PLIF flow visualization and measurements of the Richtmyer–Meshkov instability of an air/SF₆ interface

Abstract

Investigations of the Richtmyer–Meshkov instability carried out in shock tubes have traditionally used membranes to separate the two gases. The use of membranes, in addition to introducing other experimental difficulties, impedes the use of advanced visualization techniques such as planar laser-induced fluorescence (PLIF). Jones & Jacobs (1997) recently developed a new technique by which a perturbed, membrane-free gas–gas interface can be created in a shock tube. The gases enter the shock tube from opposite ends and exit through two small slots on opposite sides of the test section, forming a stagnation point flow at the interface location. A gentle rocking motion of the shock tube then provides the initial perturbation in the form of a standing wave. The original investigation using this technique utilized dense fog seeding for visualization, which allowed large-scale effects to be observed, but was incapable of resolving smaller-scale features. PLIF visualization is used in the present study to investigate the instability generated by two incident shock strengths (Ms = 1.11 and 1.21), yielding very clear digital images of the flow. Early-time growth rate measurements obtained from these experiments are found to be in excellent agreement with incompressible linear stability theory (appropriately adjusted for a diffuse interface). Very good agreement is also found between the late-time amplitude measurements and the nonlinear models of Zhang & Sohn (1997) and Sadot et al. (1998). Comparison of images from the Ms = 1.11 and 1.21 sequences reveals a significant increase in the amount of turbulent mixing in the higher-Mach-number experiments, suggesting that a mixing transition has occurred.

Enhanced verification test suite for physics simulation codes

“…The parameters used to generate theses results are those given in the experimental shock tube work of Jacobs [Col02], where the fluids are air and SF 6 , the initial temperature is 292.5 K, the pressure is 9.269×10 5 g cm -2 , the single mode sinusoidal interface disturbance wavelength is 5.93 cm, the amplitude is 0.3 cm, 2 the Atwood number is about 0.6, and the fluids are taken to be polytropic gases with gamma being 1.276 for air and 1.093 for SF 6 . Initial densities are calculated using the ideal gas equation of state.…”

“…Density results from the ALE code [Col02] for a time of about 1.7 ms after the shock hits the interface disturbance. We note that the amplitude and mushroom width from the ALE code are approximately 1.8 cm and 2.2 cm, respectively.…”

Experiments of the Richtmyer–Meshkov instability

“…Generally, as the driver Mach number, Ma, and overall speed of the flow increase, it becomes more difficult to measure important flow parameters, such as the density distribution and the mean and fluctuating velocities. Over the past decade, the RM instability has been studied in shock tubes [2], drop tanks [3], laser-driven capsules [4] and explosively driven systems [5]. These experiments illustrate the breadth of scales and Mach numbers that are experimentally accessible as well as the limitations of the experimental diagnostics as the driver Mach numbers are increased.…”

A study of planar Richtmyer-Meshkov instability in fluids with Mie-Grüneisen equations of state

“…A great deal of research has been performed on Richtmyer-Meshkov instability since its introduction. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] A common component of most previously performed experimental and computational work has been the use of gases at conditions close to room temperature and pressure. In light of this, the current investigation is focused on exploring the role of the equation of state in RichtmyerMeshkov instability specifically in relation to commonly studied perfect gas cases.…”