On the performance of a micro-scale Bach-type turbine as predicted by discrete-vortex simulations (original) (raw)
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Energies
Horizontal axis turbines are commonly used for harnessing renewable hydrokinetic energy, contained in marine and river currents. In order to encourage the expansion of electricity generation using micro-hydrokinetic turbines, several design improvements are investigated. Firstly, optimization-based design of rotor blade is used to get as close as possible to the efficiency limit of 59.3% (known as Betz limit), that counts for bare turbine rotors, placed in the free flow. Additional diffuser elements are further added to examine the potential to overcome the theoretical efficiency limit by accelerating water at the axial direction. Various diffuser geometrical configurations are investigated using the computational fluid dynamics (CFD) to obtain insight into hydrodynamics of augmented micro-hydrokinetic turbines. Moreover, the turbines are compared from the energy conversion efficiency point of view. The highest maximum power coefficient increase of 81% is obtained with brimmed (flan...
Characterization of a micro-hydrokinetic turbine in close proximity to the free surface
Ocean Engineering, 2015
Predicting hydrokinetic turbine power generation is difficult due to complex geometry, highly turbulent conditions, and difficulty capturing the transient interface existing between air and water.A threedimensional finite volume solver was used to capture the effects resulting from free surface interaction with the aid of a Volume of Fluid(VOF) multiphase solver.Depths from free surface level to blade tip with corresponding Froude numbers of 0.71, 0.92, 1.04, and 1.31 were modelled specifically to capture the transition from subcritical to supercritical flow conditions.A sharp decrease in performance was observed at the critical Froude number (Fr=1.0).Results at subcritical conditions showed acceptable agreement with previously published single phase results where the turbine is assumed to be operating in aninfinite medium.At subcritical conditions, the propeller-based turbine studied was compared to numerical and experimental results obtained for a traditional marine current turbine (MCT).As the flow became critical, a 32.2% decrease in the power coefficient was predicted and significant wake-free surface interaction was observed.
The Efficiency Comparison of Hydro Turbines for Micro Power Plant from Free Vortex
Energies
In this research paper, the relationship between a crossflow turbine and propeller turbine size changes and the pond size in a free vortex power generation system was investigated. This relationship can be written in the form of a new mathematical equation using the principles of the response surface methodology (RSM) method. This study aimed to compare the efficiency of a crossflow turbine and propeller turbine to enhance a micro power plant from free vortex. The pond size in a micro power plant from free vortex was 1 m in diameter and 0.5 m in height with a 0.2 m outlet drain at the bottom. All turbines were tested at different water flowrates of 0.2, 0.3, 0.4, 0.5, and 0.6 m3/s to identify the rpm, water head, voltage, and electric current to access the waterpower, power output, and overall efficiency. At a 0.02 m3/s water flowrate, the crossflow turbine had greater overall efficiency than the propeller turbine, reaching 9.09% efficiency. From the comparison of the results of the...
Numerical analysis of a shrouded micro-hydrokinetic turbine unit
Journal of Hydraulic Research, 2015
Computational fluid dynamics simulations were conducted for two diffuser designs that were added to a pre-existing horizontal axis hydro-kinetic turbine design. The two diffuser designs investigated in the present study had the area ratio values of 1.36 and 2.01. Each design used a short axial length to satisfy system portability constraints. The turbine-diffuser systems steady-state performance characteristics were assessed numerically. A structured, hexahedral mesh was employed to discretize the equations governing the fluid motion. Turbulent flow structures were captured through the implementation of the k-ω Shear Stress Transport (SST) model. A 39.5% and 55.8% increase in output mechanical power was observed versus the un-augmented turbine performance. As the area ratio increases from 1.36 to 2.01, the total thrust experienced by the unit nearly doubles.
Numerical simulation of 3D flow past a real-life marine hydrokinetic turbine
Advances in Water Resources, 2012
We simulate three-dimensional, turbulent flow past an axial-flow marine hydrokinetic (MHK) turbine mounted on the bed of a rectangular open channel by adapting a computational framework developed for carrying out high-resolution large-eddy simulation (LES) in arbitrarily complex domains involving moving or stationary boundaries. The complex turbine geometry, including the rotor and all stationary components, is handled by employing the curvilinear immersed boundary (CURVIB) method . Velocity boundary conditions near all solid surfaces are reconstructed using a wall model based on solving the simplified boundary layer equations . To demonstrate the capabilities of the model we apply it to simulate the flow past a Gen4 axial flow MHK turbine developed by Verdant Power for the Roosevelt Island Tidal Energy (RITE) project in the East River in New York City, USA. We carry out systematic grid refinement studies, using grids with up to 185 million nodes, for only the turbine rotor placed in an infinite free stream to show that the computed torque converges to a grid insensitive value, which is in good agreement with field measurements. We also carry out LES for the complete turbine configuration, including the pylon, nacelle and rotor, mounted on the bed of a straight rectangular open channel. The computed results illustrate the complexity of the flow and show that the power output of the complete turbine is primarily dependent on the rotor geometry and tip speed ratio, and is not affected by the stationary components of the turbine and the presence of the channel bed. The complete turbine simulation also reveals that the downstream wake of the turbine consists of three main regions: (1) the outer layer with the spiral blade tip vortices rotating in the same direction as the blades; (2) the counter-rotating inner layer surrounded by the spiral tip vortices; and (3) the core layer co-rotating with respect to the tip vortices. This study is the first to report the three-dimensional wake structure of MHK turbines.
