抄録
Structure of roll vortices was examined in the transition region of a parabolic plane jet of Re=3850. Their pairing process were controlled by acoustical bimodal excitation and small tabs attached around a jet exhaust. Conditional sampling gave the phase-averaged maps of turbulence quantities; vorticity, Reynolds stresses and production terms. At pairing enhancing mode for the case of symmetrical vortex arrangement, the weaker trailing vortex shifted inward and entangled toward the downstream stronger leading vortex at the height of the tabs. Large amounts of coherent and incoherent Reynolds stresses became distributed widely through their mutual interaction, stretching of the trailing vortex or fragmentation by the breakdown of coherent vortices. Negative energy transfer from the incoherent to coherent components was observed, being caused by the excessive enhancement of the vertical structure. At the pairing redarding mode, two adjacent vortices were observed seldom to merge each other.
