Active Circulation Control on the Blunt Trailing Edge Wind Turbine Airfoil

The adoption of blunt trailing edge airfoils for the inner regions of large wind turbine blades has been proposed. Blunt trailing edge airfoils would not only provide increased structural volume, but have also been found to improve the lift characteristics of airfoils and therefore allow for section shapes with a greater maximum thickness. Limited experimental data makes it difficult for wind turbine designers to consider and conduct tradeoff studies using these section shapes. This lack of experimental data precipitated the present analysis of blunt trailing edge airfoils using computational fluid dynamics. Several computational techniques are applied including a viscous/inviscid interaction method and several Reynolds-averaged Navier-Stokes methods.

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The influence of oscillating trailing-edge flap on the dynamic stall control of a pitching wind turbine airfoil

Journal of the Brazilian Society of Mechanical Sciences and Engineering ◽

10.1007/s40430-019-1693-z ◽

2019 ◽

Vol 41 (4) ◽

Cited By ~ 3

Author(s):

Mahbod Seyednia ◽

Mehran Masdari ◽

Shidvash Vakilipour

Keyword(s):

Wind Turbine ◽

Dynamic Stall ◽

Trailing Edge ◽

Wind Turbine Airfoil ◽

Trailing Edge Flap ◽

Stall Control

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Vortex Analytical Model of a Circulation Controlled Vertical Axis Wind Turbine

ASME 2009 3rd International Conference on Energy Sustainability, Volume 2 ◽

10.1115/es2009-90348 ◽

2009 ◽

Cited By ~ 1

Author(s):

Jay P. Wilhelm ◽

Chad C. Panther ◽

Franz A. Pertl ◽

James E. Smith

Keyword(s):

Wind Turbine ◽

Analytical Model ◽

Vertical Axis ◽

Circulation Control ◽

Vertical Axis Wind Turbine ◽

Trailing Edge ◽

Vortex Interactions ◽

Vortex Model ◽

Aspect Ratios ◽

Start Up

A possible method for modeling a Circulation Controlled - Vertical Axis Wind Turbine (CC-VAWT) is a vortex model, based upon the circulation of a turbine blade. A vortex model works by continuously calculating the circulation strength and location of both free and blade vortices which are shed during rotation. The vortices’ circulation strength and location can then be used to compute a velocity at any point in or around the area of the wind turbine. This model can incorporate blade wake interactions, unsteady flow conditions, and finite aspect ratios. Blade vortex interactions can also be studied by this model to assist designers in the avoidance of adverse turbulent operational regions. Conventional vertical axis wind turbine power production is rated to produce power in an operating wind speed envelope. These turbines, unless designed specifically for low speed operation require rotational start-up assistance. The VAWT blade can be augmented to include circulation control capabilities. Circulation control can prolong the trailing edge separation and can be implemented by using blowing slots located adjacent to a rounded trailing edge surface; the rounded surface of the enhanced blade replaces the sharp trailing edge of a conventional airfoil. Blowing slots of the CC-VAWT blade are located on the top and bottom trailing edges and are site-controlled in multiple sections along the span of the blade. Improvements in the amount of power developed at lower speeds and the elimination or reduction of start-up assistance could be possible with a CC-VAWT. In order to design for a wider speed operating range that takes advantage of circulation control, an analytical model of a CC-VAWT would be helpful. The primary function of the model is to calculate the aerodynamic forces experienced by the CC-VAWT blade during various modes of operation, ultimately leading to performance predictions based on power generation. The model will also serve as a flow visualization tool to gain a better understanding of the effects of circulation control on the development and interactions of vortices within the wake region of the CC-VAWT. This paper will describe the development of a vortex analytical model of a CC-VAWT.

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Momentum Analytical Model of a Circulation Controlled Vertical Axis Wind Turbine

ASME 2009 3rd International Conference on Energy Sustainability, Volume 2 ◽

10.1115/es2009-90352 ◽

2009 ◽

Cited By ~ 1

Author(s):

Jay P. Wilhelm ◽

Chad Panther ◽

Franz A. Pertl ◽

James E. Smith

Keyword(s):

