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LARGE EDDY SIMULATION OF VARIABLE DENSITY TURBULENT AXISYMMETRIC JETS

Ping Wang
Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, China

Jochen Frohlich
Institute for Technical Chemistry und Polymer Chemistry University of Karlsruhe; Institute of Fluid Mechanics, Dresden University of Technology, George-Bähr-Str. 3c, D-01062, Germany

Vittorio Michelassi
Nuovo Pignone, Via Felipe Matteucci 2, 50127Florence, Italy

Wolfgang Rodi
Institute for Hydromechanics,University of Karlsruhe, D-76128 Karlsruhe, Germany

Abstract

Three cases of variable-density turbulent round jets discharging from a straight circular pipe into a weakly confined low-speed co-flowing air stream are studied with the aid of large eddy simulation. The density ratios considered are 0.14 [He/air], 1.0 [air/air] and 1.5 [CO2/air], with Reynolds numbers of 7000, 21000 and 32000, respectively. Detailed comparisons of the statistics show good agreement with the corresponding experiments. They confirm that a lower-density jet develops more rapidly than a denser jet with the same exit momentum flux. The coherent structures of the three jets are investigated by visualization of the iso-surface of pressure fluctuations and vorticity. In the developing stage of the Kelvin-Helmholtz instability, large finger-shape regions of vorticity are observed for the helium jet close to the nozzle lip. This feature is not found in the air and the CO2 jet. The occurrence of strong streamwise vorticities across the shear layer in the helium jet is demonstrated by a characteristic variable related to the orientation of the vorticity.