High spatial and temporal resolution study of shock wave reflection over a coupled convex–concave cylindrical surface

Abstract

Studying the nature of transient reflections of shock waves from surfaces is important in many engineering fields, e.g. blast protection, supersonic flights, shock focusing, medical and industrial applications and more. The recent advancements in this field reveal that the major obstacle in better understanding this phenomenon by means of experimental investigations is the limited temporal and spatial resolution. An alternative approach to commonly used high-speed photography is based on the use of a single-lens reflex (SLR) camera that captures only one image per experiment. Using this method to study a transient reflection process necessitates repeating each experiment many times while retaining extremely high repeatability. In the present study, we present a solution to this obstacle by means of a fully automated shock tube facility, which has been developed in the course of this study. A typical experiment can be executed a few hundred times with a repeatability of less than 0.01 in the incident-shock-wave Mach number at moderate shock strengths (M = 1.2-1.4). The system offers a very high spatial and temporal resolution description of the transient reflection process of a shock wave over a coupled convex-concave surface. The study of this complex configuration using a fully automated shock tube enables one to observe, in greater detail than ever before, both the transient transition from regular reflection, RR, to Mach reflection, MR, and the reverse transient transition from MR to RR. The geometry studied can also be found in blunt leading-edge reflectors in which higher pressures were recorded, and the results presented also describe in detail the shock reflection process inside such a reflector. The results highlight and strengthen the recent understanding of the importance of high spatial and temporal resolution in determining the transition process from RR to MR over a coupled concave-convex surface. However, despite achieving very high statistical certainty in the experimental measurements, the question of the difference between the pseudo-steady transition criterion and the experimental results remains unresolved.

Similarity in Mach stem evolution and termination in unsteady shock-wave reflection

“…They showed that an additional Mach stem configuration is formed on the original MR. This was also shown experimentally by Ram, Geva & Sadot (2015). A similar qualitative analysis of RR over segments of wedges forming a convex surface was performed by Wang & Zhai (2020).…”

“…The following subsections present concise descriptions of the numerical computations, experimental procedure, validation and post-processing. For further information about the computations and extended validation, the interested reader is referred to Geva et al (2013), Ram et al (2015) and Geva, Ram & Sadot (2018).…”

“…From the shock-dynamics point of view, the sudden surface change produces a discontinuity along the shock wave which is in contact with the surface; this shock is the Mach stem inclined by 20°from the vertical axis with Mach strength of M w1 (figure 19a). Ram et al (2015) showed that this oblique wave can be considered vertical, with respect to the horizon, if an equivalent surface is used. Thus, it may be reasonable to assume that a Mach stem inclined by 20°that propagates over a 40°wedge is similar to a shifted case in which a vertical wave, travelling with M w,1 , propagates on another 20°wedge (figure 19b).…”

Numerical and experimental investigation of oblique shock wave reflection off a water wedge

“…In this experiment, when using the Phantom V711 camera, the thickness of the dark band was roughly equal to one pixel (450 µm). However, when using the Nikon D90, it was about 10 pixels (270 µm), similar to previous results (Ram et al 2015).…”

“…Various experimental visualization techniques have been performed in shock tube setups to determine the transition angle using either high temporal imaging or spatial imaging (Geva et al 1990; Kleine et al 2014;Mouton 2006;Naidoo & Skews 2011;Ram et al 2015;Skews & Kleine 2010;Skews & Blitterswijk 2011). Technological advances of high temporal imaging equipment have made these systems readily available to many researchers.…”