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| Release | : 2009 |
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| Release | : 2009 |
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Implicit large eddy simulation proposes to effectively rely on the use of subgrid modeling and filtering provided implicitly by physics capturing numerics. Extensive work has demonstrated that predictive simulations of turbulent velocity fields are possible using a class of high resolution, non-oscillatory finite-volume (NFV) numerical algorithms. Truncation terms associated with NFV methods implicitly provide subgrid models capable of emulating the physical dynamics of the unresolved turbulent velocity fluctuations by themselves. The extension of the approach to the substantially more difficult problem of under-resolved material mixing by an under-resolved velocity field has not yet been investigated numerically, nor are there any theories as to when the methodology may be expected to be successful. Progress in addressing these issues in studies of shock-driven scalar mixing driven by Ritchmyer-Meshkov instabilities will be reported in the context of ongoing simulations of shock-tube laboratory experiments.
| Author | : Man Long Wong |
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| Release | : 2019 |
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The Richtmyer-Meshkov instability (RMI) and the subsequent turbulent mixing driven by the interaction of shock waves with interfaces separating materials of different densities are commonly found in many natural phenomena and engineering applications with high-speed flows. One of the goals in this thesis is to develop accurate and efficient numerical methods that are suitable for numerical simulations of this kind of flows that involve both shock waves and turbulent motions. A type of high-order shock-capturing schemes that can be in explicit or spatially implicit form is developed to achieve this goal with localized dissipation nonlinear weighting technique. The scheme has the ability to preserve fine-scale features in smooth regions with minimal dissipation while still has the ability to provide sufficient numerical dissipation to capture shocks and discontinuities robustly. The explicit form of the high-order scheme is implemented in an in-house adaptive mesh refinement (AMR) framework which can efficiently employ the computational resources by dynamically allocating fine grid cells only to regions containing features of interest for multi-species Navier-Stokes simulations. As another goal of this thesis, the AMR framework is used to conduct two-dimensional (2D) and three-dimensional (3D) high-resolution simulations for the study of the RMI-induced mixing emerging from the interaction between a Mach 1.45 shock wave and a perturbed planar interface between sulphur hexafluoride and air. The numerical results are used to examine the differences between the development of RMI in 2D and 3D configurations during two different stages: (1) initial growth of hydrodynamic instability from multi-mode perturbations after the arrival of primary shock and (2) transition to chaotic or turbulent state after re-shock. The effects of the Reynolds number on the mixing in 3D simulations are also studied through varying the transport coefficients. An analysis of second-moment budgets for the highest Reynolds number 3D case is also performed. The analysis first addresses the importance of the second moment quantities: turbulent mass flux and density-specific-volume covariance for the closure of Favre-averaged Navier--Stokes (FANS) equations in this type of flow compared to single-species incompressible flows that only require Reynolds stresses for closure. The budgets of different second-moments before and after re-shock are also studied and compared in details. Further analysis is conducted on the post-transition flow to examine the validity of the modeling assumptions in the Besnard-Harlow-Rauenzahn-3 model and its variants for the unclosed terms in the FANS equations.
| Author | : Fenando F. Grinstein |
| Publisher | : Cambridge University Press |
| Total Pages | : 481 |
| Release | : 2016-06-30 |
| Genre | : Science |
| ISBN | : 1107137047 |
Reviews our current understanding of the subject. For graduate students and researchers in computational fluid dynamics and turbulence.
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| Release | : 2015 |
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The mixing of materials due to the Richtmyer-Meshkov instability and the ensuing turbulent behavior is of intense interest in a variety of physical systems including inertial confinement fusion, combustion, and the final stages of stellar evolution. Extensive numerical and laboratory studies of shock-driven mixing have demonstrated the rich behavior associated with the onset of turbulence due to the shocks. Here we report on progress in understanding shock-driven mixing at interfaces between fluids of differing densities through three-dimensional (3D) numerical simulations using the RAGE code in the implicit large eddy simulation context. We consider a shock-tube configuration with a band of high density gas (SF6) embedded in low density gas (air). Shocks with a Mach number of 1.26 are passed through SF6 bands, resulting in transition to turbulence driven by the Richtmyer-Meshkov instability. The system is followed as a rarefaction wave and a reflected secondary shock from the back wall pass through the SF6 band. We apply a variety of initial perturbations to the interfaces between the two fluids in which the physical standard deviation, wave number range, and the spectral slope of the perturbations are held constant, but the number of modes initially present is varied. By thus decreasing the density of initial spectral modes of the interface, we find that we can achieve as much as 25% less total mixing at late times. This has potential direct implications for the treatment of initial conditions applied to material interfaces in both 3D and reduced dimensionality simulation models.
