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Research Papers: Gas Turbines: Turbomachinery

Vortex Shedding and Frequency Lock in on Stand Still Wind Turbines—A Baseline Experiment

[+] Author and Article Information
Matthew Lennie

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany
e-mail: matthew.lennie@tu-berlin.de

Alireza Selahi-Moghaddam, George Pechlivanoglou, Christian Navid Nayeri, Christian Oliver Paschereit

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany

David Holst

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany

1Corresponding author.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 14, 2017; final manuscript received March 1, 2018; published online July 30, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(11), 112603 (Jul 30, 2018) (13 pages) Paper No: GTP-17-1616; doi: 10.1115/1.4039818 History: Received November 14, 2017; Revised March 01, 2018

During the commissioning and stand-still cycles of wind turbines, the rotor is often stopped or even locked leaving the rotor blades at a standstill. When the blades are at a standstill, angles of attack on the blades can be very high, and it is therefore possible that they experience vortex-induced vibrations. This experiment and analysis helps to explain the different regimes of flow at very high angles of attack, particularly on moderately twisted and tapered blades. A single blade was tested at two different flow velocities at a range of angles of attack with flow tuft visualization and hotwire measurements of the wake. Hotwire wake measurements were able to show the gradual inception and ending of certain flow regimes. The power spectral densities of these measurements were normalized in terms of Strouhal number based on the projected chord to show that certain wake features have a relatively constant Strouhal number. The shedding frequency appears then to be relatively independent of chord taper and twist. Vortex generators (VGs) were tested but were found to have little influence in this case. Gurney flaps were found to modify the wake geometry, stall onset angles, and in some cases the shedding frequency.

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Figures

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Fig. 4

Top view of the experimental setup (not to scale)

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Fig. 5

Side view of the experimental setup (not to scale)

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Fig. 2

Smoke visualization of an S809 with 5 mm gurney flap at high angles of attack (low Reynolds) in the visualization wind tunnel. Notice the steering of the trailing edge shear layer and also the interaction between the shear layers downstream.

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Fig. 1

Vortex patterns from VGs and a gurney flap on the pressure side of an airfoil

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Fig. 3

GroWiKa wind tunnel

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Fig. 6

The VG and GF configurations

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Fig. 7

Measurement point density optimized to capture the edge of the wake

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Fig. 8

Flow tufts visualization on the suction blade surface at 6 deg, 30 deg and 70 deg from left to right

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Fig. 9

Wake coordinates normalized by projected chord

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Fig. 10

V component wake velocities at a height of 360 mm (above reference) for Angles of Attack from 0 deg to 90 deg at an inflow of 14 m/s: (a) αlocal 2.6 deg, (b) αlocal 9.4 deg, (c) αlocal 12.4 deg, (d) αlocal 17.4 deg, (e) αlocal 27.4 deg, (f) αlocal 37.4 deg, (g) αlocal 47.4 deg, (h) αlocal 57.4 deg, and (i) αlocal 87.4 deg

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Fig. 13

V component wake velocities at a height of 360 mm (above reference) for angles of attack from 0 deg to 90 deg at an inflow of 20m/s: (a) αlocal 2.6 deg, (b) αlocal 9.4 deg, (c) αlocal 12.4 deg, (d) αlocal 17.4 deg, (e) αlocal 27.4 deg, (f) αlocal 37.4 deg, (g) αlocal 47.4 deg, (h) αlocal 57.4 deg, and (i) αlocal 87.4 deg

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Fig. 11

V component wake velocities across the blade span for a reference pitch 40 deg at an inflow of 14m/s: (a) αlocal 34 deg at 90 mm from reference, (b) αlocal 35 deg at 180 mm from reference, (c) αlocal 36 deg at 270 mm from reference, (d) αlocal 37 deg at 360 mm from reference, (e) αlocal 38 deg at 450 mm from reference, (f) αlocal 39 deg at 540 mm from reference, and (g) αlocal 40 deg at 630 mm from reference

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Fig. 12

V component for angles of attack from 12 deg to 19 deg with varying spanwise positions and chord lengths at an inflow of 14m/s: (a) αlocal 12.4 deg, spanwise position 360 mm, (b) αlocal 13.3 deg, spanwise position 450 mm, (c) αlocal 14 deg, spanwise position 90 mm, (d) αlocal 14.4 deg, spanwise position 540 mm, (e) αlocal 15.3 deg, spanwise position 180 mm, (f) αlocal 15.6 deg, spanwise position 630 mm, (g) αlocal 16.4 deg, spanwise position 270 mm, (h) αlocal 17.4 deg, spanwise position 360 mm, and (i) αlocal 18.3 deg, spanwise position 450 mm

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Fig. 14

V component wake velocities at a height of 360 mm (above reference) for angles of attack from 0 deg to 90 deg at an inflow of 14m/s with VGs: (a) αlocal 2.6 deg, (b) αlocal 9.4 deg, (c) αlocal 12.4 deg, (d) αlocal 17.4 deg, (e) αlocal 27.4 deg, (f) αlocal 37.4 deg, (g) αlocal 47.4 deg, (h) αlocal 57.4 deg, and (i) αlocal 87.4 deg

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Fig. 15

V component wake velocities at a height of 360 mm (above reference) for angles of attack from 0 deg to 90 deg at an inflow of 14m/s with Gurney Flaps: (a) αlocal 2.6 deg, (b) αlocal 9.4 deg, (c) αlocal 12.4 deg, (d) αlocal 17.4 deg, (e) αlocal 27.4 deg, (f) αlocal 37.4 deg, (g) αlocal 47.4 deg, (h) αlocal 57.4 deg, and (i) αlocal 87.4 deg

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