scholarly journals 3D Numerical Study of the Impact of Macro-Roughnesses on a Tidal Turbine, on Its Performance and Hydrodynamic Wake

2021 ◽  
Vol 9 (11) ◽  
pp. 1288
Author(s):  
Ilan Robin ◽  
Anne-Claire Bennis ◽  
Jean-Claude Dauvin
Keyword(s):  
Numerical Study ◽  
Pressure Coefficient ◽  
Turbulence Models ◽  
Numerical Approach ◽  
Turbine Rotor ◽  
Power Coefficient ◽  
Energetic Efficiency ◽  
Tidal Turbines ◽  
Tidal Turbine ◽  
The Impact

Biofouling is an important factor to consider when calculating the energetic efficiency of tidal farms. Despite the fact that biofouling effects have been widely investigated in the past for naval applications, very few studies concern tidal turbines. This paper proposes a numerical approach to assess the impact of biofouling on tidal turbines, which is efficient for testing many configurations. Two turbulence models are tested (RANS k-ω SST and LES Smagorinsky) for the motionless blade case to validate them. Then we chose to use the Smagorinsky model for the case of a complete tidal turbine rotor with realistically fouled blades. The pressure coefficient is strongly affected by the barnacle in the motionless blade case and the power coefficient is slightly degraded in the complete rotor case. Motionless blade cases do not represent the real biofouling behaviour for two reasons. First, sessile species settle in the down flow part of the chord where their impact is less important. Then, the surrounding turbulence provoked by the blades rotation in the rotor case reduces the impact of biofouling. In the wake, biofouling generates small vortexes that propagate into the larger ones, causing them to spread their energy.

Investigation of the Impact of Unsteady Turbulence Effects on the Aeroelastic Analysis of a Low-Pressure Turbine Rotor Blade

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Jan Philipp Heners ◽  
Damian M. Vogt ◽  
Christian Frey ◽  
Graham Ashcroft
Keyword(s):  
Rotor Blade ◽  
Numerical Study ◽  
Turbulence Models ◽  
Gibbs Phenomenon ◽  
Low Pressure ◽  
Turbine Rotor ◽  
Filter Method ◽  
Turbine Rotor Blade ◽  
Low Pressure Turbine ◽  
The Impact

Abstract The impact of the unsteadiness in the considered turbulence quantities on the numerical prediction of the aeroelastic behavior of a low-pressure turbine (LPT) rotor blade is evaluated by means of a numerical study. In this context, one of the main objectives of this work is to compare different nonlinear harmonic balance (HB) approaches—one neglecting and one considering the unsteadiness in the employed turbulence models—with a conventional nonlinear solver of the unsteady Reynolds-averaged Navier–Stokes (URANS) equations in the time domain. In order to avoid unphysical oscillations in the turbulence quantities caused by the Gibbs phenomenon in the chosen HB approach, a filter method based on the Lanczos filter is developed. The developed filter method is applied in the course of the HB simulations considering the unsteadiness in the underlying turbulence model. Furthermore, the impact of its application on the solution of the flow field and on the unsteady surface pressure of the rotor blade, in particular, is discussed in the context of this work.

scholarly journals Comparative analysis of numerical computational techniques for determination of the wind turbine aerodynamic performances

2020 ◽  
pp. 175-175
Author(s):  
Bojan Peric ◽  
Aleksandar Simonovic ◽  
Milos Vorkapic
Keyword(s):  
Wind Turbine ◽  
Pressure Coefficient ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Numerical Approach ◽  
Power Coefficient ◽  
Future Research ◽  
Computational Techniques ◽  
Thrust Coefficient ◽  
Aerodynamic Performances

The purpose of this paper is to explore and define an adequate numerical setting for the computation of aerodynamic performances of wind turbines of various shapes and sizes, which offers the possibility of choosing a suitable approach of minimal complexity for the future research. Here, mechanical power, thrust, power coefficient, thrust coefficient, pressure coefficient, pressure distribution along the blade, relative velocity contoure at different wind speeds and streamlines were considered by two different methods: the blade element momentum (BEM) and computational fluid dynamics (CFD), within which three different turbulence models were analyzed. The estimation of the mentioned aerodynamic performances was carried out on two different wind turbine blades. The obtained solutions were compared with the experimental and nominal (up-scaled) values, available in the literature. Although the flow was considered as steady, a satisfactory correlation between numerical and experimental results was achieved. The comparison between results also showed, the significance of selection, regarding the complexity and geometry of the analyzed wind turbine blade, the most appropriate numerical approach for computation of aerodynamic performances.

