两级入轨（TSTO）飞行器或将成为下一代天地运输往返系统，其具有低成本、高效率和多用途等优点，但是两级分离成功与否将直接决定入轨任务的成败。目前的并联式TSTO飞行器多采用横向级间分离，该方法会在两级间产生复杂强气动干扰而直接增加了分离风险，所以探索一种可以避免或减弱两级强气动干扰的新分离方式是十分必要的。提出并着重分析了一种并联式TSTO纵向级间分离（LSS）方案，即轨道级在助推级背面沿着飞行方向分离，对其进行了动态分离过程的数值研究。针对新分离方案，设计了一种由宽速域乘波体和可重复使用空天飞机分别作为助推级和轨道级的TSTO组合飞行器，在高超声速条件下，采用重叠动网格技术分析了不同来流攻角（AOA）下的纵向分离流动机理、非定常壁面压力分布及气动特性变化规律。结果表明：TSTO纵向分离过程中仅存在VI型激波干扰和激波汇聚等简单的弱干扰类型，两级间无明显的激波反射或激波边界层干扰；非定常压力分布特性表明助推级前缘激波是轨道级受力变化的主要影响因素；纵向分离过程中，助推级受到的气动干扰力载荷小于轨道级。此外，不同来流攻角下，两级气动干扰流场结构具有相似性，并给出了实现安全纵向分离的攻角条件。

Two Stage to Orbit （TSTO） vehicle may become an example of next-generation launch technology for its efficiency and reusability， but whether the two stages can be safely separated or not will directly determine the success or failure of the orbit mission. At present， parallel-staged TSTO vehicle mostly adopts a transverse stage separation scheme， in which strong aerodynamic interference is introduced between stages and directly increase the separation risk. Hence， it is necessary to explore a scheme to reduce or even avoid the strong aerodynamic interference during separation. In this study， a Longitudinal Stage Separation （LSS） scheme for the parallel-staged TSTO model， in which， the orbiter moves along the upper surface of the booster， is proposed and analyzed in detail by investigating the dynamic separation process numerically. A TSTO concept comprising a wide-speed waverider and a reusable space plane， as booster and orbiter respectively， was designed to investigate LSS by numerical simulation with the overset grid method. The flow mechanism， unsteady wall pressure distribution， as well as aerodynamic characteristics of LSS at different Angles of Attack （AOA） under hypersonic condition， are studied. The results show that the aerodynamic interference during LSS is simple and weak， which is only associated with type VI shock/shock interaction and the convergence of shock waves. No shock reflections or shock/boundary-layer interaction occurs between stages. The variations of pressure distribution show that the leading edge shock of the booster is the main factor affecting the aerodynamics of the orbiter. Moreover， the interference load on the booster is weaker than that of the orbiter. The interference flow structure of TSTO is similar among different AOA cases， and the appropriate AOA condition of safe LSS for the current TSTO model is presented.