Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session E5: Computational Fluid Dynamics III |
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Chair: Carlos Pantano, University of Illinois at Urbana-Champaign Room: 24A |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E5.00001: Simulation of Turbulence using Quasi Equilibrium Lattice Boltzmann Method Chakradhar Thantanapally, Dhiraj V. Patil, Sauro Succi, Santosh Ansumali Development of accurate and efficient methods for DNS of turbulence, where degrees of freedom associated with the flow scales with Reynolds number as $Re^{9/4}$, is one of the important goals of computational fluid dynamics. In this regard, Lattice Boltzmann method (LBM) is an attractive option due to high parallel scalability and its ease of application to complex geometries. Recently, it was shown that energy conserving LBM is superior over their athermal counterpart due to improved stability and increase in accuracy for high resolution simultations. However, in subgrid domain the behavior is found to be opposite. In this work, we show that via multi-relaxation time (MRT) model, it is possible to preserve the accuracy of the energy conserving LBM for both subgrid as well as high resolution simulation models. We show that introducing Prandtl number, as a means to subgrid viscosity, allows to do under resolved simulations quite efficiently and motivate this behavior via sound relaxation mechanism. The model showed to perform well over the regular thermal and athermal LBM at lower resolutions. The stability and accuracy of the model is validated using two-dimensional Taylor-Green and double periodic shear layer, and three-dimensional Kida-Pelz and Taylor-Green initial conditions. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E5.00002: Hybrid Lattice-Boltzmann model for Thermally Coupled Fluid-Solid Problem Leitao Chen, Laura Schaefer The most commonly used thermal boundary condition on solid wall in fluid problem is either type of Neumann or Dirichlet. However, the thermal boundary condition on solid wall in many practical problems is much more complicated and impossible to predict especially when the flow is unsteady or involves complex geometry such as porous media. So the best cure is to simulate fluid and solid together. Lattice-Boltzmann Method is becoming a promising alternative scheme for simulating thermal fluid flows while in the same time solving the conventional energy equation with Finite Volume method is still superior to other methods in modeling pure heat conduction in solid. In this work a 2D hybrid model is built, in which the traditional Lattice-Boltzmann BGK model on D2Q9 lattice for fluid part is coupled with the Finite Volume model on unstructured mesh for solid part. In addition, the numerical schemes on thermal fluid-solid interface for both straight and curved wall are developed. The Hybrid model is proved to be able to solve thermally coupled fluid-solid problem efficiently and accurately after several simulations are taken and their results are analyzed. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E5.00003: Navier-Stokes adjoint accuracy for aeroacoustic flow control and analysis Ramanathan Vishnampet, Jonathan Freund, Daniel Bodony Optimal control based on discrete solutions of the continuous adjoint of the compressible Navier-Stokes equations has been successful for aeroacoustic flows despite discretization truncation errors, which result in an inconsistent sensitivity gradient. For finite resolution simulations, the truncation errors can limit the success of the optimization, especially for turbulent flows; recent evidence of this is presented. The gradient obtained from the discrete adjoint, which is more challenging to formulate but is insensitive to truncation errors, is consistent, and therefore, better suited to minimize our cost functional. We formulate the discrete adjoint of the compressible Navier-Stokes equations using high-order summation-by-parts operators with simultaneous-approximation-term boundary conditions and a high-fidelity time advancement scheme. We show that the continuous and discrete approaches lead to identical adjoint difference equations except near boundaries, at the last time step, and possibly the first few time steps, which affects the gradient accuracy. We evaluate the gradient from the two approaches and discuss the consequences of the errors in the continuous formulation for control optimization in aeroacoustic problems. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E5.00004: CFD-based derivative-free optimization using polyharmonic splines, Part 1 Pooriya Beyhaghi, Daniele Cavaglieri, Thomas Bewley Nonsmooth CFD-based optimization problems are difficult, due both to the nonconvexity of the cost function and to the extreme cost of each function evaluation. In this work, we develop a derivative-free GPS optimization scheme which makes maximum use of each function evaluation. We seek to improve on the efficiency of the existing methods that have been applied to this class of problems (genetic algorithms, SMF, orthoMADS, etc). At each optimization step, the algorithm proposed creates a Delaunay triangulation based on the existing evaluation points. In each simplex so created, the algorithm optimizes a cost function based on a polyharmonic spline interpolant. This interpolation strategy behaves appropriately even when the evaluation points are clustered in particular regions of interest in parameter space (in contrast with the Kriging interpolation strategy used in existing GPS/SMF algorithms). At each optimization step, an appropriately-modeled error function is combined with the interpolant, weighted with a tuning parameter governing the trade-off between local refinement and global exploration. [Preview Abstract] |
Sunday, November 18, 2012 5:37PM - 5:50PM |
E5.00005: CFD-based derivative-free optimization using polyharmonic splines, Part 2 Daniele Cavaglieri, Pooriya Beyhaghi, Thomas Bewley The derivative-free optimization algorithm developed in Part 1 of this work (see Beyhaghi et al.).is extended to include (a) a dynamic trade-off between local refinement and global exploration, and (b) to incorporate convex constraints of various types. The resulting algorithm is then verified on representative test functions and compared with competing algorithms. In particular, we will report on recent efforts to develop high-order low-storage IMEX RK schemes for the accurate time integration of the stiff ODEs arising in large-scale DNS and LES simulations. [Preview Abstract] |
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