Transition to Turbulence through Intermittence in Inert and Reacting Jets

— Subsonic flows of different gases in the near field of inert and reacting jets is experimentally investigated. The jets flowed out of long tubes, 2 to 8 mm in diameter, into an air medium at low Reynolds numbers from 400 to 5000. The working fluids were air, carbon dioxide, propane, and Freon-22 for inert isothermal jets and propane mixed with an inert dilution (СО 2 ) for reacting jets. The tools included Hilbert visualization, PIV, thot-wire anemometry, and probe thermometry. A scenario of transition to turbulence through the intermittence mechanism in inert and reacting jets is revealed for the first time. It is realized in the Reynolds number range from 1900 to 3500, when laminar-turbulent transition occurs within the jet source, that is, the tube, in the absence of artificial disturbances. Turbulent spots generated in the tube in the transitional regime are statistical in nature and fairly stable in the jet near-field. Propagating downstream they can have a considerable effect on the dynamics of free jets and diffusion plumes.