The subject of this paper is a combined numerical/experimental study on a recently discovered shock reflection phenomenon, namely the dependence of the eventually established reflection pattern on the geometry of the initial portion of the reflecting surface, even if this initial portion comprises only a small part of the reflector. This dependence has so far only been discovered in numerical simulations and no experimental evidence for this phenomenon exists.
Recently, Lau-Chapdelaine & Radulescu (2013) demonstrated in numerical simulations that the resulting reflection pattern may be of regular or irregular type for the same wedge angle, incident shock Mach number and ratio of specific heats, depending on whether the tip of the reflecting wedge is straight or initially curved. Preliminary parametric studies by Alzamora Previtali & Timofeev (2014) have shown that the presence of a curved, concave tip influences the reflection outcome provided that the wedge angle is within a certain range in the dual solution domain where both regular and irregular (Mach) reflections are physically admissible. If a curved tip induces a Mach reflection over its concave surface, this type of reflection is maintained while the incident shock propagates over a long distance along the wedge surface. If, on the other hand, the tip is sharp, the same shock wave creates a regular reflection pattern. It was also demonstrated that one of the conditions for the effect to become observable is that the radius of curvature of the tip has to be considerably greater than the shock wave thickness – however, since a typical shock thickness is usually below one micrometer, this implies that even a minuscule tip with a radius of curvature of a fraction of a millimetre could possibly be the cause of differing reflection patterns.
The present paper aims at investigating this phenomenon in more detail both by numerical simulation and by experiments, the latter being conducted in a conventional shock tube with an optically accessible test section size of 220 mm. Different methods of time-resolved flow visualisation are used as the main diagnostic tool.
References
Lau-Chapdelaine SS, Radulescu MI (2013) Non-uniqueness of solutions in asymptotically self-similar shock reflections. Shock Waves, 23(6):595-602.
Alzamora Previtali F, Timofeev E (2014) On shock reflection from the straight wedges with circular concave tips. In: Podlaskin A, Krasovskaya I (eds.) Book of Proc. 21st International Shock Interaction Symposium, Riga, August 3-8, 2014, University of Latvia, p. 236
