Suppression of Low-Frequency Shock Oscillations over Boundary Layers by Repetitive Laser Pulse Energy Deposition

Akira Iwakawa,Takahiro Tamba,Hoang Pham,Akihiro Sasoh,Tatsuro Shoda

doi:10.3390/aerospace3020013

Abstract

The effect of repetitive energy deposition on low Strouhal number oscillations of the shock wave induced by boundary-layer interaction over a cylinder-flare model was studied. The fluctuation of the energy deposition frequency was induced in the flow, because the bubble generated by the energy deposition flowed downstream along the surface repeatedly. The region before the bubble size was affected by the energy deposition directly, so the fluctuation frequency was equal to the energy deposition frequency. However, the flare shock behavior at a position farther from the surface than the bubble size was also affected strongly by the energy deposition. For low-frequency unsteadiness and the effect of energy deposition on its unsteadiness, two categories have been observed. In the relatively small flare angle case, the flare shock was oscillated owing to the fluctuation induced by the boundary-layer interaction at the shock foot, and its oscillation occurred at 2.1 kHz with a small amplitude. The amplitude of this oscillation was decreased by highly repetitive energy depositions, and its amplitude could not be detected at a highly repetitive energy deposition. In the longer cylinder section case, the region of the shock-wave interaction was widened, and the amplitude of the flare shock oscillation was increased. In this case, the amplitude drastically decreased because of energy deposition.

Highlights

Shock-wave boundary-layer interaction (SWBLI) is a common phenomenon of supersonic flow. This interaction induces unsteady flow, such as boundary-layer separation or shock-wave oscillation. These unsteady flows are driven by the fluctuations in the upstream boundary layer or by the fluctuation of the shock wave, and the dominant driving mechanisms depend on the interaction strength
The characteristic frequency of unsteadiness in the SWBLI region is lower than other regions, such as the upstream boundary layer or downstream of the shock wave [1]
There are two possible sources of the oscillation, upstream flow fluctuation or fluctuation propagating from the downstream of the shock wave

Summary

Introduction

Shock-wave boundary-layer interaction (SWBLI) is a common phenomenon of supersonic flow. Passive control approaches such as cavities [10], vortex generators [11,12,13], micro-ramps [14], and strakes [15] are effective in reducing SWBLI unsteadiness; these approaches are effective only in limited operational condition and can cause unfavorable effects in off-design operation Active control approaches such as energy deposition [16,17] and jet injection [18,19] can widen the effective operational ranges because the operational conditions can be tuned to the flow conditions. It was reported that laser pulse energy deposition, which was one of the active controlling approaches, can suppress boundary-layer separation [16] or modulate the shock-wave oscillation frequencies [17]. The objective of this paper is to investigate the effect of the energy deposition condition on the low-frequency unsteadiness in the SWBLI region

Experimental Apparatus and Methodology

Types of Low Frequency Oscillation and the Impact of Energy Deposition

The amplitude of the Shallow model

Long Interaction Region

Framing

Conclusions