Solution of Computational Fluid Dynamics Problems on Parallel Computers with Distributed Memory

Many problems in Computational Electromagnetics (CEM) and Computational Fluid Dynamics (CFD) require millions of grid cells to properly represent the physics. Advances in parallel computing, both in hardware and software, make it feasible to solve such large scale simulations in a timely manner. The objective of this paper is to describe some of the recent work at Rockwell in performing parallel computing for providing quick-turnaround solutions to problems in CFD, CEM and other computational disciplines.

Features of the simulation of low-velocity inviscid and viscous compressible gas flows are considered, and a finite-volume discretization of gas dynamics equations at low Mach numbers on unstructured meshes is discussed. Preconditioning based on the use of physical variables is used to speed up the convergence of time marching to a steady state and to improve the accuracy of the steady-state solution. The structure of the preconditioning matrix and the diagonalization of the Jacobian of the preconditioned system of equations are discussed. The capabilities of this approach are demonstrated using model gasdynamic simulations ing a wide range of Mach numbers.

Multiphase flow simulations are essential methods for providing information such as the evolution of phase fraction (gas, liquid and solid), velocities, pressure, temperature and flow regimes at every time during a process. Dynamic flow simulations also help reservoir, drilling, and production engineers to develop a proper well design. DamBreak problem is one of the most well-known problems in computational fluid dynamics (CFD); it is a dynamic hydraulic phenomena and the numerical simulation requires sophisticated mathematical modeling. OpenFOAM, is used to run CFD simulations in this thesis.;One of the main issues in CFD is that the simulations are time-consuming. In this work, will use artificial intelligence (AI) to predict the behavior of the system at each time-step of the process at a lower run time. DamBreak problem is defined base on a two-dimensional rectangular tank with a barrier at the bottom, the liquid column (water in this study) at the left side of the tank behind the wall. As soon as the wall collapse, the water will pour down, resulting in complicated fluid dynamics. The main data-set, generated by OpenFOAM flow simulations, is used for building the smart proxy model (SPM), using the network toolbox in MATLAB. Neural network (NN) is applied with feed-forward back propagation method and the training algorithm is Levenberg Marquardt.;Results indicate that the smart proxy can run 3 seconds of the DamBreak process, which takes 8 hours of computational time with 4 processors when is done by using OpenFOAM, takes less than 2 minutes using the developed SPM on one processor. SPM is also capable of predicting the CFD results in non-cascading condition and up to around 40 time-steps in cascading condition with acceptable error (less than %10).

<div class="htmlview paragraph">Hydraulic oil flow and flow induced forces inside hydraulic spool valves have been studied using a commercially available Computational Fluid Dynamics (CFD) software package with an aim of improving hydraulic spool valve operating efforts. The main objective is to investigate flow induced forces on the spool with a range of different geometries or operating conditions and therefore to minimize or utilize their effect on spool effort. This CFD problem was treated as incompressible, turbulent, steady and adiabatic or isothermal. Integration of solved pressure field from a commercial CFD solution over related a valve component surface area was used to integrate the desirable flow induced forces. Additional viscous drag forces on the spool effect on total spool operating effort have also been investigated. The focus in this article is mainly based on studies for open center flow type four-way spool valves in cases such that the hydraulic oil flow direction towards spool. Some other spool metering cases will also be presented. CFD results are compared to experimental results with overall good correlation.</div>

A parallel implicit hole-cutting method based on background mesh for unstructured Chimera grid

Numerical algorithms in computational fluid dynamics on vector computers

Computational Fluid Dynamics (CFD) is widely used by polymer processing industries in order to evaluate polymeric fluid flows. A successful computational code must provide reliable predictions (modeling) in a fast and efficient way (simulation). In this work, a new approach to solve the governing equations of viscoelastic fluid flows is proposed. It is based on the finite-volume method with collocated arrangement of the variables, using high-order approximations for the linear and nonlinear average fluxes in the interfaces and for the nonlinear terms obtained from the discretization of the constitutive equations. The approximations are coupled to the Weighted Essentially Non-Oscillatory (WENO) scheme to avoid oscillations in the solution. The Oldroyd-B model is used to describe the rheological behavior of the viscoelastic fluid. The average values of the variables in the volumes are used during the resolution, and the point values are recovered in the post-processing step by deconvolution of the average values. The nonlinear system, resulting from the discretization of the equations, is solved simultaneously using a Newton-like method. The obtained solutions are oscillation-free and accurate, demonstrated by the application on a classic problem in computational fluid dynamics, the slip-stick flow.

