In this section, transformations from anomalous modes to primary modes are presented, which occur during or after the deceleration of the inner cylinder.
Figure 5 shows the variation of velocity vectors in the (r, z) plane at
= 5.4, where the Reynolds number is decreased from 700 to 80.
The primary mode at this aspect ratio has 4 cells.
When the Reynolds number is increased abruptly from 0 to 700, an
anomalous secondary mode with 6 cells appears.
The anomalous mode has extra cells on the end wall of cylinders
(Nakamura and Toya, 1996).
The velocity vectors and the contours of the stream function
near the end wall are shown in Fig. 6.
In Fig. 7, the profiles of the radial component of the strain rate
on the end walls are presented.
The anomalous cell at t = 3003 in Fig. 6 is accompanied by extra cells
in the regions adjacent to the inner cylinder and the outer cylinder.
At t = 2940 in Fig. 7, the positive or negative sign of the
strain rate reveals that the flow is outward in the middle part of the
end wall, while the flow is inward in regions near the inner and
outer cylinders.
As the rotation speed decreases, the extra cells merge into a single
cell and the mode changes to a normal mode with 6 cells.
Then, a pair of cells, which is adjacent to the merged cell and has a
boundary with inward flow between the two cells, becomes weak.
The mode transition in Fig. 5 is almost symmetric in the axial direction,
and there are two pairs of weakening cells.
Finally these pairs vanish, and the flow becomes a primary 4-cell mode.
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Figure 8 shows the transition from an anomalous second mode with an odd number of cells, where the aspect ratio is 4.4 and the Reynolds number decreases from 600 to 100. Figure 9 shows the profiles of the radial strain rate on the end walls under the same condition as in the case of Fig. 8. Two extra cells are formed on the end wall where an anomalous cell appears. As the rotation speed decreases, the extra cells merge and the flow becomes a normal mode with 6 cells. While the merged cell grows, a pair of cells adjacent to the merged cell disappears, and the flow changes to a primary 4-cell mode.