COHERENT STRUCTURE INTERACTIONS IN AN UNEXCITED COAXIAL JET

Based on a double triggering criterion, the axisymmetric and azimuthal structures within the initial region of an unexcited coaxial jet of m ean velocity ratio Of 0.3 (inner to outer) were recovered. Outer vorti ces, two trains of inner vortices and their amalgamation are found in the outer and inner mixing regions. Bifurcation of the amalgamated inn er vortices occurs within the first two diameters of the jet and is re sponsible for the occurrence of the azimuthal structures in the inner jet region further downstream. Co-dominance of the symmetrical and azi muthal structures having different convection velocities is observed i n the fully merged zone. Spatial separation between vortical structure s and their relative vorticities are important parameters in affecting their convection velocities, growth and decay.