| Because of the advantages of high specific impulse and simple structure etc, solid fuel ramjet (SFRJ) is an attractive propulsion system of aircraft, such as supersonic missile and ramjet assisted projectile, but the study on combustion chamber flow of SFRJ is still in the stage of exploring. Research on the analytical model for SFRJ combustor flow and numerical simulation technique for unsteady flow was carried out thoroughly by means of theoretical analysis and numerical simulation.Based on the characteristic of SFRJ combustor flow and vorticity-stream function approach, the analytical model for combustion chamber flow was established, and the surface of solid fuel was treated as velocity inlet. The basic analytical model for typical flow was established corresponding to a cosinoidal reattachment point section (Sr) injection velocity. The general solution to the analytical model was achieved corresponding to the general Sr injection velocity by superposition principle, the expressions of flow parameters which were further accord with the actual situation were given. The outcomes of basic analytical model accorded with the results obtained from numerical experiments. The research shows that:1) As velocity parameter (uh) is increased, curvatures of streamlines are increased in the neighborhood of the sidewall. Flow is basically dominated by the mainstream, which is similar to that of solid rocket motor. And velocity is comparatively low near the sidewall.2) The axial velocity and vorticity are increased linearly with increasing uh, with radial position is changed, only slight changes in axial velocity are noticed in the mainstream, axial velocity is rapidly declined to zero near the sidewall, and the decay rate is proportional to uh, vorticity reaches maximum on the sidewall, away from the sidewall, it decreases rapidly and approaches zero near the axis.3) Absolute values of the radial velocity and pressure drop increase at first, then decrease with increasing radial position, the absolute values surpass their wall values when radial position is between (?)2/2 and 1.4) Flow is converging from the sidewall and Sr to the centerline.The 2D compressible unsteady SFRJ combustor flow N-S equations casted in Arbitrary Lagrange-Euler (ALE) framework were established by extending the numerical method to dynamic mesh, and the numerical schemes were presented for ALE governing equations and boundary conditions. On the basis, the mathematical model of combustor unsteady flow involving moving boundaries was developed coupling dynamic mesh, combustion, flow, heat transfer and regression of solid grain, using low-Re k-εturbulence model, and considering the effect of mass addition on convective heat transfer and temperature on effective heat of gasification. The UDF code controlling regression and mass addition of burning surface was programmed. And the initial computational grid was evaluated. The fuel regression rate obtained from numerical simulation accorded with the test results.Whole inner flow of SFRJ including combustion chamber and nozzle was numerically simulated by the mathematical model of combustor unsteady flow. The time-dependent flow was obtained with dynamic boundaries. The flow parameters, instantaneous regression rate, reattachment point and the parameters at the outlet of port were analyzed, and the geometric effects on regression rate were studied. The research shows that:1) During burning time, the fuel port geometry is altered from a simple cylindrical geometry to a more complex geometry. The nonuniformity in the regression pattern along the grain is increasing, maximum regression point is moving downstream. And the burning surface area and volume of port are increased linearly with time.2) Combustor flow is nonuniform, combustion mainly occurs in the area where species equivalent ratio function (φ) is between -2 and 2. As motor works, the velocity and temperature reduce at the outlet of port, the pressure is increasing in combustor. The regression rate is low near the inlet, then it increases rapidly and reaches maximum at reattachment point, then it gradually decreases. There is erosive burning in small SFRJ during initial operation stage.3) With burning time, the local regression rate is decreasing, the reattachment point moves downstream. The spatially averaged regression rate is decreasing, and the decay rate is reducing.4) The growth of the burning surface area and the nonuniformity in the regression pattern leads to the decreasing regression rate. |
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