scholarly journals Investigating the Level of Fidelity of an Actuator Line Model in Predicting Loads and Deflections of Rotating Blades under Uniform Free-Stream Flow

2021 ◽  
Vol 11 (24) ◽  
pp. 12097
Author(s):  
Nikos Spyropoulos ◽  
George Papadakis ◽  
John M. Prospathopoulos ◽  
Vasilis A. Riziotis
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Stream Flow ◽  
Free Stream ◽  
Viscous Effects ◽  
Complex Flow ◽  
Aeroelastic Simulations ◽  
Helicopter Main Rotor ◽  
Ambient Turbulence ◽  
Blade Loads

In this paper, the accuracy of an in-house Actuator Line (AL) model is tested on aeroelastic simulations of a Wind Turbine (WT) rotor and a helicopter Main Rotor (MR) under uniform free-stream flow. For the scope of aeroelastic analyses, the AL model is coupled with an in-house multibody dynamics code in which the blades are modeled as beams. The advantage from the introduction of CFD analysis in rotorcraft aeroelasticity is related to its capability to account in detail for the interaction of the rotor wake with the boundary layer developed on the surrounding bodies. This has proven to be of great importance in order to accurately estimate the aerodynamic forces and thus the corresponding structural loads and deflections of the blades. In wind turbine applications, a good example of the above is the rotor/ground interaction. In helicopter configurations, the interaction of MR with the ground or the fuselage and the interaction of tail rotor with the duct in fenestron configurations are typical examples. Furthermore, CFD aerodynamic analysis is an obvious modeling option in which the above mentioned asset can be combined with the consideration of the mutual interaction of the rotor with the ambient turbulence. A WT rotor operating inside the atmospheric boundary layer under turbulent free-stream flow is such a case. In the paper, AL results are compared against Blade Element Momentum (BEM) and Lifting Line (LL) model results in the case of the WT, whereas LL and measured data are considered in the helicopter cases. Blade loads and deflections are mainly compared as azimuthal variations. In the helicopter MR cases, where comparison is made against experimental data, harmonic analysis of structural loads is shown as well. Overall, AL proves to be as reliable as LL in the canonical cases addressed in this paper in terms of loads and deflections predictions. Therefore, it can be trusted in more complex flow conditions where viscous effects are pronounced.

Numerical Study of Yawed Wind Turbine Under Unstable Atmospheric Boundary Layer Flows

2020 ◽  
Author(s):  
Dezhi Wei ◽  
Decheng Wan
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Wind Turbine ◽  
Numerical Study ◽  
Atmospheric Stability ◽  
Wind Farms ◽  
Total Power ◽  
Turbulent Structures ◽  
Ambient Turbulence ◽  
Turbine Wake

Abstract Turbine-wake interactions among wind turbine array significantly affect the efficiency of wind farms. Yaw angle control is one of the potential ways to increase the total power generation of wind plants, but the sensitivity of such control strategy to atmospheric stability is rarely studied. In the present work, large-eddy simulation of a two-turbine configuration under convective atmospheric boundary layer is performed, with different yaw angles for the front one, the effect of turbine induced forces on the flow field is modeled by actuator line. Emphasis is placed on wake characteristics and aerodynamic performance. Simulation results reveal that atmospheric stability has a considerable impact on the behavior of wind turbine, wake deflection on the horizontal hub height plane for yawed wind turbine is relatively small, compared with the result of the empirical wake model proposed for wind turbine operating in the neutral stratification, which is attributed to the higher ambient turbulence intensity and large variance of wind direction in the convective condition. And associated with the smaller wake deflection, the total power production does not increase as expected when yawing the upstream turbine. In addition, due to the existence of great quantities of disorganized coherent turbulent structures in the unstable condition, the yaw bearing moment experienced by the downstream wind turbine increases dramatically, even if the rotor plane of the first turbine is perpendicular to the inflow direction.

