Browsing by Author "Dr. H. A. Hassan, Member"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • No Thumbnail Available
    A Conservative Interblock Communication Algorithm for Dynamically Discontinuous Block Boundary Grids
    (2001-07-11) Bond, Ryan Bomar; Dr. D. S. McRae, Chair; Dr. J. R. Edwards, Member; Dr. H. A. Hassan, Member; Dr. R. E. White, Member
    An algorithm is presented for the conservative communication between gridblocks where point connectivity is not maintained across across theinterface. The algorithm is specifically designed for dynamicdiscontinuities, e.g. those that arise when dynamic r-refinementadaptation is performed on two adjacent blocks without the constraint ofboundary point connectivity. r-Refinement adaptation involves moving thepoints in the computational mesh to better resolve features in thesolution field. Discontinuously connected multiblock boundaries arenecessary for problems where adjacent blocks have significantly differentadaptation requirements or problems where one block is to be adapted whilean adjacent block is left stationary. In programs where adaptation isbeing performed in parallel, discontinuously connected multiblockboundaries allow the adaptation to continue on different processorswithout the need for communication and subsequent agreement of where theboundary points should be located. The communication between two adjacent blocks must be conservative toallow the simulation of compressible flow problems. Simply interpolatingthe boundary data to transfer information from one block to the otherviolates conservation, so other means of transferring the information mustbe employed. A technique for generating ghost cells and setting theirdependent variable values is presented. The method is conservative,accurate, robust, and computationally efficient. Tests of the algorithm on both statically and dynamically discontinuousgrids are presented, and the computational efficiency of the algorithm isdiscussed. The algorithm was tested using the diffusion equation, linearwave equation, and the set of Euler equations. Since the algorithm isapplicable to any CFD problem where conservative communication isnecessary between discontinuous blocks, it can be used when adaptationcriteria are different between adjacent blocks, when an adapted block isadjacent to an unadapted block, or when enhanced parallelism can beachieved by relaxing boundary point connectivity.
  • No Thumbnail Available
    Three Dimensional Simulation of Time-Dependent Scramjet Isolator/Combustor Flowfields Implemented on Parallel Architectures
    (2001-01-05) McDaniel, Keith Scott; Dr. J. R. Edwards, Chair; Dr. H. A. Hassan, Member; Dr. D. S. McRae, Member
    The development of a parallel Navier-Stokes solver for computing time-dependent,three-dimensional reacting flowfields within scramjet (supersonic combusting ramjet)engines is presented in this work. The algorithm combines low-diffusion upwinding methods, timeaccurate implicit integration techniques, and domain decomposition strategies to yield an effective approach for large-scale simulations. The algorithm is mapped to a distributed memoryIBM SP-2 architecture and a shared memory Compaq ES-40 architecture using the MPI-1 message-passingstandard. Two and three-dimensional simulations of time-dependent hydrogen fuel injection into a modelscramjet isolator / combustor configuration at two equivalence ratios are performed. Thesesimulations are used to gain knowledge of engine operability, inlet performance, isolatorperformance, fuel air mixing, flame holding, mode transition, and engine unstart.Results for an injection at a ratio of 0.29 show qualitative agreement withexperiment for the two-dimensional case, but revealed a slow progression towardengine unstart for the three-dimensional case. Injection at an equivalence ratio of 0.61resulted in engine unstart for both two-dimensional and three-dimensional cases.Engine unstart for the three-dimensional case occurs as a response to the formation and growthof large pockets of reversed flow along the combustor side wall. These structuresdevelop at an incipient pressure above 154 kPa and result in significant blockage of the core flow,additional compression, and chemical reaction within the boundary layer. All of these factors promotea much more rapid unstart as compared with the two-dimensional case.