Anomalous Features in Internal Cylinder Flow Instabilities subject to Uncertain Rotational Effects

TL;DR

This paper models and analyzes the flow instabilities inside a high-speed rotating cylinder caused by symmetry-breaking disturbances, revealing non-Gaussian behaviors and memory effects that can be exploited to improve turbulent mixing.

Contribution

It introduces a stochastic CFD framework combining spectral/hp element and probabilistic collocation methods to study flow instabilities under uncertain rotational effects.

Findings

Symmetry-breaking disturbances induce flow instability from the wall.

Non-Gaussian statistics emerge due to coherent vortical motions.

Flow instability causes long-term memory effects in flow dynamics.

Abstract

We study the flow dynamics inside a high-speed rotating cylinder after introducing strong symmetry-breaking disturbance factors at cylinder wall motion. We propose and formulate a mathematically robust stochastic model for the rotational motion of cylinder wall alongside the stochastic representation of incompressible Navier-Stokes equations. We employ a comprehensive stochastic computational fluid dynamics framework combining spectral/$hp$ element method and probabilistic collocation method to obtain high-fidelity realizations of our mathematical model in order to quantify the propagation of parametric uncertainty for dynamics-representative quantities of interests. We observe that the modeled symmetry-breaking disturbances cause a flow instability arising from the wall. Utilizing global sensitivity analysis approaches, we identify the dominant source of uncertainty in our proposed model. We next perform a qualitative and quantitative statistical analysis on the fluctuating fields characterizing the fingerprints and measures of intense and rapidly evolving non-Gaussian behavior through space and time. We claim that such non-Gaussian statistics essentially emerge and evolve due to an intensified presence of coherent vortical motions initially triggered by the flow instability due to symmetry-breaking rotation of the cylinder. We show that this mechanism causes memory effects in the flow dynamics in a way that noticeable anomaly in the time-scaling of enstrophy record is observed in the long run apart from the onset of instability. Our findings suggest an effective strategy to exploit controlled flow instabilities in order to enhance the turbulent mixing in engineering applications.