Reynolds-Averaged Navier-Stokes CFD Simulation of High-Speed Boundary Layers

This paper presents an investigation of Reynolds-averaged Navier-Stokes (RANS) turbulence models used in computational fluid dynamics (CFD) simulations of boundary layer flow and heat transfer in high Mach number flows. This study evaluates an industry standard RANS turbulence model (k-omega SST) and a recently proposed modification to that model (Danis and Durbin [1]), and quantifies the accuracy for predicting high Mach number boundary layer flow. The test cases were previously documented by Duan et al. (2018), who used direct numerical simulation (DNS) to calculate boundary layer flow of an ideal gas over a flat plate at freestream Mach numbers ranging from 2 to 14 and wall to recovery temperature ratios of 0.18 to 1. Boundary layer profiles were evaluated at two streamwise locations, one where the boundary layer height matched the DNS data and the second where the wall shear stress matched DNS data. Results show that the accuracy of RANS models degrades for high-speed regimes compared to incompressible or subsonic flow but that the compressibility correction factor [1] improves the results for some of the test cases

Reynolds-Averaged Navier-Stokes CFD Simulation of High-Speed Boundary Layers

This paper presents an investigation of Reynolds-averaged Navier-Stokes (RANS) turbulence models used in computational fluid dynamics (CFD) simulations of boundary layer flow and heat transfer in high Mach number flows. This study evaluates an industry standard RANS turbulence model (k-omega SST) and a recently proposed modification to that model (Danis and Durbin [1]), and quantifies the accuracy for predicting high Mach number boundary layer flow. The test cases were previously documented by Duan et al. (2018), who used direct numerical simulation (DNS) to calculate boundary layer flow of an ideal gas over a flat plate at freestream Mach numbers ranging from 2 to 14 and wall to recovery temperature ratios of 0.18 to 1. Boundary layer profiles were evaluated at two streamwise locations, one where the boundary layer height matched the DNS data and the second where the wall shear stress matched DNS data. Results show that the accuracy of RANS models degrades for high-speed regimes compared to incompressible or subsonic flow but that the compressibility correction factor [1] improves the results for some of the test cases

Labyrinth weirs: Development until 1985

The weir is a fundamental structure in hydraulic engineering, serving to retain a water body, to control a water level, facilitate flow diversion, or to measure discharge. Under particular site conditions, the cross-sectional width at the weir location is limited so that either higher overflow depths or a compressed weir expansion are set. A form of the latter arrangement is the so-called labyrinth weir, which is composed of rectangular, trapezoidal or triangular plan shaped weirs, so that the geometrical crest length is increased. Along with the recently developed Piano Key Weir, labyrinth weirs represent economically and hydraulically sound alternative for increasing spillway discharge capacity. The present paper describes their historical development, reviews the main advances until the 1980s, summarizes current design guidelines, and presents the main individuals having participating in their development

Debris-Blocking Sensitivity of Piano Key Weirs under Reservoir-Type Approach Flow

The collection of floating woody debris at flow control structures, such as spillways and weirs, can potentially result in reduced discharge efficiency (higher upstream head for a given weir discharge). Compared to less hydraulically-efficient control structures, piano key weirs have higher discharge efficiency (lower upstream heads for a given discharge), which may increase the likelihood of woody debris collection. A systematic laboratory study was conducted to evaluate the interaction between various piano key weir geometries and woody debris types and sizes. The results of individual (noncumulative) debris tests indicated that floating debris blockage probability is highly influenced by trunk diameter and upstream head. The effects of debris accumulation on the upstream head varied with the value of the debrisfree reference upstream head condition. At lower upstream reference head values, the cumulative debris tests indicated a relative increase of the debris-associated upstream head of approximately 70%; higher upstream reference head values produced upstream head increases limited to approximately 20%

Effect of water on the dislocation creep microstructure and flow stress of quartz and implications for the recrystallized grain size piezometer

Deformation experiments on Black Hills quartzite with three different initial water contents (as-is, water-added, and vacuum-dried) were carried out in the dislocation creep regime in order to evaluate the effect of water on the recrystallized grain size/flow stress piezometer. Samples were deformed in axial compression at temperatures of 750°–1100°C, strain rates between 2 × 10−7 s−1 and 2 × 10−4 s−1 and strains up to 46% using a molten salt assembly in a Griggs apparatus. An increase of the initial water content at otherwise constant deformation conditions caused a decrease in flow stress, an effect known as hydrolytic weakening. The total water content of the starting material was analyzed by Karl Fischer titration (KFT) and Fourier transform infrared (IR) spectroscopy, and quenched samples were analyzed microstructurally and by IR. Changes in the dynamic recrystallization microstructure correlate with changes in flow stress, but there is no independent effect of temperature, strain rate or water content. IR absorption spectra of the deformed spectra indicate that different water contents were maintained in the three sample sets throughout the experiments. However, the amounts of water measured within the vacuum-dried (∼260 ± 40 ppm H2O), the as-is (∼340 ± 50 ppm H2O), and the water-added (∼430 ± 110 ppm H2O) samples are significantly smaller than the initial content of the quartzite (∼640 ± 50 ppm H2O). Water from the inclusions in the starting material adds to the free fluid phase along the grain boundaries, which probably controls the water fugacity and the flow strength, but this water is largely lost during IR sample preparation. Vacuum-dried as well as water-added samples have the same recrystallized grain size/flow stress relationship as the piezometer determined for as-is samples. No independent effect of water on the piezometric relationship has been detected