Transformation of a Separated Turbulent Flow in a Conical Dimple at the Wall of a Narrow Channel and Reduction in Hydraulic Losses as Conicity Increases

Abstract

A separated flow in a narrow channel with a conical dimple at the wall with an incline angle of θ is calculated based on the solution to the unsteady Reynolds-averaged Navier–Stokes equations (URANS) closed using the modified shear stress transport (SST) model. It is noted that a sharp transition from the periodic mode with two alternately changing vortices in dimples close to cylindrical shape (θ = 10°–22.5°) to modes with periodic low-frequency vibrations of inclined single-vortex structures at moderate angles θ (30°–37.5°) and to modes with steady vortex structures at angles θ larger than 45° is observed. The relative hydraulic losses at the channel segment with the dimple remain at a level of 1.23–1.24 as θ increases to θ = 45° and, then, rapidly decrease by almost 1.5 times to 1.16 at θ = 60°.