Numerical simulation of flow instability induced by a fixed cylinder placed near a plane wall in oscillating flow

Abstract

The Honji instability of in-line forced cylinder near a plane wall is investigated using Floquet analysis and direct numerical simulation using the open-source code Nektar++. The onset of the Honji instability is analyzed over a range of the gap-to-diameter ratios (e/D) from 2.0 to 0.03125, with fixed Keulegan–Carpenter number KC = 2, Stokes number β = 150, and Re = 300. As e/D decreases from 2 to 0.375, the Honji instability is primarily on the gap side of the cylinder. For 0.25<e/D<0.375, the location of the onset of the Honji instability switches from the gap side to the top side of the cylinder. This is due to the blockage effect, which results in the two different trends in the onset of the Honji instability with decreasing e/D. For 0.125<e/D<0.25, the favorable pressure gradient suppresses the onset of instability at the gap side. The Honji instability is observed again at the top side of the cylinder at smaller gap ratio (e/D=0.0625), which is due to increased flow strength at the top side. At even small gap ratio, i.e. e/D=0.03125, the secondary vortexes and Honji instability together enhance the three-dimensional flow.