Abstract
Complex streamwise vorticity fields are observed in the evolution of non-circular jets. Generation mechanisms are investigated via Reynolds-averaged (RANS), large-eddy (LES) and direct numerical (DNS) simulations of laminar and turbulent rectangular jets. Complex vortex interactions are found in DNS of laminar jets, but axis-switching is observed only when a single instability mode is present in the incoming mixing layer. With several modes present, the structures are not coherent and no axis-switching occurs. RANS computations also produce no axis-switching. On the other hand, LES of high Reynolds number turbulent jets produce axis-switching even for cases with several instability modes in the mixing layer. Analysis of the source terms of the mean streamwise vorticity equation through post-processing of the instantaneous results shows that complex interactions of gradients of the normal and shear Reynolds stresses are responsible for the generation of streamwise vorticity which leads to axis-switching. RANS computations confirm these results. K-ε turbulence model computations fail to reproduce the phenomenon, whereas algebraic Reynolds stress model (ASM) model computations, in which the secondary normal and shear stresses are computed explicitly, succeeded in reproducing the phenomenon accurately.
| Original language | English |
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| Title of host publication | Proceedings of the 1999 3rd ASME/JSME Joint Fluids Engineering Conference, FEDSM'99, San Francisco, California, USA, 18-23 July 1999 (CD-ROM) |
| Publisher | American Society of Mechanical Engineers |
| Pages | 1 |
| Number of pages | 1 |
| ISBN (Print) | 0791819612 |
| State | Published - 1999 |
| Externally published | Yes |