scholarly journals Optimization of wind augmenters for urban power generation

2021 ◽  
Author(s):  
Hans Hamm
Keyword(s):  
Energy Source ◽  
Porous Medium ◽  
Wind Turbine ◽  
Stream Flow ◽  
Power Efficiency ◽  
Free Stream ◽  
Test Case ◽  
High Demand ◽  
Momentum Loss ◽  
Low Costs

Wind power is the most available renewable energy source to date due to the relatively low costs and advances in the field. Consequently, there is a high demand for innovative wind technology. Furthermore, providing energy near consumers, such as in inner city dwellings and urban settings, provides a more efficient and more reliable energy source. The use of architecture to augment wind energy extraction is still unresolved and the area of research is still in its infancy. The few studies conducted have shown substantial benefits by using buildings to collect wind to increase the power efficiency of wind turbines beyond the Betz limit. This study utilized computational fluid dynamics to analyze building shapes to optimize wind turbine power production. Results indicate an increase in power of up to approximately 4-8 times compared with that for the undisturbed free stream flow. Furthermore, a porous medium was used to simulate the momentum loss due to the presence of the wind turbine. The trends remained similar despite the momentum loss caused by the presence of the wind turbine. The porous medium results showed an increase of power approximately 2-3 times. The study extended the geometry to 3D to support the 2D results. The test case indicated the 3D results had a higher performance in comparison to 2D due to the 3D interactions of the vortex shedding dampening the variance of velocity in the gap region. Furthermore, a certain geometry performs better at different angles of attack providing the optimal geometry will be specifically tailored to the typical wind directions associated with the desired building location.

Effects of Free Stream Turbulence on Intermittent Boundary Layer Flows

1995 ◽  
Author(s):  
Anestis I. Kalfas ◽  
Robin L. Elder
Keyword(s):  
Boundary Layer ◽  
Stream Flow ◽  
Free Stream ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Flow Transition ◽  
Flow Conditions ◽  
Boundary Layer Flows ◽  
Laminar Separation ◽  
Free Stream Turbulence

This paper considers the effects of free stream turbulence intensity on intermittent boundary layer flows related to turbomachinery. The present experimental investigation has been undertaken under free stream flow conditions dominated by grid generated turbulence and Reynolds numbers appropriate for turbomachinery applications. Unseparated flow transition in the boundary layer has been considered using a flat plate with the C4 leading edge which has been designed to avoid laminar separation. This configuration provided the opportunity to study the effect of a realistic turbomachinery leading edge shape on transition. Boundary layer type hot-wire probes have been used in order to acquire detailed information about the effect of the free stream conditions and the leading edge configuration on the structure of the boundary layer. Furthermore, information about the intermittency distribution throughout the boundary layer has been obtained using statistical analysis of the velocity record of the flow field.

Turbulent oscillatory boundary layers at high Reynolds numbers

1989 ◽  
Vol 206 ◽  
pp. 265-297 ◽  
Author(s):  
B. L. Jensen ◽  
B. M. Sumer ◽  
J. Fredsøe
Keyword(s):  
Boundary Layer ◽  
Stream Flow ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Velocity Variation ◽  
Boundary Layer Flows ◽  
Oscillatory Boundary Layer ◽  
Rough Bed ◽  
High Reynolds ◽  
Rough Beds

This study deals with turbulent oscillatory boundary-layer flows over both smooth and rough beds. The free-stream flow is a purely oscillating flow with sinusoidal velocity variation. Mean and turbulence properties were measured mainly in two directions, namely in the streamwise direction and in the direction perpendicular to the bed. Some measurements were made also in the transverse direction. The measurements were carried out up to Re = 6 × 106 over a mirror-shine smooth bed and over rough beds with various values of the parameter a/ks covering the range from approximately 400 to 3700, a being the amplitude of the oscillatory free-stream flow and ks the Nikuradse's equivalent sand roughness. For smooth-bed boundary-layer flows, the effect of Re is discussed in greater detail. It is demonstrated that the boundary-layer properties change markedly with Re. For rough-bed boundary-layer flows, the effect of the parameter a/ks is examined, at large values (O(103)) in combination with large Re.

