This book covers the following topics: recent developments in three dimensional and unsteady turbulence boundary-layer computations; flows far from equilibrium via molecular dynamics; physics of convention-solidification interaction; the continental shelf bottom boundary layer; gravity currents in rotating systems; strange attractors in fluids: another view; eddies, waves, circulation, and mixing: statistical geofluid mechanics; regular and mach reflection of shock waves; ship propellers; coherent structures; the critical layer and stability; general circulation of the oceans; characteristic-based schemes for the euler equations; vortex flows in aerodynamics; steady and unsteady boundary-layer separation; and wind wave prediction.

Annual Review of Fluid Mechanics

This work analyses the link between the aspect ratio of a vertical-axis straight-bladed (H-Rotor) wind turbine and its performance (power coefficient). The aspect ratio of this particular wind turbine is defined as the ratio between blade length and rotor radius. Since the aspect ratio variations of a vertical-axis wind turbine cause Reynolds number variations, any changes in the power coefficient can also be studied to derive how aspect ratio variations affect turbine performance. Using a calculation code based on the Multiple Stream Tube Model, symmetrical straight-bladed wind turbine performance was evaluated as aspect ratio varied. This numerical analysis highlighted how turbine performance is strongly influenced by the Reynolds number of the rotor blade. From a geometrical point of view, as aspect ratio falls, the Reynolds number rises which improves wind turbine performance.

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Design of a vertical-axis wind turbine: how the aspect ratio affects the turbine’s performance

Numerical study of two-bucket Savonius wind turbine cluster

Computational fluid dynamics (CFD) is increasingly being used to develop blood-contacting medical devices. However, the lack of standardized methods for validating CFD simulations and blood damage predictions limits its use in the safety evaluation of devices. Through a U.S. Food and Drug Administration (FDA) initiative, two benchmark models of typical device flow geometries (nozzle and centrifugal blood pump) were tested in multiple laboratories to provide experimental velocities, pressures, and hemolysis data to support CFD validation. In addition, computational simulations were performed by more than 20 independent groups to assess current CFD techniques. The primary goal of this article is to summarize the FDA initiative and to report recent findings from the benchmark blood pump model study. Discrepancies between CFD predicted velocities and those measured using particle image velocimetry most often occurred in regions of flow separation (e.g., downstream of the nozzle throat, and in the pump exit diffuser). For the six pump test conditions, 57% of the CFD predictions of pressure head were within one standard deviation of the mean measured values. Notably, only 37% of all CFD submissions contained hemolysis predictions. This project aided in the development of an FDA Guidance Document on factors to consider when reporting computational studies in medical device regulatory submissions. There is an accompanying podcast available for this article. Please visit the journal's Web site (www.asaiojournal.com) to listen.

FDA Benchmark Medical Device Flow Models for CFD Validation.

A cross-flow wind turbine has a high torque coefficient at a low tip speed ratio; therefore, it is a good candidate for a self-starting turbine. This study aims to investigate the best configuration between guide vanes and cross-flow vertical axis wind turbine. The experiment test was carried out to determine the turbine with the highest power coefficient. The cross-flow turbine has 14, 18, and 22 blades with using 6,10 and 14 blades of guide vane (GV) was developed in this study, employing 15°, 25°, 35°, 45°, 55°, 65°, and 75° of tilt angles in fifth different wind speed conditions 4 m/s, 6 m/s, 7.5 m/s, 9.20 m/s, and 11 m/s. The turbine has 22 blades with 14 GV blades at 55° of tilt angle blades producing more remarkable turbine performance improvement than other blades. The highest power coefficient (CP) of cross-flow using 14 GV blades at 55° was 0.0162 at 0.289 TSR, which increased around 59% of the turbine's performance using GV.

Study the influence of using guide vanes blades on the performance of cross-flow wind turbine

Shear stress on blood cells and platelets transported in a turbulent flow dictates the fate and biological activity of these cells. We present a theoretical link between energy dissipation in turbulent flows to the shear stress that cells experience and show that for the case of physiological turbulent blood flow: (a) the Newtonian assumption is valid, (b) turbulent eddies are universal for the most complex of blood flow problems, and (c) shear stress distribution on turbulent blood flows is possibly universal. Further we resolve a long standing inconsistency in hemolysis between laminar and turbulent flow using the theoretical framework. This work demonstrates that energy dissipation as opposed to bulk shear stress in laminar or turbulent blood flow dictates local mechanical environment of blood cells and platelets universally.

