Three-dimensional flow and surface visualization using hydrogen bubble technique

A modified hydrogen bubble technique is developed for simultaneous three-dimensional flow visualization and surface visualization on bluff bodies. A detailed description of the technique implementation and operating principles is presented. The technique is validated on two geometries: (1) a uniform circular cylinder for ReD = 1,050 and 2,100; and (2) a dual-step cylinder for ReD = 2,100, D/d = 2, and L/D = 0.5. The results demonstrate that flow visualizations effectively capture intricate three-dimensional wake vortex development including the formation of streamwise structures and vortex interactions in the wake of a dual-step cylinder. The surface visualizations capture boundary layer separation and its variation along the span of the models. Moreover, the results reveal complex three-dimensional surface flow patterns, shedding light on the topology of vortical structures forming near dual-step cylinder junctions.Graphical Abstract