TRANSITION CHARACTERISTICS OF FLOWFIELD IN A SIMULATED SOLID-ROCKET MOTOR

The flow characteristics in a two-dimensional porous-walled duct simul ating a solid-propellant rocket motor are numerically computed to inve stigate the effects of viscosity, compressibility, and inflow turbulen ce (sigma(w)) on the flow transitions. The finite volume technique is used to solve the time-dependent compressible Navier-Stokes equations with a subgrid-scale turbulence model, and the numerical fluxes are co mputed using a modified Godunov scheme. In addition to computed axial mean velocity and turbulence intensity profiles, the axial variations of skin friction coefficient and the transverse location of peak turbu lence intensity are used to identify the mean-flow transition and turb ulence-intensity transition, respectively. In particular, a new way of identifying turbulence-intensity transition by the use of the power s pectrum of velocity fluctuations is presented for the first time in th e present study The minimum centerline Mach number for the onset of me an-flow transition is obtained as the compressibility is considered al one. The critical values of sigma(w) for the onset of turbulence-inten sity transition and mean-velocity transition advance as well as for th e concurrence and delay between the two transitions are also determine d to illustrate why some researchers could observe only a single trans ition whereas others observed two transitions.