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A Comparative Study of the Wake Dynamics during Yaw and Curtailment. - - PowerPoint PPT Presentation

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A Comparative Study of the Wake Dynamics during Yaw and Curtailment. Sren Juhl Andersen 1 June 20, 2019 Email: 1 sjan@dtu.dk Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 1 / 22 Motivation Two

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SLIDE 1

A Comparative Study of the Wake Dynamics during Yaw and Curtailment.

Søren Juhl Andersen1 June 20, 2019

Email: 1 sjan@dtu.dk Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 1 / 22

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SLIDE 2

Motivation

Two main strategies are generally be- ing investigated for improved wind farm control to mitigate the adverse wake ef- fects. Yawing a turbine, which aim to deflect the wake away from the next turbine. Derating a turbine, which aims to decrease the wake deficit.

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 2 / 22

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SLIDE 3

Motivation

The present work aims to provide a di- rect and completely equivalent compar- ison of the two operating conditions. The study is focussing on: Turbine operation Wake dynamics Potential power gain with two turbines

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 2 / 22

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SLIDE 4

Flow Solver and Turbine Modeling

EllipSys3D1,2 Finite volume and incompressible Multigrid and multiblock Parallelized with MPI Large Eddy Simulation(LES) Actuator Line3 Apply body forces along rotating lines Tabularised lift and drag coefficients Fully coupled to Flex54, which is a modal based aero-elastic tool Dynamic turbine controller.

1Michelsen, 1992, 2Sørensen, 1995, 3Sørensen and Shen, 2002, 4Øye, 1996

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 3 / 22

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SLIDE 5

Turbine and Inflow

Wind Turbine V27, comparable to the V27 at SWiFT1 R = 13.5m Zhub = 32m Inflow Uhub = 8.3283m/s TIhub = 7.7% Shear: α = 0.18

1Resor and LeBlanc, 2014

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 4 / 22

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SLIDE 6

Effect of Control Strategies

Using Flex to match streamwise thrust force for derating and yawing.

200 400 600 800 1000 1200 10 15 20 25 Yaw5 Derate5

T [kN] t[s] a)

200 400 600 800 1000 1200 10 15 20 25 Yaw1 Derate1

T [kN] t[s] b) Comparison of thrust force computed in Flex5 for yaw and derating.

200 400 600 800 1000 1200 10 15 20 25 EllipSys3D Flex5

T [kN] t[s] a)

200 400 600 800 1000 1200 10 15 20 25 EllipSys3D Flex5

T [kN] t[s] b) Comparison of thrust force computed in Flex5 and EllipSys3D as function of time for a) φ = 0◦ and b) φ = −35◦. Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 5 / 22

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SLIDE 7

Effect of Control Strategies

Matching(< 1%) mean thrust force:

  • 40
  • 30
  • 20
  • 10

10 20 30 40 16 17 18 19 20 21 Yaw Derate Normal Operation

γ[◦] T[kN]

Yawing is penalised more serverly in terms of power production:

0.6 0.7 0.8 0.9 1 0.6 0.7 0.8 0.9 1 Derate Flex5 Yaw Flex5 Derate EllipSys Yaw EllipSys 1:1

T T0 [] P P0 [] Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 6 / 22

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SLIDE 8

Effect of Control Strategies

Comparing Power of 1st Turbine from Flex5 and EllipSys3D. Total simulation time is 20 min.

200 400 600 800 1000 1200 40 80 120 160

EllipSys3D Flex5 P [kW ] t[s] a)

200 400 600 800 1000 1200 40 80 120 160

EllipSys3D Flex5 P [kW ] t[s] b)

Comparison of electrical power computed in Flex5 and EllipSys3D as function

  • f time for a) φ = 0◦ and b) φ = −35◦.

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 7 / 22

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SLIDE 9

Average Wakes

Comparing normal operation and yawing −35◦ and the corresponding derating.

X[R]

U Uhub

Yawing [R] Normal

  • peration

[R] Derating [R]

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 8 / 22

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SLIDE 10

Wake Dynamics

Comparing wake at 6R downstream Derating Normal Operation Yawing

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 9 / 22

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SLIDE 11

Center of Wake Movement

Comparing normal operation and yawing −35◦ and the corresponding derating.

X[R]

yC[R]

Subtracting median.

X[R]

y∗

C[R]

Large meandering for yawing and derated wakes in near wake

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 10 / 22

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SLIDE 12

Wake Breakdown

Wake breakdown location1:

l

R

  • nw

= −

16

U3

c

NbλCT

  • ln

0.3Ti

  • + 5.5 ln

Ti

  • .

» However, what dominates: Breakdown or smaller deficit? Using Proper Orthogonal Decomposition1 to assess wake breakdown location from minima

  • f 1st mode.

