The effects of cylindrical surface modifications on turbulent boundary layers

A study employing a combination of hydrogen bubble-wire flow visualization and hot-film anemometry measurements has been conducted to determine the effects sublayer scale streamwise surface modifications on the structure and flow characteristics of turbulent boundary layers. The surface modifications were created using very fine monofilament fishing line of an approximate non-dimensional height of h + = 4. Spanwise line spacings of 60 < s (+) < 160 were examined for a Reynolds number range 800 < Re sub theta < 1650. The hydrogen bubble-wire studies indicate that the lines appear to act as nucleation sites for low-speed streaks, but the influence of the lines on streak stabilization rapidly diminishes for y (+) > 10. Streak spacing distributions and statistics were developed from the visualization data for both modified and unmodified surfaces. These results clearly indicate that the surface modifications did affect the streak spacing characteristics, with the greatest effect of the lines on mean streak spacing distributions and statistics occurring for s (+) < 100. However, the visualizations indicate that for y (+) > 10 the determined streak spacing distributions and statistics, of an unmodified surface.