Numerical study on wide gap Taylor Couette flow with flow transition

TL;DR

This paper uses direct numerical simulation to analyze flow transitions and disturbance sources in wide gap Taylor Couette flow, revealing how flow separation and viscous layer changes lead to non-axisymmetric disturbances and flow pattern shifts.

Contribution

It provides new insights into the origin and propagation of non-axisymmetric disturbances in wide gap Taylor Couette flow through detailed analysis of viscous layer behavior and flow transition mechanisms.

Findings

Flow transitions from axisymmetric to non-axisymmetric occur between Re 425 and 575.

Sudden increase in viscous layer thickness at the outer wall indicates disturbance sources.

Transition flow shows reduced torque compared to axisymmetric Taylor-vortex flow.

Abstract

This study aims to investigate the possible sources of non-axisymmetric disturbances and their propagation mechanism in Taylor Couette flow (TCF) for wide gap problems using direct numerical simulation with a radius ratio of 0.5 and Reynolds number (Re) ranging from 60 to 650. Here, attention is focused on the viscous layer (VL) thickness in near-wall regions and its spatial distribution along the axial direction to gain an insight into the origin and propagation of non-axisymmetric disturbances. The results show that an axisymmetric Taylor-vortex flow occurs when Re is between 68 and 425. Above Re = 425, transition from axisymmetric to non-axisymmetric flow is observed up to Re = 575 before the emergence of wavy-vortex flow. From the variation of VL thickness with Re, the VL does not experience any significant changes in the flow separation region of the inner wall, as well as jet impingement region of both the inner and outer walls. However, a sudden increase in VL thickness in the flow separation region of the outer wall reveals possible source of non-axisymmetric disturbances in the flow separation region of the outer wall. These disturbances develop into the periodic secondary flow as the axisymmetric flow transforms into non-axisymmetric flow and this leads to the emergence of azimuthal wave. The periodic secondary flow contributes to sudden increase in the natural wavelength and rapid reduction in the strength of two counter-rotating Taylor vortices. This in turn leads to a substantial reduction of torque in the transition flow vis-a-vis axisymmetric Taylor-vortex flow.