Sampath Palaniswamy

Convergence acceleration for unified-grid formulation using preconditioned implicit relaxation

Improved convergence rates for a unified grid framework are achieved by combining several convergence acceleration strategies, which include local implicit time-stepping, low-speed preconditioning, and relaxation methods. It is demonstrated that good convergence can be achieved on various grid types and topologies, all speed regimes, and for both inviscid and viscous flows.

The CFD++ Computational Fluid Dynamics Software Suite

Computational Fluid Dynamics CFD is no longer the domain of just specialists. It is also being used by engineers and scientists in many disciplines who are interested in CFD as a tool to investigate other things and not as just an end in itself. The realization of this fact drives developers to produce user-friendly CFD products that automate most of the problem set up and solution process. The CFD++ software suite is a unified-grid, unified-solution, unified-computing CFD simulation capability that was designed from the outset to be effective from the users perspective. The details are explained in this paper.

A numerical study of the pulse detonation wave engine with hydrocarbon fuels

This paper explores some issues that arise in the analysis of pulse detonation wave engines with hydrocarbon fuels. One-dimensional and axisyrnmetric/two-dimensional simulations are employed along with reduced kinetic mechanisms to confirm the ability of the numerical approach to accurately compute relevant physical characteristics such as proper detonation wave speed, von-Neumann spike, aspiration, pressure time history and sequence of cycle events. It is shown that qualitatively and quantitatively reasonable results can be obtained with a careful treatment of the finite-rate-chemistry source terms. Some of the numerical difficulties that arise in dealing with unsteady detonation phenomena are discussed and improvements demonstrated. Onedimensional test cases with simplified H2-O2 and C3HgAir kinetics are used to verify correct detonation wave speed and testing boundary conditions. An axisymmetric case for the latter chemistry is studied with a generic inlet to illustrate the ability of the methodology to capture the relevant physics, namely, pressurization of thrust wall by the detonation wave and interaction of the reflected wave with rarefaction waves from the open end.

A unified-grid approach for propulsion applications

The unified-grid approach includes the integrated treatment of structured and unstructured grids as well as single and multiblock grids. Various threedimensional, two-dimensional and one-dimensional cell shapes can be utilized. It helps in building solutionadaptive meshes. The unified-grid approach includes the ability to automatically connect multiblock meshes (including patched-aligned, patched-nonaligned, and overset grids). This feature can help deal with turbomachinery problems where grids attached to the rotor stage move with respect to other stationary grid blocks. In this paper, we present these building blocks using several unit problems as illustrative examples.

Engineering Approaches for Active Flow Control Simulation

Current practice in flow control simulation often entails unsteady calculation of jet actuators, resolving their geometries in detail. This approach requires: (a) fine grids to resolve flow inside and outside actuators; (b) many time-steps to resolve high-frequency actuator flow-field; (c) many more time-steps to resolve multiple time-scales if the main flow is also unsteady. This method is very time-consuming and renders the current approach impractical from an engineering standpoint. The paper addresses these issues and suggests strategies that enable active flow control simulation within engineering design cycles.

Parallel Personal Computer Applications of CFD++, a Unified-Grid, Unified Physics Framework

Abstract The CFD++ Computational Fluid Dynamics (CFD) software suite is based on a new unified-grid, unified- physics and unified-computing framework. Implementing this within a parallel-processing environment involves many interesting aspects that are explored in the paper. Contemporary Personal Computer environments include parallel systems that can include 2-CPU machines with the Pentium II CPU and up to 4-CPU machines that use the Pentium-Pro CPU. These can be part of low speed (10Mbit/sec) or higher speed (100Mbit/sec) ethermet networks. The LINUX operating system and the public domain MPI (Message Passing Interface) offer a very convenient operating system environment and parallel-processing library on such computers and computer networks. Domain decomposition tools such as METIS (University of Minnesota) also serve as a complementary tool in being able to take advantage of parallel computing environments. This paper demonstrates the power of this environment to compute interesting small and large-scale CFD problems using the unified-grid, unified-physics approach. Examples to be presented include compressible perfect gas and compressible reacting flows, compressible low speed and incompressible flows, etc. The grid topologies that will be employed in these examples will include structured and unstructured grids, single and multiblock meshes, and various multiblock topologies including patched-aligned, patched-nonaligned and overset meshes. We will also present practical information on the effectiveness of low speed and high-speed networks, as part of standalone networks and as part of larger networks.