| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 82 === A combined numerical and experimental analysis has been car-
ried out for investigating the behavior of a pair of line
vorti- ces,mutually propelled to approach a circular cylinder.
The flow is assumed to be two-dimensional in numerical
simulations, and which condition is examined carefully in
laboratory experiments. The Reynolds number Re=.kappa./.nu.
based on the initial circu- lation .kappa. of the vortices and
the kinematic viscosity .nu. of the fluid range from 100 to
1500. The major point of interes- t is the effect of flow
separation, which induces formation of secondary vortices,
interacting then with the primary vortices. Flow behaviors are
identified and classified within different f- low regimes with
the help of six types of characteristic trajec- tories
associated with the primary and secondary vortices. Of p-
articular interest are the phenomena of rebound and reversal,
ex- hibited respectively by the primary vortices moving against
the cylinder under different flow conditions. Stable pairs of
line vortices are generated in laboratory experiments; flow
visualiz- ation shows excellent agreement with numerical
results in the c- omparisons of global flow behaviors,and in
particular trajector- ies of the points of maximum vorticity
and those of maximum val- ues of the streamfunction.
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