Computational Fluid Dynamics (CFD)

        Computational Fluid Dynamics is an integral part of the scramjet studies.  Data obtained from cold-flow and reacting CFD simulations have been used to help guide the direction of the experiments, and simulations have been run in tandem with the experiments. The two methods have produced results that are in good agreement. Very Large Eddy Simulation (VLES) is currently being used to study recessed cavity flameholders in the scramjet engine configuration. The results will be compared with experimental data from a linear array of optically addressed microelectromechanical (MEMS) pressure sensors mounted on the floor of the cavity along the cavity centerline. The sensors have been developed by Taitech specifically for work in the harsh environments of combusting flows.

        Taitech is currently working on validation of computational methods through comparison with experimental data, while offering insights into important physical problems. These studies include a consideration of injection from circular, transverse jets into supersonic flowfields and an examination of the unsteady flow physics of the opening door in a scramjet isolator and inlet.

       These computations have been performed primarily using the VULCAN (Viscous Upwind aLgorithm for Complex flow ANalysis) Navier-Stokes code, a derivative of the LARCK code developed at NASA Langley. VULCAN has been developed at Taitech and NASA Langley, and will be parallelized using generic MPI (Message Passing Interface) libraries in a data-parallel fashion. This will allow VULCAN to exploit the relatively low-cost, high-performance, massively-parallel machines now becoming available.

       Numerical simulations were performed to study the unsteady flow physics of a scramjet inlet and isolator. The purpose of these computations is to determine the capabilities of various numerical codes and the various turbulence models and their applicabilities to the inlet/isolator problem. A discrete 2-D moving door computation was performed to understand the inlet/isolator flow physics. As the flow enters the inlet through the opening gap, a flow feature similar to an underexpanded jet develops and causes separation bubbles to form on the cowl and body-side of the inlet. These separated regions considerably decrease the effective throat area and hence increase the effective contraction ratio that may cause the inlet to unstart.

        In other CFD work, a new assumed probability density function (PDF) approach has been developed that accounts for temperature and composition fluctuations in compressible reacting flows, including effects of temperature-composition correlations. This scheme has the potential to predict the gross features of turbulence-chemistry interactions with reduced computational effort. In another study, the effect of radiation in gas turbine combustion chambers was investigated. A finite-volume method was used to solve the radiative transfer equation for gray gases in axisymmetric geometries.

The Space-Time Conservation Element and Solution Element CFD Method
        The Space-Time Conservation Element and Solution Element (CE/SE) method provides a new, genuinely multidimensional framework for the numerical solution of conservation law problems, including fluid dynamics. Development of this method was motivated by the need for a more general and coherent numerical framework for accurate and efficient simulation of CFD problems. CE/SE has been used to solve shock tube problems, ZND detonation waves, implosion and explosion problems, shock propagation over a forward-facing step, acoustic waves and shock/acoustic wave interactions. It shows particular promise for computational aeroacoustics.

Development of Three Dimensional DRAGON Grid Technology
        DRAGON, or Direct Replacement of Arbitrary Grid Overlapping by Nonstructured grid, is a hybrid grid scheme. It uses the Chimera method to generate most of the grid for a given geometry, with unstructured grid for areas with complex geometries. DRAGON is capable of completely eliminating interpolation between grids, thereby preserving the conservation property of the solution. It quickly creates grids for computations of viscous flows over components with complex shapes, such as those found in engineering systems. It is currently being applied, with considerable success, to three-dimensional problems.

Send mail to chenth@taitech.com with questions or comments about this web site.
Copyright © 2001 Taitech, Inc.
Last modified: May 10, 2001