Experimental Study on the Flow Pattern of Double-hemisphere Rough Elements with Different Streamwise Spacing

Particle image velocimetry is used to study the variation around single- and double-hemisphere rough elements with different streamwise spacings immersed in boundary layer. Instantaneous velocity field information streamwise–normal streamwise–spanwise directions collected at a Reynolds number of 1800. 3R, 5R, 7R are determined as element spacing experiment, representing smaller, medium transition, larger spacing, respectively. The average velocity, shear stress, shedding frequency, proper orthogonal decomposition results flow under various working conditions were compared. downstream hemisphere will encroach on streamline following upstream hemisphere, changing means position encroached area. When reattachment destroyed, momentum mass exchange between two-hemisphere decreases. slender, blunt, element. At transition layer vortex structure shed from over cause disturbance wall-normal range. has been reattached interaction two hemispheres weakest. Here, form recirculation zone, arch vortex, periodic hairpin vortex.