10:30
Large Eddy Simulation 3
Chair: Geert Brethouwer
10:30
15 mins
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A LATTICE MODEL FOR THE EULERIAN DESCRIPTION OF HEAVY PARTICLES SUSPENSIONS IN ONE AND TWO DIMENSIONS
François Laenen, Jérémie Bec, Giorgio Krstulovic
Abstract: Modeling of heavy particles motion in turbulent flows still represents a challenge in engineering applications at high Reynolds number. Various techniques have arisen for describing such mono-dispersed solid phases with statistical methods. Some of those techniques relies on the assumption of using a velocity field to describe the particles motion, which is valid at small Stokes number, others using large-eddy simulations, or using one and two-points probability density functions in Gaussian flows. Here we present another method based on a lattice discretization of the phase space in one and two dimensions for a synthetic flow in one dimension and a turbulent flow in two dimensions for the description of a dilute solid phase in the case of a Stokes coupling between the particles and the fluid and a brownian diffusion. This method is suited for any Stokes numbers in the limit of numerical stability and shows a good agreement with the Lagrangian particles statistics like radial distribution functions and collision rates.
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10:45
15 mins
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ANALYSIS OF THE YAGLOM EQUATION AND SUBGRID MODELLING APPROACHES FOR THERMALLY DRIVEN TURBULENCE
Andrea Cimarelli, Riccardo Togni, Elisabetta De Angelis
Abstract: We report a Direct Numerical Simulation (DNS) of turbulent Rayleigh-Bénard convection in a laterally unbounded domain confined between two horizontal parallel walls, for Rayleigh number 10^5 and Prandtl number 0.7. The DNS data are used to study the properties of the subgrid-scale flux of the active temperature field in the framework of Large Eddy Simulation (LES). In particular, starting from the generalized Yaglom equation, we analyse how the thermal energy is produced, transferred and dissipated in the augmented space of scales and positions of the flow. The understanding of these processes is then used to propose appropriate formulations for the subgrid-scale flux that will be tested by means of a posteriori analysis of LES simulations performed in the same flow conditions.
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11:00
15 mins
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ODTLES: A MULTI-SCALE ANSATZ FOR HIGHLY TURBULENT FLOWS
Christoph Glawe, Heiko Schmidt, Alan R. Kerstein
Abstract: We use ODTLES, a multi-dimensional extension of the One-Dimensional-Turbulence model (ODT). ODT describes turbulent advection on a 1D sub-domain using a stochastic process for turbulent advection. These 1D sub-domains are coupled to obtain a 3D approach. ODTLES is applied to channel flow. Preliminary results for the pdf of the wall shear stress are compared to DNS.
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11:15
15 mins
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LARGE-EDDY SIMULATION OF TURBULENT CHANNEL FLOW USING THE EXPLICIT ALGEBRAIC SUBGRID-SCALE MODEL
Matteo Montecchia, Amin Rasam, Geert Brethouwer, Arne Viktor Johansson
Abstract: Large-eddy simulation (LES) of turbulent channel flow are performed with a new subgrid-scale (SGS) stress model. The simulations show that with this model we can well predict turbulent wall flows at coarse resolutions and moderately high Reynolds numbers. The commonly used dynamic Smagorinsky model fails at coarser resolutions.
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11:30
15 mins
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Stochastic Subgrid Acceleration Model for inertial particles in LES of a high Reynolds number flow
Mikhael Gorokhovski, Remi Zamansky
Abstract: In the context of Large Eddy Simulation (LES) of turbulent flow laden by solid particles, we propose a modelling of the the interaction of a particle with the unresolved scales of the flow. We consider both particles much smaller and larger than the Kolmogorov length scale. The small scales of high Reynolds number flow are characterized by strong velocity gradients. To account for those gradients, and specifically the turbulent time-scales shorter than the Stokes time, we decompose the particle acceleration in its resolved and residual parts. In the latter, the interactions with the inertial range of the turbulent flow are simulated by a stochastic process evolving along the particle trajectory.
For the case of the small particles, we introduced two processes, one for its norm, and another for its direction. Results showed that by introducing the stochastic model for the particle residual acceleration, the particle acceleration statistics from DNS is predicted fairly well.
For the particles bigger than the Kolmogorov scale, we propose another stochastic model. We derived a fluctuating drag, simulated by lognormal process. This model gives stretched tails in the particle acceleration distribution invariant with the density and the size of particle as observed experimentally.
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11:45
15 mins
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A priori and a posteriori analysis of the hybrid two-level large-eddy simulation method for high Reynolds number complex flows
Suresh Menon, Reetesh Ranjan
Abstract: We present a priori and a posteriori analysis of the assumptions and predictions of the hybrid two-level large-eddy simulation (TLS-LES) method for high Reynolds number complex flows. The TLS-LES methodology is a multi-scale framework for simulation of turbulent flows in complex configurations at practically relevant Reynolds number. It additively combines the two-level simulation (TLS) model with a conventional large-eddy simulation (LES) approach by employing a static or dynamic blending function. In the present study, first we analyze the model assumptions employed by the TLS model to obtain the small-scale solution necessary for closure of the large-scale equations. Afterward, we analyze the large-scale and small-scale solutions to assess the predictive ability of the multi-scale framework for specific turbulence physics such as role of forward and backscatter of energy and presence of co- and counter-gradient diffusion. To perform these investigations, we consider cases with increasing degree of geometrical complexity, namely, flow in a periodic channel, flow past a bump placed on the lower surface of the channel and flow past a finite-span NACA0015 airfoil.
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12:00
15 mins
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Building proper invariants for subgrid-scale eddy-viscosity models
F.Xavier Trias, David Folch, Andrey Gorobets, Assensi Oliva
Abstract: Since direct simulations of the incompressible Navier-Stokes equations are limited to relatively low-Reynolds numbers, dynamically less complex mathematical formulations are necessary for coarse-grain simulations. Eddy-viscosity models for Large-Eddy Simulation is probably the most popular example thereof: they rely on differential operators that should be able to capture well different flow configurations (laminar and 2D flows, near-wall behavior, transitional regime...). Most of them are based on the combination of invariants of a symmetric second-order tensor that is derived from the gradient of the resolved velocity field. In the present work, they are presented in a framework where all the models are represented as a combination of elements of a 5D phase space of invariants. In this way, new models can be constructed by imposing appropriate restrictions in this space. The performance of the proposed models is successfully tested for a turbulent channel flow.
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12:15
15 mins
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Autonomic Subgrid-Scale Closure for Large Eddy Simulations
Ryan King, Peter Hamlington, Werner Dahm
Abstract: Motivated by advances in constrained optimization methods, a fundamentally new autonomic closure for LES is presented that invokes a self-optimization method for the subgrid-scale stresses instead of a predefined turbulence model. This autonomic closure uses the most general dimensionally-consistent expression for the local subgrid-scale stresses in terms of all resolved-scale variables and their products at all spatial locations and times, thereby also incorporating all possible gradients of all resolved variables and products. In so doing, the approach addresses all possible nonlinear, nonlocal, and nonequilibrium turbulence effects without requiring any direct specification of a subgrid-scale model. Instead it uses an optimization procedure with a test filter to find the best local relation between subgrid stresses and resolved-scale variables at every point and time. We describe this autonomic closure approach, discuss truncation, regularization, and sampling in the optimization procedure, and present results from a priori tests using DNS data for homogeneous isotropic and sheared turbulence. Even for the simplest 2nd-order truncation of the general formulation, substantial improvements over the dynamic Smagorinsky model are obtained with this new autonomic approach to turbulence closure.
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