Scaling the Near-Field Centerline Mixing Behavior of Axisymmetric Turbulent Jets

Detailed measurements of the centerline mixing behavior in the near field of variable-density jets were performed. Real-time measurements ofjet fluid concentration for a propane jet and a methane jet issuing into still air were made utilizing Rayleigh light scattering. The initial conditions were those of fully developed pipe flow, and testing was done for flow rates yielding Reynolds numbers in the range of 3.3 x 10 3 -2.3 X 10 4 , based on the average discharge velocity, exit diameter, and initial fluid properties. Centerline decay characteristics in the near field exhibited a downstream shift with increasing Reynolds number, which was attributed to the initial velocity distribution at the jet exit. Investigation of the mean and turbulent characteristics of the initial velocity distribution yielded a proposed near-field scale variable that effectively captured this dependence on Reynolds number. Collapse of the near-field centerline velocity and concentration distributions was achieved using the proposed scaling