Numerical Study of the Wave Impact on a Square Column Using Large Eddy Simulation

2007 ◽  
Author(s):  
H. T. C. Pedro ◽  
K.-W. Leung ◽  
M. H. Kobayashi ◽  
H. R. Riggs
Keyword(s):  
Numerical Study ◽  
Turbulence Models ◽  
Simple Algorithm ◽  
Navier Stokes ◽  
Wave Impact ◽  
Eddy Simulation ◽  
Subgrid Model ◽  
Large Eddy ◽  
Volume Approximation ◽  
The Impact

This work concerns the numerical investigation of the impact of a wave on a square column. The wave is generated by a dam break in a wave tank. Two turbulence models were used: Large Eddy Simulations (LES) and Unsteady Reynolds Averaged Navier-Stokes (URANS). The numerical simulations were carried out using a finite volume approximation and the SIMPLE algorithm for the solution of the governing equations. Turbulence was modeled with the standard Smagorinsky-Lilly subgrid-model for the LES and the standard κ-ε model for the URANS. The results are validated against experimental data for the wave impact on a square column facing the flow. The results, especially for LES, show very good agreement between the predictions and experimental results. The overall accuracy of the LES, as expected, is superior to the URANS. However, if computational resources are limited, URANS can still provide satisfactory results for structural design.

Numerical Analysis of a Rooftop Vertical Axis Wind Turbine

2011 ◽  
Author(s):  
N. Cristobal Uzarraga-Rodriguez ◽  
A. Gallegos-Mun˜oz ◽  
J. Manuel Riesco A´vila
Keyword(s):  
Numerical Analysis ◽  
Wind Turbine ◽  
Numerical Study ◽  
Vertical Axis ◽  
Turbine Rotor ◽  
Aerodynamic Performance ◽  
Power Coefficient ◽  
Vertical Axis Wind Turbine ◽  
Sliding Mesh ◽  
Mesh Model

A numerical analysis of a rooftop vertical axis wind turbine (VAWT) for applications in urban area is presented. The numerical simulations were developed to study the flow field through the turbine rotor to analyze the aerodynamic performance characteristics of the device. Three different blade numbers of wind turbine are studied, 2, 3 and 4, respectively. Each one of the models was built in a 3D computational model. The effects generated in the performance of turbines by the numbers of blades are considered. A Sliding Mesh Model (SMM) capability was used to present the dimensionless form of coefficient power and coefficient moment of the wind turbine as a function of the wind velocity and the rotor rotational speed. The numerical study was developed in CFD using FLUENT®. The results show the aerodynamic performance for each configuration of wind turbine rotor. In the cases of Rooftop rotor the power coefficient increases as the blade number increases, while in the case of Savonius rotor the power coefficient decrease as the blades number increases.

scholarly journals Performance and wake characteristics of a tidal turbine under yaw

2018 ◽  
Vol 1 (1 (Aug)) ◽  
pp. 41-50 ◽  
Author(s):  
P. Modali ◽  
N. S. Kolekar ◽  
A. Banerjee
Keyword(s):  
Center Of Mass ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Thrust Coefficient ◽  
Tip Vortices ◽  
Downstream Distance ◽  
Tidal Turbine ◽  
Yaw Angle

In tidal streams and rivers, the flow of water can be at yaw to the turbine rotor plane causing performance degradation and a skewed downstream wake. The current study aims to quantify the performance variation and associated wake behavior caused by a tidal turbine operating in a yawed inflow environment. A three-dimensional computational fluid dynamics study was carried out using multiple reference frame approach using κ-ω SST turbulence model with curvature correction. The computations were validated by comparison with experimental results on a 1:20 scale prototype for a 0° yaw case performed in a laboratory flume. The simulations were performed using a three-bladed, constant chord, untwisted tidal turbine operating at uniform inflow. Yaw effects were observed for angles ranging from 5° to 15°. An increase in yaw over this range caused a power coefficient deficit of 26% and a thrust coefficient deficit of about 8% at a tip speed ratio of 5 that corresponds to the maximum power coefficient for the tested turbine. In addition, wake propagation was studied up to a downstream distance of ten rotor radius, and skewness in the wake, proportional to yaw angle was observed. At higher yaw angles, the flow around the turbine rotor was found to cushion the tip vortices, accelerating the interaction between the tip vortices and the skewed wake, thereby facilitating a faster wake recovery. The center of the wake was tracked using a center of mass technique. The center of wake analysis was used to better quantify the deviation of the wake with increasing yaw angle. It was observed that with an increase in yaw angle, the recovery distance moved closer to the rotor plane. The wake was noticed to meander around the turbine centerline with increasing downstream distance and slightly deviate towards the free surface above the turbine centerline, magnitude of which varied depending on yaw.

