injection flow and main flow. Flow details of measurement indicate that the coupling of periodic separated flow (such as low frequency swinging of separation line) with nozzle flow may cause Aft-End internal flow unsteady. Recirculation flow gains more energy from the main flow, at the same time the turbulence intensity increases.On the basis of cold gas simulation, a numerical simulation of two-phase turbulent flow was performed employing an Eulerian-Eulerian approach and K- -A.P. turbulent model. The accuracy of numerical simulation was verified and evaluated by the experimental result. It is showed that numerical calculation could give the same position of separation line with the cold gas simulation. However, numerical simulation result is of a little deferent from cold gas simulation in some details, such as recirculation velocity and turbulent intensity. The main problem of numerical simulation is that the turbulent model is not perfect, and the computational grid is notprecise enough.The effects of Reynolds number, back surface of nozzle, Aft-Dome configuration and degree of submergence on Aft-End internal flow were studied by both cold gas simulation and numerical simulation. It is showed that the separated flow is sensitive to the change of Reynolds number and Aft-End cavity configuration. Experimental investigation described in the paper may contribute to the development of internal flow study in solid rocket motors. The result is not only conducive to understand the mechanism of Aft-End internal flow, but also available for reference to the design of solid rocket motors. The detailed measurement data can act as data-base to verify the accuracy of numerical simulation.