Oil Flow Tests on Winglet (12-07-02)

What effect does turbulator tape have on the separation bubble as it encroaches on the bubble? At what rate does the bubble grow as the turbulator tape moves farther and farther aft into the region of the unturbulated bubble?

To answer these questions, Davis Horton, a student in Oxford, MS performed oil flow tests on a glider winglet. This was done as a science project. The winglet was mounted about 2 1/2 feet out from the side of a pickup truck. The truck was driven at a highway speed of about 65 mph.

These tests seem to show that even when the turbulator tape is quite far back into the bubble, it noticeably reduces the chordwise span of the bubble and, presumably, also the height of the bubble over the wing surface.

Comments by Dick Johnson

Those are very interesting oil flow photos. The one with the turb .25" fwd of the bubble LE is excellent because it shows that the separation bubble is nicely suppressed, and well attached air flows both ahead and behind the turb.

Turb locations at or aft of the bubble LE do not appear to offer as good performance, and it appears that the oil is thicker ahead of the turb in all of those photos. Is that correct? Maybe the BL is forced to be thicker by the non-optimum turb location?

What really counts is the drag coefficient. A wake rake could be used to measure that, and that would make an interesting follow-on.

Dick Johnson

Click an image to see it full size.

Winglet mounting configuration

No turbulator

Turbulator 0.25" forward of
bubble leading edge

Turbulator 0.00" forward of
bubble leading edge

Turbulator 0.125" aft of
bubble leading edge

Turbulator 0.25" aft of
bubble leading edge

Turbulator 0.50" aft of
bubble leading edge

Turbulator 1.00" aft of
bubble leading edge