Drag Measurements on Long Thin Cylinders at Small Angles and High Reynolds Numbers
NAVAL UNDERSEA WARFARE CENTER DIV NEWPORT RI
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Measurements of the drag caused by turbulent boundary layer mean wall shear stress on cylinders of aspect ratio Lla 480 and 960 at varying small angles of attack to the tow direction and at length Reynolds numbers of 8 x 106 ReL 6 x 10 are presented. The use of a full-scale, high-speed towing tank allowed turbulent boundary layers to be developed on cylinders made of either stainless steel, aluminum, titanium, or polyvinyl chloride. The diameter of all cylinders in this experiment was 12.7 mm two cylinder lengths, 3.05 m and 6.10 m, were used. The use of materials of various densities allowed critical angle tows, resulting in linear cylinder geometry for tow speeds ranging from 2.6 to 20.7 ms and angles between 0 and 120. Towing angles were measured with digital photography, and streamwise drag was measured with a strut-mounted load cell at the tow point. The measured tangential drag was very sensitive to small increases in angles at all tow speeds. The ratio of cylinder length to momentum thickness is shown to collapse the tangential drag coefficients for varying tow angles. The effects of the crossflow resulting from the small angles of tow are shown to have a significant effect on the tangential drag coefficient values. A scaling for the orthogonal force on the cylinders was determined and provides a correction to published normal drag coefficient values for pure crossflow. The presence of the axial turbulent boundary layer has a significant effect on these forces.
- Fluid Mechanics