Author details

sharply. In general, the narrowing of frequency band and the decreasing of main disturbance

In present study, a finite difference DNS method is used to investigate the response of the hypersonic flow field to freestream pulse wave, and the generation and evolution characteristics of the disturbance mode in the hypersonic boundary layer are analyzed. The effects of the pulse wave types on the generation and evolution of the disturbance mode in the hypersonic

1. The freestream disturbance waves significantly interact with the bow-shaped shock waves, which greatly changes the shock standoff distance and the distribution of flowfield parameters in the active region. The stronger the intensity of the shock wave is, the more intense the effect of the freestream pulse slow acoustic wave and the bow-shaped shock wave are. The freestream pulse wave's influence on the thermodynamic state in boundary layer is significantly greater than that on the thermodynamic state the outside boundary layer. There are many obvious disturbance characteristic regions in the hypersonic boundary layer under the action of freestream pulse disturbances. There is complex interference

2. In the nose area, the main disturbance modes in the boundary layer are distributed near the fundamental frequency, and the disturbance mode component of other frequencies is relatively small. In the nose area, the disturbance mode component ratio near the fundamental frequency decreases rapidly, the high frequency disturbance harmonic mode like the second order harmonic frequency and above significantly increases. With the evolution of the disturbance waves in the boundary layer from the upstream to the downstream, the main disturbance modes in the boundary layer are transformed from the dominant state of the fundamental frequency to the collective leadership state of the second order harmonic frequency and the third order harmonic frequency. The intensity of the bow shock in the hypersonic flowfield has significant effects on both the fundamental mode and the harmonic modes in each order. From the nose area to the non-nose area, the effect of the shock wave intensity on the harmonic frequency modes in the boundary layer is less than the recompression effect, and the effect of the shock wave intensity on the fundamental mode in the boundary layer is larger than the recomp-

3. The interaction between the strong shear structure of boundary layer and different types of freestream pulse waves have different mechanisms of action. The strong shear structure of boundary layer under the action of different types of freestream pulse waves reveals different stability characteristics. The effects of different types of freestream pulse waves are significant on the distribution of modes in boundary layer and the evolution of disturbance modes along with the streamwise. The narrowing of frequency band and the decreasing of main disturbance mode clusters exist in the boundary layer both for

freestream pulse fast acoustic wave, slow acoustic wave and entropy wave.

boundary layer are investigated. The study drew the conclusions as follow:

in the boundary layer under the action of the pulse wave.

mode clusters exist in the boundary layer both for all cases.

38 Advances in Some Hypersonic Vehicles Technologies

5. Conclusions

ression effect.

Xiaojun Tang<sup>1</sup> \*, Juan Yu<sup>2</sup> , Tianli Hui<sup>1</sup> , Fenglong Yang<sup>1</sup> and Wentao Yu1

\*Address all correspondence to: tangxiaojun2214@163.com

