Numerical study of passive cavity control on high-pressure ratio single expansion ramp nozzle under over-expansion condition

Abstract

Single expansion ramp nozzle (SERN) is widely used in the propulsion system of hypersonic vehicle; it has good effect on weight loss, and also can reduce the nozzle base drag and friction loss effectively. But under the condition of transonic region, the flow is severely over-expanded in the SERN, and the corresponding performance of SERN is sharply declined. In order to improve the SERN performance under over-expansion condition, the passive flow control technique application of passive cavity on SERN is investigated numerically by solving Reynolds average Navier–Stokes equations, and with standard two-equation k-ɛ turbulent models adopted. The influences of major geometric parameters of passive cavity on the flow field and performance of passive cavity SERN are deeply explored. Results show passive cavity structure has active influence on the performance of SERN under the over-expansion condition. The shock position moves upstream and separation region increases in the passive cavity SERN. The number of the shock train in the passive cavity SERN decreases. And the second peak of the pressure distribution is obviously higher than that it has for the baseline SERN. The performance of passive cavity SERN is related to the size of separation zone and its starting position, which is determined by the position of the first hole in the passive cavity. Percent of porosity has a dominant influence on the flow field of passive cavity SERN. The position of the first hole in the passive cavity changes with the variation of percent of porosity, and the corresponding starting position of the flow blowing out from the passive cavity is different, resulting in the different position and intensity of the anterior oblique compression shock wave. The axial thrust coefficient of passive cavity SERN decreases with the increase in percent of porosity accordingly. The flow structures of passive cavity SERN change little with variety of aperture and cavity depth when percent of porosity remains constant, the axial thrust coefficient of passive cavity SERN are almost tantamount at this case. Compared to the effect of percent of porosity, the influence of aperture and cavity depth on flow field are much smaller. The influence of aperture and cavity depth on the performance of the passive cavity SERN can be ignored in the design.