16 16.5 17 17.5 18 18.5 19 19.5 20 20.5 21 12 13 14 15 16 17 18 19 20 Derate Baseline Yaw

T[kN]

l

R

  • nw [R]

Yawed wakes break down faster

1Sørensen et al., Royal Society, 2015

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 11 / 22

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SLIDE 13

Power Gain of 2 Turbines - Example

1st turbine in EllipSys3D, while 2nd turbine is Flex5. X = 5R and yawing 15◦

200 400 600 800 1000 1200 50 100 150

P [kW] Baseline Operation: P

tot = 109 + 36 = 145kW

200 400 600 800 1000 1200 50 100 150

P [kW] Yaw Operation: P

tot = 84 + 56 = 140kW

200 400 600 800 1000 1200

t [s]

50 100 150 200 250

P [kW] P1 + P 2 Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 12 / 22

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SLIDE 14

Mean Power Gain of 2 Turbines

Estimating power gain of two turbines by summing the difference in instantaneous power production of controlled turbine and baseline turbine. Normalising by sum of instantaneous power production of baseline turbines. Then taking the time average to get the mean power gain. < ∆Ptot >= 100 ·

  • (P1,E,control − P1,E,base) + (P2,F,control − P2,F,base)

(P1,E,base + P2,F,base)

  • 5

10 15 20

X [R]

  • 14
  • 12
  • 10
  • 8
  • 6
  • 4
  • 2

2

< Ptot> [%]

5 10 15 20

X [R]

  • 14
  • 12
  • 10
  • 8
  • 6
  • 4
  • 2

2

< Ptot> [%]

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 13 / 22

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SLIDE 15

Distribution of Total Power Production

φ = −35◦ φ = −30◦ φ = −15◦ φ = −5◦

X = 5R X = 10R Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 14 / 22

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SLIDE 16

Distribution of Total Power Production

Conclusions and Discussions

Yawing is penalized harder in terms of power production than derating. Reducing streamwise thrust increases wake movement/meandering, particular for short distances behind the turbine Additionally, yawing does not only deflect the wake, but potentially also initiates the beneficial breakdown sooner. Neither yawing nor derating appears beneficial for this scenario. However, yawing has a distinct peak around 3 − 7R downstream in terms of potential power increase, i.e. the wake needs to deflect sufficiently before and at the same time exploit earlier recovery Derating has a more constant potential in the far wake, but larger at closer distances(X < 10R) However, the overall benefit for a two turbine system is still largely uncertain. Particular as yawing involves significantly higher uncertainties than derating. Narrow distributions when derating, and very wide distributions for yaw. Is this actual flow control?

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 15 / 22

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SLIDE 17

Distribution of Total Power Production

Acknowledgements

CCA on Virtual Atmosphere PossPow and CONCERT TotalControl

Thanks for your attention.

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 16 / 22

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SLIDE 18

Distribution of Total Power Production

Acknowledgements

CCA on Virtual Atmosphere PossPow and CONCERT TotalControl

Thanks for your attention.

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 17 / 22

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SLIDE 19

Distribution of Total Power Production

Extra Slide: Comparing EllipSys3D and Flex5 2nd Turbine

200 400 600 800 1000 1200 40 80 120 160 200

EllipSys3D Flex5

P [kW ] t[s] a) 200 400 600 800 1000 1200 40 80 120 160 200

EllipSys3D Flex5

P [kW ] t[s] b)

Comparison of electrical power of 2nd turbine at a downstream distance of 10R computed in Flex5 and EllipSys3D for a) φ = 0◦ and b) φ = −30◦. For EllipSys3D, it is the 2nd turbine of 4, i.e. added blockage. Mean difference in power is a) approx. 4% and b) approx. 6%. Could correct using Troldborg and Forsting, Wind Energy, 2017, 20:2011-2020 and perhaps Mann et al. Wind Energy Science, 3, 293-300, 2018.

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 18 / 22

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SLIDE 20

Power Gain 2nd Turbine

Power gain of 2nd turbine

5 10 15 20 5 10 15 20 25 30

P2

5 10 15 20

  • 2

2 4 6 8 10 12 14

P2

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 19 / 22

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SLIDE 21

Potential Power Gain

Estimating power gain of 2nd turbine using time and rotor averaged velocity in wake(< U >) compared to normal operation(UNO) normalized by flow with no first turbine

  • U0. ∆P1 is power loss on 1st turbine.

∆ P2 = 100 · < U >3 − < UNO >3 < U0 >3

X[R] X[R] X[R] X[R] X[R] γ = −35◦ γ = −30◦ γ = −25◦ γ = −15◦ γ = −5◦ ∆ P2[%] Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 20 / 22

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SLIDE 22

Rotational Speed

Rotor speed. 200 400 600 800 1000 1200

t [s]

3 3.5 4 4.5 5

[r/s]

Normal Operation Yawing Derating

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 21 / 22

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SLIDE 23

Pitch

Rotor speed. 200 400 600 800 1000 1200

t [s]

  • 0.5

0.5 1 1.5 2 2.5

[r/s]

Normal Operation Yawing Derating

Andersen A Comparative Study of the Wake Dynamics during Yaw and Curtailment. June 20, 2019 22 / 22