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

TL;DR

This study investigates how the nutation angle influences flow patterns and dynamo action inside a precessing cylinder, revealing critical dependencies on angle and flow regimes through experiments, simulations, and dynamo modeling.

Contribution

It provides new insights into the impact of nutation angle on flow breakdown, turbulence transition, and dynamo self-excitation conditions in precessing cylinders.

Findings

Prograde rotation causes earlier flow breakdown.

Retrograde rotation sustains forced modes at higher Poincaré numbers.

Optimal dynamo conditions occur at 90° nutation angle.

Abstract

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 (Poincar\'e number), and the accompanying transition between a laminar and turbulent flow. Compared to the reference case with a 90{\deg} nutation angle, prograde rotation leads to an earlier breakdown, while in the retrograde case the forced mode continues to exist also for higher Poincar\'e numbers. Depending largely on the occurrence and intensity of an axisymmetric double-roll mode, a kinematic dynamo study reveals a sensitive dependency of the self-excitation condition on the nutation angle and the Poincar\'e number. Optimal dynamo conditions are found for 90{\deg} angle which, however, might shift to slightly retrograde precession for higher Reynolds numbers.