| The trajectories of the tip vortices of a model wind turbine rotor are quantitatively tracked for twenty-seven separate test conditions. Three pitch angles are used (−8°, −3° and 3°). Three tip speed ratios are examined (2, 5 and 10). Finally, data for rotors with one, two and three blades are presented. The pitch of the ensuing helical wake is found to be modeled well by the reciprocal of the rotor tip speed ratio. The radial locations of the tip vortices stay relatively constant at 97% radius. The exception to this is when the rotor is operating under a high thrust loading condition. The tip vortices will then propagate radially at a rate equal to 0.024 nondimensional radial units per radian of rotation until the following blade passes. At that time, the rate decreases to 0.010. Three tests were used to determine the axial settling of the inboard sheet. It is found to be approximately modeled by the tip vortex axial settling rate. The empirical wake settling data from this investigation are programmed into an existing prescribed wake/thin lifting surface computer program. When comparing thrust predictions with measured values, the codes generally agree within 5% for moderate tip speed ratios. The revised code tends to predict less thrust. The time for calculations has been reduced by 40%. The code is also much more stable. An extensive set of three component hot film measurements was collected. In addition to being a valuable resource for modelers, the data set helped show the superior flow field predicting capabilities of the revised code. Velocity profiles near a tip vortex are contained in the data set and show strong induced velocities in the axial, radial and tangential directions. |