Many modifications have been made on conventional hydrokinetic turbines rotor blades to improve the performances. The rotor blade modification in this research paper is a blade combination where the circle-shaped conventional model is combined with the one of a concave elliptical model. Two different blade geometries have been analyzed using a detailed computational Fluid Dynamics approach. The blade design will affect the simplicity of construction and cost of manufacture of turbine rotors. The aim is to analyze the influence of the blade combination towards the performance of hydrokinetic turbine for installation at a selected site. The research includes experimental method using open-type water tunnel of rotor's prototype with 2 different blade models of similar dimensions. The experiment shows, there are influences of the modification of the rotor blade to the performances of the turbine. The optimized blade design improves the performances of the Tip Speed Ratio (TSR) by 78 % while the Coefficient of thrust (CT) is improved by 58.3% at peak co-efficient of performance value of 0.47 for both the blade designs.
Performance Analysis of a Low Head Water Vortex Turbine
MIST journal of science and technology, 2021
A small hydropower plant is an environment-friendly renewable energy technology. The run-of-river type gravitational water vortex turbine can be designed to produce electricity at sites with low water heads. In this study, an experimental investigation was undertaken on this type of turbine with a water tank and a runner which is connected to a shaft. At the end of the shaft, a rope brake was attached to measure the output power, torque and overall efficiency of the vortex turbine by varying flow rates. The designed vortex turbine can achieve an overall efficiency of 52.67%. The experimental results were validated with available data in the literature and theories associated with the turbine. The results also showed that the flow rate plays a vital role in generating power, torque as well as overall efficiency. The project was completed using local resources and technologies. Moreover, as water is used as the input power, this project is eco-friendly which has no adverse effect on the environment.
Gravity-Driven Vortex Turbines for Small Scale Hydraulic Power Stations
Large scale hydraulic power stations relying on dams and reservoirs are under severe criticism due to environmental considerations and agricultural and historical heritage areas they flood, although are “renewable” energy sources. However, the Earth is rich in smaller streams and water sources which flow with moderate slopes and when collected together, represent an significant and globally distributed energy source for the World. This paper aims to present an analysis of such an alternative hydraulic power plant: Gravity-driven vortex turbine power plants. They exploit the “sink” or “bathtub” vortices that are created by the tangential component of the inward flow and/or naturally created by the Coriolis acceleration. A turbine to extract energy is placed at the hub of the sink vortex, where it is in a configuration that perfectly fits to the Eulerian mathematical model for a radial flow hydraulic turbine. It is also environment-friendly since it does not obstruct fish migration and provides aeration of the water. An inviscid, two-dimensional analysis shall be made to demonstrate the relevant parameters and a prototype application will be presented.
Design of A Micro Hydro Power Plant Based on The Vortex Flow of Water
This research focuses on the gravitational creation of a water vortex stream, which is a novel technique in hydropower engineering. The water enters a wide straight inlet and then through a vertical conical tube, creating a vortex that exits at the shallow basin's centre floor. The blades of the turbine can spin in the vortex, which generates electricity from a generator. The gravitational vortex turbine is the name for this kind of turbine. The turbine is driven by the vortex's dynamic force rather than the pressure differential. Since no discretization of the flow domain is needed, this study relies on simulation to provide the specifics of water vortex creation. The computational fluid dynamics (CFD) models' boundary conditions are added depending on the experiment configuration. Two different hole sizes for water discharge were tested in two different environments. The first condition's effect shows that the vortex heights in the experiment and CFD agree. The final vortex height of the CFD model differs from the experiment outcome in the second condition. More turbulent flow has set in as the discharge hole becomes larger, creating more errors in the CFD model's prediction of water vortex formation.
Transient analysis of micro-hydrokinetic turbines for river applications
Ocean Engineering, 2017
Transient simulations are conducted to characterize a single turbine and multiple turbines in an inline and a staggered array using k-ω shear-stress transport (SST) turbulence model. Performance characteristics predicted by transient analysis at various operating conditions were compared to those predicted by steady-state analysis. Transient results indicated that a power coefficient of 0.43 would be generated at the best efficiency point which corresponds to 1.4% deviations between transient and steady-state solutions for a single unit. Flow separation is observed at the tip speed ratio lower than that at the design point. The relative power of the upstream turbine is obtained to be nearly unity in both inline and staggered arrays. The relative power of the downstream turbine in the staggered array is not influenced by the presence of the upstream turbine and it is the same as that of the upstream turbine. On the other hand, the relative power of the downstream turbine in an inline array is reduced to 0.18 at a downstream separation of 6D t. The massive drop in the power generation by the downstream turbine resulted from the presence of strong wake flow induced by the upstream turbine.