Vortex core

Flame Propagation in Vortices Propagation Velocity along a Vortex Core.45... 

The first literature concerning the flame propagation along a vortex core can be found in the journal Fuel in 1953. In Letters to the Editors, Moore and Martin [1] reported that when a combustible mixture was ejected... 

Before discussing about the flame speed along a vortex core, it is first necessary to be familiar with the flames in various vortex flows. To date, four types of vortex flows have been used to study the flame behaviors. They are (1) a swirl flow in a tube [1,10], (2) vortex ring [2,3,12,13,16], (3) a forced vortex flow in a rotating tube [11], and (4) line vortex [22]. 

The existence of the vortex core can be observed in a very special case. Figure 4.2.9 exhibits a Schlieren sequence of vortex ring combustion of pure fuel. In this case, propane fuel was ejected through an orifice into an open air, and the vortex ring was ignited by an electric spark at the bottom. Although the boundary... 

Vector profile of vortex ring combustion, showing induced velocities along the vortex core. (Lean propane/air mixture, equivalence ratio O = 0.8, Do = 60 mm, P= 0.6 MPa, dotted lines show the flame front taken with the ICCD camera. The right inset shows the relative position of the PIV laser sheet relative to the flame.)... 

It can be seen that the prediction 6a underestimates any results. This is because axial expansion is unrealistic, as indicated in Figure 4.2.8. On the other hand, prediction 5a covers almost all the results, except when the value of Vg is smaller than lOm/s. This is probably because of the usage of the mean pressure averaged over twice the radius of the vortex core in the model by Asato et al. [16], which is in quantitative agreement with the present vortex ring whose core diameter is about 25% the ring diameter. 

Asato, K., Wada, H., Himura, T., and Takeuchi, Y., Characteristics of flame propagation in a vortex core Validity of a model for flame propagation. Combustion and Flame, 110, 418 8,1997. 

In Chapter 4.2, S. Ishizuka presents his recent experimental and theoretical results on flame propagation along a vortex core. The validity of the existing models linking flame speed, vortex parameters, and mixture properties is discussed in the light of experimental results. 

Fig. 23. Snapshots of typical configurations of vortex core defects (isolated completely full triangles or completely empty triangles of neighboring sites, denoted by triangles standing on top or on bottom, respectively), for 0=1/2 and two temperatures as indicated. Case (a) to T < Ti,case(b)to T> Ti.(From Landau. )...

The soot formation and its control was studied in an annular diffusion flame using laser diagnostics and hot wire anemometry [17, 18]. Air and fuel were independently acoustically forced. The forcing altered the mean and turbulent flow field and introduced coherent vortices into the flow. This allowed complete control of fuel injection into the incipient vortex shedding process. The experiments showed that soot formation in the flame was controlled by changing the timing of fuel injection relative to air vortex roll-up. When fuel was injected into a fully developed vortex, islands of unmixed fuel inside the air-vortex core led to... 

Spectroscopic and spatial characterization of superconducting vortex core states with a scanning tunneling microscope. J. Vac. Sci. Technol. A 8, 450-454. H. F., Robinson, R. B., and Waszczak, J. V. (1990a). Vortex-core structure observed with a scanning tunneling microscope Phys. Rev. Lett. 64, 2711-2714. 

Fig. 57. Specific heat contribution y(H) of the vortex core electrons in the mixed state (normalized by the Sommerfeld parameter /n) of the Yj[Lu jrNi2B2C samples from fig. 56 as function of the applied magnetic field (normalized by //c2(0)). The straight line y(H)

Fig. 61. Magnetic field dependence of the specific heat contribution y(H) of the vortex core electrons in the mixed state for Y(Nio.7sPto.25)2B2C. The dashed line is a fit according to eq. (8) with /) = 0.17, the solid line corresponds to the y(H)

In this regard, Melander and Hussain [10] have made significant advances in casting fresh light on the perplexing problems of vortex core dynamics and the coupling between large scales and fine scales in the vicinity of a coherent structure. Essentially, they postulated that the dynamics of coherent structures is... 

In fig.4 (lower panel) it is schematically presented the structure of the SC vortex in the SDW/CDW + SC state. Since arising of the CDW results in the lattice modulation so that wave of dislocation walls is formed (fig.4 (middle panel)). As known, such dislocation walls are effective centers for pinning of SC vortices. Note that in such a structure every fifth wall is equivalent to first one ( cn+4 - c ). In this a model a vortex core has AF SDW structure which is also outside a core too. Because of equivalence of c and c +4 dislocation walls vortex core becames to be two part in form fluctuating in space (cf. with [14]). 

Despite the previously debated d-wave symmetry of the superconducting gap in YNi2B2C as suggested from the interpretation of specific-heat (Cp) data (Nohara et al., 1997), additional mechanisms for the T3 dependence of the electronic part of Cp and its unusual magnetic-field dependence were discussed, including the shrinking of the vortex core radius with increasing field (Nohara et al., 1999). The influence of disorder is discussed in Section 6.2. Measurements of the microwave... 

FIGURE 50 Single vortex in YNi2B2C. (a) Constant local-field contour at a distance of X from the center of the vortex core (after Yethiraj et alv 1998). (b) Vortex core imaged by STS (from... 

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