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Theory to predict shear stress on cells in turbulent blood flow

The purpose of this research work is to investigate experimentally and computationally the feasibility of improving the performance of the vertical-axis Savonius wind turbine. The authors first performed a series of wind tunnel investigations on semi-cylindrical three-bladed Savonius rotor scale models with different overlap ratios and without overlap. These experiments were conducted in front of a low-speed subsonic wind tunnel at different Reynolds numbers. Pressures around the concave and convex surfaces of each blade, as well as the static torque for the rotor models, were measured. Using these experimental data, the authors calculated aerodynamic characteristics such as drag coefficients, static torque coefficients, and power coefficients. The authors then performed computational fluid dynamics (CFD) simulations using the commercial CFD software FLUENT and GAMBIT to analyze the static rotor aerodynamics of those models. The experimental and computational results were then compared for verification. Three different models with different overlap ratios were designed and fabricated for the current study to find the effect of overlap ratios. The results from the experimental part of the research show a significant effect of overlap ratio and Reynolds number on the improvement of aerodynamic performance of the Savonius wind turbine. At higher Reynolds number, the turbine model without overlap ratio gives better aerodynamic coefficients, and at lower Reynolds number, the model with moderate overlap ratio gives better results.

/pdf/wind-tunnel-testing-and-numerical-simulation-on-aerodynamic-1bht7yj6az.pdf

Wind tunnel testing and numerical simulation on aerodynamic performance of a three-bladed Savonius wind turbine

Savonius wind turbine is the simplest type of vertical axis rotor that has a relatively low efficiency. Operation of the Savonius wind turbine is based on the difference of the drag force on its semi-spherical blades, depending on whether the wind is striking the convex or the concave part of the blades. This turbine is being used in various countries around the world due to the simplistic design, cheap technology for construction, and a good starting torque independent of wind direction at low wind speeds. Due to its simple design and low construction cost, this rotor is mainly used for water pumping as well as wind power on small scale. The main goal of this current research is to investigate the aerodynamic performance of Savonius wind turbine. Wind tunnel investigation was carried out to find the aerodynamic characteristics like, drag coefficient, torque coefficient, and power coefficient of three blade Savonius wind turbine rotor models with and without overlap ratio (ratio of overlap distance between two adjacent blades and rotor diameter ,OR = a/D) at various Reynolds numbers. Numerical investigation was also carried out to find those aerodynamic characteristics. For numerical investigation, commercial computational fluid dynamic (CFD) software GAMBIT and FLUENT were used. Afterwards those two results were compared for verification. Three different models with different overlap ratio were designed and i fabricated for the current study to find the effect of overlap ratios. The results from the experimental part of the research show a significant effect of overlap ratio and Reynolds number on the improvement of aerodynamic performance of the Savonius wind turbine. At higher Reynolds number turbine Model without overlap ratio gives better aerodynamic coefficients and at lower Reynolds number Model with moderate overlap ratio gives better results.

/pdf/experimental-and-numerical-investigations-on-aerodynamic-qiwmzt79v4.pdf

Experimental and Numerical Investigations on Aerodynamic Characteristics of Savonius Wind Turbine with Various Overlap Ratios

Laminar mixed convection in a lid-driven square cavity with two isothermally heated square internal blockages is numerically investigated. The top lid of the cavity is moving rightwards with a constant speed. The two blockages are maintained at an isothermal hot temperature, while the walls of the cavity are maintained at a cold temperature. The flow and heat transfer behavior is studied for various placements of the blockages through analyzing the local Nusselt number distribution around the edges of the blockages and the average Nusselt number at the blockage surfaces at various Richardson and Reynolds numbers. Investigations are performed in a range of Reynolds number (100–500), Richardson number (0.1–10), and at a fixed Prandtl number (0.71). Computations are done using the ANSYS FLUENT commercial code based on a finite volume method. It is observed that, the average Nusselt number on the blockage surfaces increases with increasing Reynolds number at any Richardson number. The average Nusselt number c...

Laminar Mixed Convection in a Lid-Driven Square Cavity with Two Isothermally Heated Square Internal Blockages

We experimentally probe the local dissipation scale distribution Q(η) and temporal fluctuations of the turbulent kinetic energy dissipation rate e in the strongly anisotropic flow past a backward facing step A shift in Q(η) and corresponding reduction in the relative intermittency of e is observed with increasing mean shear S We offer physical arguments to elucidate the role of strong shear on the small-scale structure A local mean-shear dissipation Reynolds number, ReS ≡ ⟨e⟩/(S2ν), is proposed that may define a family of universal small-scale structures of turbulence

https://www.engr.colostate.edu/~vskaran/MDV_POF_2013.pdf

Khandakar Niaz Morshed

Papers

Theory to predict shear stress on cells in turbulent blood flow

Wind tunnel testing and numerical simulation on aerodynamic performance of a three-bladed Savonius wind turbine

Experimental and Numerical Investigations on Aerodynamic Characteristics of Savonius Wind Turbine with Various Overlap Ratios

Laminar Mixed Convection in a Lid-Driven Square Cavity with Two Isothermally Heated Square Internal Blockages

Intermittency and local dissipation scales under strong mean shear