An Experiment Investigation On Turbulence Characteristics Of Wind Turbine Near Wake Field By Time-resolved PIV

When wind turbine is running some complex turbulent structures will generate in thenear wake flow field. Therefore, some harmful factors such as flow resistance andaerodynamic noise also generate at the same time.So the investigations on turbulentcharacteristics of wind turbine near wake field should be carried out immediately.In orderto capture the evolution details of flow filed and explore complex turbulent structure,highsampling frequency which the traditional PIV can not obtain must be implemented.So thetime-resolved PIV was used for this wind turbine wake field experiment investigation.The upper part flow filed of a horizontal axis wind turbine near wake was tested inwind tunnel closed section. Rotor diameter is292mm.The sampling frequency is1000Hzand2000Hz separately. Continuous instantaneous velocity field and vorticity fieldinformations in different working conditions were obtained. Based on the continuousvorticity nephogram the evolution tendency of tip vortex and center vortex as phase anglewas observed. In addition,in order to show the phenomenon that tip vortexes and othervortexes move to downstream helically, the three-dimensional wind turbine near wake wasreconstructed.By calculating instantaneous velocity field, parametric informations such as averagevelocity, average vorticity, RMS of fluctuating velocity, reynold stress, turbulent kineticenergy and space correlation coefficient which associate with filed turbulent characteristicswere obtained.Then those above informations were analyzed quantitatively. The resultsshowed as follows:at same working condition, average velocity increases as the increase ofradial position.Its increase degree is bigest in the center votex area.And in the tip votexarea increase degree is weaker than which in center votex area.Average velocity decreasesas the increase of axial position.Its decrease degree is bigest in the center votex area.In thetip votex area the decrease degree quite weak. Besides, at trajectory of tip votex core axialfluctuating velocity is the weakest. On the contrary radial fluctuating velocity is thestrongest. On the whole, the area which turbulent characteristics is distinct fasten on centervotex and tip votex area which RMS of fluctuating velocity, reynold stress,and turbulentkinetic energy are the greatest relatively. But tip votex area second to center votex area. Anda circular area exists in tip votex area which adjacent to the tip. Its diameter range from 0.08R to0.17R as different wind speed. Compared with other area under same condition,fluctuating velocity of this area is the strongest.Moreover, there is a regular in tip votexand center votex area that the positive and negative correlation appear alternately alongwith axial by observing the axial and radial space correlation coefficient which manifestthat many coherent structures exist in the wind turbine near wake filed.Fitting curve fromaxial space correlation coefficient is similar with trajectory of tip votex core.So thisphenomenon can used to predict the trajectory of whole tip votex.Turbulent characteristics of wind turbine near wake field was investigated Throughthe work above in this paper.Flow details and turbulent characteristics in the filed wasknown clearly，the emphasis of the research work in the future was found，and experiencefor the sake of the further investigation was accumulated.