Effect of blade tip grooving on the performance of an axial fan at different tip clearances in the absence and presence of inlet guide vanes

2019 ◽  
Vol 234 (1) ◽  
pp. 72-84
Author(s):  
Masoud Kharati-Koopaee ◽  
Hossein Moallemi
Keyword(s):  
Numerical Study ◽  
Guide Vane ◽  
Pressure Coefficient ◽  
Tip Clearance ◽  
Axial Fan ◽  
Guide Vanes ◽  
Inlet Guide Vanes ◽  
Blade Tip ◽  
Torque Coefficient ◽  
The Impact

This research aims at the numerical study of the blade tip grooving effect on the performance of a ducted axial fan at different tip clearances in the absence and presence of inlet guide vanes. To do this, significant parameters of the fan (i.e. pressure and torque coefficients as well as fan efficiency) comprising single- and double-grooved tips are evaluated and compared with those of the original fan. Validation of the considered numerical model is performed through comparison of the numerical findings with experimental results of a single-stage ducted fan, which comprises a set of 37 guide vane and 24-blade rotor rotating at the speed of 3600 r/min. Results reveal that grooving the blade tip causes the fan parameters to increase and higher fan parameters could be attained adopting single-grooved tip. It is shown that employing grooved blades causes the sensitivity of fan parameters to the change in the tip clearance to diminish. Results exhibit that the impact of grooving the blade on the reduction of sensitivity of fan parameters to the change in the tip clearance for the single-grooved tip in the absence of guide vanes is more remarkable than the other cases and in this case, as the tip clearance increases from the lower to the upper considered value, the decreased percentages in pressure coefficient, torque coefficient, and fan efficiency are 29.8%, 8.9%, and 22.8%, respectively. Numerical findings show that the influence of grooving the blade on the fan parameters in the presence of guide vanes is lower than that without guide vanes and in the presence of guide vanes, the highest average increase percentages in pressure coefficient, torque coefficient, and fan efficiency relative to those of the original fan, which is observed in the single grooved tip, are 3.1%, 1.4%, and 1.7%, respectively.

Experimental study of the duct-effects of the tidal current turbines in multi-row-staggered layout

2020 ◽  
Author(s):  
Yaling Chen ◽  
Binliang Lin ◽  
Jinxi Guo
Keyword(s):  
Tidal Current ◽  
Turbine Rotor ◽  
Power Performance ◽  
Tidal Current Energy ◽  
Tidal Turbines ◽  
Initial Stage ◽  
Tidal Turbine ◽  
Wake Zone ◽  
The Stability ◽  
Current Energy

<p>Tidal turbine array was optimized to increase the power production in order to improve the commercial competitivity of tidal current energy with other forms of energy generation. Due to duct-effects, the power performance of turbines in the staggered layout was better than that of the aligned layout. However, shear layer with enhanced turbulence occurred between the duct zone and isolated wake zone downstream, which had influence on the performance stability and increased the fatigue failure of tidal turbines. The study conducted a series of laboratory experiments to investigate the duct-effects of tidal turbines located in multi-row array with staggered layout. The turbine rotor was represented by porous disc. The flow thrust and time-varying velocity were measured using micro strain gauge and acoustic doppler velometer, respectively. Results showed that the flow was accelerated between turbines with the increment around 20% behind the first row, while the duct-effects were weakened as distance increased downstream. The shear-induced turbulence was enlarged by the duct-effect when it diffused mainly towards individual wake zone at the initial stage. As the turbulence filled the whole individual wake zones, it diffused rapidly to lateral sides and jointed together, and the turbulence intensity across the array wake was significantly higher than that of the free flow. Correspondingly, the performance of turbine rotor located downstream was improved limitedly by the duct-effects, and the stability was reduced clearly. It indicated that the advantage of the duct-effect induced in the staggered layout was limited in the near wake as the lateral interval between two turbine centres was 2 times of rotor diameter.</p><p>Keywords<strong>:</strong> Turbine rotor array; Staggered layout; Duct-effects; Turbine performance; Shear-induced turbulence</p>

