Stretching of material lines in shock-accelerated gaseous flows

Kumar, Sanjay; Orlicz, Gregory C; Tomkins, Christopher; Goodenough, C.; Prestridge, Kathy; Vorobieff, Peter; Benjamin, R. F.

doi:10.1063/1.2031347

Cited by 66 publications

(33 citation statements)

References 52 publications

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“…For cylindrical interfaces, a nitrocellulose membrane was used by Haas & Sturtevant (1987) to confine the test gas within the cylindrical volume. Later, the jet technique, developed by Jacobs (1992), became a primary way of forming a circular gas cylinder (Jacobs 1993;Tomkins et al 2008;Zhai et al 2014b), an elliptical gas cylinder (Zou et al 2010), two gas cylinders (Tomkins et al 2003), three gas cylinders (Kumar et al 2005) and a gas curtain (Orlicz et al 2009;Balakumar et al 2012;Tomkins et al 2013).…”

Section: Introductionmentioning

confidence: 99%

On the interaction of a planar shock with an polygon

Luo

Wang

et al. 2015

J. Fluid Mech.

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The interaction of a planar shock wave (M ≈ 1.2) with an SF 6 polygonal inhomogeneity surrounded by air is experimentally investigated. Six polygons including a square, two types of rectangle, two types of triangle, and a diamond are generated by the soap film technique developed in our previous work, in which thin pins are used as angular vertexes to avoid the pressure singularities caused by the surface tension. The evolutions of the shock-accelerated SF 6 polygons are captured by a high-speed schlieren system from which wave systems and the interface characteristics can be clearly identified. Both regular and irregular refraction phenomena are observed outside the volume, and more complex wave patterns, including transmitted shock, refracted shock, Mach stem and the interactions between them, are found inside the volume. Two typical irregular refraction phenomena (free precursor refraction, FPR, and free precursor von Neumann refraction, FNR) are observed and analysed, and the transition from FPR to FNR is found, providing the experimental evidence for the transition between different wave patterns numerically found in the literature. Combined with our previous work (Zhai et al., J. Fluid Mech., vol. 757, 2014, pp. 800-816), the reciprocal transitions between FPR and FNR are experimentally confirmed. The velocities and trajectories of the triple points are further measured and it is found that the motions of the triple points are self-similar or pseudo-stationary. Besides the shock dynamics phenomena, the evolutions of these shocked heavy polygonal volumes, which are quite different from the light ones, are captured and found to be closely related to their initial shapes. Specifically, for square and rectangular geometries, the different width-height ratios result in different behaviours of shock-shock interaction inside the volume, and subsequently different features for the outward jet and the interface. Quantitatively, the time-variations of the interface scales, such as the width and the normalized displacements of the edges, are obtained and compared with those from previous work. The comparison illustrates the superiority of the interface formation method and the significant effect of the initial interface shape on the interface features. Furthermore, the characteristics of the vortex core, including the velocity and vortex spacing, are experimentally measured, and the vortex velocity is compared with those from some circulation models to check the † Email address for correspondence: sanjing@ustc.edu.cn Interaction of planar shock waves with SF 6 polygons 367 validity of the models. The results in the present work enrich understanding of the shock refraction phenomenon and the database of research into Richtmyer-Meshkov instability (RMI).

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Section: Introductionmentioning

confidence: 99%

On the interaction of a planar shock with an polygon

Luo

Wang

et al. 2015

J. Fluid Mech.

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“…Zhang et al also observed that this density-gradient steepening will feed back into the dynamics of the flow through the baroclinic term and in fact leads to increased secondary baroclinic vorticity production, which at intermediate times becomes significant in regions of high acceleration (where ∇p becomes significant in addition to the enhanced ∇ρ). Kumar et al (2005) performed an experimental study of shock-induced mixing using PLIF visualization for several initial configurations of gaseous inhomogeneities. They examined one aspect of mixing at early time, namely the stirring of the fluid by the primary instability.…”

Section: Introductionmentioning

confidence: 99%

An experimental investigation of mixing mechanisms in shock-accelerated flow

et al. 2008

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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.

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“…Intricate experiments with three gas cylinders have been performed (44), and others are currently under way to further stress computational fluid dynamics models.…”

Section: A Computational Fluid Dynamics Model For Shock-induced Mixinmentioning

confidence: 99%

Algorithm for model validation: Theory and applications

Sornette

Davis²,

Ide

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

102

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Validation is often defined as the process of determining the degree to which a model is an accurate representation of the real world from the perspective of its intended uses. Validation is crucial as industries and governments depend increasingly on predictions by computer models to justify their decisions. We propose to formulate the validation of a given model as an iterative construction process that mimics the often implicit process occurring in the minds of scientists. We offer a formal representation of the progressive build-up of trust in the model. Thus, we replace static claims on the impossibility of validating a given model by a dynamic process of constructive approximation. This approach is better adapted to the fuzzy, coarsegrained nature of validation. Our procedure factors in the degree of redundancy versus novelty of the experiments used for validation as well as the degree to which the model predicts the observations. We illustrate the methodology first with the maturation of quantum mechanics as the arguably best established physics theory and then with several concrete examples drawn from some of our primary scientific interests: a cellular automaton model for earthquakes, a multifractal random walk model for financial time series, an anomalous diffusion model for solar radiation transport in the cloudy atmosphere, and a computational fluid dynamics code for the Richtmyer-Meshkov instability.A t the heart of the scientific endeavor, model building involves a slow and arduous selection process, which can be roughly represented as proceeding according to the following steps: (i) start from observations and/or experiments; (ii) classify them according to regularities that they may exhibit: the presence of patterns, of some order, also sometimes referred to as structures or symmetries, is begging for ''explanations'' and is thus the nucleation point of modeling; (iii) use inductive reasoning, intuition, analogies, and so on, to build hypotheses from which a model is constructed (by model, we understand an abstract conceptual construction based on axioms and logical relations developed to extract logical propositions and predictions); (iv) test the model obtained in step iii with available observations, and then extract predictions that are tested against new observations or by developing dedicated experiments. The model is then rejected or refined by an iterative process, a loop going from i to iv. A given model is progressively validated by the accumulated confirmations of its predictions by repeated experimental and/or observational tests.The validation of models is becoming a major issue as humans are increasingly faced with decisions involving complex tradeoffs in problems with large uncertainties, as for instance in attempts to control the growing anthropogenic burden on the planet (1) within a risk-cost framework (2, 3) based on predictions of models. For policy decisions, federal, state, and local governments increasingly depend on computer models that are scrutinized by scientific agenci...

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Stretching of material lines in shock-accelerated gaseous flows

Cited by 66 publications

References 52 publications

On the interaction of a planar shock with an polygon

On the interaction of a planar shock with an polygon

An experimental investigation of mixing mechanisms in shock-accelerated flow

Algorithm for model validation: Theory and applications

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