Zhansen Qian’s research while affiliated with China Aerodynamics Research and Development Center and other places

The TSTO (two-stage-to-orbit) model is one of the most feasible candidates for the next generation aerospace vehicle with its efficiency on aerodynamics and propulsion obtained by each stage vehicle in the entire flight envelope. But it must face the problem of the two-body separation that determines the success of the orbital flight. The mechanism of the stage-separation process for the parallel arrangement mode is not yet fully grasped at present. To address this critical issue, a type of large lift-body, like-scale, parallel arrangement TSTO vehicle with the turbo-based combined cycle engine (TSTO-TBCC model) was adopted to investigate the stage aerodynamic interference and separation process by numerical simulation method with dynamic overset grid technology. And the influence of flap pre-deflection, angle of attack, and flying Mach number on the safety of stage-separation was mainly explored. The results indicate that, it is difficult to achieve a safe stage-separation model for the present TSTO-TBCC at the balance state between aerodynamic lift and gravity. The method to change flap pre-deflection is of limited usefulness in improving the safety of the stage-separation. When the flap pre-deflecting angle |δf| is increased from 5° to 30°, the separation between stages always failed. Meanwhile the method of reducing the angle of attack has a higher efficiency, and a safe stage-separation model can be achieved at an angle of attack −2°. For the flight Mach number of 3.0 to 6.0 under the condition of approximately equal dynamic pressure trajectory, the two stages of TSTO-TBCC can be safely separated only when the angle of attack is reduced to −2°. Since the increment of lift produced by the change of the Mach number is lower than the increment of the angle of attack by 1°, the safety of the stage-separation for TSTO-TBCC is not sensitive to the flight Mach number.

To compromise the compression efficiency and the starting properties, the inner contraction ratio (ICR) of a general high Mach number inlet is usually designed in the range of dual solution area. When going into an unstarted status, the high Mach inlet needs an assistant method to restart. This work explores a variable geometry method to restart the inlet. The rotating cowl is adopted to a typical Mach 4 cruising inlet, and the unsteady computation method with a dynamic Chimera grid technique is applied to simulate the rotating process of the inlet cowl. The change characteristics of the restarted performance at different rotating angle amplitude of the inlet cowl are investigated systematically. The numerical results reveal that the unstarted status of this typical inlet induced by the effect of high backpressure failed to restart if the inlet cowl rotating angle amplitude is under a small critical value, which is called lower critical angle. The inlet could restart if the cowl rotating angle amplitude is a little larger than the lower critical angle, and the flow may rapidly go to a steady condition after the inlet cowl returns to the design position. However, the performance of the restarted inlet is still worse than the design condition, because of the existence of an stable separation bubble on its shoulder, even if the inlet cowl stops rotating. The separation bubble becomes shrunk with an increasing the cowl rotating angle amplitude. When the inlet cowl rotating angle amplitude reaches a large critical value which is called upper critical angle, the separation bubble disappears, and all the separation is swallowed by the mean flow. Therefore the design performance of the inlet can be recovered, which means that the flow mass capture coefficient, total pressure recovery coefficient, drag and the outlet Mach number go back to the design level. It also shows that within the range of the lower and upper critical angles, the larger the rotating angle amplitude is, the more rapidly the separation bubble reaches stable state.