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

Interest in the use of the large eddy simulation (LES) technique for computation of turbulent flows of industrial relevance has increased considerably This is in part due to the availability of low cost, powerful supercomputers Today, a computer cluster capable of one TFOPS sustained performance for a complex flow LES calculation costs about one hundred thousand dollars Another reason for the increased interest in LES is the recent added capabilities for multi-physics and integrated flow simulations As part of Stanford’s DOE/ASC program, we have demonstrated and validated high fidelity simulations of multi-phase reacting turbulent flows in highly complex configurations in propulsion systems The overarching problem in this program is simulation of flow through a complete jet engine, which is an extremely complex machine LES computations of the entire engine flow are not feasible even with the most advanced supercomputers available The Reynolds averaged Navier-Stokes (RANS) technique was used for the turbomachinery components and the combustor was simulated using LES These simulations provided an early example of integrated simulations where different codes with different fidelity compute different portions of the system A simulation environment had to be developed for the various codes to communicate with each other in an efficient and stable fashion This integration technology and the associated science are suggested as the means for using LES in vehicle aerodynamics where Reynolds numbers are too high for high fidelity computation of the flow around the entire vehicle LES can then be used in regions where RANS models are known to be inaccurate, and where LES provides access to flow quantities such as turbulent pressure fluctuations for predicting noise Several examples of integrated simulations will be presented, including separation control for a high-lift system using synthetic jets

Application of High Fidelity Numerical Simulations for Vehicle Aerodynamics

: This report describes work performed to investigate real-time feedback control of mixing in a heated jet and to demonstrate the resulting technique in a laboratory environment. Large- scale direct numerical simulations were performed for jets with various types of actuation and were useful for optimization of the actuators with regard to Strouhal number and amplitude. The integral of the squared velocity and the integral of the concentration were found to be appropriate objective functions for evaluating the performance of a given actuator. In the simulation effort evolution strategies and simulated annealing were used for optimization of the jet actuators. In an experimental study of a jet using a miniature (RAM 750) engine, use of a genetic algorithm showed that it could drive the system to undesirable states during optimization. A classical proportional-integral controller was used to provide real-time feedback control of plume temperature.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA383185&Location=U2&doc=GetTRDoc.pdf

Real-Time Feedback Control of Mixing in a Heated Jet

/pdf/les-based-characterization-of-a-suction-and-oscillatory-4jp06ins70.pdf

LES-based characterization of a suction and oscillatory blowing fluidic actuator

Progress toward highly resolved simulations of shock/turbulence interaction is described, with a focus on the scientific reasons for studying this problem as well as the computational issues involved. We illustrate the importance of computing shock/turbulence interaction at Reynolds numbers of at least one order of magnitude larger than previously done. We also illustrate the need to study the effect of turbulent Mach number on the interaction process. Scaling data for the code is used to estimate the computational resources needed for these novel simulations on petascale systems.

http://iopscience.iop.org/article/10.1088/1742-6596/125/1/012045/pdf

Toward petascale shock/turbulence computations

/pdf/a-stable-hybrid-implicit-explicit-scheme-for-large-eddy-2c5bxvgq0l.pdf

Parviz Moin

Papers

Application of High Fidelity Numerical Simulations for Vehicle Aerodynamics

Real-Time Feedback Control of Mixing in a Heated Jet

LES-based characterization of a suction and oscillatory blowing fluidic actuator

Toward petascale shock/turbulence computations

A Stable Hybrid Implicit/Explicit Scheme for Large-Eddy Simulation of Compressible Flows in Complex Geometries