We investigated flows sustained in precessing spherical and spheroidal cavities by means of laboratory experiments and direct numerical simulations.
One of the most interesting features of this system is that weak precession of a container can drive developed turbulence of the confined fluid in it. We experimentally determined the critical parameter, in a weak precession regime, for which the steady flow becomes unstable in a precessing sphere and in a slightly elongated spheroid. Interestingly, the spheroid requires much stronger precession than a sphere to drive unsteady flow for a given spin rate.
Next, we experimentally and numerically investigated the statistics of sustained turbulence in a precessing sphere. A remarkable feature is that large-scale flow structures are predominantly determined by the precession rate, and they weakly depend on the spin angular velocity. The most developed turbulence is always sustained when the precession angular velocity is about 10 percents of the spin. Our numerical simulations also show that these developed turbulence can enhance the mixing of a confined fluid, and they require only 10 spin periods to mix the fluid almost perfectly.
Finally, to demonstrate that this flow system can provide us with a standard platform for various fluid experiments, we show the results of a study on the physical mechanism of flow visualizations using reflective flakes.