Effect of Rotational Speed on the Stability of Two Rotating Side-by-side Circular Cylinders at Low Reynolds Number

TL;DR

This study numerically investigates how rotational speed influences flow stability around two side-by-side rotating cylinders at low Reynolds numbers, revealing that counter-rotation can suppress vortex shedding and flow destabilization.

Contribution

The paper introduces a numerical analysis of flow stability around rotating cylinders using energy gradient theory, highlighting the effects of rotation and Reynolds number on flow behavior.

Findings

Counter-rotation suppresses unsteady vortex shedding.

Higher Reynolds number shortens the wake length.

Flow stability is most affected at shear layers.

Abstract

Flow around two rotating side-by-side circular cylinders of equal diameter D is numerically studied at the Reynolds number Re=40-200 and various rotation rate theta_i. The incoming flow is assumed to be two-dimensional laminar flow. The governing equations are the incompressible Navier-Stokes equations and solved by the finite volume method (FVM). The ratio of the center-to-center spacing to the cylinder diameter is T/D=2. The objective of the present work is to investigate the effect of rotational speed and Reynolds number on the stability of the flow. The simulation results are compared with the experimental data and a good agreement is achieved. The stability of the flow is analyzed by using the energy gradient theory, which produces the energy gradient function K to identify the region where the flow is the most prone to be destabilized and the degree of the destabilization. Numerical results reveal that K is the most significant at the separated shear layers of the cylinder pair. With Re increases, the length of the wake is shorter and the vortex shedding generally exhibits a symmetrical distribution for theta_i <theta_crit. It is also shown that the unsteady vortex shedding can be suppressed by rotating the cylinders in the counter-rotating mode.