EVOLUTION OF VORTICAL STRUCTURES IN INDETERMINATE-ORIGIN NOZZLE JETS

摘要

Passive jet control is achieved by using nozzles of indeterminate origin (IO), i.e., nozzles, which are jagged or non-uniform around their circumference. The structure and flow field of round jets of water were studied using the Laser Induced Fluorescence (LIF) technique. Typical jet Reynolds numbers (based on the nozzle diameter and bulk velocity) are 5000-10,000. The jet structures for IO nozzles are compared to those produced by conventional round nozzles. The IO nozzles introduce strong streamwise vortex pairs, which influence the near-jet structure and spreading by deforming the primary spanwise (Kelvin-Helmholtz) vortex rings. The valleys of the IO nozzle entrain ambient fluid into the jet and generate incursion streamwise vortex pairs, which penetrate into the jet core. After reorganization, excursion streamwise vortex pairs transport jet fluid into the surrounding fluid at peak locations. The evolution of these structures with streamwise distance and their implications are discussed.