Flow characteristics of a round jet with divergent and convergent tapered annulus

The flow characteristics of round air jets with tapered annulus was investigated experimentally. The divergent and convergent tapered annulus was installed concentrically inside of the round nozzle. The effects of the length of annulus, the diameter of annulus on the mean and fluctuating velocities, and the velocity ratio of the inner jet to outer jet at the nozzle exit were examined by the hot-wire measurement and flow visualization. In the case of the jets with the divergent tapered annulus, the outer jet was accelerated and the inner jet was decelerated. The spread of jet with the divergent tapered annulus increased in the near field of the jet. On the other hands, with convergent tapered annulus, the outer jet was decelerated and the inner jet was accelerated. The spreads of round jet with the convergent tapered annulus was smaller than the other jet. It is found that the flow characteristics of a round jet with tapered annulus was the similar to that of a plane jet with deflecting plates.