《2021中国的航天》白皮书展望了未来五年，中国航天开启全面建设航天强国新征程，将持续开展可重复使用航天运输系统关键技术攻关和演示验证。而实现便捷、高效、航班化的天地往返和远距离运输是未来航天运输系统的重要发展方向。水平起降并联两级入轨（Two Stage to Orbit，TSTO）飞行器，具有低成本、高效率、多用途等优点，可实现一小时全球旅行和星际探索，是未来可重复使用空间运输系统的重要战略规划。TSTO飞行器由助推级和轨道级组成，两级一般在高超声速或超高速条件下进行级间分离。级间分离成功与否直接决定了TSTO飞行任务的成败，所以TSTO级间分离被列为高超声速空气动力学领域的关键难题之一。

并联TSTO在高超声速级间分离过程中，由于两级尺度一般处于同一量级，激波主导的非定常气动干扰历时长、强度大，容易与两级分离运动产生强耦合关系，增强动态分离的非定常效应。所以两级间的复杂强气动干扰具有非定常、高动态（特征时间尺度小）、强耦合（激波干扰与多体运动耦合）等特征，直接增加了级间分离失败风险。因此并联TSTO级间分离中的非定常流动机理、分离参数影响规律以及接近真实飞行分离的自由动态分离实验模拟尤为重要。研究人员借助近些年来逐渐发展的数值模拟、准定常（静态）风洞实验方法，结合十分有限的理论分析，在并联TSTO级间分离的流动与机理认识方面取得了进展，但是研究结果一般缺乏级间分离的非定常、高动态、强耦合等关键特征，所以非定常流动机理分析不足，而且高超声速飞行条件下的动态分离风洞实验作为并联TSTO级间分离的研究验证手段也十分匮乏。

本论文面向国家可重复使用空间运输系统的重要规划布局，针对TSTO级间分离涉及到的高速多体分离空气动力学关键问题，研究并联TSTO高超声速级间分离的非定常流动机理、安全分离方案及其风洞实验验证。相关的研究成果可为新一代TSTO气动设计及多体高速安全分离问题提供流动理论指导和验证手段支撑。主要研究内容和创新性成果如下：

（1）提出一种并联TSTO融合体飞行器概念并设计了用于高超声速级间分离非定常流动研究的复杂构型两级空天飞行器。该TSTO由乘波体助推级和空天飞机轨道级组成。研究并厘清了轨道级入射角、质心对并联TSTO横向分离的影响规律，揭示非定常激波干扰与多体运动耦合新现象以及复杂流动机理，提出强干扰条件下压心与质心的空间相对变化在时间上的无量纲变化率表征动稳定性，针对横向分离方案给出安全分离准则。

（2）提出针对并联TSTO飞行器的纵向级间分离新概念，通过数值和实验研究了纵向分离非定常流动干扰机理和气动特性，获得了攻角对纵向分离的影响规律以及安全分离条件。首次将激波针模型应用于并联TSTO飞行器，提出纵向分离轨道级减阻方法，阐释不同激波针-并联TSTO融合体复杂外形纵向分离的气动阻力规律，对比分析不同激波针构型的减阻效果及气动特性，给出减阻优化方案。

（3）国内外首次于激波风洞中开展米量级尺度的并联TSTO主动式（模拟带动力分离）自由动态分离实验，完成并联TSTO纵向分离方案原理性实验验证，证明了纵向分离概念优势及方案可行性，即基于两级小间隙弱气动干扰特征，两级可实现相对更平稳安全分离。同时，发展了激波风洞多体自由动态分离实验方法（包含多项关键技术），验证了激波风洞高速分离实验与测量技术的可靠性，为高超声速多体分离高焓风洞验证提供实验手段支撑。

“China's Space Program: A 2021 Perspective” looks forward to a new journey towards a strong space presence in the next five years, and will continue to strengthen research into key technologies for reusable space transport systems (RSTS), and conduct test flights accordingly. The realization of convenient, efficient, and regular launches for space and long-distance transportation is an important development direction for future RSTS. The parallel-staged two-stage-to-orbit (TSTO) vehicle with horizontal take-off and landing is an important aerospace concept for future RSTS, with advantages such as low cost, high efficiency, and multi-role capability, enabling for one-hour global travel and interstellar exploration. TSTO vehicle consists of a booster and an orbiter, and the two stages generally separate under hypersonic or hypervelocity conditions. The success or failure of stage separation directly determines the success or failure of TSTO flight missions, so TSTO stage separation is listed as one of the key challenges in the field of hypersonic aerodynamics.

