Measurements in confined jets with varying outer stream turbulence

The effects of the freestream turbulence level on the velocity and turbulence intensity of confined jets are investigated. The mean velocity and turbulence intensity for an axisymmetric confined jet, a square jet in a coflowing stream, and an axisymmetric confined jet with equal velocity are evaluated using an LDA. For the axisymmetric jets, measurements were conducted in the range x/D = 0-8 and 25-60, where x is the axial distance from the nozzle plane and D is the nozzle diameter, using nozzle diameters of 12.7 mm and 1.8 mm, respectively. For the square jet, the measurements were performed with a 4 x 4 mm nozzle in the range x/H = 5-25, where H is the nozzle height. The freestream to jet velocity ratio ranged from 0.11-0.75. The data reveal that the freestream turbulence affects the rate of decay of excess velocity on the centerline over freestream velocity; the freestream turbulence affects the turbulence profile across the mixing region; and the mean velocity profiles are similar at different freestream turbulence levels.