Coherent Structures in a Fully Developed Stage of a Non-isothermal Round Jet

Direct numerical simulation (DNS) was performed for a non-isothermal air jet of the Reynolds number equal to 1 200 in order to reveal coherent structures of the jet. Fourth-order central finite difference was applied to the simulation. Effort was also made for experimental visualization (dye mixing and PTV) supporting the validity of instantaneous structures by DNS. Computational results for two kind of inlet profiles suggested that nozzle conditions scarcely affect turbulent statistics and coherent structures in jet-established-stage. Two-point correlations of velocity and temperature show similar distributions denoting that temperature can be used as a indicator of a vortex. Conceptual model of hairpin-shape vortex was proposed and validated by the two-point correlations and the PDF analysis for vorticity alignment; the hairpin-shape vortex stands with legs inclined downstream, and the inclination angle and the tilting angle between two legs are -45° and 40°, respectively.