Download or read book Fractal Grid turbulence and Its Effects on a Performance of a Model of a Hydrokinetic Turbine written by Altayeb Mahfouth and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on generating real world turbulence levels in a water tunnel rotor test using fractal grids and characterizing the effect of the fractal grid generated-turbulence on the performance of hydrokinetic turbines. The research of this thesis is divided into three studies: one field study and two laboratory studies. The field study was conducted at the Canadian Hydro Kinetic Turbine Test Centre (CHTTC) on the Winnipeg River. An Acoustic Doppler Velocimeter (ADV) was used in the field study to collect flow measurements in the river. The laboratory studies were conducted at the University of Victoria (UVic) fluids research lab and the Sustainable Systems Design Lab (SSDL). In addition, the Particle Image Velocimetry (PIV) technique was used in the experiential studies to obtain quantitative information about the vector flow field along the test section, both upstream and downstream of the rotor's plane.The first study is a field study aiming to provide real flow characteristics and turbulence properties at different depths from the free-surface to boundary layer region of a fast river current by conducting a field study in the Winnipeg River using ADV. A novel technique to deploy and control an ADV from free-surface to boundary layer in a fast-current channel is introduced in this work. Flow characteristics in the river, including mean flow velocities and turbulence intensity profiles are analyzed. The obtained results indicate that the maximum mean velocity occurs below the free-surface, suggesting that the mean velocity is independent of the channel depth. From the free-surface to half depth, it was found that changes in both the mean velocity and turbulence intensity are gradual. From mid-depth to the river bed, the mean velocity drops rapidly while the turbulence intensity increases at a fast rate. The turbulent intensity varied from 9% at the free-surface to around 17.5% near the river bed. The results of this study were used in the second lab study to help designing a fractal grid for a recirculating water flume tank. The goal was to modify the turbulence intensity in the water tunnel such that the generated turbulence was similar to that in the river at a location typical of a hydrokinetic device. The properties of fractal-generated turbulence were experimentally investigated by means of 2D Particle Image Velocimetry (PIV). The streamwise turbulent intensity profiles for different grids along the channel are presented. Additionally, visualization of the average and fluctuating flow fields are also presented. The results are in good agreement with results in literature. The third and final study investigated the power coefficient of a scale hydrokinetic turbine rotor in controlled turbulent flow (7.4 % TI), as well as in the low-turbulence smooth flow (0.5% TI) typical of lab scale testing. PIV was employed for capturing the velocity field. The results show that using realistic TI levels in the water tunnel significantly decrease the turbine's power coefficient compared to smooth flow, highlighting the importance of considering this effect in future experimental campaigns.
Download or read book The Effect of Multiple Scales on Fractal grid generated Turbulence written by Alexis Kathleen Omilion and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Fractal grids, having patterns that repeat at different length scales, mimic the multi-scale characteristic of objects of complex appearance in nature, such as branching pulmonary network, river network, trees, and cumulus clouds. Understanding the role that multiple length scales have in momentum and energy transport is essential for effective utilization of fractal grids in a wide variety of engineering applications. While previous studies have solidified the dominant effect of the largest scale of fractal grids, effects of the additional scales on the generated turbulent flow remain unclear. This research is to determine how the smaller fractal scales (and the interaction between the multiple scales) influence the turbulence statistics of the induced flow and the pressure drop across a fractal square grid using well-controlled water-tunnel experiments. Instantaneous and ensemble-averaged velocity fields are obtained by a planar Particle Image Velocimetry (PIV) for a set of fractal square grids (N = 1, 2, 3 and 4) at the Reynolds number of 3400. The static pressure drop across the grids are measured by a differential pressure transducer. Flow fields indicate that the multiple jets, wakes and the shear layers produced by the multiple scales are the fundamental flow physics that promote momentum transport in the turbulence. In addition, the multiple scales cause a redistribution of the turbulent kinetic energy and a change in the vortex shedding mechanism behind the grids. The grid of 3 fractal scales (N = 3) produces higher turbulence intensity levels than the grid with 4 fractal scales (N = 4) despite having a lower blockage ratio and pressure drop, owing to the suppression of vortex shedding by the additional scale of the grid of N = 4. To better predict the location of peak turbulence intensity, the wake interaction length scale model is modified to incorporate the effects of the interactions among multiple scales by the effective mesh size and an empirical scaling coefficient Beta. Considering the capability of fractal grids to enhance momentum and energy transport, this work can potentially benefit a wide variety of applications where energy-efficient mixing or convective heat transfer is a key process.
