Flow Visualization and Characteristics of a Coaxial Jet with a Tabbed Annular Nozzle

摘要

Flow visualization and measurements of mean and fluctuating velocities were performed on a coaxial jet with a velocity ratio of 0.6 at a Reynolds number of 3 000 in an open water tank using hot-film anemometry, particle image velocimetry (2D and stereoscopic PIV) and laser-induced fluorescence (LIF). Axisymmetric and streamwise vortical structures were revealed in the near-field of the coaxial jet. The annular nozzle has six vortex generators in order to enhance the streamwise vortices generated in the mixing layer. Furthermore, the annular jet was excited by a shaker in order to enhance the axisymmetric vortices. For the tabbed coaxial jet, jet spreading downstream was greater than for the jet without tabs. The cause of the entrainment increment is the development of axisymmetric and streamwise vortex structures. In the case of excited jets, significant axisymmetric and streamwise vortical structures develop, and the jet width expands from the exit nozzle. Consequently, the flow rate of the excited jet with tabs is larger than that of the unexcited jet without tabs.