Tip Flowfield of a Low Aspect Ratio Circulation Control Wing With Spanwise Variation in Efflux

2012 ◽  
Author(s):  
Matthew Perry ◽  
David Miklosovic
Keyword(s):  
Aspect Ratio ◽  
Vortex Formation ◽  
Stereoscopic Particle Image Velocimetry ◽  
Naval Research ◽  
Circulation Control ◽  
Trailing Edge ◽  
Planar Velocity ◽  
Momentum Coefficient ◽  
Component Velocity ◽  
Jet Interactions

A stereoscopic particle image velocimetry (SPIV) system was used in a low-speed wind tunnel to measure the external flowfield of a circulation control (CC) wing having an aspect ratio of 1.1. This ongoing project, sponsored by the Office of Naval Research, sought to further the knowledge of the jet interactions and the wingtip vortex formation through 3-component, planar velocity surveys. The CC wing tested had a 20% elliptic airfoil section with a trailing edge Coanda surface that was intended to increase circulation control effectiveness through a segmented system that could create spanwise massflow efflux profiles. To date, 1.2 TB of raw SPIV data have been acquired in one of two wake station planes at z/c = 1.25 over the vertical region of 0.13 < y/b < 0.87 (i.e, the tip region). The three-component velocity data revealed the nature of the interaction of the jet with the external flowfield and the temporal variability at an overall momentum coefficient of 0.08 with spanwise variations in the trailing edge efflux. The results from these tests will be used to quantify, for the first time, the effects of spanwise massflow distributions on the 3D velocity field near the trailing edge, the stall modes, jet interactions, and the overall performance of a CC wing of this geometry.

Pneumatic flow control studies using steady blowing on a supercritical aerofoil

2009 ◽  
Vol 113 (1139) ◽  
pp. 53-63
Author(s):  
C. Wong ◽  
K. Kontis
Keyword(s):  
Boundary Layer ◽  
Experimental Studies ◽  
Force Balance ◽  
Boundary Layer Control ◽  
Circulation Control ◽  
Suction Surface ◽  
Trailing Edge ◽  
Momentum Coefficient ◽  
Control Regime ◽  
Layer Control

Abstract Experimental studies have been conducted on a NASA 17-percent thick supercritical aerofoil with a Coanda trailing edge at subsonic speeds in both the boundary-layer control and circulation control regimes. Detailed boundary-layer surveys were performed along the mid span on the suction surface and around the Coanda trailing edge. The wake located at 43% chord-length behind the aerofoil was measured with a single-component hotwire anemometer, and the profile drag coefficients were calculated from the integration of wake momentum deficit. Lift forces and pitching moments were recorded from –20deg to +20deg incidence using a 3-component force balance. In the circulation control regime, the boundary-layer results indicated that separation bubbles are not present at high incidences compared to the boundary-layer control regime, and that minimised the potential for flow separation delay around the Coanda trailing edge. The spectral analysis of the wake showed a significant reduction of wake fluctuations at high incidences and improvement of the stability at the edge of the wake. The study of aerodynamic forces suggested the need to increase the blowing momentum coefficient if the circulation control is used near the stalling angle-of-attack.

The Effect of Pitching Frequency on the Hydrodynamics of Oscillating Foils

2019 ◽  
Vol 86 (10) ◽  
Author(s):  
Arman Hemmati ◽  
Alexander J. Smits
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Strouhal Number ◽  
Vortex Formation ◽  
Free Swimming ◽  
Trailing Edge ◽  
Wake Structure ◽  
Abrupt Transition ◽  
Vortex Streets ◽  
Karman Street

Abstract The effects of two different pitching frequencies (that is, Strouhal number, St) on the wake structure generated by two foils of aspect ratio 1.0 are examined numerically at a Reynolds number of 10,000. Strouhal numbers of 0.5 and 0.2 were studied, the first corresponding approximately to the peak in efficiency and the second corresponding to the point where the thrust is equal to the drag (the free-swimming condition). The two foils have either a square trailing edge or a convex trailing edge that mimics the shape of the caudal fin exhibited by certain species of fish. In previous works, the convex trailing edge panel was found to have higher thrust and efficiency compared with the square panel trailing edge. Here, these differences are related to their characteristic vortex formation and detachment processes leading to differences in wake coherence and extension. The wake of the square panel at St = 0.2 transitions slowly from a reverse von Kármán street (2S) pattern to a paired (2P) system as the wake develops downstream, whereas at St = 0.5, the wake almost immediately takes on a 2P form with an attendant split in the wake structure. For the convex panel, the transition from a 2S to a 2P structure at St = 0.2 is slower than that seen for the square panel, and for St = 0.5, the wake undergoes an abrupt transition leading to two distinct vortex streets that evolve at a considerably slower rate than seen for the square panel.

