Energies

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21 pages, 10396 KiB

Open AccessArticle

Performance and Wake Characterization of a Model Hydrokinetic Turbine: The Reference Model 1 (RM1) Dual Rotor Tidal Energy Converter

by Craig Hill, Vincent S. Neary, Michele Guala and Fotis Sotiropoulos

Energies 2020, 13(19), 5145; https://doi.org/10.3390/en13195145 - 02 Oct 2020

Cited by 11 | Viewed by 2443

Abstract

The mechanical power and wake flow field of a 1:40 scale model of the US Department of Energy’s Reference Model 1 (RM1) dual rotor tidal energy converter are characterized in an open-channel flume to evaluate power performance and wake flow recovery. The NACA-63(4)-24 [...] Read more.

The mechanical power and wake flow field of a 1:40 scale model of the US Department of Energy’s Reference Model 1 (RM1) dual rotor tidal energy converter are characterized in an open-channel flume to evaluate power performance and wake flow recovery. The NACA-63(4)-24 hydrofoil profile in the original RM1 design is replaced with a NACA-4415 profile to minimize the Reynolds dependency of lift and drag characteristics at the test chord Reynolds number. Precise blade angular position and torque measurements were synchronized with three acoustic Doppler velocimeters (ADV) aligned with each rotor centerline and the midpoint between the rotor axes. Flow conditions for each case were controlled to maintain a hub height velocity,

u_{h u b} =

1.04 ms

^{- 1}

, a flow Reynolds number,

R e_{D} =

4.4 × 10

^{5}

, and a blade chord length Reynolds number,

R e_{c} =

3.1 × 10

^{5}

. Performance was measured for a range of tip-speed ratios by varying rotor angular velocity. Peak power coefficients,

C_{P} =

0.48 (right rotor) and

C_{P} =

0.43 (left rotor), were observed at a tip speed ratio,

λ =

5.1. Vertical velocity profiles collected in the wake of each rotor between 1 and 10 rotor diameters are used to estimate the turbulent flow recovery in the wake, as well as the interaction of the counter-rotating rotor wakes. The observed performance characteristics of the dual rotor configuration in the present study are found to be similar to those for single rotor investigations in other studies. Similarities between dual and single rotor far-wake characteristics are also observed. Full article

(This article belongs to the Special Issue Fluid Dynamics in Marine and Hydrokinetic Energy System)

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16 pages, 1989 KiB

Open AccessArticle

An Actuator Surface Model to Simulate Vertical Axis Turbines

by Lucy Massie, Pablo Ouro, Thorsten Stoesser and Qianyu Luo

Energies 2019, 12(24), 4741; https://doi.org/10.3390/en12244741 - 12 Dec 2019

Cited by 13 | Viewed by 2272

Abstract

An actuator surface model (ASM) to be employed to simulate the effect of a vertical axis turbine on the hydrodynamics in its vicinity, particularly its wake is introduced. The advantage of the newly developed ASM is that it can represent the complex flow [...] Read more.

An actuator surface model (ASM) to be employed to simulate the effect of a vertical axis turbine on the hydrodynamics in its vicinity, particularly its wake is introduced. The advantage of the newly developed ASM is that it can represent the complex flow inside the vertical axis turbine’s perimeter reasonably well, and hence, is able to predict, with a satisfying degree of accuracy, the turbine’s near-wake, with a low computational cost. The ASM appears to overcome the inadequacy of actuator line models to account for the flow blockage of the rotor blades when they are on the up-stream side of the revolution, because the ASM uses a surface instead of a line to represent the blade. The ASM was used on a series of test cases to prove its validity, demonstrating that first order flow statistics—in our study, profiles of the stream-wise velocity—in the turbine’s vicinity, can be produced with reasonable accuracy. The prediction of second order statistics, here in the form of the turbulent kinetic energy (TKE), exhibited dependence on the chosen grid; the finer the grid, the better the match between measured and computed TKE profiles. Full article

(This article belongs to the Special Issue Fluid Dynamics in Marine and Hydrokinetic Energy System)

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17 pages, 906 KiB

Open AccessArticle

A Formulation of the Thrust Coefficient for Representing Finite-Sized Farms of Tidal Energy Converters

by Karina Soto-Rivas, David Richter and Cristian Escauriaza

Energies 2019, 12(20), 3861; https://doi.org/10.3390/en12203861 - 12 Oct 2019

Cited by 5 | Viewed by 2035

Abstract

Tidal energy converter (TEC) arrays in tidal channels generate complex flow phenomena due to interactions with the local environment and among devices. Models with different resolutions are thus employed to study flows past TEC farms, which consider multiple spatial and temporal scales. Simulations [...] Read more.

