Study On Strain Characteristics Of Wind Turbine Blade Based On Digital Speckle Method

In order to explore the strain characteristics of wind turbine blades and analyze the strain changes of prototype blades and modified blades,the experiment took small horizontal axis wind turbine as the research object.Based on 3D-DSCM(3D Digital Speckle Correlation method),strain measurement of wind turbine blades was carried out,and the following work was carried out:(1)to carry out the retrofit v-shaped blade tip vane,zigzag leaf blade external characteristic experiment,verified the blade under the average output power and the average wind energy utilization coefficient,blade6 m/s rated wind speed,v-shaped blade average power output increased by 4.18%,a prototype blade zigzag blade average power output is wind turbine prototype increased by 1.71%;In terms of average wind energy utilization coefficient,the V-shaped blade and serrated blade increase 18.58 % and 13.85 % respectively compared with the prototype blade.The average output power and average wind energy utilization coefficient meet the design requirements.(2)The strain characteristics of the prototype blade were tested by digital speckle correlation method.It was found that the strain concentration region of the prototype blade structure was 0.7r from the blade root radius,and the strain value was 9.5%-19.3% higher than other positions.The blade strain increases with the increase of centrifugal force load and aerodynamic load,and the centrifugal force load is the main factor causing the increase of blade strain.When the impeller resonance occurs,the resonance driving effect causes the blade to produce alternating strain,and the alternating cycle law deteriorates and the strain amplitude increases exponentially.In addition,the resonance force produces a focal effect at the blade root position,which causes the strain of the blade to increase gradually along the chord direction.(3)V,zigzag blade tip modification have certain improvement effect on leaf strain,under the same power,v-shaped blade of each measuring point strain value is reduced and reduce the range between 4.83% and9.72%,but the v-shaped blade from the blade root radius of 0.7 R strain value increase,v-shaped blade tip modification has damage on the blade tip position stiffness,And the test results show that the V-shaped blade is most unsuitable for the resonance region.Saw-toothed blades have improved the overall blade strain both under general working conditions and in the resonance region.Saw-toothed blades in the resonance region have the smallest variation in the size of the alternation strain,which is reduced by 0.07(14.2%)compared with the prototype blade.The tip position is improved due to the tip pit produced by the high tip ratio and the large aerodynamic pressure.The strain increase at the radius of 0.7r from the blade root can be eliminated.Therefore,serrated blade tip modification can effectively improve the overall strain characteristics of the blade,and the overall strain of the blade is uniform.According to the test results,the strain characteristics of the prototype blade under different working conditions are obtained.Compared with the strain changes of the prototype blade,the overall strain of the v-shaped blade decreases under the same power,and the blade tip opening serrated groove is the most conducive to the improvement of blade strain characteristics.The experimental results provide some reference value for further research on blade modification.