Unsteady flow evolution in porous chamber with surface mass injection, part 1: Free oscillation

Unsteady flow evolution in a porous chamber with surface mass injection sim ulating a nozzleless rocket motor has been investigated numerically. The an alysis is based on a large-eddy-simulation technique in which the spatially filtered and Favre averaged conservation equations for large, energy-carry ing turbulent structures are solved explicitly. The effect of the unresolve d scales is modeled semi-empirically by considering adequate dissipation ra tes for the energy present in the resolved scale motions. The flowfield is basically governed by the balance between the inertia force and pressure gr adient, as opposed to viscous effects and pressure gradient corresponding t o channel flows without transpiration. It accelerates from zero at the head end and becomes supersonic in the divergent section of the nozzle. Three s uccessive regimes of development, laminar, transitional, and fully turbulen t flow, are observed. Transition to turbulence occurs away from the porous wall in the midsection of the motor, and the peak in the turbulence intensi ty moves closer to the wall farther downstream as the local Reynolds number increases. Increase in pseudoturbulence level at the injection surface cau ses early transition to turbulence. As the flow develops farther downstream , the velocity profile transits into the shape of a fully developed turbule nt pipe flow with surface transpiration. The compressibility effect also pl ays an important role, causing transition of the mean velocity profiles fro m their incompressible flow counterparts as the local Mach number increases . The flow evolution is characterized primarily by three nondimensional num bers: injection Reynolds number, centerline Reynolds number, and momentum f lux coefficient.