Abstract
A spectral DNS code was used to study the growth and spreading of turbulent spots in a nominally laminar, zero-pressure gradient boundary layer. In addition to the flat wall case, the interaction of these spots with passive surface textures (riblets and fins) was examined. The dimensions of these textures were chosen based on parametric studies performed in past work, with the goal of achieving maximum reduction of spot spreading. The flat plate, surface textures, and initial spot perturbation were simulated via an immersed boundary method, and a “suction-wall” allowed the available channel code to model a boundary layer. In all cases, self-similar arrowhead shaped spots formed. The λ2 variable was used to visualize the vortical structures within a spot, and a developed spot was found to consist primarily of a multitude of hairpin vortices. The riblets and the fins both decreased the average spot spreading rate by 7-8% from the flat wall value.
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