The influence of nozzle-exit geometric profile on statistical properties of a turbulent plane jet

Abstract

The paper reports an investigation of the influence of geometric profile of a long slot nozzle on the statistical properties of a plane jet discharging into a large space. The nozzle-exit profile was varied by changing orifice-plates with different exit radii (r) over the range of 0 < r/h < 3.60, where h is the slot-height. The present measurements were made at a slot-height based Reynolds number (Reh) of 1.80 × 104 and a slot aspect ratio (span/height) of 72. The results obtained show that both the initial flow and the downstream flow are dependent upon the ratio r/h. A “top-hat” mean exit velocity profile is closely approximated when r/h approaches 3.60. The decay and spread rates of the jet’s mean velocity decrease asymptotically as r/h is increased, with the differences becoming small as r/h approaches 3.60. A decrease in r/h results in a higher formation rate of the primary vortices in the near-field. The far-field values of the centerline turbulence intensity are higher for smaller r/h, and display asymptotic-like convergence as r/h approaches 3.60. Overall, the effect of r/h on the mean and turbulence fields decreases as r/h increases.