Results are presented of direct numerical simulations (DNS) of a viscous, laminar ring. The effects of different generator configurations and velocity programs on the formation and posthyphen;formation characteristics of the ring are studied. It is shown that during the formation phase of the ring, total circulation and impulse in the flowfield are approximately the same for the lsquo;lsquo;nozzlersquo;rsquo; and lsquo;lsquo;orificersquo;rsquo; generators. It is also found that throughout this period the slug flow model underhyphen;predicts the total circulation in the flow. During the formation phase, the simulation results for the time evolution of total circulation and location of the vortex spiral center are in agreement with the experimental findings of Didden lsqb;J. Appl. Mech. Phys. (ZAMP)30, 101 (1979)rsqb;. The results of the flow visualization studies show that during the posthyphen;formation phase a vortex bubble is formed. As the bubble propels itself forward a wake is formed in the rear of the bubble. The impulse and vorticity from the bubble are continuously shed into this wake. It is found that the total value of the circulation in the flow varies as (t1ast;)minus;0.33which is consistent with Maxworthyrsquo;s lsqb;J. Fluid Mech.81, 465 (1977)rsqb; prediction of the decay of circulation for a vortex ring. The transport of a passive Shvabhyphen;Zeldovich scalar variable is used to study the mixing and to obtain the maximum product formation in a chemical reaction of the typeA+Brarr;Productsin a vortex ring. It is found that as the bubble containing the fuel propels itself forward, the outside oxidizer flow is entrained into it and reacts to form a product. Some of this product then is dehyphen;entrained into the wake of the bubble. copy;1996 American Institute of Physics.
展开▼
