Hiroshi Higuchi
Syracuse University

A simple water channel experiment shows the phenomenon of tip vortices and downwash similar to that behind an aircraft despite large differences in scaling parameters. In this study, a rectangular flat plate of 5 cm chord length with an aspect ratio of 4.2 was placed at 4.5 angle of attack in the water channel with a 0.6 m 0.6 m 2.44 m test section. The Reynolds number based on the chord length was 5.7 10 ³.

The hydrogen bubble technique was used for flow visualization. The photograph in Fig. 1 was taken from down-stream with a thin platinum wire located slightly below the model and 18 chord lengths downstream. In Fig. 2, a laser sheet placed at 28 chord lengths downstream of the trail-ing edge illuminated the cross-sectional view of the vortices. The effect of the separated flow at the trailing edge is also visible near the midspan.

Figure 1: Model study (end view).

Figure 2: Model study (cross-sectional view).

The trailing vortices and downwash phenomenon of an aircraft in flight are seen clearly in Fig. 3. In this situation, a Cessna Citation VI was flown immediately above the fog bank over Lake Tahoe at approximately 313 km/h or 170 knots. ^[1] Aircraft altitude was about 122 m (400 ft) above the lake, and the weight was approximately 8400 kg. As the trailing vortices descended over the fog layer due to the downwash, the flow field in the wake was made...