NUMERICAL PREDICTIONS OF THE BIFURCATION OF CONFINED SWIRLING FLOWS

The bifurcation of confined swirling flows was numerically investigated by employing both the k-epsilon and algebraic stress turbulence models. Depending upon the branch solution examined, dual flow patterns were predicted at certain swirl levels. In the lower-branch solution which is obtained by gradually increasing the swirl level from a low-swirl flow, the flow changes with increasing swirl number from the low-swirl flow pattern to a high-swirl flow pattern. In the upper-branch solution which is acquired by gradually decreasing the swirl level from a high-swirl flow, on the other hand, the flow can maintain itself in the high-swirl flow pattern at the swirl levels where it exhibits the low-swirl flow pattern in the lower branch. The bifurcation of confined swirling flows was predicted with either the k-epsilon model or the algebraic stress model being employed. Both the k-epsilon and algebraic stress models result in comparable and sufficiently good predictions for confined swirling hows if high-order numerical schemes are used. The 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.