Analysis and Measurements of Wakes from Multi-blade Turbines in a Boundary-Layer Wind Tunnel

  • 黃 健恩

Student thesis: Master's Thesis

Abstract

An experiment was carried out to study complex turbulence in the wakes originated from stand-alone 2 3 and 4-blade wind turbines placed in the turbulent boundary-layer wind tunnel (turbulence intensity of 10% at the hub height) with two conditions:(1) the measurements in the vertical plane and (2) the measurements in the horizontal plane when the turbine works in +20° -20° and 0° yaw angle conditions The calibration-free Cobra Probe was used to measure the three instantaneous velocity components in the wakes from the stand-alone turbine Turbulence key statistics are analyzed and presented including time-averaged velocity turbulence intensity momentum flux and power spectrum Besides we use the BEM theory to predict the streamwise wind velocity to compare with the results of the measurements at the downwind position X/D=1 in the turbulence (the data obtained from this experiment) and uniform incoming flow (the data duplicate from the reference Lyu (2017)[1]) The results of the measurements indicate that the distribution of time-averaged velocity declines immediately downstream of the turbine models and then recovers with the wake-wise direction The turbulence intensity has a strong enhancement at the tip-levels in the near-wake region Momentum flux demonstrates how the kinetic energy of the flow is transported to recover the velocity deficit in the wakes In particular the wakes of the statistics are deflected to the side when the turbine works in a yaw angle condition and the maximum of the key turbulence statistics are in the four-blade turbine case The plots of the energy spectrum from the results are close to the inertial subrange with a global slope of -5/3 to confirm further the measured device is reliable The comparisons of the prediction from the BEM theory and the measurements in the turbulence and uniform inflow conditions demonstrate that the wind velocity deficit recovers faster in the turbulence case because of the turbulence mixing and the BEM theory can be used to predict the approximate value of the wind velocity in the near wake
Date of Award2018 Aug 9
Original languageEnglish
SupervisorYu-Ting Wu (Supervisor)

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