Download or read book Fractal Flow Design How to Design Bespoke Turbulence and Why written by Yasuhiko Sakai and published by Springer. This book was released on 2016-06-21 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on turbulent flows generated and/or influenced by multiscale/fractal structures. It consists of six chapters which demonstrate, each one in its own way, how such structures and objects can be used to design bespoke turbulence for particular applications and also how they can be used for fundamental studies of turbulent flows.
Download or read book Turbulence Modelling Approaches written by Konstantin Volkov and published by BoD – Books on Demand. This book was released on 2017-07-26 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate prediction of turbulent flows remains a challenging task despite considerable work in this area and the acceptance of CFD as a design tool. The quality of the CFD calculations of the flows in engineering applications strongly depends on the proper prediction of turbulence phenomena. Investigations of flow instability, heat transfer, skin friction, secondary flows, flow separation, and reattachment effects demand a reliable modelling and simulation of the turbulence, reliable methods, accurate programming, and robust working practices. The current scientific status of simulation of turbulent flows as well as some advances in computational techniques and practical applications of turbulence research is reviewed and considered in the book.
Download or read book Fractal Classical and Active Grid Turbulence written by Robert Jason Hearst and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Effects of Inlet Turbulence and Rotor stator Interactions on the Aerodynamics and Heat Transfer of a Large scale Rotating Turbine Model Volume 1 written by Robert P. Dring and published by . This book was released on 1987 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book On Turbulence and Its Effects on Aerodynamics of Flow Through Turbine Stages written by Galina Ilieva Ilieva and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In reality, the flows encountered in turbines are highly three-dimensional, viscous, turbulent, and often transonic. These complex flows will not yield to understanding or prediction of their behavior without the application of contemporary and strong modeling techniques, together with an adequate turbulence model, to reveal effects of turbulence phenomenon and its impact on flow past turbine blades. The discussion primarily targets the turbulence features and their impact on fluid dynamics; streaming of blades, and efficiency performance. Turbulence as a phenomenon, turbulence effects and the transition onset in turbine stages are discussed. Flow parameters distribution past turbine stages, approaches to turbulence modeling, and how turbulent effects change efficiency and require an innovative design, among others are presented. Furthermore, a comparison study regarding the application and availability of various turbulence models is fulfilled, showing that every aerodynamic effect, encountered of flow pass turbine blades can be predicted via different model. This work could be very helpful for researchers and engineers working on prediction of transition onset, turbulence effects, and their impact on the overall turbine performance.
Download or read book Grid Orthogonality Effects on Predicted Turbine Midspan Heat Transfer and Performance written by Robert J. Boyle and published by . This book was released on 1995 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Study of Turbulence Generation and Control by Fractal Grids written by S. M. M. Salim and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulence generation and control have been an immense interest among scientists and researchers due to the fact that nearly all industrial flows are turbulent. In some cases, turbulence is highly desired, for example chemical plants need higher turbulence for the efficient mixing of various substances whereas, in oil and pipe industries, whereas, turbulence in the pipe flows causes higher energy input to sustain the flow along the pipe length. Thus, control of turbulence directly contributes to cutting costs. The existing approaches to control such flows are case specific and no single universal approach exists owing to the lack of understanding of underlying physics. Many approaches have been taken to generate turbulence in laboratory set-ups for the past hundred years to study turbulence control. One such approach is the use of a rectangular grid through which the fluid is forced to generate so called grid turbulence. In contrast, we have made use of fractal geometry to generate turbulence for similar study. The self-similar edge characteristic of the fractal grids is thought to play the vital role in the enhanced mixing properties. Four sets of fractal grids, each with equal flow area, were used in the study. Our results from the experiments conducted in a circular wind tunnel indicate that it is possible to significantly improve the generation and control of turbulence by the introduced fractal approach.
