One major drawback of the eddy viscosity subgrid‐scale stress models used in large‐eddy simulations is their inability to represent correctly with a single universal constant different turbulent fields in rotating or sheared flows, near solid walls, or in transitional regimes. In the present work a new eddy viscosity model is presented which alleviates many of these drawbacks. The model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model is based on an algebraic identity between the subgrid‐scale stresses at two different filtered levels and the resolved turbulent stresses. The subgrid‐scale stresses obtained using the proposed model vanish in laminar flow and at a solid boundary, and have the correct asymptotic behavior in the near‐wall region of a turbulent boundary layer. The results of large‐eddy simulations of transitional and turbulent channel flow that use the proposed model are in good agreement with the direct simulation data.

A dynamic subgrid‐scale eddy viscosity model

We present an overview of the lattice Boltzmann method (LBM), a parallel and efficient algorithm for simulating single-phase and multiphase fluid flows and for incorporating additional physical complexities. The LBM is especially useful for modeling complicated boundary conditions and multiphase interfaces. Recent extensions of this method are described, including simulations of fluid turbulence, suspension flows, and reaction diffusion systems.

Lattice boltzmann method for fluid flows

Considerable confusion surrounds the longstanding question of what constitutes a vortex, especially in a turbulent flow. This question, frequently misunderstood as academic, has recently acquired particular significance since coherent structures (CS) in turbulent flows are now commonly regarded as vortices. An objective definition of a vortex should permit the use of vortex dynamics concepts to educe CS, to explain formation and evolutionary dynamics of CS, to explore the role of CS in turbulence phenomena, and to develop viable turbulence models and control strategies for turbulence phenomena. We propose a definition of a vortex in an incompressible flow in terms of the eigenvalues of the symmetric tensor ${\bm {\cal S}}^2 + {\bm \Omega}^2$ are respectively the symmetric and antisymmetric parts of the velocity gradient tensor ${\bm \Delta}{\bm u}$. This definition captures the pressure minimum in a plane perpendicular to the vortex axis at high Reynolds numbers, and also accurately defines vortex cores at low Reynolds numbers, unlike a pressure-minimum criterion. We compare our definition with prior schemes/definitions using exact and numerical solutions of the Euler and Navier–Stokes equations for a variety of laminar and turbulent flows. In contrast to definitions based on the positive second invariant of ${\bm \Delta}{\bm u}$ or the complex eigenvalues of ${\bm \Delta}{\bm u}$, our definition accurately identifies the vortex core in flows where the vortex geometry is intuitively clear.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112095000462

On the identification of a vortex

http://home.eps.hw.ac.uk/~ab226/tmp/implicit/lele_92.pdf

Compact finite difference schemes with spectral-like resolution

/pdf/turbulence-and-the-dynamics-of-coherent-structures-i-1o6o6m60fm.pdf

Turbulence and the dynamics of coherent structures. I. Coherent structures

The preferential concentration of inertial particles in isotropic turbulence is studied using wavelets, enabling the joint scale-space analysis of the flow field of the carrier phase, the concentration field of the dispersed phase, and interphase conditioned statistics

Wavelet multiresolution analysis of particle-laden turbulence

The direct numerical simulation technique is used to explore concepts for manipulation of turbulent boundary layers. Significant drag reduction was achieved when at each instant the normal component of velocity at the wall was prescribed to be 180 deg out of phase with the normal velocity slightly above the wall. The drag reduction is accompanied with significant reduction in the intensity of the wall-layer structures and reductions in the magnitude of Reynolds stresses throughout the flow. Suitability of wall pressure and shear stress fluctuations for detection of flow structures above the wall are examined.

On the active control of wall-bounded turbulent flows

The dynamic modeling procedure for large eddy simulation of turbulent flows is reviewed and recent developments in the theoretical aspects and applications are described. Methods for inclusion of backscatter of energy from small to large scale motions are presented. New formulations of the dynamic procedure are proposed which are optimized based on the subgrid scale flux vector or the energy dissipation rate instead of the subgrid scale stress tensor. Recent results from application of the model to forced isotropic turbulence with an inertial subrange, flow over a backward facing step at Reynolds number of 28000, and flow over a concave curved surface are presented.

Developments and applications of dynamic models for large eddy simulation of complex flows

Resolution of wall layer turbulent structures in large eddy simulation of high Reynolds number flows of aeronautical interest requires inordinate computational resources. LES with wall models is therefore employed in engineering applications. We report on recent advances at the Center for Turbulence Research (CTR) in the development of wall boundary conditions for complex turbulent flows computed on unstructured grids. We begin by describing a novel application of wall modeled LES to a high lift airfoil system. This flow field is very complex involving boundary layers, free shear flows, separation and laminar/turbulence transition. We then describe a non-equilibrium model that requires the solution of the full 3D RANS equations in the near wall region. This model is successfully applied to a spatially evolving transitional and a high Reynolds number flat plate boundary layer. Finally we describe a new approach to LES using differential filters. An important byproduct of this approach is the derivation of slip velocity boundary conditions for wall modeled LES. This methodology is successfully applied to flow over NACA4412 airfoil at near stall conditions.

Wall-Modeling in Complex Turbulent Flows

A subgrid-scale capillary breakup model has been developed by coupling a Eulerian interface-capturing approach to a Lagrangian point particle method. At the fully resolved scale, the evolution of p...

Parviz Moin

Papers

Wavelet multiresolution analysis of particle-laden turbulence

On the active control of wall-bounded turbulent flows

Developments and applications of dynamic models for large eddy simulation of complex flows

Wall-Modeling in Complex Turbulent Flows

Subgrid-scale Capillary Breakup Model for Liquid Jet Atomization