Experimental Study of Investigations Between Weak Shock Wave and Turbulence

Abstract

The project to develop the low sonic boom supersonic transportation system is now proceeding in Japan Aerospace Exploration Agency (JAXA). For this project, the establishment of precise boom prediction method is one of the important issues. For the sonic boom propagation toward ground, it has been pointed out that the existence of the atmospheric turbulence has the possibility to affect the sonic boom strength that is the magnitude of the over pressure. For the precise prediction of the sonic boom strength observed at the ground, the effect of the interaction with the turbulence should be included. Until now, a lot of efforts have been devoted to investigate the mechanism of the interaction between the turbulence and weak shock wave which is called sonic boom. The post shock pressure modulations resulting from the interaction with jets were studied using conical shock tube by Ribner et.al. In his study, the jet blew either in the same or in the opposite direction of the shock wave propagation. The impingement of the shock wave on the opposing jet resulted in a spiked overpressure variation. Interaction of the shock wave with a jet in the same direction led to a rounded variation. Lipkens, et al. conducted laboratory model experiments of a weak shock wave modulation through a turbulent flow. A shock wave was generated using an electric spark and a turbulent jet flow was ejected from a slit. The turbulence caused enormous variability in the waveform of the post-shock overpressure. On average, the slit jet led to an increase in the rise time and a decrease in the peak overpressure. However, the standard deviation became much larger than the average decrement; implying that in some cases the peak overpressure was enhanced although in majority it was weakened. Such‘ statistical’behavior cannot be reproduced by deterministic computational fluid dynamics simulation. The associated mechanisms of the pressure modulation warrant further investigation, specifically to determine under what conditions the shock strength is increased or decreased, and how the shock shape is deformed in the interaction process. Based on this background, our research group conducted the study of the turbulence effect on the weak shock wave by using slit jet. However, for the better understanding of this phenomena, the experiment using uniform turbulent flow is desired. Therefore, we have settled the experiment using grid turbulent wind tunnel. In this paper, as a first step of the above study, the result of the characteristics test experiment of the required facilities such as wind tunnel and shock tube which is for the weak shock generator will be reported.