**1. Introduction**

Airframe-propulsion integration design is one of the key techniques of airbreathing hypersonic vehicles [1] to reduce overall drag and achieve positive thrust margins at hypersonic speeds [2]. The engine and airframe aerodynamics therefore become highly coupled [3]. Airframe-propulsion integration methodologies for the hypersonic vehicle have been extensively studied by many researchers [4–7]. A waverider is any supersonic or hypersonic lifting body that is characterized by an attached, or nearly attached, bow shock wave along its leading edge. Since its high lift-to-drag ratio, the waverider has become one of the most promising designs for air-breathing hypersonic vehicles. In the present study, the cone-derived waverider is used and optimized as the basis for the entire vehicle [8], and the engine is generated maintaining the shock wave attaching to the leading edge.

The design of the scramjet, which is a key part of the hypersonic vehicle technology, involves a lot of subjects. Typically, it includes components such as inlet, isolator, combustor, and nozzle. Considering both good performance of every component and interaction effects between each two components, the design progress becomes quite complicated. To effectively solve these difficulties, the present work proposes a method for integrated design and performance analysis of the scramjet flowpath. Aerodynamic performance and flow fields are analyzed one after another for the scramjet and component.

The whole process is in the order of zero-dimensional thermodynamic analysis [9], quasi-one-dimensional estimated analysis [10], and three-dimensional computational fluid dynamics analysis [11–13]. The scramjet flowpath is designed with an inward-turning inlet [12], a constant-area circular isolator, a circular combustor with a cavity [11], and a three-dimensional flow-stream traced nozzle [13]. Firstly, geometry parameters and flow conditions of both the inlet and the exit for each subsystem are obtained from the result of the stream function analysis and optimization [14]. Secondly, two design codes are developed, one of which is the quasi-one-dimensional estimation program for the combustor and the other is the aerodynamic force and heat estimation for the whole hypersonic vehicle. Lastly, the CFD method is applied for performance analysis of the jaws inlet, back pressure characteristics of the inlet with a constant-area isolator, and flow field characteristics of the combustor with a cavity.
