Upstream influence on the near field of a plane turbulent jet

The effects of the mean and turbulence characteristics of the upstream (initial) boundary layer on the evolution of the flow in the near field of a plane jet have been experimentally investigated for four initial conditions. Rates of jet widening and centerline mean velocity decay as well as the kinematic and geometric virtual origins show evidence of systematic dependence on initial conditions. The growth rate of longitudinal turbulence intensity, and the mass flux are higher when the initial boundary layer is laminar than when turbulent. Immediately downstream of the exit, the nondimensional entrainment rates for the laminar initial boundary layer cases reach peak values which are about twice the delayed peak values for the fully turbulent initial boundary layer cases. Within the first 40 slit widths, increases in total average streamwise momentum flux range from 20% to 56%, the larger increases occurring for the laminar initial boundary layers; about 10% of each increase is due to the turbulence field. While such increases violate the traditionally accepted momentum flux invariance, they are consistent with the negative mean static pressure data.