Abstract
Flow structure in the near field of an annular jet is investigated experimentally by means of LDV for three ratios of the inner to outer diameter of an annular nozzle. The jet leaves the nozzle exit with an inward velocity component; a recirculating vortex region is formed between the nozzle exit and the stagnation point located on jet center line at the distance ranging from 0.6D to 1.2D, depending on the exit velocity and the nozzle diameter ratio. The dependence on the exit velocity larger than 10m/s is very slight and the stagnation point does not go beyond 1.2D from the exit with approaching the exit velocity to zero. The existence of a wall at the inner nozzle body has a negligible effect on the flow structure except for the static pressure in the recirculating vortex region, which tends to become proportional to the dynamic pressure of the issuing jet.
