Wind Tunnel Testing of Jets and Tabs for Active Load Control of Wind Turbine Blades

Cooperman, Aubryn; Brunner, Matthew J.; Dam, C. van

doi:10.2514/6.2012-1024

Cited by 17 publications

(11 citation statements)

References 8 publications

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“…In conjunction, an increase in suction can be observed on the lower surface, with peak suction increased from CP,min = -0.39 to -0.92. The same trend can be noted in the work of Cooperman et al 32 . The lack of pressure taps beyond x/c = 0.94 means that the pressure difference across the mini-tab and the pressure difference at the trailing edge could not be analysed fully, however the trends in the data presented suggests that a pressure difference is present at the trailing edge.…”

Section: Pressure Measurementssupporting

confidence: 86%

An Experimental Study of Mini-Tabs for Aerodynamic Load Control

Heathcote¹,

Gursul²,

Cleaver³

2016

54th AIAA Aerospace Sciences Meeting

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Aircraft and wind turbines are exposed to increased loads during gusts and turbulence, necessitating a stronger and stiffer structure. The field of aerodynamic load control aims to reduce this need, mitigating the extreme loads at the fluid structure interface. Force, Particle Image Velocimetry and pressure measurements were conducted on a NACA0012 airfoil equipped with mini-tabs, small span-wise tabs that were to the airfoil's upper surface, at a Reynolds number of 6.61 x 10 5 . Mini-tabs of height h/c = 0.02 and 0.04 were employed across a range of chord-wise locations to investigate the effects of mini-tab height and chord-wise position. Overall, the mini-tab was found to have a lift reducing effect which increased with height. It was found that the effect of the chord-wise location was highly dependent on the angle of attack. Placement close to the trailing edge induced a large effect at zero degrees. Peak suction over the lower surface increased resulting in a reduction of ΔCL = -0.48. Approaching stall, effectiveness decreased as the mini-tab became immersed in the separated flow. Placement at xf/c = 0.60 produced an almost constant lift reduction between α = 0° and 5° of ΔCL ≈ -0.60, with a gradual reduction to stall. A mini-tab positioned close to the leading edge (xf/c = 0.08) was found to separate the flow effectively at low incidences but with no noticeable change in lift observed. It was found that the flow separation produced by the minitab effectively eliminated the suction peak on the upper surface. However, placement close to the leading edge has increasing effectiveness towards stall, as the shear layer induced by the separation was displaced further from airfoil surface. Peak lift reduction at stall was found to be ΔCL ≈ -0.67. The optimum chord-wise location for peak lift reduction is dependent on the airfoil angle of attack: the position of the mini-tab for maximum lift reduction moves towards the leading edge as the angle of attack increases.

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Section: Pressure Measurementssupporting

confidence: 86%

An Experimental Study of Mini-Tabs for Aerodynamic Load Control

Heathcote¹,

Gursul²,

Cleaver³

2016

54th AIAA Aerospace Sciences Meeting

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“…For both airfoils, the flow conditions are Re = 1.8 × 10 6 and α = 0 ° with the simulations conducted fully turbulent. For the NACA 0012, the computation value of drag matched the experimental interpolated value of C D = 0.0097 . For the NACA 0018, OVERFLOW‐2 over predicts the value for the drag; the experiment showed the drag to be C D = 0.0091, whereas OVERFLOW‐2 calculated it to be C D = 0.0109.…”

Section: Validationmentioning

confidence: 61%

“…Microjets were also tested experimentally in the UC Davis Aeronautical Wind Tunnel, using a model designed as a test‐bed for AALC systems . The airfoil has a modified S819 profile in which the thickness at 95% chord has been doubled, with suitable smoothing applied, to allow installation of trailing edge devices.…”

Section: Validationmentioning

confidence: 99%

Comparison of pneumatic jets and tabs for Active Aerodynamic Load Control

Blaylock¹,

Chow²,

Cooperman³

et al. 2013

Wind Energy

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A fast, efficient way to control loads on utility scale wind turbines is important for the growth of the wind industry. Microtabs and microjets are two Active Aerodynamic Load Control devices, which address this need. Both act perpendicular to the surface of the airfoil, and these actively controlled devices are used to mitigate changes in aerodynamic loading experienced by wind turbine rotors due to wind gusts, wind shear, or other atmospheric phenomena. This work explores the aerodynamic effects of microjets and then compares them to those of microtabs. Flow around an airfoil with an activated microjet at the trailing edge has been simulated using the Reynolds-averaged Navier-Stokes solver OVERFLOW-2. Using a Chimera overset grid topology, a microjet has been placed near the trailing edge of the lower surface of a NACA 0012 airfoil. For a jet velocity about half of the freestream velocity, the microjet can change the lift up to ΔC L = 0.2, but the amount of change varies with the momentum coefficient of the jet. The change in lift is not symmetric for positive and negative angles of attack due to changes in the boundary layer thickness with angle of attack. Increasing the Reynolds number reduces the effectiveness of the microjet only slightly. The effects of jet velocity, jet activation time, and airfoil angle of attack on airfoil lift, drag, and pitching moment are compared with previous work, which illustrates the deployment of a microtab at the 95% chord location of a NACA 0012 airfoil. This study shows that microjets and microtabs have very similar responses in lift and pitching moment, but the drag for the microjet is noticeably lower.

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“…7 To provide more internal volume for instrumentation, the chord thickness gradually increases from the mid-chord to double the original S819 thickness at 0.95 , tapering smoothly to a sharp trailing edge. The red contour around the trailing edge on Figure 3 shows the modification.…”

Section: Figure 2 Left) Uc Davis Aeronautical Wind Tunnel; Right) Momentioning

confidence: 99%

“…The S819m is a stall regulated wind turbine blade airfoil previously used at UC Davis to study trailing edge blowing and microtabs. 7 It is constructed of six spanwise milled aluminum sections that can be separated to access 1/32 diameter pressure taps along the central line. The root mounts to the pyramidal force balance below the test section.…”

Section: Figure 2 Left) Uc Davis Aeronautical Wind Tunnel; Right) Momentioning

confidence: 99%

Low-Cost Detection of Boundary Layer Separation with Dynamic Pressure Measurements

Edelman

Pensado

Dam

2016

8th AIAA Flow Control Conference

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Passive flow control methods are widely deployed on aircraft and active control methods are now being considered for application as well. However, there is currently no practical method of detecting incipient or fully developed flow separation, requiring manual activation of an active control system. This study proposes the use of low-cost, durable electret microphones to detect trailing edge flow separation. An × . stall regulated wind turbine blade airfoil is mounted in the UC Davis AWT subsonic wind tunnel with microphones at pressure taps near the trailing edge of the suction surface. Tests are run over a Reynolds number range of × to × with fixed and natural transition. Separation indicators including time domain and several spectral domain RMS calculations from fluctuating pressure signals are studied. Each is assessed for sensitivity to installation location, flight condition, premature boundary layer transition, and minimal calibration requirements. The results show a normalized backwards difference first derivative of provides a robust condition independent separation indicator over the range of conditions tested.

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Wind Tunnel Testing of Jets and Tabs for Active Load Control of Wind Turbine Blades

Cited by 17 publications

References 8 publications

An Experimental Study of Mini-Tabs for Aerodynamic Load Control

An Experimental Study of Mini-Tabs for Aerodynamic Load Control

Comparison of pneumatic jets and tabs for Active Aerodynamic Load Control

Low-Cost Detection of Boundary Layer Separation with Dynamic Pressure Measurements

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