Large Eddy Simulations of Ventilated Micro Hydrokinetic Turbine

2017 ◽  
Author(s):  
Cosan Daskiran ◽  
Bashar Attiya ◽  
I-Han Liu ◽  
Jacob Riglin ◽  
Alparslan Oztekin
Keyword(s):  
Axial Direction ◽  
Large Eddy Simulations ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Multiphase Model ◽  
Thrust Coefficient ◽  
Tip Speed Ratio ◽  
Hydrokinetic Turbine ◽  
Large Eddy ◽  
Aeration Process

Large eddy simulations of pre-designed micro-hydrokinetic turbine were conducted to investigate the oxygen transfer from air to water. Simulations were performed in extreme conditions having a tip-speed ratio of 3.8 that is higher than the tip-speed ratio at turbine’s design point. Air was injected from the turbine hub downstream in axial direction. Both single phase and multiphase simulations were performed to reveal the influence of air admission on the flow structures and the turbine performance. The mixture multiphase model was employed in multiphase simulation. The results indicated that turbine power generation was reduced roughly 10.5% by air admission, however the torque applied on turbine surface in axial direction did not vary significantly by aeration. The aeration assisted in the suppression of vortices within the flow field. The deviation of the power coefficient and the thrust coefficient was reduced roughly 32% through the inclusion of aeration process.

Micro-Hydrokinetic Turbine Operating in the Vicinity of a Free Surface: Multiphase Large Eddy Simulations

2019 ◽  
Author(s):  
Bashar Attiya ◽  
Muhannad Altimemy ◽  
Cosan Daskiran ◽  
I-Han Liu ◽  
Alparslan Oztekin
Keyword(s):  
Free Surface ◽  
Multiphase Flow ◽  
Froude Number ◽  
Stream Water ◽  
Speed Ratio ◽  
Power Performance ◽  
Thrust Coefficient ◽  
Vof Model ◽  
Hydrokinetic Turbine ◽  
Large Eddy

Abstract Large Eddy Simulation (LES) turbulence and multiphase Volume of Fluid (VOF) model are employed to predict the spatial and temporal characteristics of the turbulent flow structures near micro-hydrokinetic turbine operating in the proximity of a free surface. The turbine power performance and the free surface dynamics, and its interaction with the turbine are characterized by examining the results of both single-phase and multiphase flow simulations. Simulations are conducted at the turbine’s best efficiency point at a tip speed ratio of 1.86 with the rotation rate of 150 rpm and the free stream water velocity of 2.25 m/s. The multiphase flow simulation is carried out at Froude number of 1.06. The results indicate slight interaction between the deformed free surface and the turbine wake structures. Acceleration in the flow velocity is observed near the free surface due to the physical confinement. The results indicate that turbine power generation is reduced by about 2.0%, and the thrust coefficient is reduced by 1.60%. It is demonstrated that the turbine performance at this Froude number is hardly influenced by the presence of the free surface.

scholarly journals Modeling and performance calculation of a horizontal axis wind and hydrokinetic turbine: Numerical study

2018 ◽  
Vol 2 (2) ◽  
pp. 70-79
Author(s):  
Anastas Todorov Yangyozov ◽  
Damjanka Stojanova Dimitrova ◽  
Lazar Georgiev Panayotov
Keyword(s):  
Numerical Study ◽  
Numerical Calculations ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Ansys Cfx ◽  
Hydrokinetic Turbine ◽  
Wide Range ◽  
And Performance ◽  
Performance Calculation

A small turbine, working with air and water to generate electricity, was designed and its performance was reported in this paper. The rotor diameter is 150mm. The numerical calculations of the power coefficient, torque, and tip speed ratio of turbine were carried out for a wide range of inlet velocities. The flow passing through the turbine was investigated with commercial CFD code ANSYS CFX 18

scholarly journals On the Performance of Small-Scale Horizontal Axis Tidal Current Turbines. Part 1: One Single Turbine

2020 ◽  
Vol 12 (15) ◽  
pp. 5985 ◽  
Author(s):  
Ramin Alipour ◽  
Roozbeh Alipour ◽  
Seyed Saeid Rahimian Koloor ◽  
Michal Petrů ◽  
Seyed Alireza Ghazanfari
Keyword(s):  
Tidal Current ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Small Scale ◽  
Ansys Fluent ◽  
Thrust Coefficient ◽  
Tidal Current Energy ◽  
Tip Speed Ratio ◽  
Blade Number ◽  
Stability Performance