Download or read book Analysis and Application of Decaying Turbulence with Initial Fractal Geometry written by Hiroki Suzuki and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this paper, we address high-Schmidt-number (Sc) scalar turbulent mixing that results from grid-generated turbulence using the initial fractal geometry of the velocity profile. More specifically, as was proposed in our recent study, we adopt an initial flow field generated by a fractal grid and apply it to a water channel experiment based on a high-Sc-number scalar-mixing layer in order to create grid-generated turbulence, and thus solve our current research problem. The high-Sc-number scalar and velocity fields of the grid-generated turbulence are then measured using planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV), respectively. By means of fractal analysis, this study specifically addresses the turbulent mixing phenomena in which the fractal dimension of the mixing interface of an observed high-Sc-number scalar field is calculated. Additionally, we discuss the efficiency of using fractal grids as devices for enhancing high-Sc-number scalar turbulent mixing by observing turbulent intensities and dissipation by PIV.
Download or read book The Effects of Blockage Ratio and Distance from a Free Surface on the Performance of a Hydrokinetic Turbine written by Peter Creciun and published by . This book was released on 2013 with total page 55 pages. Available in PDF, EPUB and Kindle. Book excerpt: Blockage ratio and distance below a free surface are two factors that potentially affect hydrokinetic turbine performance. The extent of the effects of these parameters is considered by determining the coefficient of performance of a simple turbine blade rotating at 250 RPM in a 3.5-m/s flow of water using FLUENT Computational Fluid Dynamics software. The effects of blockage ratio are tested in a circular duct of varying diameter (0.5588 to 10.668 meters (22 to 420 inches)), while the effects of distance below a free surface are tested in a river bed, where the depth of the turbine is varied (0.3175 to 4.1148 meters (12.5 to 162 inches)). The coefficient of performance is shown to vary only slightly for values of blockage ratio below about 0.4. As the blockage ratio increases beyond 0.4, the coefficient of performance increases greatly and graphically tends toward a vertical asymptote as the blockage ratio approaches 1. Turbine depth is shown to have little or no effect on a turbine's coefficient of performance, except when the turbine is very close to the surface, at which point the coefficient of performance increases; however, the model or mesh employed to obtain these results may not be sufficient. It is suggested that a finer mesh or a two-phase model including air above the river be used in the further study of this topic.
Download or read book Statistical Analyses of Fractal Grid Generated Turbulence written by Adrian Chin Hsiung Chong and published by . This book was released on 2008 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Influence of Jet grid Turbulence on Turbulent Boundary Layer Flow and Heat Transfer written by Chung-Der Young and published by . This book was released on 1989 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Simulating Collisions for Hydrokinetic Turbines FY2010 Annual Progress Report written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Computational fluid dynamics (CFD) simulations of turbulent flow and particle motion are being conducted to evaluate the frequency and severity of collisions between marine and hydrokinetic (MHK) energy devices and debris or aquatic organisms. The work is part of a collaborative research project between Pacific Northwest National Laboratory (PNNL) and Sandia National Laboratories, funded by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Wind and Water Power Program. During FY2010 a reference design for an axial flow MHK turbine was used to develop a computational geometry for inclusion into a CFD model. Unsteady simulations of turbulent flow and the moving MHK turbine blades are being performed and the results used for simulation of particle trajectories. Preliminary results and plans for future work are presented.
Download or read book Effects of Stratification and Molecular Diffusivity on the Mixing Efficiency of Decaying Grid Turbulence c by Chris Robert Rehmann written by Chris Robert Rehmann and published by . This book was released on 1995 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Windtunnel Turbulence Generated by Square Fractal Grids written by Richard Elian Seoud and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Modelling Turbulence in Engineering and the Environment written by Kemal Hanjalić and published by Cambridge University Press. This book was released on 2011-10-20 with total page 403 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive account of advanced RANS turbulence models including numerous applications to complex flows in engineering and the environment.