Tidal energy converter (TEC) arrays in tidal channels generate complex flow phenomena due to interactions with the local environment and among devices. Models with different resolutions are thus employed to study flows past TEC farms, which consider multiple spatial and temporal scales. Simulations over tidal cycles use mesoscale ocean circulation models, incorporating a thrust coefficient to model the momentum sink that represents the effects of the array. In this work, we propose an expression for a thrust coefficient to represent finite-sized farms of TEC turbines at larger scales,

C_{t F a r m}

, which depends on the spatial organization of the devices. We use a coherent-structure resolving turbulence model coupled with the actuator disk approach to simulate staggered turbine configurations in more detail, varying the separation among devices and the ratios between the channel depths and hub heights. Based on these simulations, we calculate the resultant force for various subsets of devices within the farm, and their corresponding effective thrust coefficient,

C_{t F a r m}

. We conclude that the thrust coefficient depends solely on the lateral separation of the devices,

S_{y}

, for farms with only two rows. For farms with more than two rows, the streamwise distance,

S_{x}

, must be considered as well. With the proposed expression, it is possible to calculate efficiently the effects of finite-sized TEC farms and incorporate a momentum sink into ocean circulation models, without assuming a constant coefficient derived from an infinite farm approximation. Full article

(This article belongs to the Special Issue Fluid Dynamics in Marine and Hydrokinetic Energy System)

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20 pages, 4017 KiB

Open AccessArticle

Wake Characteristics and Power Performance of a Drag-Driven in-Bank Vertical Axis Hydrokinetic Turbine

by Jiyong Lee, Mirko Musa, Chris Feist, Jinjin Gao, Lian Shen and Michele Guala

Energies 2019, 12(19), 3611; https://doi.org/10.3390/en12193611 - 21 Sep 2019

Cited by 6 | Viewed by 2083

Abstract

Preliminary design of a new installation concept of a drag-driven vertical axis hydrokinetic turbine is presented. The device consists of a three-bladed, wheel-shaped, turbine partially embedded in relatively shallow channel streambanks. It is envisioned to be installed along the outer banks of meandering [...] Read more.

Preliminary design of a new installation concept of a drag-driven vertical axis hydrokinetic turbine is presented. The device consists of a three-bladed, wheel-shaped, turbine partially embedded in relatively shallow channel streambanks. It is envisioned to be installed along the outer banks of meandering rivers, where the flow velocity is increased, to maximize energy extraction. To test its applicability in natural streams, flume experiments were conducted to measure velocity around the turbine and power performance using Acoustic Doppler Velocimetry and a controlled motor drive coupled with a torque transducer. The experiment results comprise the power coefficient, the spatial evolution of the mean velocity deficit, and a description of the flow structures generated by the turbine and responsible for the unsteadiness of the wake flow. Applying a triple decomposition on the Reynolds stresses, we identify the dominant contribution to such unsteadiness to be strongly associated with the blade passing frequency. Full article

(This article belongs to the Special Issue Fluid Dynamics in Marine and Hydrokinetic Energy System)

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20 pages, 8388 KiB

Open AccessArticle

On Blockage Effects for a Tidal Turbine in Free Surface Proximity

by Nitin Kolekar, Ashwin Vinod and Arindam Banerjee

Energies 2019, 12(17), 3325; https://doi.org/10.3390/en12173325 - 28 Aug 2019

Cited by 25 | Viewed by 3038

Abstract

Experiments with a three-bladed, constant chord tidal turbine were undertaken to understand the influence of free surface proximity on blockage effects and near-wake flow field. The turbine was placed at various depths as rotational speeds were varied; thrust and torque data were acquired [...] Read more.

Experiments with a three-bladed, constant chord tidal turbine were undertaken to understand the influence of free surface proximity on blockage effects and near-wake flow field. The turbine was placed at various depths as rotational speeds were varied; thrust and torque data were acquired through a submerged sensor. Blockage effects were quantified in terms of changes in power coefficient and were found to be dependent on tip speed ratio and free surface to blade tip clearance. Flow acceleration near turbine rotation plane was attributed to blockage offered by the rotor, wake, and free surface deformation. In addition, particle image velocimetry was carried out in the turbine near-wake using time- and phase-averaged techniques to understand the mechanism responsible for the variation of power coefficient with rotational speed and free surface proximity. Slower wake propagation for higher rotational velocities and increased asymmetry in the wake with increasing free surface proximity was observed. Improved performance at high rotational speed was attributed to enhanced wake blockage, and performance enhancement with free surface proximity was due to the additional blockage effects caused by the free surface deformation. Proper orthogonal decomposition analysis revealed a downward moving wake for the turbine placed in near free surface proximity. Full article

(This article belongs to the Special Issue Fluid Dynamics in Marine and Hydrokinetic Energy System)

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17 pages, 5088 KiB

Open AccessArticle

Experimental and Numerical Investigation of Wake Interactions of Marine Hydrokinetic Turbines

by Clemente Gotelli, Mirko Musa, Michele Guala and Cristián Escauriaza

Energies 2019, 12(16), 3188; https://doi.org/10.3390/en12163188 - 20 Aug 2019

Cited by 17 | Viewed by 2993

Abstract

To study the performance and environmental impacts of marine hydrokinetic (MHK) turbine arrays, we carry out an investigation based on laboratory experiments and numerical models able to resolve the dynamics of turbulent wake interactions and their effects on the river bed. We investigate [...] Read more.

