Numerical investigation of effect of the design parameters of the counter-flow jet for drag reduction in hypersonic low-Reynolds number regime

Abstract

Due to the correlation of design parameters of the counter-flow jet in addition to the complexity of the flow field, understanding the mechanism of the counter-flow jet for drag reduction and flow control remains challenging. Furthermore, to satisfy the demands of the space transportation system, investigating the counter-flow jet's suitability for a range of flight conditions is critical. To solve these problems, a study was performed by varying the pressure ratio (PR) and exit Mach number of the counter-flow jet at hypersonic low-Reynolds number regime. For numerical simulations, laminar, axisymmetric Navier–Stokes equations were solved by the total variation diminishing scheme with second-order accuracy in space and the explicit strong stability preserving the Runge–Kutta method. With given numerical conditions, the flow field was categorized as the long penetration mode (LPM) based on the penetration length and the fluctuation of the flow field at the high-Reynolds number regime. By reducing the free-stream flow Reynolds number while keeping other parameters unchanged, the flow field transitioned from the LPM to a stable LPM, short penetration mode, or long penetration with periodically oscillation mode. The critical Reynolds number for the transition of the flow field is highly dependent on the exit Mach number of the counter-flow jet and PR. The extended jet layer was the primary reason for the fluctuation of the drag coefficient. Furthermore, with the counter-flow jet at certain flight conditions, drag can be reduced by up to 78% regardless of the stability of the flow field.