Influence of the Preseparation Flow Structure on the Characteristics of the Separation Region Behind a Backward-Facing Step

Abstract

This paper presents the results of investigations of the influence of the separated flow structure behind a rib located before the edge of the backward-facing step on the parameters of the separation region behind it. Numerical investigations were carried out by the method of large eddy similution in a plane air channel. The velocity of the developed turbulent flow at the inlet to the channel was assumed to be 25 m/s with a level of initial turbulence for three velocity components of 5%. The Reynolds number calculated by the initial velocity and the step height was 15,500. It has been shown that the creation of a preseparation region causes the two-dimensional flow to transform into a three-dimensional one before the edge of the back-facing step with the formation of nonuniform verticity along its length. This restructuring of the flow leads to an increase in the inhomogeneity of velocity parameters in the separated mixing layer. The flow expansion behind the step increased and was accompanied by local separation on the upper wall of the channel. The two separation regions caused a rapid growth of pulsations throughout the channel behind the step.