Vortices structure

The study of laminar vortical structures has been well documented in the Taylor-Couette (TC) flow for an extensive range of gap sizes [33]. Of particular interest are the experimentally determined boundaries in the map of flow regimes [34], and specifically the flow regime where the propagating helical vortex and stationary toroidal vortex modes become stable simultaneously and interact in the axisym-... 

Gutmark, E., T. P. Parr, D.M. Hanson-Parr, and K.C. Schadow. 1988. Evolution of vortical structures in flames. 22nd Symposium (International) on Combustion Proceedings. Pittsburgh, PA The Combustion Institute. 523-29. 

Yu, K., K. J. Wilson, T. P. Parr, R. A. Smith, and K.C. Schadow. 1996. Characterization of pulsating spray droplets and their interaction with vortical structure. AIAA Paper No. 96-0083. 

The experimental studies show that heating accelerates the flow and arrests jet growth absolute values of turbulence intensity increase but not as rapidly as the mean velocities. So, normalized turbulence intensities are lower. The effects of the amount of heating and its distribution on the evolution of the computed jet have been previously reported in [7]. These results show all the qualitative features that have been found in the experiments. In this paper, the findings of the study related to the effects of heat release on the vortical structure and entrainment characteristics of the jet are described. 

Toyoda, K., and F. Hussain. 1989. Vortical structures of noncircular jets. 4th Asian Congress of Fluid Mechanics Proceedings. Hong Kong. A117-27. 

The air flow was visualized by injecting smoke into the combustor settling chamber. Without air forcing, the naturally existing axial and helical vortices are weak and disorganized. Images of these natural vortical structures could not be clearly captured during this experiment. 

For all cases, the enhancement levels decrease in the axial direction, and are again associated with a loss of coherence and breakdown of the vortical structures. 

In their milestone work, Melander and Hussain found that the method of complex helical wave decomposition was instrumental in modeling both laminar as well as turbulent shear flows associated with coherent vortical structures, and revealed much new important data about this phenomenon than had ever been known before through standard statistical procedures. In particular, this approach plays a crucial role in the description of the resulting intermittent fine-scale structures that accompany the core vortex. Specifically, the large-scale coherent central structure is responsible for organizing nearby fine-scale turbulence into a family of highly polarized vortex threads spun azimuthally around the coherent structure. 

Figure 13 plots an example of the processed PIV frame. The turbulent velocity field and its boundaries, solid wall, and liquid-free surface are simultaneously shown in Figure 13. The turbulence structures such as the coherent vortical structure near the bottom wall and its modification after release from the no-slip boundary condition near the free surface of the open-channel flow, and the evolvement of the free-surface wave can be seen in Figure 13. This simultaneous measurement technique for free-surface level and velocity field of the liquid phase using PIV has been successfully applied to the investigation of wave-turbulence interaction of a low-speed plane liquid wall-jet flow (Li et al., 2005d), and the characteristics of a swirling flow of viscoelastic fluid with deformed free surface in a cylindrical container driven by the constantly rotating bottom wall (Li et al., 2006c).

Figure 20 An example of the approximated 3D bubble shape and corresponding flow structure estimated from the measurement using PIV/LIF combining with double-SIT system (a) characteristic vorticity structure around the bubble (bubble moves in the y-z plane) (b) reconstructed 3D bubble shape (c) relation between bubble location and measured plane for PIV and (d) 3D bubble trajectory (Fujiwara et al., 2004a) (see Plate 7 in Color Plate Section at the end of this book).

In all early experiments including the one by Poll (1979), existence of attachment-line vortical structures is well established. It is thus natural to investigate the sub-critical instability by looking at the role of convecting vortical structures in explaining LEG from the solution of two-dimensional Navier-Stokes equation in the attachment-line plane itself, similar to the vortex-induced instability problem studied in Lim et al. (2004) and Sengupta et al. (2003) for zero pressure gradient flow. 

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