Abstract
Experiments were performed to investigate the effect of a line of roughness elements on flat-plate boundary layer transition. Each roughness element was a cylinder 2 mm in both diameter and height. Eleven elements formed a row in the spanwise direction. Wedge-shaped turbulent regions ("turbulence wedges") developed downstream from the respective roughness elements. Further downstream, two adjacent wedges merged together and then a two-dimensional turbulent boundary layer was formed. Mean and fluctuating velocities were measured by hot-wire anemometers. From the velocities an intermittency factor and turbulent dissipation, etc. were obtained. The manner how the three-dimensional turbulence wedges change into two-dimensional boundary layer were investigated. At first, the fluctuating velocity on the generator of roughness element and center between roughness elements overshot Spalart distribution. And further downstream, both distribution of fluctuating velocity undershot it.
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