The effect of nutation angle on the flow inside a precessing cylinder and its dynamo action

The effect of the nutation angle on the flow inside a precessing cylinder is experimentally explored and compared with numerical simulations. The focus is laid on the typical breakdown of the directly forced m =1 Kelvin mode for increasing precession ratio (Poincare number) and the accompanying transition between laminar and turbulent flows. Compared to the reference case with a 90 degrees nutation angle, prograde rotation leads to an earlier breakdown, while in the retrograde case, the forced mode continues to exist also for higher Poincare numbers. Depending largely on the occurrence and intensity of an axisymmetric double-roll mode, a kinematic dynamo study reveals a sensi-tive dependence of the self-excitation condition on the nutation angle and the Poincare? number. Optimal dynamo conditions are found for 90 degrees angle which, however, might shift to slightly retrograde precession for higher Reynolds numbers.(c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http:// creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/5.0134562