Parviz Moin

Bio: Parviz Moin is an academic researcher from Stanford University. The author has contributed to research in topics: Turbulence & Large eddy simulation. The author has an hindex of 116, co-authored 473 publications receiving 60521 citations. Previous affiliations of Parviz Moin include Center for Turbulence Research & Ames Research Center.

Recent results on the structure of turbulent shear flows using simulation databases

Abstract: During the past year the use of large eddy and direct simulation databases has maEn possible significant advances in our unEnrstanding of the organized structures in turbulent shear flows. Here, I summarize some of these contributions, and cite the references where they are published in their entirety.

Active Turbulence Control in Wallbounded Flow Using Direct Numerical Simulations

Abstract: An exploratory study of concepts for active control of turbulent boundary layers using the direct numerical simulation technique was performed. Significant drag reduction was achieved when the surface boundary condition was modified such that it could suppress the large-scale structures present in the wall region. This was achieved by prescribing the normal component of velocity at the wall to be 180° out of phase with the normal velocity slightly above the wall at each instant. The drag reduction was 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 was examined. A preliminary result obtained by applying the present control strategy to a transitional flow is also briefly described, from which one can infer a possible linkage between the control strategy and flow stability.

Backscatter of turbulent kinetic energy in chemically-reacting compressible flows

Abstract: This study addresses the dynamics of kinetic-energy backscatter in the context of large-eddy simulations (LES) of turbulent chemically-reacting compressible flows. As a case study, a-priori analyses of direct numerical simulations (DNS) of reacting and inert supersonic, time-developing, hydrogen-air turbulent mixing layers with complex chemistry and multi-component diffusion are conducted herein to examine the effects of compressibility and combustion on subgrid-scale (SGS) backscatter of kinetic energy. General formulations of SGS backscatter with dilatation are provided, including an LESbased energy-transfer diagram that illustrates the conversion dynamics. Lastly, influences of SGS backscatter on the Boussinesq eddy viscosity are analyzed. 2. Background The energy-cascade hypothesis predicts that turbulent kinetic energy is generated at the largest scales in a flow and then transferred to progressively smaller and smaller scales until it is dissipated by molecular viscosity. This energy cascade typically holds in a statistically-averaged sense, but it does not always describe the local behavior of a turbulent flow. The turbulent dissipation associated with the smallest, viscous scales, is actually the difference between two energy fluxes, namely, the forwardscatter, corresponding to the classical energy cascade, and the backscatter, a reversal of this process in which energy is transferred from the small scales back to the large scales (Lesieur & �

A dynamic subgrid‐scale eddy viscosity model

Abstract: 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.

Lattice boltzmann method for fluid flows

Abstract: 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.

On the identification of a vortex

Abstract: 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.