Keywords: 
• 合成冷/热射流 /
• 边界层 /
• 转捩控制 /
• 线性稳定性

Abstract: To investigate the stability and transition control mechanism of supersonic boundary layer, a coupled method of velocity/temperature control based on synthetic cold/hot jet is proposed. Based on the prior dual-synthetic jet actuator, a high performance synthetic cold/hot jet is achieved by adding a cooling/heating module. By placing the actuator under the flat-plate, periodic blow-suction is produced and low momentum jets are injected into the boundary layer to control the transition. Numerical simulations are conducted to study the propagation and evolvement of the unstable waves in the supersonic flat-plate boundary layer with Ma = 4.5. Influences of wall blow-suction, synthetic jet temperature, perturbation frequency, and perturbation amplitude on control effect of the unstable wave are mainly studied. The flow field and control effect are analyzed using the temporal mode of linear stability theory. The results show that without jet control, the first and second mode perturbation wave coexist simultaneously with the second mode dominant in the two-dimensional wave. In the effect of the wall blow-suction, the second mode appears to be more unstable while the first mode is suppressed. Under the control of the coupled speed-temperature, the jet temperature has significant influences on the area of the unstable region and the growth rate of the perturbation mode. When the jet temperature is different from the inlet fluid temperature, the fluctuation of temperature accelerates the transition of laminar flow to turbulent flow, and the velocity profile becomes more full, which leads to a more stable flow field. The control effect of high frequency blow-suction disturbance on flow field are better than that of low frequency. When the control frequency is higher than 400 Hz, the imaginary part of the eigenvalue ωi of the second mode disturbance wave decreases, and the disturbance component accelerates the correction between velocity profile and temperature profile of supersonic boundary layer, thus making a more stable second mode. When the disturbance amplitude decreases to 1% of the main flow speed, only the second mode is detected of low time growth rate, which results in a better control effect. However, as the disturbance amplitude further decreases, the first mode reemerges, and its wave number overlaps with that of the second mode at first, and then, separates from each other. The research results provide a new idea for supersonic boundary layer transition control from laminar flow to turbulent flow.