Velocity measurements in the near wake of a horizontal axis wind turbine

Abstract

Single film hot-film measurements in the near

wake of a horizontal axis wind turbine are

performed in the Delft University of Technology

Open Jet Facility in order to capture the blade

azimuth dependent velocity vectors. A novel

approach to determine the average, blade

azimuth dependent, velocity vector is

proposed. It makes use of the asymmetric

response of hot-films that have the film parallel

to its probe. Contrary to the traditional

approach in which the direction of velocity

components cannot be determined and which

poorly predicts relatively small velocity

components, the proposed method yields

velocity direction as part of the solution and

consistently predicts relatively small velocity

components. An uncertainty analysis is

performed on the velocity magnitude and flow

angle, quantifying the data quality.

Furthermore, comparisons with previously

published data on the same rotor, in the same

wind tunnel are made. The comparisons

increase confidence in the data and reveal the

advantages of the proposed velocity

determination method. Qualitatively, the

velocity signals derived with the proposed

approach are in agreement with expectations

from a general vortex wake model, also the

relatively small tangential and radial velocity

components.