To study the performance and environmental impacts of marine hydrokinetic (MHK) turbine arrays, we carry out an investigation based on laboratory experiments and numerical models able to resolve the dynamics of turbulent wake interactions and their effects on the river bed. We investigate a scaled Sabella D10 mounted on a mobile bed for a single and two aligned turbines, measuring the flow velocity, the rotor angular velocity, and the scour on the sediment bed. Numerical simulations are performed using a detached-eddy simulation (DES) turbulence model coupled with the blade-element momentum (BEM) approach, which can capture the mean flow and resolve the dynamics of turbulent coherent structures in the wakes. The simulations show a good agreement on the velocity statistics obtained experimentally. Power and thrust coefficients for the downstream turbine show an average decrease and a larger variability due to the turbulent intensity produced by the upstream turbine, as compared to the single turbine case. Results of this investigation also provide a framework to assess the predictive capabilities, scope, and applicability of computational models parameterizing the turbines using BEM, for testing different turbine designs and siting strategies within the MHK array. Full article

(This article belongs to the Special Issue Fluid Dynamics in Marine and Hydrokinetic Energy System)

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20 pages, 4464 KiB

Open AccessArticle

Effects of the Current Direction on the Energy Production of a Tidal Farm: The Case of Raz Blanchard (France)

by Van Thinh Nguyen, Alina Santa Cruz, Sylvain S. Guillou, Mohamad N. Shiekh Elsouk and Jérôme Thiébot

Energies 2019, 12(13), 2478; https://doi.org/10.3390/en12132478 - 27 Jun 2019

Cited by 10 | Viewed by 2912

Abstract

This study aims to investigate the influence of the current direction on the energy production of a tidal turbines array. It is based on a three-dimensional (3D) numerical simulation of the flow where the turbines are represented with actuator disks. The case study [...] Read more.

This study aims to investigate the influence of the current direction on the energy production of a tidal turbines array. It is based on a three-dimensional (3D) numerical simulation of the flow where the turbines are represented with actuator disks. The case study consists of modelling the energy extraction of a small array of turbines (staggered and aligned layouts) placed in the Raz Blanchard (Alderney Race, France). The simulations are performed with hydrodynamic data (current magnitude and direction) representative of a mean tide, with several resistance forces and ambient turbulence intensities. The influence of the current direction on the energy production is highlighted by comparing the simulations forced with the real current direction with those in which the angle of incidence between the incoming flow and the turbine’s axis is “switched off” (bi-directional flow). When the flow is aligned with the turbines’ axis (misalignment “switched off”), the staggered layout produces more than the aligned arrangement. Comparison of the two types of simulations (misalignment switched off or not) shows that the misalignment of the flow around a predominant direction reduces the energy produced by the staggered layout and increases the production of the aligned layout. Furthermore, it suggests that the mean energy produced per machine is almost the same for both layouts. Higher turbulence intensity reduces the positive effect of the directional spreading on the aligned layout production and limits the negative effect on the staggered layout production. Full article

(This article belongs to the Special Issue Fluid Dynamics in Marine and Hydrokinetic Energy System)

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24 pages, 7792 KiB

Open AccessArticle

Tip-Bed Velocity and Scour Depth of Horizontal-Axis Tidal Turbine with Consideration of Tip Clearance

by Tianming Zhang, Wei Haur Lam, Yonggang Cui, Jinxin Jiang, Chong Sun, Jianhua Guo, Yanbo Ma, Shuguang Wang, Su Shiung Lam and Gerard Hamill

Energies 2019, 12(12), 2450; https://doi.org/10.3390/en12122450 - 25 Jun 2019

Cited by 10 | Viewed by 3025

Abstract

The scouring by a tidal turbine is investigated by using a joint theoretical and experimental approach in this work. The existence of a turbine obstructs a tidal flow to divert the flow passing through the narrow channel in between the blades and seabed. [...] Read more.

The scouring by a tidal turbine is investigated by using a joint theoretical and experimental approach in this work. The existence of a turbine obstructs a tidal flow to divert the flow passing through the narrow channel in between the blades and seabed. Flow suppression is the main cause behind inducing tidal turbine scouring, and its accelerated velocity is being termed as tip-bed velocity (V_tb). A theoretical equation is currently proposed to predict the tip-bed velocity based on the axial momentum theory and the conservation of mass. The proposed tip-bed velocity equation is a function of four variables of rotor radius (r), tip-bed clearance (C), efflux velocity (V₀) and free flow velocity (V_∞), and a constant of mass flow coefficient (C_m) of 0.25. An experimental apparatus was built to conduct the scour experiments. The results provide a better understanding of the scour mechanism of the horizontal axis tidal turbine-induced scour. The experimental results show that the scour depth is inversely proportional to tip-bed clearance. Turbine coefficient (K_t) is proposed based on the relationship between the tip-bed velocity and the experimental tidal turbine scour depth. Inclusion of turbine coefficient (K_t) into the existing pier scour equations can predict the maximum scour depth of a tidal turbine with an error range of 5–24%. Full article

(This article belongs to the Special Issue Fluid Dynamics in Marine and Hydrokinetic Energy System)

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