1. Introduction

With the progress that human achieved in the exploration of aviation and aerospace fields, the hypersonic vehicle technology has developed quickly. The design of hypersonic vehicle is a

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

complex problem based on hypersonic aerodynamics and involving multidisciplinary and multi-domain. Problems of hypersonic aerodynamics and aerodynamic heating, structures and materials technology are the main technological difficulties. There remains much variance between hypersonic flow and supersonic flow about the problem of aerodynamics. For the hypersonic boundary layer, entropy layer and shock wave layer overlapping each other, while it is high temperature and low density flow in boundary layer, which undoubtedly makes the hypersonic boundary layer flow more complex. Therefore, hypersonic aerodynamics is a key technology in the research and development of hypersonic vehicle. Various flow disturbance problems, usually exists in the flying environment of vehicle. For instance, the explosive blast wave [1], reverse jet [2, 3], the non-uniformity flow, the instability of flight, the rough wall and so on, which would happen in flying. It can be seen disturbances are common in flow fields. It's significantly different about the ideal hypothesis state of the steady flowfield and the flow condition existing in disturbance waves. The disturbance in the flowfield will have a significant influence on aerothermodynamics characteristics. The disturbance, whether it is strong or weak, will interfere with the flowfield, especially the shock and boundary layers. After the disturbance in the flowfield interference with shock wave and boundary layer, the disturbance wave will be induced. Then the induced wave will cause further interaction with boundary layer, and create new unstable waves. The stability characteristic of boundary layer and the laminar-turbulent transition mechanism will be significantly changed due to the induced unstable waves. Laminar-turbulent transition not only affects the aerodynamic heating of the wall of hypersonic vehicle, but directly changes the aerodynamic force. Especially, laminarturbulent transition will greatly increases aerodynamic drag, which reduces the lift drag ratio of hypersonic vehicle significantly and increases the requirement of thermal protection.

aims to study hypersonic flowfield and the stability characteristics of boundary layer under the freestream pulse wave. It should be mentioned that the significantly different showed in the influence mechanism of the wave types of continuous disturbance on the stability of boundary layer that had been pointed out by some scholars [6, 15, 16]. Ma and Zhong [15, 16] investigated the response of hypersonic plate boundary layer under different types of disturbance waves using direct numerical simulation and linear stability theory. It is found that acoustic disturbance has the greatest influence on the stability of boundary layer, and it is pointed out that the action mechanism of freestream entropy wave disturbance and vortex wave disturbance is similar to that of the fast acoustic wave disturbance, but different from the slow wave disturbance. Although it is significantly different between pulse disturbance wave and continuous disturbance wave in form, there is reason to believe that the response characteristics of hypersonic boundary layer are also significantly different under different freestream pulse waves. Therefore, the receptivity characteristics of hypersonic boundary layer

Numerical Study of Hypersonic Boundary Layer Receptivity Characteristics Due to Freestream Pulse Waves

http://dx.doi.org/10.5772/intechopen.70660

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under freestream pulse waves with different types are discussed in this paper.

of the disturbance mode in the hypersonic boundary layer are discussed.

the two-dimensional unsteady compressive N-S equation can be expressed as:

∂ð Þ f-f<sup>v</sup> ∂x þ

f<sup>v</sup> ¼ 0 τxx τxy uxτxx þ uyτxy þ k

∂Q ∂t þ

2. Basic equations and numerical method

Where the state vector Q can be expressed as:

Similarly, f, fv , g, gv can be expressed respectively as:

f ¼ ρux ρux

2.1. Navier-Stokes equation

In this investigation, the numerical simulations of hypersonic flowfield over a blunt wedge under the action of freestream pulse wave were conducted using a high order finite difference scheme. The response property of hypersonic flowfield under the action of freestream pulse wave analyzed, and the hypersonic boundary layer stability is investigated. The receptivity characteristic of hypersonic boundary layer under the action of different freestream pulse waves was compared, and the effects of the pulse wave types on the generation and evolution

According to the forms of conservation equation, momentum equation and energy equation, the three basic equations of fluid governing equations can be written as a general form, that is,

> ∂ g-g<sup>v</sup>

<sup>2</sup> <sup>þ</sup> <sup>P</sup> <sup>ρ</sup>uxuy <sup>ρ</sup><sup>E</sup> <sup>þ</sup> <sup>P</sup> ux

<sup>T</sup>

<sup>∂</sup><sup>y</sup> <sup>¼</sup> <sup>0</sup> (1)

(4)

<sup>Q</sup> <sup>¼</sup> ρ ρux <sup>ρ</sup>uy <sup>ρ</sup><sup>E</sup> <sup>T</sup> (2)

<sup>T</sup> (3)

∂T ∂x

Therefore, it is necessary to accurately predict the hypersonic unstable flowfield and the flowfield response characteristic induced disturbance waves during the design and development process of hypersonic aircraft. Considering the complexity and expensiveness of the hypersonic vehicle wind tunnel test, it is of practical significance to conduct the numerical simulation of hypersonic unsteady flowfield. In recent years, the hypersonic flowfield response induced by different disturbance waves and the influences of the disturbance wave on the stability of the boundary layer are studied by many scholars using numerical or experimental methods. Ma and Zhong [4] investigated the response of hypersonic boundary layer over a blunt cone to freestream acoustic waves at Mach 7.99. The receptivity of a flat plate boundary layer to a freestream axial vortex is discussed by Boiko [5]. Zhong [6] investigated the leading-edge receptivity to freestream disturbance waves for hypersonic flow over a parabola. The effect of wall disturbances on hypersonic flowfield, and the response of hypersonic boundary layer to wall disturbances are also widely studied [7–10]. Literature [11] points out that, after the interaction between any form of freestream disturbance and the shock wave as well as the boundary layer in hypersonic flow field, three independent forms of disturbance waves, including acoustic disturbance (fast and slow acoustic disturbance), entropy wave disturbance, and vortex wave disturbance will be generated. Among these investigations, most scholars are committed to study the effects of freestream continuous disturbance or the effects of wall disturbance on the stability of boundary layer and laminar-turbulent transition [12–14]. There is still less research on the effects of freestream pulse disturbance on the stability of boundary layer, and the mechanism in this field is still not fully understood. So, this paper aims to study hypersonic flowfield and the stability characteristics of boundary layer under the freestream pulse wave. It should be mentioned that the significantly different showed in the influence mechanism of the wave types of continuous disturbance on the stability of boundary layer that had been pointed out by some scholars [6, 15, 16]. Ma and Zhong [15, 16] investigated the response of hypersonic plate boundary layer under different types of disturbance waves using direct numerical simulation and linear stability theory. It is found that acoustic disturbance has the greatest influence on the stability of boundary layer, and it is pointed out that the action mechanism of freestream entropy wave disturbance and vortex wave disturbance is similar to that of the fast acoustic wave disturbance, but different from the slow wave disturbance. Although it is significantly different between pulse disturbance wave and continuous disturbance wave in form, there is reason to believe that the response characteristics of hypersonic boundary layer are also significantly different under different freestream pulse waves. Therefore, the receptivity characteristics of hypersonic boundary layer under freestream pulse waves with different types are discussed in this paper.

In this investigation, the numerical simulations of hypersonic flowfield over a blunt wedge under the action of freestream pulse wave were conducted using a high order finite difference scheme. The response property of hypersonic flowfield under the action of freestream pulse wave analyzed, and the hypersonic boundary layer stability is investigated. The receptivity characteristic of hypersonic boundary layer under the action of different freestream pulse waves was compared, and the effects of the pulse wave types on the generation and evolution of the disturbance mode in the hypersonic boundary layer are discussed.
