The “simultaneous separation” sequence, involving the concurrent unlocking of the booster and protective cover from an air-breathing hypersonic vehicle, facilitates axial separation by utilizing the pressurized gas filling of the internal flow path. However, during the initial separation phase under this sequence, complex and variable pressure oscillations arise within the vehicle's internal flow path due to the interaction of moving shock waves, shock trains, and gas filling. Beyond conventional collision risks, a potential overpressure risk from the gas filling process is introduced into this sequence. Numerical simulations of developing flow field within the vehicle's internal flow path during protective cover separation were carried out, using overset moving mesh technology and solving the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations. The temporal flow field structures and unsteady pressure characteristics within the internal flow path were obtained. The evolution mechanism of the internal flow field during protective cover separation, as well as the influence mechanism between protective cover motion and stage distance variation on the flow field development during initial separation phase, were analyzed. The results indicate that during the initial separation phase under the “simultaneous separation” sequence, the filling and venting process of the internal flow path exhibits five distinct stages characterized by significantly different flow phenomena: gap-induced jet flow, moving shock sweep, shock train forward movement, gas backflow, and venting transition. The maximum pressure observed within the internal flow path during protective cover separation is primarily attributable to shock system pressurization, shock train pressurization, and gas filling pressurization/accumulation, rather than the pressure jump induced by the moving shock. The operational state of the internal flow path, whether started or unstarted, determines if the influence of cover motion and stage distance variation on the internal flow field manifests as a unidirectional dependency or a coupled interaction relationship.

To parametrically assess the aerodynamic-propulsion integrated performance of air-breathing hypersonic vehicles and comprehensively elucidate the influence rules of overall vehicle parameters on their performance, this paper proposes a parametric calculation method for integrated performance grounded in thrust-drag equilibrium. This method comprehensively considers the coupling between lift-drag characteristics and engine features, thereby providing a solid basis for subsequent research. Under this research framework, with a focus on the vehicle's cruising conditions at a constant altitude and speed, an in-depth exploration is made into the effects of overall parameters such as cruising angle of attack, engine performance, and aerodynamic performance on the vehicle's integrated performance. Research results reveal that, for typical vehicle configurations, the angle of attack corresponding to the optimal lift-drag ratio of 8.1° differs from that of 6.7° corresponding to the maximum cruising specific impulse. When the vehicle's aerodynamic performance remains constant, within a certain range, installing an engine with a higher baseline specific impulse and a specific impulse that decreases as the equivalence ratio increases can endow the vehicle with more excellent integrated performance. When the engine's thrust characteristics are invariant, through optimizing the aerodynamic shape to reduce the vehicle's zero-angle-of-attack lift coefficient, lift-curve slope, zero-lift drag coefficient, and lift-induced drag coefficient, while concurrently increasing the zero-angle-of-attack baseline flow coefficient and the flow-coefficient change rate, the vehicle's integrated performance can be effectively enhanced.Through the research presented in this paper, it is expected to provide guidance for the overall parameter design of air-breathing hypersonic vehicles.