On the evolution of spherical gas interfaces accelerated by a planar shock wave

Abstract

The interaction of a planar shock wave with a spherical gas interface (SF6 or helium) surrounded by air is studied experimentally and numerically. By means of the high-speed schlieren photography with high time resolutions and the numerical method VAS2D, the detailed flow field structures including the evolution of interfaces and the development of wave patterns are obtained. The sequences of schlieren frames of SF6 show that the refracted shock wave converges inside the volume and causes the shock focusing within the bubble interface, resulting in an outward jet. The SF6 jet is different from the krypton jet studied because of the difference in their acoustic impedances. The pressure perturbation plays an important role in the jet formation. Quantitative data of the evolving interface length, height, and vortex spacing as well as the displacements of the interface and the jet are acquired and compared. The generation and distribution of vorticity are also analyzed numerically and are found to be the dominant factors for the interface deformation and the resulting turbulent mixing. Furthermore, the velocities of the interfaces and shock waves obtained from the x-t diagrams in the experimental and numerical photographs are compared with those predicted from one-dimensional gasdynamics. In this way, the air contaminations of both gases are re-evaluated and it is shown that the contamination by air inside the helium bubble is significant while it has just small influence in the SF6 case, which confirms the findings in literatures.

On the interaction of a planar shock with a light polygonal interface

“…The development of shock-accelerated polygonal interfaces, illuminated by a DC regulated light source (DCR III, SCHOTT North America, Inc.), is captured by high-speed schlieren photography as presented in figure 2. In order to facilitate the light passing through the test section vertically, two parallel planar mirrors with a diameter of 200 mm are added in the traditional Z-fold schlieren system (Zhai et al 2011;Si et al 2012). In the present study, the frame rate of the high-speed video …”

“…The shapes of the gas interface in previous studies mainly include the single-mode interface (Meshkov 1969;Brouillette 2002;Jacobs & Krivets 2005;Mariani et al 2008;Long et al 2009;Balakumar et al 2012;, the spherical or cylindrical bubble formed by a soap film (Haas & Sturtevant 1987;Hosseini & Takayama 2005;Layes, Jourdan & Houas 2009;Haehn et al 2011Haehn et al , 2012Zhai et al 2011;Si et al 2012), the membrane-less gas cylinder (Jacobs 1992(Jacobs , 1993Tomkins et al 2008;Zhai et al 2014;Zou et al 2010) or gas curtain Orlicz et al 2009;Balakumar et al 2012;Balasubramanian et al 2012;Tomkins et al 2013) formed by the jet technique and the inclined planar interface (Wang et al 2012;McFarland et al 2014). Besides these classical interface shapes, Mikaelian (2005) theoretically and numerically studied the RMI on an initial interface with a discontinuous change in its first derivative.…”

“…The numerical method VAS2D (Sun & Takayama 1999) is adopted to simulate the process of shock-polygonal interface interaction. This method has been well validated for shock-body interaction (Sun & Takayama 1999), shock-bubble interaction (Zhai et al 2011) and shock-polygonal heavy interface interaction . In the numerical algorithm, the governing equations adopt the two-dimensional Euler equations which can be written in vectorial form as…”

Experimental investigation of cylindrical converging shock waves interacting with a polygonal heavy gas cylinder

“…In the case of a planar shock, different techniques developed to form the initial interfaces have been reported in the literature. Typically, the interfaces of different shapes between two gases include spherical bubbles formed by a soap film (Haas & Sturtevant 1987;Layes, Jourdan & Houas 2003;Ranjan et al 2005;Zhai et al 2011;Si et al 2012), circular gas cylinders (Haas & Sturtevant 1987;Hosseini & Takayama 2005;Tomkins et al 2008;Luo et al 2014b), elliptical gas cylinders On converging shock and polygonal interface interaction 227 (Zou et al 2010), single-/multi-mode interfaces generated by vibration (Jacobs & Sheeley 1995;Mariani et al 2008;Long et al 2009) or by a gas curtain (Balakumar et al 2008;Orlicz et al 2009;Balasubramanian et al 2012), rectangular blocks generated by a microfilm membrane supported by a fine wire mesh (Bates, Nikiforakis & Holder 2007), and three-dimensional interfaces with a minimum surface feature formed by the soap film technique free of supporting meshes . Recently, some polygonal interfaces have been formed in our group using thin pins to restrict the soap film and the results indicate that the soap film is a flimsy but durable material during the interface formation Zhai et al 2014;Luo et al 2015).…”

Jet formation in shock-heavy gas bubble interaction

“…Considerable work was also performed by domestic researchers, such as Li et al [21], Bai et al [22], and Tian et al [23]. Recent work by Zhai et al [24] emphasized the complex process involved during the shock focusing experimentally and computationally on the converging bubble scenario. It can be found that previous studies mainly concentrate on the development of initial perturbation and subsequently the occurrence of turbulent mixing after the shock wave passage.…”