A Turbulent Cylindrical Wall Jet Equipped with a Front-Facing Step Impinging Normally on a Flat Plate

摘要

This is an experimental study of a turbulent cylindrical wall jet that issues from an annular nozzle, flows along a cylindrical wall and finally impinges normally on a flat plate. In order to disturb the flow near the wall and to control the thickness of the wall shear layer, a front-facing step is equipped at an arbitrary location on the cylindrical wall. This type of jet flow has properties characterized by a pressure increase and boundary layer growth in the downstream direction, so that the flow separates from the cylindrical wall and reattaches to the impingement plate. This report mainly concerns the effects on the separation and reattachment properties of the flow with various nozzle-step distances and step-impingement distances. Mean velocity and static pressure on the cylindrical wall were measured. The flow patterns in the x-y plane normal to the cylindrical wall in the region near the step and before the impingement plate were obtained by the mean flow vectors and the flow visualization by an oil film method. The results show that the flow patterns can be classified into three main types.