壁面粗度のスパン方向不連続により生成された二次流れ（二次流れの存在と運動量輸送）

概要

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An experimental study in the fully developed two-dimensional channel flow was performed to investigate the possibility of a spanwise discontinuity of wall roughness as a device to generate secondary currents associated with longitudinal vortex. A k-type rough wall, which consists of an array of two-dimensional rectangular roughness elements, is placed to make spanwise discontinuity of wall roughness. Mean velocity and turbulent intensity were measured with hot-wire anemometers and crossed wire probes. Velocity vector plot in a cross streamwise plane clearly shows that the discontinuity of wall roughness is able to generate secondary currents. And, the secondary currents are associated with longitudinal vorticity. The contours of the longitudinal momentum flux are consistent with the distribution of secondary currents. Transport to the near-wall by the downwash is greater than the upward transport by the upwash. Transport of momentum toward the wall due to secondary currents is quite large compared to that caused by turbulence.