2009 年 57 巻 663 号 p. 160-165
Mixing and spreading characteristics of an orifice free jet are investigated changing the orifice plate thickness t/do, where do is the nozzle exit diameter, ranged from 0.01 to 1.5. Schlieren images show high mixing and spreading performances at t/do = 0.5 and Reynolds number Re = 1.5×104 because at the t/do = 0.5 the jet fluctuates by the separated flow from the inner edge of orifice alternates attachment and detachment to the outer edge. Hot-wire anemometry measurements are also performed to investigate the mean and fluctuating velocity profiles. It is found that the jet potential core length is insensitive to Re at Re > 7.0 × 103, but significantly influenced by the orifice plate thickness. The potential core length for t/do = 0.5 is the shortest reflecting the fluctuation at the nozzle exit.