Measurement on Vortex Generators

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Measurement on Vortex Generators for Wind
Turbines Clara Velte Martin O. L.
Hansen Dalibor Cavar Knud Erik Meyer MEK/Section
of Fluid Mechanics DTU
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Vortex generators are commonly used on wind
turbine blades and airplane wings
From 1 Wind Turbine Technology, Spera D.A
(editor) ASME Press 1994.
From 2 Kermode A.C., Mechanics of flight,
Pearson (11th edition) 2006.
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Schematic explanation of how a VG works By
creating a longitudinal vortex, high momentum air
is transferred down into the bottom of the BL to
increase momentum and thus resistance to adverse
pressure gradients with the result of delaying
stall.
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Example of the potential of applying VGs on WT
blades ELKRAFT 1000 kW Turbine at Avedøre LM
blade using NACA airfoils for outer part and
thick FFA airfoils for the inner part
From 3 S. Øye, The effect of Vortex Generators
on the performance of the ELKRAFT 1000 kW
Turbine, 9th IEA Symp. On Aerodynamics of Wind
Turbines, 1995.
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• To optimize the use of VGs, DSF has funded a
  project to study
• the detailed flow behind the devices and thus
  better understand the physics. A fundamental
  study.
• PIV and LDA measurements in low speed wind
  tunnel at DTU - to create a benchmark
• Simulations using CFD

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4 Lin J.C., Review of Research on low-profile
vortex generators to control boundary-layer
separation, Progress in Aerospace Sciences 38
(2002) 389-420 Low profile VG,
0.1lth/?lt0.5 Other names in literature
micro VG, sub BL VG (SBLVG), micro vanes
etc. Conventional VG h/?1
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The good behaviour of micro VGs is explained by
the full nature of a turbulent BL
At h0.2d u/U80.75
Reproduced from 4
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It is demonstrated on a backfacing ramp that
micro VGs reduce separation just as well as
conventional VGs, but with lesser 3D effects.
No VGs
VGs h/?1
VGs h/?0.2
Reproduced from 4
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The 3-D flow is also visible in measured pressure
at different spanwise positions (Reproduced from
4)
VGs h/?1
VGs h/?0.2
Separation
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5 Godard G., Stanislas M., Control of a
decelerated boundary layer. Part 1 Optimization
of passive vortex generators, Aerospace Science
and Technology Progress in Aerospace Sciences 10
(2006) 181-191 A bump is designed to keep the
flow on the verge of separation. The wall shear
stress is measured with a hot film
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It is concluded that an optimum geometry
is Counter rotating triangular VGs h/? 0.37,
L/h 2.5, l/h2, ??/h6, ?18o
Reproduced from 5
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SPIV was used for characterization of the flow
?x/h22
?x/h38
?x/h57
Reproduced from 5
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Non-dimensional streamwise velocity at point of
minimum skin friction in plane of symmetry
(Reproduced from 5)
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- The flowfield (velocity, turbulence) will be
measured and described very thoroughly. - CFD
computations will be performed and compared
with measurements.
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Status The wind tunnel is under severe
reconstruction. The main reason is for obtaining
better optical access. Methods are being tested
to decrease effects from reflections. LES
computations of the clean bump have been
initiated.
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Reconstruction of Test Section
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Some sample results, stereoscopic PIV
x/h4
The colour indicates the out-of-plane velocity
component and the arrows the in-plane velocities.
x/h6
x/h10
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Rhodamine 6G
Absorbs light at 530 nm Emits light at 560
nm Camera equipped with green pass filter (532
nm) Low sensitivity to temperature pH-value
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Application of R6G to model