**1. Introduction**

In recent years, with the ramjet engine matures and scramjet engine has achieved remarkable progress, a new-generation hypersonic vehicle powered by air-breathing engine has attracted widespread concerns in the international community and has become the focus of the future development in the field of aerospace. However, the development of this new generation air-breathing hypersonic vehicle faces many new key issues and requires great progresses in aerodynamics, structure thermal protection, propulsion technology and flight control [1, 2].

The sustained long-range maneuverable flight in the near-space atmosphere within a wide Mach range makes the experience of aerodynamic environment surrounding the hypersonic

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vehicles extremely complicated, which is characterized as complex flow fields, high enthalpy and long duration aeroheating with medium/low heat flux. Also, the interaction between the aerodynamic force/aeroheating flux of the external flow field and the heat transfer/thermal stress/deformation and other physical field of the internal physical field in the thermal protection system (TPS) will become extremely strong. Furthermore, the massive application of lightweight flexible materials and large thin-walled structure, especially the flight control rudder and other components will lead to another problem of aerothermoelasticity [3], which should consider the influence of sustained aeroheating. Therefore, the coupling between multi-physics such as flow field, heat and structure should be taken into account for a new-generation air-breathing hypersonic vehicle with the ability of hypersonic long-range maneuverable flight in the near-space atmosphere.

This chapter is to systematically study and analyze the coupling characteristics and mechanism of multi-physics coupling problems such as fluid-thermal-structural coupling of hypersonic vehicle, to construct a reasonable multi-physics coupling model, and to propose effective coupling analysis strategy based on computational fluid dynamics (CFD), computational thermodynamics (CTD) and computational structural dynamics (CSD), so as to provide theoretical support and analysis tools for further study of non-ablative thermal protection, aerothermoelasticity and other key issues. The following sections will focus on the modeling and analysis of several representative multi-physics coupling problems encountered on the fuselage, inlet, and wing of hypersonic vehicles.

with low rigidity is no longer negligible and induces thermal stress and thermal deformation while the fluid-thermal-structural coupling problem mainly characterized as the coupling between aerodynamic force/heat and heat transfer/thermal stress/deformation. In particular, the aerothermoelastic problem behaves more prominently for the large thin-walled flexible structures such as the wings and flight control rudders in which the fluid-thermal-structural coupling should consider the inertial effect and vibration of the

Modeling and Analysis of Fluid-Thermal-Structure Coupling Problems for Hypersonic Vehicles

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**Figure 1.** Coupling mechanism of multi-physics coupling problems for hypersonic vehicle.

The modeling of so-called multi-physics coupling problem mainly refers to constructing the mathematical-physical model to describe the coupling behavior of the multi-physical fields, namely, the partial differential equation systems (PDEs) to describe the multi-physics coupling problem and the corresponding initial/boundary conditions. And then, the analysis is to solve the partial differential equations by numerical simulation method to obtain the physical properties and behaviors. This modeling and analysis can generally be divided into two different types [4, 5], that is, the monolithic coupling approach and the partitioned coupling approach. According to the characteristics of multi-physics coupling problems, the global strategy for modeling and analysis is shown in **Figure 2**. The monolithic coupling approach is used respectively for the aerodynamic force/heat coupling within the fluid and the thermostructural dynamic problems within the solid. In contrast, the partitioned coupling approach is applied for the fluid-thermal coupling and fluid-thermal-structural coupling problem

structures.

through the fluid-solid coupling interface.

**Figure 2.** Global strategy for modeling and analysis approaches.
