Angular momentum transport in a very wide gap TC geometry η = 0.1.

  • Hamede, Mohammed Hussein (Brandenburg University of Technology Cottbus)
  • Merbold, Sebastian (Brandenburg University of Technology Cottbus)
  • Egbers, Christoph (Brandenburg University of Technology Cottbus)

Please login to view abstract download link

From the early work of Taylor (1923) until today, the TC flow was studied for different geometries, in this study the results are presented for TC flow in very wide gap geometry η = 0.1 which is rarely studied before Merbold et al. (2023), and the scope of the study is the counter-rotating regime. The flow was investigated for shear Reynolds number 2 × 104 ≤ Res ≤ 1.31 × 105, and rotation rates −0.06 ≤ μ ≤ 0. Using a High-speed Particle Image Velocimetry technique, ur and uφ the radial and azimuthal velocities, are measured at different heights, 10 above and 10 below the apparatus midheight, with axial distance ∆z = 4mm between each height. From the measured velocities, the dependence of the system’s global response which can be quantified by the angular momentum transports, on the rotation ratio is studied. The results show that for the different studied Res cases, the angular momentum transport increases for slight counter-rotating rates, and achieves a maximum at −0.011 ≤ μmax ≤ −0.007, where this increase is due to the strengthening of the Large-scale circulation in the flow. This result is in agreement with the previously studied TC flows in narrower geometries. But in contrast to these studies, the angular momentum transport decreases for higher counter-rotation rates where it achieves a minimum and tends to increase again for higher counter-rotating rates where it is expected to achieve a second maximum as shown in figure 1. The space-time behavior of the flow was studied for the high counter-rotating cases, where we observe the existence of small-scale patterns next to the outer cylinder that travels inward through the gap. From our observations of the flow structures, especially the inward traveling patterns, the existence of a shear layer instability is assumed which causes the increase in the angular momentum transport at this high counter-rotating cases. Further, the spatial two-point auto-correlation coefficient of the azimuthal velocity fluctuation at different radial positions for the flows with different μ was studied. For the highest studied counter rotating case μ = −0.06, the auto-correlation profiles for the flow next to the outer cylinder achieve a minimum for φr/d ≈ 1.25, which is interpreted as the size of the newly observed patterns.