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Diffuser Augmented Horizontal Axis Tidal Current Turbines  [cached]
Nasir Mehmood,Zhang Liang,Jawad Khan
Research Journal of Applied Sciences, Engineering and Technology , 2012,
Abstract: The renewal energy technologies are increasingly popular to ensure future energy sustenance and address environmental issues. The tides are enormous and consistent untapped resource of renewable energy. The growing interest in exploring tidal energy has compelling reasons such as security and diversity of supply, intermittent but predictable and limited social and environmental impacts. The tidal energy industry is undergoing an increasing shift towards diffuser augmented turbines. The reason is the higher power output of diffuser augmented turbines compared to conventional open turbines. The purpose of this study is to present a comprehensive review of diffuser augmented horizontal axis tidal current turbines. The components, relative advantages, limitations and design parameters of diffuser augmented horizontal axis tidal current turbines are presented in detail. CFD simulation of NACA 0016 airfoil is carried out to explore its potential for designing a diffuser. The core issues associated with diffuser augmented horizontal axis tidal current turbines are also discussed.
An investigation of diffuser for water current turbine application using CFD
Palapum khunthongjan,,Adun janyalertadun
International Journal of Engineering Science and Technology , 2011,
Abstract: The use of water stream as the energy resource has long time happened but its velocity is pretty low so it’s not found in wide range of uses. Here the study purposes accelerate water velocity by installingdiffuser. The problems were analyzed by one dimension analysis and computational fluid dynamics (CFD); domain of flowing problem will cover diffuser and turbine area that be substituted by porous jump condition. In this study flow identified as axisymmetric steady flow, inlet boundary identified as uniform flow, sizes of diffuser was still but the diffuser angle. The study found that the more widendiffuser angle, the more velocity of water stream toward the turbine. A 20° angle of diffuser was to add 1.9 times of water velocity and 1.7 times of energy if compared to the diffuser-uninstalled turbine. If the angle was about 0-20° and 50-70° the force toward diffuser became high instantly; where as the force toward the rotor will be still and the maximum rate of rotor power augmentation possibly was 3.5.
CFD Numerical simulations of Francis turbines
Laín,Santiago; García,Manuel; Quintero,Brian; Orrego,Santiago;
Revista Facultad de Ingeniería Universidad de Antioquia , 2010,
Abstract: in this paper the description of the internal flow in a francis turbine is addressed from a numerical point of view. the simulation methodology depends on the objectives. on the one hand, steady simulations are able to provide the hill chart of the turbine and energetic losses in its components. on the other hand, unsteady simulations are required to investigate the fluctuating pressure dynamics and the rotor-stator interaction. both strategies are applied in this paper to a working francis turbine in colombia. the employed cfd package is ansys-cfx v. 11. the obtained results are in good agreement with the in site experiments, especially for the characteristic curve.
A study of diffuser angle effect on ducted water current turbine performance using CFD  [PDF]
Palapum Khunthongjan,Adun Janyalertadun
Songklanakarin Journal of Science and Technology , 2012,
Abstract: The water current has used as the energy resource for long time however its velocity is very low therefore there arenot found in wide range of uses. This study purposes accelerate water velocity by installing diffuser. The problems wereanalyzed by one dimension analysis and computational fluid dynamics (CFD); the domain covers the diffuser and turbinewhich substituted by porous jump condition is install inside. The flow was identified as axisymmetric steady flow, the inletboundary is identified as uniform flow, all simulation use the same size of diffuser, only the diffuser angles are vary. The resultsshow that velocities of water current in diffuser are increase when the diffuser angle are widen. The angle of diffuser is 20°,the velocity is increase to 1.96 times, compared to free stream velocity. If the angle was about 0-20° and 50-70° the forcetoward diffuser became high instantly; where as the force toward the rotor will be still and the maximum rate of diffuseraugmentation possibly was 3.62 and rotor power coefficient was 2.14.
CFD Analysis on the Effect of Radial Gap on Impeller-Diffuser Flow Interaction as well as on the Flow Characteristics of a Centrifugal Fan  [PDF]
K. Vasudeva Karanth,N. Yagnesh Sharma
International Journal of Rotating Machinery , 2009, DOI: 10.1155/2009/293508
Abstract: The flow between the impeller exit and the diffuser entry (i.e., in the radial gap is generally considered to be complex). With the development of PIV and CFD tools such as moving mesh techniques, it is now possible to arrive at a prudent solution compatible with the physical nature of flow. In this work, numerical methodology involving moving mesh technique is used in predicting the real flow behavior, as exhibited when a target blade of the impeller is made to move past corresponding vane on the diffuser. Many research works have been undertaken using experimental and numerical methods on the impeller-diffuser interactive phenomenon. It is found from the literature that the effect of radial gap between impeller and diffuser on the interaction and on the performance of the fan has not been the focus of attention. Hence numerical analysis is undertaken in this work to explore and predict the flow behavior due to the radial gap. This has revealed the presence of an optimum radial gap which could provide better design characteristics or lower loss coefficient. It is found that there is a better energy conversion by the impeller and enhanced energy transformation by the diffuser, corresponding to optimum radial gap. The overall efficiency also found to increase for relatively larger gap.
