Rectangular jets

VORTEX DYNAMICS, ENTRAINMENT. AND NONPREMIXED COMBUSTION IN RECTANGULAR JETS... 

Figure 13.4 Instantaneous isosurfaces of the vorticity magnitude for the AR = 3 rectangular jet [34], 1 — single ribs aligned with corners, 2 — vortex rings, and 3 — braid (rib) vortices... 

The database of jet simulations can also be used to obtain insights on the potential impact of AR on non-premixed rectangular-jet combustion. 

The goal of this work has been to characterize the effects of the unsteady vor-ticity dynamics on jet entrainment and nonpremixed combustion. The main focus of the numerical simulations of rectangular jets has been on the vortic-ity dynamics underlying axis switching when the initial conditions at the jet exit involve laminar conditions, negligible streamwise vorticity, and negligible azimuthal nonuniformities of the momentum thickness. 

Grinstein, F. F. 1995. Self-induced vortex ring dynamics in subsonic rectangular jets. J. Physics Fluids 7 2519-21. 

Grinstein, F.F. 1993. Vorticity dynamics in spatially-developing rectangular jets. AIAA Paper No. 93-3286. 

Winter et al. [119, 120] studied phase changes in the system PS/PVME under planar extensional as well as shear flow. They developed a lubrieated stagnation flow by the impingement of two rectangular jets in a specially built die having hyperbolic walls. Change of the turbidity of the blend was monitored at constant temperature. It has been found that flow-induced miscibility occurred after a duration of the order of seconds or minutes [119]. Miscibility was observed not only in planar extensional flow, but also near the die walls where the blend was subjected to shear flow. Moreover, the period of time required to induce miscibility was found to decrease with increasing flow rate. The LCST of PS/PVME was elevated in extensional flow as much as 12 K [120]. The shift depends on the extension rate, the strain and the blend composition. Flow-induced miscibility has been also found under shear flow between parallel plates when the samples were sheared near the equilibrium coexistence temperature. However, the effect of shear on polymer miscibility turned out to be less dramatic than the effect of extensional flow. The cloud point increased by 6 K at a shear rate of 2.9 s. ... 

For a rectangular jet the wetted perimeter concept must be used (Marple, 1970). That is, the opening width A to be used in computing the Reynolds number is defined as A = 4 (area/perimeter). For a rectangle of length L and width W, A = 2WLI (W + L). When Lf> W,... 

Marple and Rubow (1986) state that the jet Reynolds number in an impactor can be expressed in terms of the air mass flow rate m. Show that for a round jet impactor Re = mW/p, and for a rectangular jet impactor Re = 2mW/p. Marple and Rubow point out that this is a useful form for the Reynolds number since m is constant for all stages of the impactor. 

Impactor 50 percent cut points can be estimated from the equation for rectangular jets of length L and width W or... 

The use of multiple tube banks as a droplet collector has also been studied by Calvert (R-12). He reports that collection efficiency for closely packed tubes follows equations for rectangular jet impaction which can be obtained graphically from Fig. 14-115 by using a dimensional parameter p which is based on the tube geometry p = 2li/b, where b is the open distance between adjacent tubes in the row (orifice width) and It is the impaction length (distance between orifice and impingement plane), or approximately the distance between center-lines of successive tube rows. Note that the impaction parameter is plotted to the one-half power in Fig. 14-115 and that the radius of the droplet is used rather than the diameter. Collection efficiency overall for a given size of particle is predicted for the entire tube bank by... 

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