Gust load alleviation on an aircraft wing by trailing edge Circulation Control

Circulation control (CC) is a high-lift methodology that can be used on a variety of aerodynamic applications. This technology has been in the research and development phase for over sixty years primarily for fixed wing aircraft where the early models were referred to as “blown flaps”. Circulation control works by increasing the near surface velocity of the airflow over the leading edge and/or trailing edge of a lifting surface This phenomenon keeps the boundary layer jet attached to the wing surface thus increasing the lift generated on the surface. The circulation control airflow adds energy to the lift force through conventional airfoil lift production and by altering the circulation of stream lines around the airfoil. For this study, a 10:1 aspect ratio elliptical airfoil with a chord length of 11.8 inches and a span of 31.5 inches was inserted into the West Virginia University Closed Loop Wind Tunnel and was tested at varying wind speeds (80, 100, and 120 feet per second), angle of attack (zero to sixteen degrees), and blowing coefficients, ranging from 0.0006 to 0.0127 depending on plenum pressure. By comparing the non-circulation controlled wing with the active circulation control data, a trend was found as to the influence of circulation control on the stall characteristics of the wing for trailing edge active control. For this specific case, when the circulation control is in use on the 10:1 elliptical airfoil, the stall angle decreased, from eight degrees to six degrees, while providing a 70% increase in lift coefficient. It should be noted that due to the trailing edge location of the circulation control exit jet, a “virtual” camber is created with the free stream air adding length to the overall airfoil. Due to this phenomena, the actual stall angle measured increased from eight degrees on the un-augmented airfoil, to a maximum of twelve degrees.

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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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AMELIA CESTOL Test: Acoustic Characteristics of Circulation Control Wing with Leading- and Trailing-Edge Slot Blowing

51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition ◽

10.2514/6.2013-978 ◽

2013 ◽

Cited By ~ 4

Author(s):

William Horne ◽

Nathan Burnside

Keyword(s):

Circulation Control ◽

Trailing Edge ◽

Acoustic Characteristics

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Active Circulation Control on the Blunt Trailing Edge Wind Turbine Airfoil

AIAA Journal ◽

10.2514/1.j056223 ◽

2018 ◽

Vol 56 (2) ◽

pp. 554-570 ◽

Cited By ~ 6

Author(s):

He-Yong Xu ◽

Chen-Liang Qiao ◽

Hui-Qiang Yang ◽

Zheng-Yin Ye

Keyword(s):

Wind Turbine ◽

Circulation Control ◽

Trailing Edge ◽

Blunt Trailing Edge ◽

Wind Turbine Airfoil

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2D Parametric Study Using CFD of a Circulation Control Inlet Guide Vane

Volume 6: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-28058 ◽

2007 ◽

Cited By ~ 2

Author(s):

H. E. Hill ◽

W. F. Ng ◽

P. P. Vlachos ◽

S. A. Guillot ◽

D. Car

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Pressure Ratio ◽

Operating Conditions ◽

Circulation Control ◽

Trailing Edge ◽

Pressure Losses ◽

Supply Pressure ◽

Edge Radius

Circulation control inlet guide vanes (IGVs) may provide significant benefits over current IGVs that employ mechanical means for flow turning. This paper presents the results of a two-dimensional computational study on a circulation control IGV that takes advantage of the Coanda effect for flow vectoring. The IGV in this study is an uncambered airfoil that alters circulation around itself by means of a Coanda jet that exhausts along the IGV’s trailing edge surface. The IGV is designed for an axial inlet flow at a Mach number of 0.54 and an exit flow angle of 11 degrees. These conditions were selected to match the operating conditions of the 90% span section of the IGV of the TESCOM compressor rig at the Compressor Aero Research Laboratory (CARL) located at Wright-Patterson AFB, the hardware that is being used as the baseline in this study. The goal of the optimization was to determine the optimal jet height, trailing edge radius, and supply pressure that would meet the design criteria while minimizing the mass flow rate and pressure losses. The optimal geometry that was able to meet the design requirements had a jet height of h/Cn = 0.0057 and a trailing edge Radius R/Cn = 0.16. This geometry needed a jet to inflow total pressure ratio of 1.8 to meet the exit turning angle requirement. At this supply pressure ratio the mass flow rate required by the flow control system was 0.71 percent of the total mass flow rate through the engine. The optimal circulation control IGV had slightly lower pressure losses when compared with a reference cambered IGV.

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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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