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.

Similarity of organized structures in turbulent shear flows

Abstract: Recent analysis of databases generated by direct numerical simulations of homogeneous turbulent shear flows have revealed the presence of coherent structures similar to those in turbulent boundary layers. In this paper these findings and tentative conclusions on their significance are discussed.

Risk Quantification in Unsteady Flow Simulations using Adjoint-based Approaches

Abstract: In this paper, we study the unsteady flow past a circular cylinder subject to rotational oscillations. The uncertainties induced by the unknown frequency, magnitude and phase with respect to the vortex shedding are treated as sources of stochasticity, and we consider the problem of quantifying the tail probability distribution of the aerodynamic forces. Specifically we estimate the probability that the overall time-averaged drag exceeds a given critical value. First we compare adjoint-based and Monte Carlo based estimates. Then, we demonstrate that using an adjoint method, we can design a better statistical estimator and an importance sampling strategy and obtain accurate predictions with a computational cost orders of magnitude lower than brute force Monte-Carlo method.

Model consistency in the large eddy simulation of turbulent channel flows

Abstract: Various combinations of filters and subgrid scale stress models for large eddy simulation of the Navier-Stokes equations are studied by a priori tests and numerical simulations Consistency between model and filter is found to be essential to ensure accurate results Results and limitations of the a priori test are discussed The effect of grid refinement is also examined

Large-eddy simulation of multiphase flows in complex combustors

Abstract: Large-eddy simulation (LES) is a promising technique to accurately predict reacting multi-phase flows in practical combustors involving complex physical phenomena of turbulent mixing and combustion dynamics. Our goal in the present work is to develop a computational tool based on particle-tracking schemes capable of performing hi-fidelity multiphase flow simulations with models to capture liquid-sheet breakup, droplet evaporation, droplet deformation and drag. An Eulerian low-Mach number formulation on arbitrary shaped unstructured grids is used to compute the gaseous phase. The dispersed phase is solved in a Lagrangian framework by tracking a large number of particles on the unstructured grid. The interphase mass, momentum, and energy transport are modeled using two-way coupling of point-particles. A series of validation simulations are performed in coaxial and realistic gas-turbine combustor geometries to evaluate the predictions made for multiphase, turbulent flow.

Ensemble-averaged LES of time-evolving plane wake

Abstract: The ensemble-averaged dynamic procedure (EADP) introduced during the 1996 CTR Summer Program is tested on a time-evolving plane wake, an inhomogeneous flow that is statistically non-stationary. Convergence of the results with respect to the LES ensemble size is investigated, and it is found that an ensemble of as few as 16 realizations yields accurate converged results. New modeling concepts are tested in which quantities that explicitly require the knowledge of several realizations of the same flow are included.

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.