The blade number of a current tidal turbine is one of the essential parameters to increase the stability, performance and efficiency for converting tidal current energy into rotational energy to generate electricity. This research attempts to investigate the effect of blade number on the performance of a small-scale horizontal tidal current turbine in the case of torque, thrust coefficient and power coefficient. Towards this end and according to the blade element momentum theory, three different turbines, i.e., two, three and four-bladed, were modeled using Solidworks software based on S-814 airfoil and then exported to the ANSYS-FLUENT for computational flow dynamics (CFD) analysis. SST-K-ω turbulence model was used to predict the turbulence behavior and several simulations were conducted at 2 ≤ tip speed ratio ≤ 7. Pressure contours, turbulence kinetic energy contours, cut-in-speed-curves, and streamlines around the blades and rotors were extracted and compared to provide an ability for a deep discussion on the turbine performance. The results show that in the case of obtainable power, the optimal value of tip speed ratio is around 5, so that the maximum power was achieved for the four-bladed turbine. Out of optimal condition, higher blade number and lower blade number turbines should be used at less than and greater than the optimal values of tip speed ratio, respectively. The results of simulations for the three-bladed turbine were validated against the experimental data with good agreement.

scholarly journals Performance assessment and optimization of a helical Savonius wind turbine by modifying the Bach’s section

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
M. Niyat Zadeh ◽  
M. Pourfallah ◽  
S. Safari Sabet ◽  
M. Gholinia ◽  
S. Mouloodi ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Performance Assessment ◽  
Turbulent Flows ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Basic Model ◽  
Turbine Performance ◽  
Primary Model ◽  
Savonius Wind Turbine

AbstractIn this paper, we attempted to measure the effect of Bach’s section, which presents a high-power coefficient in the standard Savonius model, on the performance of the helical Savonius wind turbine, by observing the parameters affecting turbine performance. Assessment methods based on the tip speed ratio, torque variation, flow field characterizations, and the power coefficient are performed. The present issue was stimulated using the turbulence model SST (k- ω) at 6, 8, and 10 m/s wind flow velocities via COMSOL software. Numerical simulation was validated employing previous articles. Outputs demonstrate that Bach-primary and Bach-developed wind turbine models have less flow separation at the spoke-end than the simple helical Savonius model, ultimately improving wind turbines’ total performance and reducing spoke-dynamic loads. Compared with the basic model, the Bach-developed model shows an 18.3% performance improvement in the maximum power coefficient. Bach’s primary model also offers a 12.4% increase in power production than the initial model’s best performance. Furthermore, the results indicate that changing the geometric parameters of the Bach model at high velocities (in turbulent flows) does not significantly affect improving performance.

Numerical Research on the Characteristics of Lift-Drag Type Vertical Axis Wind Turbine

2012 ◽  
Vol 189 ◽  
pp. 448-452
Author(s):  
Yan Jun Chen ◽  
Guo Qing Wu ◽  
Yang Cao ◽  
Dian Gui Huang ◽  
Qin Wang ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Vertical Axis ◽  
Chord Length ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Tip Speed Ratio ◽  
Middle Range ◽  
Parabolic Form ◽  
Cfd Method

Numerical studies are conducted to research the performance of a kind of lift-drag type vertical axis wind turbine (VAWT) affected by solidity with the CFD method. Moving mesh technique is used to construct the model. The Spalart-Allmaras one equation turbulent model and the implicit coupled algorithm based on pressure are selected to solve the transient equations. In this research, how the tip speed ratio and the solidity of blade affect the power coefficient (Cp) of the small H-VAWT is analyzed. The results indicate that Cp curves exhibit approximate parabolic form with its maximum in the middle range of tip speed ratio. The two-blade wind turbine has the lowest Cp while the three-blade one is more powerful and the four-blade one brings the highest power. With the certain number of blades, there is a best chord length, and too long or too short chord length may reduce the Cp.

Performance study of twisted Darrieus hydrokinetic turbine with novel blade design

2021 ◽  
pp. 1-37
Author(s):  
Mabrouk Mosbahi ◽  
Mouna Derbel ◽  
Mariem Lajnef ◽  
Bouzid Mosbahi ◽  
Zied Driss ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Maximum Power ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Small Scale ◽  
Performance Study ◽  
Hydrokinetic Turbine ◽  
Blade Shape ◽  
Water Turbine ◽  
Water Canals

Abstract Twisted Darrieus water turbine is receiving growing attentiveness for small-scale hydropower generation. Accordingly, the need for raised water energy conversion incentivizes researchers to focalise on the blade shape optimization of twisted Darrieus turbine. In view of this, an experimental analysis has been performed to appraise the efficiency of a spiral Darrieus water rotor in the present work. To better the performance parameters of the studied water rotor with twisted blades, three novel blade shapes, namely U-shaped blade, V-shaped blade and W-shaped blade, have been numerically tested using a computational fluid dynamics three-dimensional numerical model. Maximum power coefficient of Darrieus rotor reaches 0.17 at 0.63 tip-speed ratio using twisted blades. Using V-shaped blades, maximum power coefficient has been risen up to 0.185. The current study could be practically applied to provide more effective employment of twisted Darrieus turbines and to improve the generated power from flowing water such as river streams, tidal currents, or other man made water canals.

