Effects of wall thermal condition on flow field in a supersonic inlet isolator

Abstract

In high-speed airbreathing engines like scramjets, supersonic combustion takes place in the engine combustor from which heat flux can propagate to the inlet isolator situated upstream. Due to this propagation, the wall temperature of the inlet isolator will elevate and affect the flow field significantly. In the present work, numerical computations have been carried out to study the flow field inside a supersonic inlet isolator under wall thermal condition at a fixed stagnation condition and upstream Mach number of 2.41. 2D Reynolds Averaged Navier-Stokes (RANS) equation with k−ω Shear Stress Transport (SST) turbulence model are implemented for the computation. The numerical scheme has been validated with available experimental data at the same flow condition. Thermal effect on the inlet isolator walls is modeled with steady isothermal as well as time-dependent fluctuating temperature profiles. Sinusoidal oscillation of temperature with varying frequency and amplitude has been considered to impose fluctuating thermal perturbation to the walls. In both the steady and fluctuating cases, it is found that the oblique shock train structures along with their interactions with wall boundary layers are significantly affected by temperature elevation. Ramp boundary layer separation due to strong geometry generated shocks has been found to be increased with the increase of wall temperature. For fluctuating wall heating, dominant ramp separation shows hysteresis behavior between increasing and decreasing half cycles of oscillation. Frequency variation at higher amplitude (A = 2.0, 1.5) cases has qualitatively similar effect on this hysteresis loop, whereas at a relatively lower amplitude (A = 1.0), at high frequency cases (f = 50 Hz and 100 Hz) hysteresis is found to be reduced. Instantaneous pressure and temperature response at various points substantiate this finding. The total pressure loss downstream of the shock train increases with wall temperature for the steady case and behaves differently in increasing and decreasing half cycles of fluctuating wall heating cases. Although same thermal condition has been maintained on both walls, it is observed that the temperature at near ramp region is higher than near lip areas. This is a general scenario for both steady and fluctuating cases even at the downstream of isolator where shock train is weakened. It is hypothesized that changes in fluid property and flow parameters due to the variation in the shock interaction near walls are the reasons behind this observation.