縦リブによる d 形粗面境界層の抵抗減少制御

概要

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In order to control the turbulent energy production and transport processes due to the coherent vortices associated with the bursting phenomenon in a d-type rough wall turbulent boundary layer, longitudinal thin ribs were placed within the transverse grooves with a suitable spanwise spacing. Direct measurements of the local skin friction coefficient show the effectiveness of the present drag reduction technique using the longitudinal ribs. Maximum drag reduction rates to d-type rough wall flow and smooth wall flow are -10% and -3%, respectively. The drag reduction rate can be reasonably expressed in terms of the rib Reynolds number. Compariston of some mean flow properties between the modified flow and the d-type rough wall flow provide experimental facts that the present control device reduces the turbulent energy production rate.