scholarly journals Optimization of wind augmenters for urban power generation

2021 ◽  
Author(s):  
Hans Hamm
Keyword(s):  
Energy Source ◽  
Porous Medium ◽  
Wind Turbine ◽  
Stream Flow ◽  
Power Efficiency ◽  
Free Stream ◽  
Test Case ◽  
High Demand ◽  
Momentum Loss ◽  
Low Costs

Wind power is the most available renewable energy source to date due to the relatively low costs and advances in the field. Consequently, there is a high demand for innovative wind technology. Furthermore, providing energy near consumers, such as in inner city dwellings and urban settings, provides a more efficient and more reliable energy source. The use of architecture to augment wind energy extraction is still unresolved and the area of research is still in its infancy. The few studies conducted have shown substantial benefits by using buildings to collect wind to increase the power efficiency of wind turbines beyond the Betz limit. This study utilized computational fluid dynamics to analyze building shapes to optimize wind turbine power production. Results indicate an increase in power of up to approximately 4-8 times compared with that for the undisturbed free stream flow. Furthermore, a porous medium was used to simulate the momentum loss due to the presence of the wind turbine. The trends remained similar despite the momentum loss caused by the presence of the wind turbine. The porous medium results showed an increase of power approximately 2-3 times. The study extended the geometry to 3D to support the 2D results. The test case indicated the 3D results had a higher performance in comparison to 2D due to the 3D interactions of the vortex shedding dampening the variance of velocity in the gap region. Furthermore, a certain geometry performs better at different angles of attack providing the optimal geometry will be specifically tailored to the typical wind directions associated with the desired building location.

scholarly journals Large-Eddy Simulation of Wind Turbine Flows: A New Evaluation of Actuator Disk Models

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3745
Author(s):  
Tristan Revaz ◽  
Fernando Porté-Agel
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Wind Turbine ◽  
Wake Flow ◽  
Test Case ◽  
Flow Solver ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Layer Flow ◽  
Advanced Model

Large-eddy simulation (LES) with actuator models has become the state-of-the-art numerical tool to study the complex interaction between the atmospheric boundary layer (ABL) and wind turbines. In this paper, a new evaluation of actuator disk models (ADMs) for LES of wind turbine flows is presented. Several details of the implementation of such models are evaluated based on a test case studied experimentally. In contrast to other test cases used in previous similar studies, the present test case consists of a wind turbine immersed in a realistic turbulent boundary-layer flow, for which accurate data for the turbine, the flow, the thrust and the power are available. It is found that the projection of the forces generated by the turbine into the flow solver grid is crucial for rotor predictions, especially for the power, and less important for the wake flow prediction. In this context, the projection of the forces into the flow solver grid should be as accurate as possible, in order to conserve the consistency between the computed axial velocity and the projected axial force. Also, the projection of the force is found to be much more important in the rotor plane directions than in the streamwise direction. It is found that for the case of a wind turbine immersed in a realistic turbulent boundary-layer flow, the potential spurious numerical oscillations originating from sharp force projections are not harmful to the results. By comparing an advanced model which computes the non-uniform distribution of the turbine forces over the rotor with a simple model which assumes uniform effects of the turbine forces, it is found that both can lead to accurate results for the far wake flow and the thrust and power predictions. However, the comparison shows that the advanced model leads to better results for the near wake flow. In addition, it is found that the simple model overestimates the rotor velocity prediction in comparison to the advanced model. These elements are explained by the lack of local feedback between the axial velocity and the axial force in the simple model. By comparing simulations with and without including the effects of the nacelle and tower, it is found that the consideration of the nacelle and tower is relatively important both for the near wake and the power prediction, due to the shadow effects. The grid resolution is not found to be critical once a reasonable resolution is used, i.e. in the order of 10 grid points along each direction across the rotor. The comparison with the experimental data shows that an accurate prediction of the flow, thrust, and power is possible with a very reasonable computational cost. Overall, the results give important guidelines for the implementation of ADMs for LES.

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