Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session E34: CFD: Algorithms for Complex Flows |
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Chair: David Trebotich, Lawrence Berkeley National Laboratory Room: 2024 |
Sunday, November 23, 2014 4:45PM - 4:58PM |
E34.00001: ABSTRACT WITHDRAWN |
Sunday, November 23, 2014 4:58PM - 5:11PM |
E34.00002: Large-eddy simulation of wind turbine wake interactions on locally refined Cartesian grids Dionysios Angelidis, Fotis Sotiropoulos Performing high-fidelity numerical simulations of turbulent flow in wind farms remains a challenging issue mainly because of the large computational resources required to accurately simulate the turbine wakes and turbine/turbine interactions. The discretization of the governing equations on structured grids for mesoscale calculations may not be the most efficient approach for resolving the large disparity of spatial scales. A 3D Cartesian grid refinement method enabling the efficient coupling of the Actuator Line Model (ALM) with locally refined unstructured Cartesian grids adapted to accurately resolve tip vortices and multi-turbine interactions, is presented. Second order schemes are employed for the discretization of the incompressible Navier-Stokes equations in a hybrid staggered/non-staggered formulation coupled with a fractional step method that ensures the satisfaction of local mass conservation to machine zero. The current approach enables multi-resolution LES of turbulent flow in multi-turbine wind farms. The numerical simulations are in good agreement with experimental measurements and are able to resolve the rich dynamics of turbine wakes on grids containing only a small fraction of the grid nodes that would be required in simulations without local mesh refinement. [Preview Abstract] |
Sunday, November 23, 2014 5:11PM - 5:24PM |
E34.00003: A low-cost RK time advancing strategy for energy-preserving turbulent simulations Francesco Capuano, Gennaro Coppola, Luigi de Luca, Guillaume Balarac Energy-conserving numerical methods are widely employed in direct and large eddy simulation of turbulent flows. Semi-discrete conservation of energy is usually obtained by adopting the so-called skew-symmetric splitting of the non-linear term, defined as a suitable average of the divergence and advective forms. Although generally allowing global conservation of kinetic energy by convection, it has the drawback of being roughly twice as expensive as standard divergence or advective forms alone. A novel time-advancement strategy that retains the conservation properties of skew-symmetric-based schemes at a reduced computational cost has been developed in the framework of explicit Runge-Kutta schemes. It is found that optimal energy-conservation can be achieved by properly constructed Runge-Kutta methods in which only divergence and advective forms for the convective term are adopted. The new schemes can be considerably faster than skew-symmetric-based techniques. A general framework for the construction of optimized Runge-Kutta coefficients is developed, which has proven to be able to produce new methods with a specified order of accuracy on both solution and energy. The effectiveness of the method is demonstrated by numerical simulation of homogeneous isotropic turbulence. [Preview Abstract] |
Sunday, November 23, 2014 5:24PM - 5:37PM |
E34.00004: Multirate time-stepping least squares shadowing method for unsteady turbulent flow Hyunji Jane Bae, Parviz Moin The recently developed least squares shadowing (LSS) method reformulates unsteady turbulent flow simulations to be well-conditioned time domain boundary value problems. The reformulation can enable scalable parallel-in-time simulation of turbulent flows (Wang et al. Phys. Fluid [2013]). A LSS method with multirate time-stepping was implemented to avoid the necessity of taking small global time-steps (restricted by the largest value of the Courant number on the grid) and therefore result in a more efficient algorithm. We will present the results of the multirate time-stepping LSS compared to a single rate time-stepping LSS and discuss the computational savings. [Preview Abstract] |
Sunday, November 23, 2014 5:37PM - 5:50PM |
E34.00005: Adaptation of a Multi-Block Structured Solver for Effective Use in a Hybrid CPU/GPU Massively Parallel Environment David Gutzwiller, Mathieu Gontier, Alain Demeulenaere Multi-Block structured solvers hold many advantages over their unstructured counterparts, such as a smaller memory footprint and efficient serial performance. Historically, multi-block structured solvers have not been easily adapted for use in a High Performance Computing (HPC) environment, and the recent trend towards hybrid GPU/CPU architectures has further complicated the situation. This paper will elaborate on developments and innovations applied to the NUMECA FINE/Turbo solver that have allowed near-linear scalability with real-world problems on over 250 hybrid GPU/GPU cluster nodes. Discussion will focus on the implementation of virtual partitioning and load balancing algorithms using a novel meta-block concept. This implementation is transparent to the user, allowing all pre- and post-processing steps to be performed using a simple, unpartitioned grid topology. Additional discussion will elaborate on developments that have improved parallel performance, including fully parallel I/O with the ADIOS API and the GPU porting of the computationally heavy CPUBooster convergence acceleration module. [Preview Abstract] |
Sunday, November 23, 2014 5:50PM - 6:03PM |
E34.00006: High Resolution DNS of Turbulent Flows using an Adaptive, Finite Volume Method David Trebotich We present a new computational capability for high resolution simulation of incompressible viscous flows. Our approach is based on cut cell methods where an irregular geometry such as a bluff body is intersected with a rectangular Cartesian grid resulting in cut cells near the boundary. In the cut cells we use a conservative discretization based on a discrete form of the divergence theorem to approximate fluxes for elliptic and hyperbolic terms in the Navier-Stokes equations. Away from the boundary the method reduces to a finite difference method. The algorithm is implemented in the Chombo software framework which supports adaptive mesh refinement and massively parallel computations. The code is scalable to 200,000$+$ processor cores on DOE supercomputers, resulting in DNS studies at unprecedented scale and resolution. For flow past a cylinder in transition (Re$=$300) we observe a number of secondary structures in the far wake in 2D where the wake is over 120 cylinder diameters in length. These are compared with the more regularized wake structures in 3D at the same scale. For flow past a sphere (Re$=$600) we resolve an arrowhead structure in the velocity in the near wake. The effectiveness of AMR is further highlighted in a simulation of turbulent flow (Re$=$6000) in the contraction of an oil well blowout preventer. [Preview Abstract] |
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