Study of Afterburning in Solid Rocket Booster Jet: Towards a Model for Afterburning in Large Eddy Simulations

2014 ◽  
Author(s):  
Adèle Poubeau ◽  
Roberto Paoli ◽  
Daniel Cariolle
Keyword(s):  
Three Dimensional ◽  
Axial Direction ◽  
Large Eddy Simulations ◽  
Chemical Mechanism ◽  
Computational Domain ◽  
Time Step ◽  
Simple Method ◽  
Large Eddy ◽  
Solid Rocket ◽  
Comparison Of The Results

This paper focuses on two decisive steps towards Large Eddy Simulation of a solid rocket booster jet. First, three-dimensional Large Eddy Simulations of a non-reactive booster jet including the nozzle were obtained at flight conditions of 20 km of altitude. A particularly long computational domain (400 nozzle exit diameters in the jet axial direction) was simulated, thanks to an innovative local time-stepping method via coupling multi instances of a fluid solver. The dynamics of the jet is analysed and comparison of the results with previous knowledge validates the simulations and confirms that this computational setup can be applied for Large Eddy Simulations of a reactive booster jet. The second part of this paper details the implementation of a simple method to study the hot plume chemistry. Despite its limitations, it is accurate enough to observe the various steps of the chemical mechanism and assess the effect of uncertainties of the rate parameters on chlorine reactions. It was also used to reduce the set of chemical reactions into a short scheme involving a minimum of species and having a limited impact on the physical time step of the Large Eddy Simulations.

scholarly journals Experimental Investigation of Helical Cross-Flow Axis Hydrokinetic Turbines, Including Effects of Waves and Turbulence

2011 ◽  
Author(s):  
Peter Bachant ◽  
Martin Wosnik
Keyword(s):  
Cross Flow ◽  
Surface Flow ◽  
Frame Rate ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Grid Turbulence ◽  
Flow Axis ◽  
Power Extraction ◽  
Tip Speed Ratio ◽  
Hydrokinetic Turbines

The performance characteristics of two cross-flow axis hydrokinetic turbines were evaluated in UNH’s tow and wave tank. A 1m diameter, 1.25m (nominal) height three-bladed Gorlov Helical Turbine (GHT) and a 1m diameter, four-bladed spherical-helical turbine (LST), both manufactured by Lucid Energy Technologies, LLP were tested at tow speeds up to 1.5 m/s. Relationships between tip speed ratio, solidity, power coefficient (Cp), kinetic exergy efficiency, and overall streamwise drag coefficient (Cd) are explored. As expected, the spherical-helical turbine is less effective at converting available kinetic energy in a relatively low blockage, free-surface flow. The GHT was then towed in waves to investigate the effects of a periodically unsteady inflow, and an increase in performance was observed along with an increase in minimum tip speed ratio at which power can be extracted. Regarding effects of turbulence, it was previously documented that an increase in free-stream homogenous isotropic turbulence increased static stall angles for airfoils. This phenomenon was first qualitatively investigated on a smaller scale with a NACA0012 hydrofoil in a UNH water tunnel, using an upstream grid turbulence generator and using high frame-rate PIV to measure the flow field. Since the angle of attack for a cross-flow axis turbine blade oscillates with higher amplitude as tip speed ratio decreases, any delay of stall should allow power extraction at lower tip speed ratios. This hypothesis was tested experimentally on a larger scale in the tow tank by creating grid turbulence upstream of the turbine. It is shown that the range of operable tip speed ratios is slightly expanded, with a possible improvement of power coefficient at lower tip speed ratios. Drag coefficients at higher tip speed ratios seem to increase more rapidly than in the non-turbulent case.

A Study on Water Pumping by Using a Small Multi-Blades Windmill for Used in a Remote Area

2013 ◽  
Vol 724-725 ◽  
pp. 527-530
Author(s):  
Yuttachai Keawsuntia
Keyword(s):  
Wind Velocity ◽  
Life Time ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Pump System ◽  
Tip Speed Ratio ◽  
Water Pumping ◽  
Overall Efficiency ◽  
Water Base ◽  
Rotor Model

The objective of this research is to study the small multi-blades windmill for water pumping by using a studying performance of windmill which has a curvature plate ratio of 0.07 and determine overall efficiency and evaluate economic of the system. The results from the test run of windmill rotor model in the wind tunnel at a wind velocity of 3 m/s, the windmill give maximum power coefficient of 0.296 at a tip speed ratio of 1.18. The results from the test run of the windmill-pump system at 2 m head have an overall efficiency of 0.239 at the wind velocity of 1.2 m/s. The output of 2.38 L/min, which implies a rate of return for water pumping at 0.038 USD per cubicmetre of water base on 10 year-life time of windmill.

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