Numerical Analysis of Blockage Ratio Effect on a Portable Hydrokinetic Turbine

2016 ◽  
Author(s):  
Cosan Daskiran ◽  
Jacob Riglin ◽  
Alparslan Oztekin
Keyword(s):  
Free Stream ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Power Coefficient ◽  
Stream Velocity ◽  
Blockage Ratio ◽  
Ratio Effect ◽  
Turbine Performance ◽  
Hydrokinetic Turbine

Three-dimensional steady state Computational Fluid Dynamics (CFD) analyses were performed for a pre-designed micro-hydrokinetic turbine to investigate the blockage ratio effect on turbine performance. Simulations were conducted using a physical turbine rotor geometry rather than low fidelity, simplified actuator disk or actuator lines. The two-equation k-ω Shear Stress Transport (SST) turbulence model was employed to predict turbulence in the flow field. The turbine performance at the best efficiency point was studied for blockage ratios of 0.49, 0.70 and 0.98 for three different free stream velocities of 2.0 m/s, 2.25 m/s and 2.5 m/s. Distinct blockage ratio results at a free stream velocity of 2.25 were compared to a previous numerical study incorporating the same rotor geometry within an infinite flowing medium. The pressure gradient between turbine upstream and turbine downstream for blocked channel flows elevated the turbine performance. The increment in blockage ratio from 0.03 to 0.98 enhanced power coefficient from 0.437 to 2.254 and increased power generation from 0.56 kW to 2.86 kW for the present study.

The Influence of Roughness on a High-Pressure Steam Turbine Stage: An Experimental and Numerical Study

2014 ◽  
Author(s):  
Juri Bellucci ◽  
Filippo Rubechini ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Lorenzo Arcangeli ◽  
...  
Keyword(s):  
High Pressure ◽  
Steam Turbine ◽  
Numerical Study ◽  
Practical Interest ◽  
Numerical Approach ◽  
Fine Tuning ◽  
High Pressure Steam ◽  
Pressure Steam ◽  
High Pressure Stage ◽  
The Impact

This work deals with the influence of roughness on high-pressure steam turbine stages. It is divided in three parts. In the first one, an experimental campaign on a linear cascade is described, in which blade losses are measured for different values of surface roughness and in a range of Reynolds numbers of practical interest. The second part is devoted to the basic aspects of the numerical approach, and consists of a detailed discussion of the roughness models used for computations. The fidelity of such models is then tested against measurements, thus allowing their fine-tuning and proving their reliability. Finally, comprehensive CFD analysis is carried out on a high-pressure stage, in order to investigate the influence of roughness on the losses over the entire stage operating envelope. Unsteady effects that may affect the influence of the roughness, such as the upcoming wakes on the rotor blade, are taken into account, and the impact of transition-related aspects on the losses is discussed.

Numerical Prediction of the Hydrodynamic Performance of a Horizontal Tidal Turbines

2015 ◽  
Author(s):  
Cheng Liu ◽  
Changhong Hu
Keyword(s):  
Power Efficiency ◽  
Turbulence Models ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Renewable Energy Resources ◽  
Tidal Current Energy ◽  
Tidal Turbines ◽  
Critical Issues ◽  
Tidal Turbine ◽  
Sst Turbulence Model

Tidal current energy is one of the most promising renewable energy resources. The prediction of the hydrodynamic loads and power efficiency are the critical issues for verifying the new designs. Besides, Optimization of turbine arrangement is important for a tidal turbine farm. The hydrodynamic behavior of a turbine operating in the wake of an upstream turbine needs to clarify. In this paper we present a CFD approach in which the CFD library of OpenFOAM is utilized for prediction of the performance of a three bladed horizontal axis tidal turbine (HATT) in a test tunnel environment. The Reynolds Average Navier Stokes (RANS) equation with Shear Stress Transport (SST) turbulence model is applied. The steady-state solver is tested for present numerical simulation. The Multi Reference Framework (MRF) method is adopted for dealing with grid relative rotation. Turbulence models effects and the mesh generation are well described. The resultant power and thrust coefficients of these simulations are compared with experimental results at various tip speed ratios (TSRs).

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