CFD Simulation of Twin Vertical Axis Tidal Turbines System  [cached]
Syed Shah Khalid,Zhang Liang,Sheng Qi-hu
Research Journal of Applied Sciences, Engineering and Technology , 2013,
Abstract: As concerns about rising fossil-fuel prices, energy security and climate-change increase, renewable energy can play a vital role in producing local, clean and inexhaustible energy to supply world rising demand for electricity. In this study, hydrodynamic analysis of vertical axis tidal turbine operating side-by-side is numerically analyzed. Two-dimensional numerical modeling of the unsteady flow through the blades of the turbine is performed using ANSYS CFX, hereafter CFX; this is based on a Reynolds-Averaged Navier-Stokes (RANS) model. The purpose is to find an optimal distance between the turbines where interaction effect is minimal and constructive, where the turbines operate more efficiently than stand alone turbine. A transient simulation is done on Vertical Axis Tidal Turbine (VATT) using the Shear Stress Transport Turbulence (SST) model. Main hydrodynamic parameters like torque T, coefficients of performance CP and coefficient of torque CT are investigated. The gap spacing between the turbines has an important role in performance improvement and also in vortex shedding suppression for the flows around two counters rotating systems. The simulation results are validated with Ye and Calisal data. The results of this study prove that the total power output of a twin-turbine system with an optimal layout can be about 24% higher than two times that of a stand-alone turbine. We conclude that the optimally configured counter-rotating twin turbines should be a side-by-side arrangement.
Diffuser Optimation at Exhaust System with Catalytic Converter for 110 cc Mopet with Fluid Flow CFD Simulation  [PDF]
Tresna P. Soemardi,Ahmad Indra Siswantara,Erwin
Makara Seri Teknologi , 2003,
Abstract: CFD simulation used to get behavior of exhaust gas through catalyst, this result will be used to optimize geometry form to perform uniform stream distribution to catalyst, and CFD Simulation will used to analyze backpressure that happened at the model.
Power generation from wind turbines in a solar chimney  [PDF]
Tudor Foote, Ramesh K. Agarwal
International Journal of Energy and Environment , 2013,
Abstract: Recent studies have shown that shrouded wind turbines can generate greater power compared to bare turbines. A solar chimney generates an upward draft of wind inside a tower and a shroud around the wind turbine. There are numerous empty silos on farms in the U.S. that can be converted to solar chimneys with minor modifications at modest cost. The objective of this study is to determine the potential of these silos/chimneys for generating wind power. The study is conducted through analytical/computational approach by employing the commercial Computational Fluid Dynamics (CFD) software. Computations are performed for five different geometric configurations consisting of a turbine, a cylindrical silo, and/or a venturi and/or a diffuser using the dimensions of typical silos and assuming Class 3 wind velocity. The incompressible Navier-Stokes equations with the Boussinesq approximation and a two equation realizable k – ε model are employed in the calculations, and the turbine is modeled as an actuator disk. The power coefficient (Cp) and generated power are calculated for the five cases. Consistent with recent literature, it was found that the silos with diffusers increase the Cp beyond Betz’s limit significantly and thus the generated power. It should be noted that Cp is calculated by normalizing it by the turbine area swept by the wind. This study shows the potential of using abandoned silos in the mid-west and other parts of the country for localized wind power generation.
Experimental Investigation of Performance of the Wind Turbine with the Flanged-Diffuser Shroud in Sinusoidally Oscillating and Fluctuating Velocity Flows  [PDF]
Kazuhiko Toshimitsu, Hironori Kikugawa, Kohei Sato, Takuya Sato
Open Journal of Fluid Dynamics (OJFD) , 2012, DOI: 10.4236/ojfd.2012.24A024
Abstract: The wind turbine with a flanged-diffuser shroud—so called “wind-lens turbine”—is developed as one of high performance wind turbines by Ohya et al. In this paper, the wind turbine performance is investigated for both steady and unsteady winds. The compact-type wind lens turbine shows higher efficiency than the only rotor wind turbine. Also, the flow structure around the compact-type wind turbine is made clear by CFD and PIV in steady wind. Furthermore, the performances of the only rotor and the compact-type wind-lens turbines for unsteady wind are experimentally and numerically investigated. Experimental and numerical results are presented to demonstrate the dependence of frequency of the harmonic oscillating velocity wind on power coefficient. Consequently, the compact-type wind-lens turbine show better performance than the only rotor one in sinusoidally oscillating velocity wind. Furthermore, the numerical estimation can predict the power coefficient in the oscillating flows to an accuracy of 94% to 102%. In addition, the dependence of the turbine performance on turbulent intensity and vortex scale of natural fluctuating wind is presented.
CFD-Based Performance Analysis and Experimental Investigation of Design Factors of Vertical Axis Wind Turbines under Low Wind Speed Conditions in Thailand  [PDF]
Suchaya Unsakul, Chaianant Sranpat, Pongchalat Chaisiriroj, Thananchai Leephakpreeda
Journal of Flow Control, Measurement & Visualization (JFCMV) , 2017, DOI: 10.4236/jfcmv.2017.54007
Abstract: This paper presents effects of design factors on mechanical performance of Vertical Axis Wind Turbines (VAWTs), and an experimental investigation of optimal VAWT performance under low wind speed conditions in Thailand. Design factors include types of wind turbines, number of blades, types of materials, height-to-radius ratios, and design modifications. Potential VAWT models with different design factors are numerically analyzed within a virtual wind tunnel at various wind speeds by utilizing XflowTM?Computational Fluid Dynamics (CFD) software. The performance curves of each VAWT are obtained as plots of power coefficients against tip speed ratios. It is found that the type of wind turbine, number of blades, and height-to-radius ratio have significant effects on mechanical performance whereas types of materials result in shifts of operating speeds of VAWTs. Accordingly, an optimal VAWT prototype is developed to operate under actual low speed wind conditions. The performance curve from experimental results agrees with the CFD results. The proposed methodology can be used in the computer design of VAWTs to improve mechanical performance before physical fabrication.
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