During the hypersonic stage separation for the parallel-staged TSTO vehicle, since the scales of the two stages are generally at the same level, the unsteady aerodynamic interference dominated by shock waves has a long duration and high intensity, which easily leads to strong coupling with the separation motion of two stages and enhances the unsteady effects of dynamic separation. So the complex strong aerodynamic interference between two stages has characteristics such as unsteadiness, high dynamic (small feature time scale) and strong coupling (shock wave interaction and multi-body motion coupling), which directly increases the risk of stage separation failure. Therefore, the unsteady flow mechanism, influence of separation parameters, and close to real flight separation simulation of free dynamic separation experiments in parallel-staged TSTO stage separation are particularly important. Researchers have made progress in understanding the flow and mechanism of parallel-staged TSTO stage separation using numerical simulations, and quasi-steady or static wind tunnel experiments that have gradually developed in recent years, combined with very limited theoretical analysis. However, research results generally lack key characteristics of stage separation such as unsteadiness, high dynamic and strong coupling, so the analysis of the unsteady flow mechanism is insufficient. Moreover, hypersonic dynamic separation wind tunnel experiments are also very scarce as an investigation and verification method for parallel-staged TSTO stage separation.

Therefore, this dissertation focuses on the important plan of the national RSTS and the key high-speed multi-body separation aerodynamics involved in TSTO stage separation. The unsteady flow mechanism, safety stage separation scheme, and the wind tunnel experimental verification of parallel-staged TSTO hypersonic stage separation are investigated. The results of this research can provide the flow theory instructions and verification means support for the aerodynamic design of the next-generation TSTO vehicles and the high-speed safety separation of multi-body systems. The main research content and innovative achievements are as follows:

(1) A concept of a parallel-staged TSTO fusion vehicle is proposed and a complex two-stage aerospace vehicle is designed for the study of unsteady flow of hypersonic stage separation between two stages. The parallel-staged TSTO consists of a wave-rider booster and an aerospace orbiter vehicle. The dissertation studies and reveals the influence of orbiter incidence angle and center of gravity on the transverse stage separation (TSS) of parallel-staged TSTO vehicle, as well as the new phenomenon and flow mechanism of unsteady shock wave interaction and multi-body motion coupling; proposes a nondimensional rate of change in time for the spatial relative change between the pressure center and the center of gravity under strong interference conditions to characterize dynamic stability; and provides the safety separation criterion for TSS.

(2) A new concept of longitudinal stage separation (LSS) for parallel-staged TSTO vehicles is proposed, and the unsteady flow interaction mechanism and aerodynamic characteristics of longitudinal stage separation are studied through numerical and experimental methods. The influence of the angle of attack on the LSS and safety separation conditions is obtained. Moreover, the aerospike model is applied to the parallel-staged TSTO vehicle for the first time and a corresponding drag reduction approach for the orbiter in LSS is proposed. The aerodynamic drag law of the different aerospike TSTO vehicles during LSS are investigated. In addition, the drag reduction effect and aerodynamic interference characteristics of different aerospike models are compared and analyzed. Therefore, the optimization plan for drag reduction is presented.

(3) For the first time domestically and internationally, large-scale parallel-staged TSTO vehicle in meters active free-flight stage separation experiments to simulate power separation are conducted in the shock tunnel, and the principle of the parallel-staged TSTO LSS is experimentally verified. The feasibility and advantage of LSS concept, i.e., based on the weak aerodynamic interference characteristics of small interstage gap, the two-stage can achieve relatively smoother and safer separation. Meanwhile, the multi-body free-flight experimental methods (contain multiple key technologies) in the shock tunnel are developed. The reliability of the high-speed separation experiment and measurement technology in the shock tunnel is verified. Furthermore, the experimental support for validation of hypersonic multi-body separation in high enthalpy wind tunnel is provided.