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| Release | : 2011 |
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| Author | : Akshay Subramaniam |
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| Release | : 2018 |
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The Richtmyer-Meshkov instability arising from the interaction of shock waves with material interfaces occurs in many natural and engineering contexts. It plays an important role in supersonic combustion, supernova explosions and presents a major roadblock in achieving sustained fusion in Inertial Confinement Fusion (ICF). The first part of the thesis focuses on high resolution simulations of the Richmyer-Meshkov instability that seek to deduce the effect of spatial inhomogeneity. Simulations performed with high order compact finite difference schemes are compared to experiments and show good qualitative and quantitative comparison. Analysis of the simulation results is focused on understanding the turbulence energy dynamics and mixing processes. A scale dependent coarse-graining approach is developed and used to decipher the energy dynamics in scale space. The coarse-graining analysis shows the effect of compressibility in inhomogeneous Richtmyer-Meshkov flows. A new mixing measure based on entropy generation by diffusive mass flux is introduced and evidence for a mixing cascade in scale space is presented. Results of energy and mixing scaling obtained from the simulations here are compared with experimental results of other inhomogeneous Richtmyer-Meshkov flows and similarities are drawn. In the second portion of the thesis, a new high order Eulerian method for simulating large deformation phenomena in solids as well as flow in liquids and gases in a unified manner is presented. The method uses an inverse deformation gradient tensor to track deformations and the hyperelastic formalism is used in order to maintain thermodynamic consistency. The accuracy and resolution properties of the method are demonstrated through one and two dimensional test problems. The method is extended to be able to simulate interactions between multiple materials using a diffuse interface approximation. The Richtmyer-Meshkov instability between copper and aluminum is simulated and a grid resolution study shows the superior resolution properties compared to previous methods. Finally, a new algorithm to treat sliding at material interfaces is presented in the context of a diffuse interface Eulerian method.
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| Total Pages | : 782 |
| Release | : 1995 |
| Genre | : Power resources |
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| Release | : 2010 |
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In the large eddy simulation (LES) approach large-scale energy-containing structures are resolved, smaller (presumably) more isotropic structures are filtered out, and unresolved subgrid effects are modeled. Extensive recent work has demonstrated that predictive simulations of turbulent velocity fields are possible based on subgrid scale modeling implicitly provided by a class of high-resolution finite-volume algorithms. This strategy is called implicit LES. The extension of the approach to the substantially more difficult problem of material mixing IS addressed, and progress in representative shock-driven turbulent mixing studies is reported.
| Author | : Thomas B. Gatski |
| Publisher | : Academic Press |
| Total Pages | : 343 |
| Release | : 2013-03-05 |
| Genre | : Science |
| ISBN | : 012397318X |
Compressibility, Turbulence and High Speed Flow introduces the reader to the field of compressible turbulence and compressible turbulent flows across a broad speed range, through a unique complimentary treatment of both the theoretical foundations and the measurement and analysis tools currently used. The book provides the reader with the necessary background and current trends in the theoretical and experimental aspects of compressible turbulent flows and compressible turbulence. Detailed derivations of the pertinent equations describing the motion of such turbulent flows is provided and an extensive discussion of the various approaches used in predicting both free shear and wall bounded flows is presented. Experimental measurement techniques common to the compressible flow regime are introduced with particular emphasis on the unique challenges presented by high speed flows. Both experimental and numerical simulation work is supplied throughout to provide the reader with an overall perspective of current trends. An introduction to current techniques in compressible turbulent flow analysis An approach that enables engineers to identify and solve complex compressible flow challenges Prediction methodologies, including the Reynolds-averaged Navier Stokes (RANS) method, scale filtered methods and direct numerical simulation (DNS) Current strategies focusing on compressible flow control
