On the influence of initial conditions on a turbulent plane jet: the role of nozzle exit area

Abstract

The dependence of statistical flow properties of a turbulent plane jet on the nozzle-exit area was investigated experimentally. Jet flows from three plane nozzles were measured using hot wire anemometry at an identical Reynolds number (Re = Uco H / nu) of 9,000 and nozzle aspect ratio of 36, but with nozzle-exit areas of A = 900 mm2, 3600 mm2 and 14400 mm2, whereby Uo,c was the mean exit velocity, nu was the kinematic viscosity of air, and H was the slot opening width. Results demonstrated a longer potential core and a higher decay rate for the case with a larger nozzle-exit area. The centerline turbulence intensity (u*) showed a strong dependence on A in the near field but this dependence weakened progressively as the jet propagated downstream. The jet flow from the nozzle with a larger exit area produced a relatively higher near field turbulence intensity, indicating a significant dependence of near field vortical structures on the nozzle-exit area. The centerline turbulence intensity profiles became selfsimilar, collapsing on a single curve only for x/H >= 10. Overall, the dependence of the mean and turbulent velocity field on nozzle-exit area was significant, confirming the influence of initial and boundary conditions.