The Experts below are selected from a list of 15363 Experts worldwide ranked by ideXlab platform

Michael F. Modest - One of the best experts on this subject based on the ideXlab platform.

  • An effective particle tracing scheme on structured/unstructured grids in hybrid Finite Volume/PDF Monte Carlo methods
    Journal of Computational Physics, 2001
    Co-Authors: Michael F. Modest
    Abstract:

    Abstract To date, PDF/Monte Carlo simulations, either in stand-alone Codes or in hybrid Finite Volume/PDF Monte Carlo programs, appear to have been mostly carried out with cells of similar size. In many situations, such as capturing sharp gradients in a flow field, fine grids or unstructured solution-adaptive grids must be used in the Finite Volume Code, resulting in a cell system with large variations in cell size. Such grids present a challenge for a combined PDF/Monte Carlo Code. In this paper, a new particle tracing scheme is proposed, in which we introduce the concept of variable time steps. Using locally adaptive time steps in the integration of particle equations, the particles' parameters are updated more frequently in regions of strong gradients than in those of flat gradients, which greatly improves the time efficiency of particle tracing. To reduce statistical errors, a particle splitting and combination procedure is also used. The new scheme allows the hybrid Finite Volume/PDF Monte Carlo Code to use any grid that is constructed in the Finite Volume Code. This relaxation of restrictions on the grid makes it possible to couple PDF/Monte Carlo methods to all popular commercial CFD Codes and, consequently, extend existing CFD Codes' capability to simulate turbulent reactive flow in a more accurate way. The numerical performance of the new particle tracing scheme and the solution procedure are illustrated by considering a turbulent heat transfer problem in a parallel channel and a turbulent diffusion combustion problem in a cylindrical combustor.

  • A HYBRID Finite Volume/PDF MONTE CARLO METHOD TO CAPTURE SHARP GRADIENTS IN UNSTRUCTURED GRIDS
    2000
    Co-Authors: Michael F. Modest
    Abstract:

    The hybrid Finite Volume/PDF Monte Carlo method has both the advantages of the FiniteVolume method’ s efficiencyin solving flow fields and the PDF method’ s exactness in dealing with chemical reactions. It is, therefore, increasingly used in turbulent reactive flow calculations. In order to resolve the sharp gradients of flow velocities and/or scalars, finegrids or unstructured solution -adaptive grids have to be used in the Finite Volume Code. As a result, the calculation domain is covered by a grid system with very large variations in cell size. Such grids present a challenge for a combined PDF/Monte Carlo Code. To date, PDF calculations have generally been carried out with large cells, which assure that each cell has a statistically meaningful number of particles. Smaller cells would lead to smaller numbers of particles and correspondingly larger statistical errors. In this paper, a particle tracing scheme with adaptive time step and particle splitting and combination is developed, which allows the PDF/Monte Carlo Code to use any grid that is constructed in the Finite Volume Code. This relaxation of restrictions on the grid makes it possible to couple PDF/Monte Carlo methods to all popular commercial CFD Codes and, consequently, extend existing CFD Codes’ capability to simulate turbulent reactive flow in a more accurate way. To illustrate the solution procedure, a PDF/ Monte Carlo Code is combined with FLUENT to solve a turbulent diffusion combustion problem in an axisymmetric channel.

N. Balakrishnan - One of the best experts on this subject based on the ideXlab platform.

  • an upwind Finite difference scheme for meshless solvers
    Journal of Computational Physics, 2003
    Co-Authors: D. Sridar, N. Balakrishnan
    Abstract:

    In this paper, we present a new upwind Finite difference scheme for meshless solvers. This new scheme, capable of working on any type of grid (structure, unstructured or even a random distribution of points) produces superior results. A means to construct schemes of specified order of accuracy is discussed. Numerical computations for different types of flow over a wide range of Mach numbers are presented. Also, these results were compared with those obtained using a cell vertex Finite Volume Code on the same grids and with theoretical values wherever possible. The present framework has the flexibility to choose between various upwind flux formulas.

Yufei Zhang - One of the best experts on this subject based on the ideXlab platform.

  • grid convergence study on a Finite Volume Code nsawet
    53rd AIAA Aerospace Sciences Meeting, 2015
    Co-Authors: Haixin Chen, L I Zhao, F U Song, Yufei Zhang
    Abstract:

    A grid convergence study using the in-house Finite Volume flow solver NSAWET is presented. Solutions of three two-dimensional flow problems including the isentropic vortex advection, the inviscid flow around NACA0012 airfoil and the turbulent flow over flat plate are compared with theoretical or other numerical data. All the flow conditions, geometries and meshes are obtained from well-recognized public database in order to ensure a fair and effective comparison. The generalized Richardson extrapolation method is adopted for error estimation. Using the Roe’s scheme in NSAWET, results show excellent asymptotic features and formally second-order accuracy. Shock may deteriorate the prediction accuracy of pressure drag due to the order reduction of reconstruction near discontinuity. The so-called hyper-convergence for transonic nonlifting case, where an accuracy much higher than firstorder is observed, may originate from the constant-lift computation. The possible consequences are raised for similar grid convergence studies. Then a process successively composed of verifications on basic numerical properties, pressure drag prediction and friction drag prediction is suggested.

D. Sridar - One of the best experts on this subject based on the ideXlab platform.

  • an upwind Finite difference scheme for meshless solvers
    Journal of Computational Physics, 2003
    Co-Authors: D. Sridar, N. Balakrishnan
    Abstract:

    In this paper, we present a new upwind Finite difference scheme for meshless solvers. This new scheme, capable of working on any type of grid (structure, unstructured or even a random distribution of points) produces superior results. A means to construct schemes of specified order of accuracy is discussed. Numerical computations for different types of flow over a wide range of Mach numbers are presented. Also, these results were compared with those obtained using a cell vertex Finite Volume Code on the same grids and with theoretical values wherever possible. The present framework has the flexibility to choose between various upwind flux formulas.

Haixin Chen - One of the best experts on this subject based on the ideXlab platform.

  • grid convergence study on a Finite Volume Code nsawet
    53rd AIAA Aerospace Sciences Meeting, 2015
    Co-Authors: Haixin Chen, L I Zhao, F U Song, Yufei Zhang
    Abstract:

    A grid convergence study using the in-house Finite Volume flow solver NSAWET is presented. Solutions of three two-dimensional flow problems including the isentropic vortex advection, the inviscid flow around NACA0012 airfoil and the turbulent flow over flat plate are compared with theoretical or other numerical data. All the flow conditions, geometries and meshes are obtained from well-recognized public database in order to ensure a fair and effective comparison. The generalized Richardson extrapolation method is adopted for error estimation. Using the Roe’s scheme in NSAWET, results show excellent asymptotic features and formally second-order accuracy. Shock may deteriorate the prediction accuracy of pressure drag due to the order reduction of reconstruction near discontinuity. The so-called hyper-convergence for transonic nonlifting case, where an accuracy much higher than firstorder is observed, may originate from the constant-lift computation. The possible consequences are raised for similar grid convergence studies. Then a process successively composed of verifications on basic numerical properties, pressure drag prediction and friction drag prediction is suggested.