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.

Large-Eddy Simulations of Longitudinal Vortices Embedded in a Turbulent Boundary Layer

Abstract: Large-eddy simulations of pairs of artificially generated longitudinal vortices embedded in a two-dimensional turbulent boundary layer are performed to study the dynamics of the vortical structures and to provide the unsteady inflow data for use in a future turbomachinery simulation. An immersed boundary method is employed to represent the wall-mounted half-delta wings that generate the counter-rotating vortex pairs. Two vortex pair configurations, with "common flow" between the vortices toward the end wall (common flow down) and away from the end wall (common flow up), respectively, are investigated. Mean velocities and Reynolds stresses compare well with experimental data, demonstrating the accuracy of the numerical approach and, in particular, the efficacy of immersed boundary treatment of the vortex generators. The large coherent vortices are characterized by streamwise velocity defect and negative mean pressure. The boundary layer in the common flow region is thinned by the vortices in the common-flow-down case and thickened by them in the common-flow-up case.

Unstructured Large Eddy Simulation Technology for Prediction and Control of Jet Noise

Abstract: Development of concepts for reduction of jet noise has relied heavily on expensive experimental testing of various nozzle designs. For example, the design of nozzle serrations (chevron) and internal mixer/ejector nozzles have relied largely on laboratory and full-scale testing. Without a deeper understanding of the sources of high-speed jet noise it is very difficult to effectively design configurations that reduce the noise and maintain other performance metrics such as nozzle thrust. In addition, the high complexity of the flow limits the success of a parametric black-box optimization.Copyright © 2010 by ASME and United Technologies Research Center

A dynamic eddy-viscosity model based on the invariants of the rate-of-strain

Abstract: Large-eddy simulation (LES) seeks to predict the dynamics of spatially filtered turbulent flows. By construction, the LES solution contains only scales of size ≥ ∆, where ∆ denotes some user-chosen length scale of the spatial filter. A large-eddy simulation based on an eddy-viscosity model and a Navier-Stokes simulation differ only in diffusion coefficient. Therefore, we focus on the question: “When does eddy diffusivity reduce a turbulent flow to eddies of size ≥ ∆?”. It is deduced that the eddy viscosity νe has to depend on the two invariants q and r of the filtered rate-of-strain tensor. We present a dynamic version of the resultant eddy-viscosity model and present results from LES of isotropic turbulence and turbulent channel flow.

Study of Rotor Tip-Clearance Flow Using Large-Eddy Simulation

Abstract: A large-eddy simulation has been performed to study the temporal and spatial dynamics of a rotor tip-clearance flow, with the objective of determining the underlying mechanisms for low pressure fluctuations downstream of the tip-gap. Simulation results are compared with experimental measurements, and favorable agreements are observed in both qualitative and quantitative sense. Typical vortical structures such as the tip-leakage vortex and tip-separation vortices are revealed, and their evolution is shown to be strongly influenced by the moving endwall and the blade wake. These vortical structures are the main sources of turbulence energy and Reynolds stresses as well as low-pressure fluctuations. Cavitation-inception analysis shows a high correlation between cavitation and the tip-leakage vortex.

Large eddy simulation of the flow in a transpired channel

Abstract: The flow in a transpired channel has been computed by large eddy simulation. The numerical results compare very well with experimental data. Blowing decreases the wall shear stress and enhances turbulent fluctuations, while suction has the opposite effect. The wall layer thickness normalized by the local wall shear velocity and kinematic viscosity increases on the blowing side of the channel and decreases on the suction side. Suction causes more rapid decay of the spectra, larger mean streak spacing and higher two-point correlations. On the blowing side, the wall layer structures lie at a steeper angle to the wall, whereas on the suction side this angle is shallower.

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.