FLOW
VISUALIZATION IN THE WAKE OF A FULL-SCALE 2.5 MW BOEING MOD-2 WIND
TUBINE [1-2]
(Peter)
H.-T. Liu
Wind Turbine Test Site
A wind turbine test site at Goodnoe Hill near Goldendale,
Washington was established in 1979 by the Depart-ment of Energy to understand
the performance of large wind turbines in the full-scale environment. The
site consisted of a cluster of 3 2.5 MW Boeing MOD-2 wind turbines with a 94-m
rotor diameter and a 61-m tall tower (Fig. 1). Flow-visualization
experiments were conducted to investigate several wake phenomena.
For example, tethered smoke generators was deployed to investigate the
evolution of the tip vortices (Figs. 2 through 4). Nearly
vertical smoke trails released from model rockets were used to
measure the wake velocity deficit (Figs. 5 through 6).
Fig. 1. Boeing 2.5 MW MOD 2 Wind Turbine at Goodnoe Hill Test Site
Instability of Rotor Tip
Vortices - Reversal of Vortex Core
Smoke released downstream of the rotor blades from a tethered generator was used to visualize the evolution of the rotor-tip vortices (Fig. 1). The smoke generator releases a large volume of smoke continuously for several minutes. When the rotor blades cut in front of the smoke trail, a section of the helical vortex generated locally becomes visible as smoke is entrained and trapped in the low-pressure core (Fig. 2). The vortex becomes unstable when it passes through the wake of the turbine tower. The vortex reverses its course forming a long "spout" shooting at high speeds away from the turbine wake (Figs. 2 through 4). As the rotor blades cut across the tower wake, the vortex core experiences a sudden change in the ambient pressure. It is believed that the vortex reversal, a form of intability, is triggered by the above vortex-wake interaction.
Fig. 2. Three Stages of Vortex
Instability (End View): Forward Spout (Left), During Reversal (Middle), and
Reversed Spout (Right)
Fig. 3. A Reversed Spout Shooting Away from
the Turbine Wake at a High Speed (End View)
Fig. 4. Time Lapse Photographs of Reversed Spout
(Side View)
Wake Geometry and
Velocity Deficit Measured with Smoke Trails
Nearly
vertical smoke trails were released from model rockets in the turbine wake
(Fig. 5). Time lapse photo-graphs of the smoke trails were used to visualize
and measure the wake height and velocity downstream of the wind turbine (Figs.
6).
Fig. 5. Smoke Trails Released inside
and outside of Turbine Wake
Fig. 6.
Displacement of Smoke Trails and Velocity Deficit Derived from Time Lapse
Photographs
References
[1] Hiester, T. R., Liu, H.-T., and Waite, J. W. (1983)
"Results of MOD-2 Wake Flow Visualization," presented at 1983
American Solar Energy Society Meeting, June 1 – 3. .
[2]
Liu, H.-T., Hiester, T. R., Waite, J. W., Tacheron, P. H., and Srnsky, R. A.
(1983) "Flow Visualiza-tion Study of a
MOD-2 Turbine Wake," Pacific Northwest Laboratory
Technical Report PNL-4535, UC-60, June and Flow Research
Report No. 238, October 1982. .
