Flow Separation and Reattachment in Confined Jet Mixing

An experimental and theoretical investigation was conducted to study flow separation and reattachment for a confined axisymmetric jet. The fluid was air with an initially uniform velocity jet mixing with an initially uniform (but lower velocity) secondary flow. Both streams were at the same temperature and mixed in a constant-diameter duct. The location of the points of separation and reattachment and the line of zero velocity were determined by injecting smoke into the flow. Measurements were made over a wide range of diameter ratios (nozzle diameter to mixing tube diameter) and velocity ratios (jet velocity to secondary velocity at the inlet). The separation point was strongly affected by the velocity ratio—moving upstream with an increase in velocity ratio. Reattachment, however, was only slightly affected by velocity ratio. A single parameter, such as the Curtet number, was found to be inadequate in describing separation and reattachment over all diameter ratio and velocity ratio conditions.