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Effect of a Swing Rudder on The Yaw Alignment of Small Wind TurbinesThe University of Tokyo Mitsumasa IinoThe University of Tokyo Makoto Iida1Thank you for choosing me as a full presenter,As I explained formerly I have investigated the effect of swing rudder on the yawing motion of turbines.First, I explain the background of my reseach.1Effect of wind direction change on small wind turbinesYaw errorLoad imbalance on rotor planeReduction of PowerYaw rateGyro moment

Yaw control of horizontal axis SWTAerodynamic force on rotor and rudder(upwind)Aerodynamic force on rotor(downwind)Active yaw

Yawed flow affects power and structural performance2Wind direction is one of the issue that degrade the turbine performance and structural strength.Yaw error induces load imbalance on each blade and cyclic load induces heavy fatigue load,Moreover the power is reduced by reduction of axial wind speed.Large yaw rate is also induced by changes of wind direction.Such yaw rate can induce severe blade structural load because of gyro moment effect.So turbine should control yaw posture to improve performance.

Among horizontal axissmall wind turbines yaw control are mainly these three type Upwind turbine with rudder, downwind turbine, and active yaw.Most of turbines with several kW uses upwind turbine and a rudder.

2Rudders of small wind turbinesDesign parametersTail fin areaBoom lengthNumber of finPosition of tail fin (higher than nacelle etc.)Many parameters Optimum design has not yet achieved

3This is pictures from small wind turbine catalogue.It is clear that there is no concrete solution for rudder type.Among the rudder type the swing rudder system is proposed as effective rudder system.The swing rudder is a rudder pivoted on the nacelle and move independently.The effect is only investigated in limited experiments, so the theoretical mechanism is unclear.Then I explain the purpose of my research.

3Purpose and methodEstablish theoretical design and evaluation method of small wind turbines with a swing rudderMethodAeroelastic simulation code NRELFASTBlade element and momentum theoryMultibody dynamicsCompare Swing rudder and Fixed rudder

Model targetZephyr AirDolphinRated power 1.1kWDiameter 1.8mCut in wind speed 2.5m/s

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The purpose of my research is to establish theoretical design and evaluation method of small wind turbine with a swing rudder.In this presentation we composed a turbine model with swing rudder and investigated the effect of swing rudder comparing with fixed rudder.

The model is based on this turbine zephyr airdolphin that is the only product utilizing swing rudder system.Next I explain the wind condition of this research.

4WindCondition510- 120(every 10)3,4,5,6,7,8,9,10,11,121,2,3,4,5,6,7,8,9,10Turbine statusOperatingSingle direction change, various parametersTimeDirection

In this research the wind condition is set to be a simple single direction change with constant wind speed.There are three parameters with this condition.The amount of direction change The time to finish direction changeAnd the wind speed.To reveal the character of swing rudder the parameter of wind condtion is varied widely.Next I show an example of the results of time series data.5Yaw error time seriesYaw error decreases with swing rudder at T=1,2 s

Allover yaw error decreases as Tmax increases

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Swing rudder Tmax=6Fixed rudder Tmax=6Swing rudder Tmax=10Fixed rudder Tmax=10TimeDirection

Swing rudder Tmax=1Fixed rudder Tmax=1Swing rudder Tmax=2Fixed rudder Tmax=2

Swing rudder Tmax=1Fixed rudder Tmax=1Swing rudder Tmax=2Fixed rudder Tmax=2Maximum yaw error reduction by swing rudderU[m/s]max[deg]Tmax[s]Yaw error reduction [%]46014.31 46022.42 46061.21 460103.11 This is time series data varying The time of direction changeFrom this figure the overall yaw character is very similar with swing rudder and fixed rudderHowever focusing on the maximum yaw error there are several percent of difference.And the with Tmax=1 or 2 Maximum yaw error is decreased by swing rudder.As Tmax increase the yaw error decreases with both rudder type.Next I show the comparison of maximum yaw error with swingrdder and fixed rudder.6Yaw error reductionTmax = 1 or 2 sMaximum yaw error reduced by swing rudderTmax > 2 s Maximum yaw error increased by swing rudder

7TimeDirection

This is comparison of maximum yaw errorAt Tmax = 1 or 2 maximum yaw error is reduced by swing rudder And at Tmax more than 2 the maximum yaw error is mostly increased by swing rudder.As wind speed increases the reduction of yaw error decreases.Next I explain the difference between the case yaw error reduced and increased.Act7

Case1U=4m/s Tmax=1 max=60the absolute value of rudder error is larger than yaw error at yaw error peakCase2U=4m/s Tmax=10 max=60the absolute value of rudder error is smaller than yaw error at yaw error peakMotion of rudder1.Maximum yaw errorreduced by Swing rudder2.Maximum yaw errorincreased by Swing rudder8

Wind directionYaw ErrorRudder errorDefinition ofRudder, Yaw errorTimeDirection

This is the yaw error and rudder error.Rudder error refers to the difference between rudder posture and wind direction as yaw error refers to the difference between nacelle and wind direction.Case 1 shows the case yaw error reduced by swing rudder.in this case rudder error exceeds when yaw error is its peak.So the nacelle is more aligned to the wind direction.Case 2 shows the case yaw error increased by swing rudder.8Yaw rate and blade root load reductionYaw rate is reduced up to about 8%Blade root bending moment reduced up to 6%

9TimeDirection

In the same manner as maximum yaw errorYaw rate and blade root bending moment is shown in slide.Unlike yaw error the yaw rate and blade root is reduced by swing rudder in almost all cases.

9Summary and ConclusionSummaryModeling small wind turbine with a swing rudderComparison between swing and fixed rudder

ConclusionYaw error reductiondirection change is happen in 1 or 2 secPossibility to increase yaw error by swing rudder Yaw rate and blade root load reduced by the swing rudderRudder significantly influences the designLoad estimation of IEC61400-2 Ed.2 Aeroelastic modeling

10To summarize my presentation, The swing rudder and fixed rudder is compared using simulation model.As a conclusionIn view of maximum yaw error, swing rudder reduces maximum yaw error under sudden direction change because Nacelle is more aligned to wind direction than the rudder. however there is some possibility to increase yaw error using swing rudder.However swing rudder is effective for reducing yaw rate and blade root load in almost all cases.And the difference is up to several percent. So the rudder has significant effect on the design of wind turbines.For example load estimation using aeroelastic modeling.

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