A new high-performance general-purpose graphics processing unit (GPGPU) computational fluid dynamics (CFD) library is introduced for use with structured-grid CFD algorithms. A novel set of parallel tridiagonal matrix solvers, implemented in CUDA, is included for use with structured-grid CFD algorithms. The solver library supports both scalar and block-tridiagonal matrices suitable for approximate factorization (AF) schemes. The computational routines are designed for both GPU-based CFD codes or as a GPU accelerator for CPU-based algorithms. Additionally, the library includes, among others, a collection of finite-volume calculation routines for computing local and global stable timesteps, inviscid surface fluxes, and face/node/cell-centered interpolation on generalized 3D, multi-block structured grids. GPU block tridiagonal benchmarks showed a speed-up of 3.6x compared to an OpenMP CPU Thomas Algorithm results when host-device data transfers are removed. Detailed analysis shows that a structure-of-arrays (SOA) matrix storage format versus an array-of-structures (AOS) format on the GPU improved the parallel blocktridiagonal performance by a factor of 2.6x for the parallel cyclic reduction (PCR) algorithm. The GPU block tridiagonal solver was also applied to the OVERFLOW-2 CFD code. Performance measurements using synchronous and asynchronous data transfers within the OVERFLOW-2 code showed poorer performance compared to the cache-optimized CPU Thomas Algorithm. The poor performance was attributed to the significant cost of the rank-5 sub-matrix and sub-vector host-device data transfers and the matrix format conversion. The finite-volume maximum time-step and inviscid flux kernels were benchmarked within the MBFLO3 CFD code and showed speed-ups, including the cost of host-device memory transfers, ranging from 3.2-4.3x compared to optimized CPU code. It was determined, however, that GPU acceleration could be increased to 21x over a single CPU core if host-device data transfers could be eliminated or significantly reduced.
The effects of varying axial gap on the unsteady flow field between the stator and rotor of a transonic compressor stage are important because they can result in significant changes in stage mass flow rate, pressure rise, and efficiency. Some of these effects are analyzed with measurements using digital particle image velocimetry (DPIV) and with time-accurate simulations using the 3D unsteady Navier-Stokes computational fluid dynamics solver TURBO. Generally there is excellent agreement between the measurements and simulations, instilling confidence in both. Strong vortices of the wake can break up the rotor bow shock and contribute to loss. At close spacing vortices are shed from the trailing edge of the upstream stationary blade row in response to the unsteady, discontinuous pressure field generated by the downstream rotor bow shock. Shed vortices increase in size and strength and generate more loss as spacing decreases, a consequence of the effective increase in rotor bow shock strength at the stationary blade row trailing edge. A relationship for the change in shed vorticity as a function of rotor bow shock strength is presented that predicts the difference between close and far spacing TURBO simulations.
This paper will outline a steady flow control technique that augments the diffusion process within a stator passage via a continuous co-flowing secondary flow stream along the suction surface. The technique is similar to that used for flow vectoring in nozzles where a secondary flow stream is used to enhance the diffusion and vectoring of high speed jets. Diffusion factors in excess of 0.95 are simulated and the “penalty” for the secondary system is addressed with an availability and simple power analysis. Losses within the secondary flow stream were included in the availability analysis, but it did not account for losses within a delivery system of this secondary flow. This was accomplished through the ID power analysis which assessed this technique’s impact on the efficiency of an axial compression stage and the sensitivity of this efficiency to the secondary flow system’s efficiency. Also, a system level analysis is presented to assess the merits that may be realized in a notional engine with this type of flow control. Particularly, impacts on specific fuel consumption and thrust-to-weight ratio were addressed. A cascade experiment was performed to demonstrate the concept and was conducted in a blow-down cascade tunnel. Significant improvements in diffusion were qualitatively seen from the DPIV measurements despite limitations in achieving the desired secondary flow conditions.
Circulation control inlet guide vanes (IGVs) may provide significant benefits over current IGVs that employ mechanical means for flow turning. This paper presents the results of a two-dimensional computational study on a circulation control IGV that takes advantage of the Coanda effect for flow vectoring. The IGV in this study is an uncambered airfoil that alters circulation around itself by means of a Coanda jet that exhausts along the IGV’s trailing edge surface. The IGV is designed for an axial inlet flow at a Mach number of 0.54 and an exit flow angle of 11 degrees. These conditions were selected to match the operating conditions of the 90% span section of the IGV of the TESCOM compressor rig at the Compressor Aero Research Laboratory (CARL) located at Wright-Patterson AFB, the hardware that is being used as the baseline in this study. The goal of the optimization was to determine the optimal jet height, trailing edge radius, and supply pressure that would meet the design criteria while minimizing the mass flow rate and pressure losses. The optimal geometry that was able to meet the design requirements had a jet height of h/Cn = 0.0057 and a trailing edge Radius R/Cn = 0.16. This geometry needed a jet to inflow total pressure ratio of 1.8 to meet the exit turning angle requirement. At this supply pressure ratio the mass flow rate required by the flow control system was 0.71 percent of the total mass flow rate through the engine. The optimal circulation control IGV had slightly lower pressure losses when compared with a reference cambered IGV.
The effects of varying axial gap on the unsteady flow field between the stator and rotor of a transonic compressor stage are important because they can result in significant changes in stage mass flow rate, pressure rise and efficiency. Some of these effects are analyzed with measurements using Digital Particle Image Velocimetry (DPIV) and with time-accurate simulations using the 3D unsteady Navier-Stokes CFD solver TURBO. Generally there is excellent agreement between the measurements and simulations, instilling confidence in both. Strong vortices of the wake can break up the rotor bow shock and contribute to loss. At close spacing vortices are shed from the trailing edge of the upstream stationary blade row in response to the unsteady, discontinuous pressure field generated by the downstream rotor bow shock. Shed vortices increase in size and strength and generate more loss as spacing decreases, a consequence of the effective increase in rotor bow shock strength at the stationary blade row trailing edge. A relationship for the change in shed vorticity as a function of rotor bow shock strength is presented that predicts the difference between close and far spacing TURBO simulations.
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