NUMERICAL PREDICTIONS OF THE BIFURCATION OF CONFINED SWIRLING FLOWS

The bifurcation of confined swirling flows was numerically investigate d by employing both the k-epsilon and algebraic stress turbulence mode ls. Depending upon the branch solution examined, dual flow patterns we re predicted at certain swirl levels. In the lower-branch solution whi ch is obtained by gradually increasing the swirl level from a low-swir l flow, the flow changes with increasing swirl number from the low-swi rl flow pattern to a high-swirl flow pattern. In the upper-branch solu tion which is acquired by gradually decreasing the swirl level from a high-swirl flow, on the other hand, the flow can maintain itself in th e high-swirl flow pattern at the swirl levels where it exhibits the lo w-swirl flow pattern in the lower branch. The bifurcation of confined swirling flows was predicted with either the k-epsilon model or the al gebraic stress model being employed. Both the k-epsilon and algebraic stress models result in comparable and sufficiently good predictions f or confined swirling hows if high-order numerical schemes are used. Th e reported poor performance of the k-epsilon model was clarified to be mainly attributable to the occurrence of the bifurcation and the use of low-order numerical schemes.