4 research outputs found
Prandtl number effects in MRT Lattice Boltzmann models for shocked and unshocked compressible fluids
For compressible fluids under shock wave reaction, we have proposed two
Multiple-Relaxation-Time (MRT) Lattice Boltzmann (LB) models [F. Chen, et al,
EPL \textbf{90} (2010) 54003; Phys. Lett. A \textbf{375} (2011) 2129.]. In this
paper, we construct a new MRT Lattice Boltzmann model which is not only for the
shocked compressible fluids, but also for the unshocked compressible fluids. To
make the model work for unshocked compressible fluids, a key step is to modify
the collision operators of energy flux so that the viscous coefficient in
momentum equation is consistent with that in energy equation even in the
unshocked system. The unnecessity of the modification for systems under strong
shock is analyzed. The model is validated by some well-known benchmark tests,
including (i) thermal Couette flow, (ii) Riemann problem, (iii)
Richtmyer-Meshkov instability. The first system is unshocked and the latter two
are shocked. In all the three systems, the Prandtl numbers effects are checked.
Satisfying agreements are obtained between new model results and analytical
ones or other numerical results.Comment: 17 pages, 8 figure
Fluid Flow and Heat Transfer in Cellular Solids
To determine the characteristics and properties of cellular solids for an application, and to allow a systematic practical use by means of correlations and modelling approaches, we perform experimental investigations and develop numerical methods. In view of coupled multi-physics simulations, we employ the phase-field method. Finally, the applicability is demonstrated exemplarily for open-cell metal foams, providing qualitative and quantitative comparison with experimental data
Fluid Flow and Heat Transfer in Cellular Solids
To determine the characteristics and properties of cellular solids for an application, and to allow a systematic practical use by means of correlations and modelling approaches, we perform experimental investigations and develop numerical methods. In view of coupled multi-physics simulations, we employ the phase-field method. Finally, the applicability is demonstrated exemplarily for open-cell metal foams, providing qualitative and quantitative comparison with experimental data
Rayleigh-Taylor and Richtmyer-Meshkov instabilities: A journey through scales
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordHydrodynamic instabilities such as Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities usually appear
in conjunction with the Kelvin-Helmholtz (KH) instability and are found in many natural phenomenon and engineering applications. They frequently result in turbulent mixing, which has a major impact on the overall flow development
and other effective material properties. This can either be a desired outcome, an unwelcome side effect, or just an unavoidable consequence, but must in all cases be characterized in any model. The RT instability occurs at an interface
between different fluids, when the light fluid is accelerated into the heavy. The RM instability may be considered a
special case of the RT instability, when the acceleration provided is impulsive in nature such as that resulting from a
shock wave. In this pedagogical review, we provide an extensive survey of the applications and examples where such
instabilities play a central role. First, fundamental aspects of the instabilities are reviewed including the underlying
flow physics at different stages of development, followed by an overview of analytical models describing the linear,
nonlinear and fully turbulent stages. RT and RM instabilities pose special challenges to numerical modeling, due to
the requirement that the sharp interface separating the fluids be captured with fidelity. These challenges are discussed
at length here, followed by a summary of the significant progress in recent years in addressing them. Examples of
the pivotal roles played by the instabilities in applications are given in the context of solar prominences, ionospheric
flows in space, supernovae, inertial fusion and pulsed-power experiments, pulsed detonation engines and scramjets.
Progress in our understanding of special cases of RT/RM instabilities is reviewed, including the effects of material
strength, chemical reactions, magnetic fields, as well as the roles the instabilities play in ejecta formation and transport, and explosively expanding flows. The article is addressed to a broad audience, but with particular attention to
graduate students and researchers that are interested in the state-of-the-art in our understanding of the instabilities and
the unique issues they present in the applications in which they are prominent.Science and Technology Facilities CouncilScience and Technology Facilities Counci