Wind Turbine ◽

Analytical Model ◽

Vertical Axis ◽

Power Production ◽

Circulation Control ◽

Vertical Axis Wind Turbine ◽

Trailing Edge ◽

Operating Range ◽

Wind Speeds ◽

Stream Tubes

A possible method for analytically modeling a CC-VAWT (Circulation Controlled Vertical Axis Wind Turbine) is the momentum model, based upon the conservation of momentum principal. This model can consist of a single or multiple stream tubes and/or upwind and downwind partitions. A large number of stream tubes and the addition of the partition can increase the accuracy of the model predictions. The CC-VAWT blade has blowing slots located on the top and bottom trailing edges and have the capability to be site controlled in multiple sections along the span of the blade. The turbine blade, augmented to include circulation control capabilities, replaces the sharp trailing edge of a standard airfoil with a rounded surface located adjacent to the blowing slots. Circulation control (CC), along with a rounded trailing edge, induces the Coanda effect, entraining the flow field near the blowing slots thus preventing or delaying separation. Ultimately, circulation control adds momentum due to the mass flow of air coming out of the blowing slots, but is negligible compared to the momentum of the free stream air passing through the area of the turbine. In order to design for a broader range of operating speeds that will take advantage of circulation control, an analytical model of a CC-VAWT is helpful. The analytical modeling of a CC-VAWT could provide insight into the range of operational speeds in which circulation control is beneficial. The ultimate goal is to increase the range of operating speeds where the turbine produces power. Improvements to low-speed power production and the elimination or reduction of startup assistance could be possible with these modifications. Vertical axis wind turbines are typically rated at a particular ratio of rotational to wind speed operating range. In reality, however, wind speeds are variant and stray from the operating range causing the power production of a wind turbine to suffer. These turbines, unless designed specifically for low speed operation, may require rotational startup assistance. The added lift due to circulation control at low wind speeds, under certain design conditions, will allow the CC-VAWT to produce more power than a conventional VAWT of the same size. Circulation control methods, such as using blowing slots on the trailing edge are modeled as they are applied to a VAWT blade. A preliminary CC-VAWT was modeled using a standard NACA 0018 airfoil, modified to include blowing slots and a rounded trailing edge. This paper describes an analytical momentum model that can be used to predict the preliminary performance of a CC-VAWT.

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Experimental Testing of a Wind Tunnel Model for Use in a Vertical Axis Wind Turbine

Volume 1: Advances in Aerospace Technology ◽

10.1115/imece2010-38816 ◽

2010 ◽

Cited By ~ 2

Author(s):

Chad C. Panther ◽

Kenny A. Williams ◽

Jay P. Wilhelm ◽

James E. Smith

Keyword(s):

Wind Tunnel ◽

Rapid Prototyping ◽

Wind Turbine ◽

Model Building ◽

Experimental Testing ◽

Vertical Axis ◽

Scale Model ◽

Circulation Control ◽

Vertical Axis Wind Turbine ◽

Trailing Edge

Experimental testing was performed on a circulation controlled airfoil with upper and lower trailing edge blowing slots, controlled by span wise pneumatic valves. The augmented blade was designed for application to a circulation controlled vertical axis wind turbine. The design is based upon a conventional NACA0018 shape, replacing the sharp trailing edge with a rounded Coanda surface and blowing slots. A scale model with a chord of 8 inches and span of 16.5 inches was created using an ABS plastic rapid prototyping machine. In the past, circulation control wind tunnel models have been constructed with a separate blowing slot and trailing edge using conventional machining methods. The slot must be tediously aligned along the span for a consistent height which ultimately affects the uniformity and performance of the circulation control jet in combination with the flow rate. The rapid prototyping machine eased fabrication as a modular trailing edge section was printed which includes the Coanda surface, blowing slot, and diffuser all in one piece. Pressure taps were integrated by the prototyping machine into both the printed skin and trailing edge module. This method left additional space inside the model for circulation control valving components and eliminated the need for machining pressure ports. This paper will outline the model building procedures, wind tunnel test rig, and experimental results. Aerodynamic forces were determined by both load cells and surface pressure measurements; the agreement between the two methods will be analyzed and addressed. Test conditions include various angles of attack (±20°) at Cμ = 0, 0.02, 0.06, and 0.10; the test Reynolds number was kept constant at 300K. The results indicate that the blade performed at ΔCl/Cμ near 30 for Cμ = 0.02.

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Wall-Resolved LES Modeling of a Wind Turbine Airfoil at Different Angles of Attack

Journal of Marine Science and Engineering ◽

10.3390/jmse8030212 ◽

2020 ◽

Vol 8 (3) ◽

pp. 212 ◽

Cited By ~ 2

Author(s):

Irene Solís-Gallego ◽

Katia María Argüelles Díaz ◽

Jesús Manuel Fernández Oro ◽

Sandra Velarde-Suárez

Keyword(s):

Boundary Layer ◽

Wind Turbine ◽

Acoustic Waves ◽

Urban Environments ◽

Far Field ◽

Noise Generation ◽

Noise Propagation ◽

Trailing Edge ◽

Wind Turbine Airfoil ◽

Les Model

Noise has arisen as one of the main restrictions for the deployment of wind turbines in urban environments or in sensitive ecosystems like oceans for offshore and coastal applications. An LES model, adequately planned and resolved, is useful to describe the noise generation mechanisms in wind turbine airfoils. In this work, a wall-resolved LES model of the turbulent flow around a typical wind turbine airfoil is presented and described in detail. The numerical results obtained have been validated with hot wire measurements in a wind tunnel. The description of the boundary layer over the airfoil provides an insight into the main noise generation mechanism, which is known to be the scattering of the vortical disturbances in the boundary layer into acoustic waves at the airfoil trailing edge. In the present case, 2D wave instabilities are observed in both suction and pressure sides, but these perturbations are diffused into a turbulent boundary layer prior to the airfoil trailing edge, so tonal noise components are not expected in the far-field noise propagation. The results obtained can be used as input data for the prediction of noise propagation to the far-field using a hybrid aeroacoustic model.

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