Wind profile prediction at different scales plays a crucial role for efficient operation of wind turbines and wind power prediction. This problem can be approached in two different ways: one is based on statistical signal processing techniques and both linear and nonlinear models can be employed either separately or combined together for profile prediction; on the other hand, wind/atmospheric flow analysis is a classical problem in computational fluid dynamics (CFD) in applied mathematics, which employs various numerical methods and algorithms, although it is an extremely time-consuming process with high computational complexity. In this work, a new method is proposed based on synergy's between the signal processing approach and the CFD approach, by alternating the operations of a quaternion-valued least mean square (QLMS) algorithm and the large eddy simulation (LES) in CFD. As demonstrated by simulation results, the proposed method has a much lower computational complexity while maintaining a comparable prediction result.

The unsteady flow of the compressible viscous gas past two coaxial cylinders put together (Fig. 1) is investigated using the implicit iterative scheme [1] for full unsteady Navier-Stokes equations. It is shown that the flow picture in the recirculation region depends on the amplitude and the frequency of the oscillations of freestream parameters. The critical value of amplitude is determined at which the recirculation flow is destroyed. The aerodynamic performances are determined as the functions of the parameters governing the unsteady process in the freestream.

Flow of viscous compressible gas is considered in the airfoil cascade of the thin plates with great negative angle of attack. Influence of wall boundary layer upon a mode of flow choking in the airfoil cascade is estimated in the article.

This work deals with two-dimensional flow of viscous compressible gas from a source in an apex of wedge. In case of adiabatic walls and transfer coefficients arbitrarily depending on temperature, the possibility of self-similar solutions is established. New analytical solutions are compared with the previous solutions for a gas with power-law transfer coefficients. Making use of small perturbation method gas flow in a slender wedge is considered analytically.

A three-dimensional large-eddy-simulation computational fluid dynamics (CFD) program, developed for studying the transport of smoke during a fire in an enclosure, is applied to four flow problems relevant to nonfire situations. This evaluation is relevant to the use of the program for indoor air quality modeling as well as its use in modeling the early phases of smoldering fires. The program uses finite-difference techniques to solve the Navier-Stokes equations, with an approach emphasizing high spatial resolution and efficient flow-solving techniques. Subgrid scale effects are addressed with the Smagorinsky model. The flow problems include simple geometries, with forced, natural, and mixed convection flows as well as a realistic test room with a displacement ventilation system and tracer gas release. Grid effects and computing time are investigated. Results are compared with the experimental data, and issues important to defining the problems in CFD are highlighted. In general the program predicts the experimental data reasonably well, with very fast computing times. However, care must be taken in defining convection from heated surfaces, and adequate grid resolution is needed to model the dispersion of a tracer gas in the enclosure.

SUMMARYThe solution of problems in computational fluid dynamics (CFD) represents a classical field for the application of advanced numerical methods. Many different approaches were developed over the years to address CFD applications. Good examples are finite volumes, finite differences (FD), and finite elements (FE) but also newer approaches such as the lattice‐Boltzmann (LB), smooth particle hydrodynamics or the particle finite element method. FD and LB methods on regular grids are known to be superior in terms of raw computing speed, but using such regular discretization represents an important limitation in dealing with complex geometries. Here, we concentrate on unstructured approaches which are less common in the GPU world. We employ a nonstandard FE approach which leverages an optimized edge‐based data structure allowing a highly parallel implementation. Such technique is applied to the ‘convection‐diffusion’ problem, which is often considered as a first step towards CFD because of similarities to the nonconservative form of the Navier–Stokes equations. In this regard, an existing highly optimized parallel OpenMP solver is ported to graphics hardware based on the OpenCL platform. The optimizations performed are discussed in detail. A number of benchmarks prove that the GPU‐accelerated OpenCL code consistently outperforms the OpenMP version. Copyright © 2011 John Wiley & Sons, Ltd.

Effect of the storage format of sparse linear systems on parallel CFD computations

The study of hydrodynamics and thermal characteristics inside a lid‐driven cavity has been one of the most captivating problems in computational fluid dynamics. In this numerical work, the mixed convection phenomenon inside a two‐dimensional, tall lid‐driven cavity with top and bottom lids moving in opposite directions, +x and –x, respectively, has been explored for non‐Newtonian power‐law fluids. The cavity contains a uniformly heated equilateral triangular obstacle at its geometric center. Numerical experimentation is performed for a range of flow governing parameters, such as aspect ratio (0.25, 0.5, and 0.75), Prandtl number (1, 50, and 100) Richardson number (0.1, 1, and 10), power‐law index (0.6–1.4) and Grashof number of 104. The physical perceptions of the cavity are explained by using streamline and isotherm contours. The fluid movement is limited adjacent to the moving wall concerning the Richardson number at the lower Prandtl number. With a rise in the aspect ratio of the cavity, the flow‐pattern becomes more dispersed inside the cavity. Heat transfer enhancement is observed at a lower aspect ratio equal to 0.25.