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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.


Papers
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Journal ArticleDOI
TL;DR: Chan, Johnson and Moin this paper examined the dynamics of the bubble-mass flux from large-to small-bubble sizes, which depends on the rate of break-up events and the distribution of child bubble sizes.
Abstract: Breaking waves generate a distribution of bubble sizes that evolves over time. Knowledge of how this distribution evolves is of practical importance for maritime and climate studies. The analytical framework developed in Part 1 (Chan, Johnson & Moin, J. Fluid Mech., vol. 912, 2021, A42) examined how this evolution is governed by the bubble-mass flux from large- to small-bubble sizes which depends on the rate of break-up events and the distribution of child bubble sizes. These statistics are measured in Part 2 as ensemble-averaged functions of time by simulating ensembles of breaking waves, and identifying and tracking individual bubbles and their break-up events. The large-scale break-up dynamics is seen to be statistically unsteady, and two intervals with distinct characteristics were identified. In the first interval, the dissipation rate and bubble-mass flux are quasi-steady, and the theoretical analysis of Part 1 is supported by all observed statistics, including the expected as small bubbles are also depleted more quickly. This suggests the emergence of different physical mechanisms during different phases of the breaking-wave evolution, although size-local break-up remains a dominant theme. Parts 1 and 2 present an analytical toolkit for population balance analysis in two-phase flows.

9 citations

Journal ArticleDOI
TL;DR: In this article, it is argued that high-order finite difference schemes yield solutions with comparable accuracy to the spectral methods with the same number of degrees of freedom, and the effects of random inflow conditions on the downstream evolution of turbulence are discussed.

9 citations

Book ChapterDOI
01 Jan 1979
TL;DR: In this paper, the methods presented in this paper have been applied to the flows described, and important results concerning the nature of these flows have been obtained, and they believe that LES shows promise for the future, and that its development should be continued.
Abstract: We believe that LES shows promise for the future, and that its development should be continued. The methods presented in this paper have been applied to the flows described, and important results concerning the nature of these flows have been obtained. For details see our reports [9, 11] or forthcoming papers.

9 citations

Proceedings ArticleDOI
07 Jun 2004
TL;DR: In this article, a large-eddy simulation (LES) solver was used to analyze the dynamics of rotor tip-clearance flow and determine the underlying mechanism for the tip-leakage cavitation.
Abstract: In order to analyze the dynamics of rotor tip-clearance flow and determine the underlying mechanism for the tip-leakage cavitation, a newly developed large-eddy simulation (LES) solver which combines an immersed-boundary method with a generalized curvilinear structured grid has been employed. An analysis of the LES results has been performed to understand the mean flow field, turbulence characteristics, vortex dynamics, and pressure fluctuations in the turbomachinery cascade with tip gap. Based on thorough analysis of the flow field, a guideline for reducing viscous losses in the cascade is provided. Analyses of the energy spectra and space-time correlations of the velocity fluctuations suggest that the tip-leakage vortex is subject to pitchwise wandering motion. The largest pressure drop and most intense pressure fluctuations due to the formation of the tip-leakage vortex are found in the region where the tip-leakage vortex is strongest. The effects of tip-gap size and an end-wall groove on the tip-clearance vortical structures and on the velocity and pressure fields have been investigated to explore ways for minimizing the detrimental effects of cavitation. Attempts to investigate the vortex-rotor interaction and to enhance the LES capability for realistic rotors are also discussed.

9 citations

01 Jan 1991
TL;DR: In this paper, the effects of transverse curvature on axial flow over cylinders were investigated by means of direct numerical simulations of turbulent axial flows over cylinders and two cases of Reynolds number of about 3400 and layer-thickness-tocylinder-radius ratios of 5 and 11 were simulated All essential turbulence scales were resolved in both calculations and a large number of turbulence statistics were computed.
Abstract: The effects of transverse curvature are investigated by means of direct numerical simulations of turbulent axial flow over cylinders Two cases of Reynolds number of about 3400 and layer-thickness-to-cylinder-radius ratios of 5 and 11 were simulated All essential turbulence scales were resolved in both calculations, and a large number of turbulence statistics were computed The results are compared with the plane channel results of Kim et al (1987) and with experiments With transverse curvature the skin friction coefficient increases and the turbulence statistics, when scaled with wall units, are lower than in the plane channel The momentum equation provides a scaling that collapses the cylinder statistics, and allows the results to be interpreted in light of the plane channel flow The azimuthal and radial length scales of the structures in the flow are of the order of the cylinder diameter Boomerang-shaped structures with large spanwise length scales were observed in the flow

9 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a new eddy viscosity model is presented which alleviates many of the drawbacks of the existing subgrid-scale stress models, such as the inability to represent correctly with a single universal constant different turbulent fields in rotating or sheared flows, near solid walls, or in transitional regimes.
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.

6,747 citations

Journal ArticleDOI
TL;DR: An overview of the lattice Boltzmann method, a parallel and efficient algorithm for simulating single-phase and multiphase fluid flows and for incorporating additional physical complexities, is presented.
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.

6,565 citations

Journal ArticleDOI
TL;DR: In this article, the authors propose a definition of vortex in an incompressible flow in terms of the eigenvalues of the symmetric tensor, which 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.
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.

5,837 citations

Journal ArticleDOI
TL;DR: In this article, the authors present finite-difference schemes for the evaluation of first-order, second-order and higher-order derivatives yield improved representation of a range of scales and may be used on nonuniform meshes.

5,832 citations