Evaluation of wind loads by a passive yaw control at the extreme wind speed condition and its verification by measurements

Transcription

1 Evaluation of wind loads by a passive yaw control at the extreme wind speed condition and its verification by measurements Dec/11/2017 Soichiro Kiyoki Takeshi Ishihara Mitsuru Saeki Ikuo Tobinaga (Hitachi, Ltd.) (Tokyo University) (Hitachi, Ltd.) (Hitachi, Ltd.)

2 Contents 1.Introduction 2.Proposal of evaluation method 3.Verification by actual measurement 4.Influence of change rate of wind direction 5.Conclusions 1

3 1. Introduction 2

4 1-1 Background Wind turbine design Assume various situations that may be experienced in the life time. Among them, the extreme wind speed condition is one of most severe conditions. Passive yaw control Passive yaw control is one of strategies to reduce loads in extreme wind speed condition. To perform passive yaw control, it is necessary to adopt downwind form and direct yaw torque to reduce yaw misalignment. Downwind turbine, which has downwind form in power production, has the advantage that it is not necessary to turn yaw in shifting to passive yaw control. Moreover, it is necessary to adjust the yaw response of wind turbine by appropriately applying the braking force etc. Nacelle Frame Wind Tower Bearing Brake Caliper Downwind Rotor Yaw Torque Brake Disk Tower Design load cases (IEC Ed.3.1) Driving force by wind Yaw brake system(example) Mechanism of passive yaw control 3

5 1-2 Background and Purpose Description of standards(iec, GL) Active yaw control Yaw misalignment to be considered Steady wind model : ±15deg Turbulent wind model : ± 8deg Passive yaw control Turbulent wind model shall be used. Yaw misalignment will be governed by the turbulent wind direction changes and the turbine yaw dynamic response. Specific evaluation method is not defined. Purposes of research (1) The evaluation method of wind loads in the passive yaw control was examined. (2) The method was verified by actual measurement. (3) Influence of new parameter using in the method was investigated by aeroelastic analysis. Descriptions for the passive control in IEC Ed.3.1 4

6 2. Proposal of evaluation method 5

7 2-1 Proposal of evaluation method Conventional method (active yaw control) Proposal method (passive yaw control) Input Wind conditions Wind direction fast change: input slow change: not input Input Wind conditions New parameter Wind direction fast change: input slow change: input (constant) Initial yaw misalignment consider max. and min. Initial yaw misalignment appropriate (stabilization time) Wind turbine Yaw response fixed except for yaw control Wind turbine Yaw response appropriate dynamic behavior Aeroelastic analysis Aeroelastic analysis Result Data exclusion initial stabilization time of rotational speed etc. Wind turbine behavior average yaw misalignment : basically initial value Result Data exclusion initial stabilization time of rotational speed etc. initial stabilization time of yaw misalignment Wind turbine behavior average yaw misalignment : depend on inputs Strength evaluation Strength evaluation 6

8 3. Verification by actual measurement 7

9 3-1 Analysis condition Item Setting Remarks Wind turbine model HTW (Hitachi) Downwind Turbulence model Kaimal spectrum General Random seed number 6 Statistical evaluation Mean wind speed 40, 44m/s From measurement Turbulence intensity 9.4% From measurement Turbulent 3-dimensional components σ1:σ2:σ3=1:0.8:0.5 Flat terrain Change rate of wind direction deg./s (constant) From measurement Initial yaw misalignment -10deg. For early stabilization Wind shear (α) 0.11 General value (EWM) Inclination 0deg. Sea wind Yaw brake torque Dynamic and static friction Analysis time 910s (target: 310~910s) 0~310s: stabilization time Analysis software BLADED (DNV GL) 8

10 3-2 Evaluation of yaw misalignment 10minutes 10-min. Average Averaged Yaw Yaw Misalignment[deg] Measurement(13-15hour) Measurement( hour) Simulation( hour) minutes 10-min. Averaged Wind Wind Speed[m/s] Yaw misalignments are large at low wind speed but converge to small values at high wind speed. The predicted (simulated) values were in good agreement with the measured values. 9

11 3-3 Evaluation of blade flapwise bending moment 1 10-min. Statistics of Normalized Blade 10 minutes Flapwese Statistics Bending of Normalized Moment MYS[-] min. minutes Averaged Wind Speed[m/s] [m/s] Measurement Max. Measurement Mean Measurement Min. Simulation Max. Simulation Mean Simulation Min. The predicted mean and minimum values were in good agreement with measured values, The predicted maximum values were slightly larger than measured values (safety side). Proposed method was verified to evaluate the loads in passive yaw control correctly. 10

12 4. Influence of change rate of wind direction 11

13 4-1 Analysis condition Wind turbine model Item Setting Remarks HTW (Hitachi, Ltd.) Turbulence model Kaimal spectrum General Random seed number 6 Statistical evaluation Mean wind speed 55m/s General in design Turbulence intensity 11% General in design Turbulent 3-dimensinal component σ1:σ2:σ3=1:0.8:0.5 Change rate of wind direction 0, ±0.01, ±0.02, ±0.05, ±0.1, ±0.2, ±0.5 deg./s (constant) Initial yaw misalignment -/+10deg. (reverse sign of wind direction change rate) Flat terrain Evaluation object For early stabilization Wind shear (α) 0.11 General value Inclination 0deg. Sea wind Yaw brake torque Analysis time Analysis software Dynamic and static friction 910s (target:310~910s) BLADED (DNV GL) 12

14 4-2 Influence to yaw misalignment 10-min. 10min Averaged Yaw Misalignment[deg] [deg] Each Seed Mean value Long-period Change Rate Change of Rate Wind of Wind Direction [deg/s] As change rate of wind direction increases, yaw misalignment also increases. Yaw misalignment is offset to minas side by about 2deg. This may be caused by the left-right unbalance of the rotor aerodynamic force. 13

15 4-3 Influence to blade flapwise bending moment 10-minute max. blade flapwise bending moment Blade Flapwise Bending Moment normalized Normalized by by the the loads Load of Active active Yaw yaw Control[-] control [-] Each Seed & Each Blade Typical value Long-period Change Rate Change of Rate Wind of Wind Direction [deg/s] As change rate of wind direction increases, flapwise bending moment increases. The loads are larger when the direction of wind direction change is positive than negative. This may be caused by yaw misalignment. it is necessary to consider rate and direction of wind direction change. The load reduction effect of passive yaw control is confirmed because the load ratio to active yaw control is less than 1. 14

16 5. Conclusions 15

17 5-1 Conclusions Wind loads and yaw misalignment by a passive yaw control at the extreme wind speed condition were evaluated by aeroelastic analysis and the following results were obtained. (1)The method evaluating the wind loads in passive yaw control was proposed by setting a new parameter change rate of wind direction. (2)As a result of verifying above method by actual measurement, yaw misalignment was in good agreement. Average and minimum value of blade flapwide bending moment were in good agreement and the maximum value was slightly larger (safe side). (3)The influence of change rate of wind direction was investigated by aeroelastic analysis. It was shown that the left-right unbalance of rotor aerodynamic force affects yaw misalignment and blade extreme loads. (4)It was shown that blade extreme loads at the extreme wind speed may be reduced by passive yaw control. 16

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