Experiments on an elliptic circulation control aerofoil

2013 ◽  
Vol 730 ◽  
pp. 99-144 ◽  
Author(s):  
Drew A. Wetzel ◽  
John Griffin ◽  
Louis N. Cattafesta
Keyword(s):  
Outer Region ◽  
Tangential Velocity ◽  
Local Maximum ◽  
Leading Edge ◽  
External Flow ◽  
Wall Jet ◽  
Circulation Control ◽  
Trailing Edge ◽  
Momentum Coefficient ◽  
Similarity Scale

AbstractExperiments are performed on an elliptic circulation control aerofoil in an open-jet wind tunnel facility. The influence of blowing from a single trailing-edge slot on the external flow is assessed using two-component particle image velocimetry (PIV) and steady surface pressure measurements. The test section configuration (open jet or closed wall) significantly affects the leading-edge region of the flow field. PIV is also used to measure the curved wall jet and its interaction with the external flow near the trailing edge. PIV measurements of the curved wall jet reveal mean tangential velocity similarity in the outer region of the flow above the location where the tangential velocity reaches a local maximum. The length and velocity parameters required for similarity scale with the product of the chord Reynolds number and the momentum coefficient in accordance with the recent publication by Stalnov, Kribus & Seifert (J. Renew. Sustain. Energy, vol. 2, 2010, p. 063101). The separation location is also a function of the product of these parameters. The dataset is used to assemble equations to predict the similarity length scales, velocity scales and separation location. These equations compare well with the present measurements.

Effect of Leading Edge Blowing Slots on Stall Angles of a 10:1 Elliptical Airfoil

2010 ◽  
Author(s):  
Jonathan Kweder ◽  
Mary Ann Clarke ◽  
James E. Smith
Keyword(s):  
Aspect Ratio ◽  
Closed Loop ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Circulation Control ◽  
West Virginia University ◽  
Trailing Edge ◽  
Wind Speeds ◽  
Stall Angle

Traditional uses of circulation control have been studied since the early 1960’s and have been developed primarily using trailing edge slots over a rounded trailing edge in order to take advantage of the Coanda˘ effect. The leading edge activated slots allow jets of air to enter the freestream flowing around the airfoil thus enhancing the energy of the lift force. The main purpose of circulation control for fixed wing aircraft is to increase the lifting force when large lifting forces and/or slow speeds are required, such as at take-off and landing. While there is a significant increase in the lifting forces achievable through the use of circulation control, there is also an inherent increase in the drag force on the airfoil (Abramson, 2004, Loth, 1976, 1984). Current effects of circulation control on stall angles of airfoils are not well documented and thus needs to be studied. Stall occurs when a sudden reduction in lift occurs caused by a flow separation between the incoming air flow and the lifting surface. The angle at which this happens is commonly called the critical angle of attack, and is typically between eight and twenty degrees depending on the wing profile, aspect ratio, camber, and planform area. 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 internal plenum pressure. By comparing the non-circulation controlled wing with the active leading edge slot circulation control data, a trend was found as to the influence of the circulation control exit jet on the stall characteristics of the wing. For this specific case, when the circulation control is in use on the 10:1 elliptical airfoil, the stall angle decreases, from eight degrees to six degrees, while providing up to a 46% increase in lift coefficient.

Vortex formation of a finite-span synthetic jet: effect of rectangular orifice geometry

2014 ◽  
Vol 745 ◽  
pp. 180-207 ◽  
Author(s):  
Tyler Van Buren ◽  
Edward Whalen ◽  
Michael Amitay
Keyword(s):  
Aspect Ratio ◽  
Near Field ◽  
Vortex Formation ◽  
Synthetic Jet ◽  
Stereoscopic Particle Image Velocimetry ◽  
Flow Structures ◽  
Geometrical Parameters ◽  
Neck Length ◽  
Finite Span ◽  
Aspect Ratios

AbstractThe formation and evolution of flow structures of a finite-span synthetic jet issuing into a quiescent flow were investigated experimentally using stereoscopic particle image velocimetry (SPIV). The effect of two geometrical parameters, the orifice aspect ratio and the neck length, were explored at a Strouhal number of 0.115 and a Reynolds number of 615. Normalized orifice neck lengths of 2, 4 and 6 and aspect ratios of 6, 12, and 18 were examined. It was found that the effect of the aspect ratio is much larger than the effect of the neck length, and as the aspect ratio increases the size of the edge vortices decreases and the presence of secondary structures is more evident. Moreover, axis switching was observed and its streamwise location increases as the aspect ratio increases. The effect of the neck length on the flow structures and the evolution of the synthetic jet was found to be secondary, where the effect was only in the very near field (i.e. close to the jet’s orifice).

Elliptic Airfoil Stall Analysis With Trailing Edge Slots

2010 ◽  
Author(s):  
Jonathan Kweder ◽  
Mary Ann Clarke ◽  
James E. Smith
Keyword(s):  
Lift Coefficient ◽  
Leading Edge ◽  
Surface Velocity ◽  
Circulation Control ◽  
West Virginia University ◽  
Trailing Edge ◽  
Near Surface ◽  
Wind Speeds ◽  
Edge Location ◽  
Stall Angle

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.

Vortex Analytical Model of a Circulation Controlled Vertical Axis Wind Turbine

2009 ◽  
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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