The bathtub vortex (i.e., sink flow with swirl velocity) is a well-known phenomenon.
The appearance of swirl in the sink flow and the formation of the bathtub vortex can result from many factors.
Fundamentally, there have been several experimental and numerical studies to investigate the possibility of self-rotation phenomenon and the related instability in the sink flow. However, there is no consensus among the researchers about either the possibility or impossibility of this phenomenon.
In fact, one can see different and conflicting findings from the above mentioned studies, that is, some researchers accept the existence of self-rotation in the sink flow and some refuse.
In the present work, the possibility of circulation generation in the sink flow is studied numerically.
The Froude number of sink flow studies, defined as Fr = [square root of [Q.sup.2]/g[H.sup.5]], is always lower than 0.5 value.
First, the results corresponding to the stability of the sink flow and the effect of Re number on the azimuthal velocity [V.sub.[theta]] and circulation [GAMMA] are shown in Figs.
This result is consistent with the results obtained for the sink flow with a rotating body [22].
Knowing the inlet values of [V.sub.[theta].sup.*] as is the case in the present numerical study will be useful for understanding the nature of the swirl appearance in the sink flow. Fig.
The experimental studies [10-13] claimed that the swirl appears in the sink flow when either the drain flow rate or the Re number reaches some critical value.
