An experimental investigation of mixing mechanisms in shock-accelerated flow

Abstract

An experimental investigation of mixing mechanisms in a shock-induced instability flow is described. We obtain quantitative two-dimensional maps of the heavy-gas (SF 6 ) concentration using planar laser-induced fluorescence for the case of a shockaccelerated cylinder of heavy gas in air. The instantaneous scalar dissipation rate, or mixing rate, χ, is estimated experimentally for the first time in this type of flow, and used to identify the regions of most intense post-shock mixing and examine the underlying mechanisms. We observe instability growth in certain regions of the flow beginning at intermediate times. The mixing rate results show that while these unstable regions play a significant role in the mixing process, a large amount of mixing also occurs by mechanisms directly associated with the primary instability, including gradient intensification via the large-scale strain field in a particular non-turbulent region of the flow.

Richtmyer-Meshkov Instability in Reactive Mixtures

“…The contribution of the initial patterns to the instantaneous mixing rate was measured to be up to 80% of the peak mixing rate, in non-reactive measurements [8]. On the other hand, for reactive mixtures, we expect the scaling effect to alter shock induced mixing, and favor the process at selected wave numbers.…”

“…The two dimensional plane has Cartesian coordinates x and y, to which correspond unitary vectors and . At time t = t 0 the shock impinges the interface, a reflected rarefaction (i.e., the expansion fan), and a transmitted corrugated shocks depart from the point of impact [8] as shown in We seek to evaluate the time dependent solution to the problem, i.e., the pressure p, velocity vector , the density ρ, and reaction progress variable λ. The solution vector is written as .…”

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

“…We mainly limit our attention to the convergence effects and the baroclinic mechanism of the cylindrically converging RM instability with large initial deformation of the gas interfaces. It should be mentioned that the turbulent mixing is very interesting and important in the study of RM instability (Dimotakis 2005;Tomkins et al 2008;Balakumar et al 2012;Lombardini, Pullin & Meiron 2014a,b) but is outside the scope of the present work. Under the current conditions, the characteristics of the cylindrical converging shock are described first, and rich phenomena of the polygonal interfaces accelerated by the cylindrical converging shock and the reflected shock from the focal point, during the early stage of the RM instability, are obtained for the first time.…”

“…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).…”

Experiments of the Richtmyer–Meshkov instability

“…The first velocity field measurements and first large-scale vorticity measurements were made about a decade ago in RM flows using particle image velocimetry (PIV) [8], with more vorticity measurements since then [9]. Since that time, the spatial resolution has increased for both velocity measurements using PIV [10] and density measurements using planar laser induced fluorescence (PLIF) [11]. Although great improvements have been made in experimental diagnostics, we are at the nascent stages of application of these methods to a variety of RM flows to understand mixing down to the smallest scales.…”