Parametric Study of Boundary-Layer Receptivity to Freestream Hot-Spot Perturbation over a Blunt Compression Cone

Abstract

This paper presents the numerical simulations of transient flow under the interaction between freestream hotspot perturbations and bow-shock on Purdue's blunt compression cone with the effects of different nosebluntness and various freestream Mach numbers. The basic flow conditions are referring to Boeing/AFOSR Mach-6 Quiet tunnel (BAM6QT) at Purdue University. The simulations in this paper consist of two cases of different nose-radii and two cases of different freestream Mach numbers. The detailed analysis of the receptivity mechanisms is carried out with linear stability theory (LST). The simulation results agree well with LST analyses. The parametric study is performed by the comparisons of the simulation results with the Mach-6 results that have been carried out previously. The study shows the sharper cone destabilizes the boundary layer, and the higher freestream Mach number stabilizes it. The receptivity mechanisms under both effects are shown to be the same: the second mode instability is induced by the fast acoustic waves behind the shock in the nose region.2 disturbances and nonlinear breakdown of them. Therefore, the study of second mode receptivity and instability is particularly important.Most of the hypersonic vehicles have blunt noses in order to reduce aerodynamic heating. The bow-shock in front of the blunt nose creates an entropy layer, which will be swallowed by the boundary layer in downstream [8]. There is strong vorticity created by the entropy layer, which may affect the receptivity process in the flow region near the shock. In addition, the swallowing process of entropy layer has a strong effect on the boundary layer stability [7].Kovasznay [11] showed that weak disturbances in compressible flow can be decomposed into acoustic, entropy and vorticity disturbance. It is well-known [10] that, regardless of the type of disturbances in the freestream hitting the shock, the interaction with the shock always generates all three kinds of disturbances, namely acoustic, entropy and vorticity disturbances. However, the mechanisms of the interaction of various types of disturbance with the shock are individually different, which would lead to difference in travelling angle and amplitude of the generated disturbances. In nature, the disturbances exist in freestream during flight in atmosphere consist of all three kinds. Thus, detailed boundary layer receptivity studies of all three types of freestream disturbance and shock interaction are necessary for completely understanding the mechanism of hypersonic boundary layer receptivity over blunt body. The receptivity to freestream acoustic disturbances has been studied extensively by many researchers [3,4]. There is experimental effort at Purdue University to use laser equipments to generate hotspots in a wind tunnel [3,4]. The goal is to study the generation of the second mode by using freestream entropy perturbations.The study in this paper is motivated by the experiments at Purdue University. The purpose of the current study is to conduct numerical inves...

Second Mode Suppression in Hypersonic Boundary Layer by Roughness: Design and Experiments

“…In the study of the smooth compression cone at the current freestream condition by Wheaton et al [22], no transition was observed, and the maximum N factor obtained from linear stability equation (LST) reached 14 at the end of the cone. In addition, Huang and Zhong [23,[25][26][27][28] have conducted extensive numerical and stability studies of boundary-layer receptivity to freestream hotspot perturbations with the same freestream conditions over a compression cone.…”

Boundary Layer Instabilities Generated by Freestream Laser Perturbations

“…Past computational and theoretical receptivity studies have included investigations of acoustic waves, 5-7 of vorticity waves, 8 of discrete particles, 9 and of small entropic disturbances. [10][11][12][13][14] However, receptivity experiments are difficult to perform, making it challenging to validate the computational and theoretical studies. Experimental studies have largely been in the subsonic regime, and the few existing high-speed studies typically use disturbances that are not easily characterized.…”