SCALING THE NEAR-FIELD CENTERLINE MIXING BEHAVIOR OF AXISYMMETRICAL TURBULENT JETS

Detailed measurements of the centerline mixing behavior in the near fi eld of variable-density jets were performed. Real-time measurements of jet fluid concentration for a propane jet and a methane jet issuing i nto still air were made utilizing Rayleigh light scattering. The initi al conditions were those of fully developed pipe how and testing was d one for how 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 numb er, which was attributed to the initial velocity distribution at the j et exit. Investigation of the mean and turbulent characteristics of th e initial velocity distribution yielded a proposed near-field scale va riable that effectively captured this dependence on Reynolds number. C ollapse of the near-field centerline velocity and concentration distri butions was achieved using the proposed scaling.