Cryogenic Tunnel Activities at the University of Tsukuba
Cryogenic wind tunnel is a useful apparatus to get high Reynolds-number flow independent of Mach-number. In the high Reynolds-number flow, thickness of boundary layer becomes thinner. Then the surface conditions of the body have much effects on the flow phenomena and on drag. Using cryogenic wind tunnel, we made researches of the effects of surface roughness of a cylinder. Grooves engraved parallel to flow on a flat plate, i.e., riblet, are effective to reduce drag. We measured the effects of grooves along circumference of a cylinder. It showed a marked reduction in drag. The effects of V-grooves are classified into two cases. The one is the original effects of riblet, i.e., to supress bursting and turbulent sepration. In the other case, V-grooves contributes to keep laminar boundary layers long along the surface. In this case, pressure distribution around the surface resembles closely to that of potential flow.
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