Motion fields generated by the oscillatory motion of a circular cylinder in a linearly stratified fluid

• Published in: Experimental thermal and fluid science 1997, Vol.14 (3), p.277-296
• Main Authors: Xu, Yunxiu, Boyer, Don L., Fernando, Harinda J.S., Zhang, Xiuzhang
• Format: Article
• Language: English
• Subjects: Buoyancy; Cylinders (shapes); Exact sciences and technology; Fluid dynamics; Fundamental areas of phenomenology (including applications); Kinematics; Mathematical models; Mixing; motion of cylinders in stratified fluid; Nonhomogeneous flows; Oscillations; Physics; Rotational flow and vorticity; Separated flows; Stratified flows; Viscosity of liquids; Wave transmission
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/S0894-1777(96)00130-6

The motion field generated by either the horizontal or the vertical finite-amplitude oscillation of a long right circular cylinder in a linearly stratified fluid is investigated by a series of laboratory experiments; the oscillation frequencies considered cover a range both less than and greater than the bouyancy frequency. The governing parameters are shown to be the oscillation amplitude to cylinder diameter ratio a/ D, the oscillation frequency to bouyancy frequency ratio ω/ N, and the viscous to bouyancy time-scale ratio T vb = ND 2/ v (or the Stokes number β = ωD 2/ v), where v is the kinematic viscosity of the fluid. Flow regime diagrams are deeeloped as functions of a/ D and ω/ N for a fixed T vb. The characteristic flow types for the horizontal oscillation case include weakly detached flow, localized mixing, layering, and single intrusion, whereas the vertical oscillation leads to weakly detached flow, localized mixing, and single and double intrusions. Both oscillation directions lead to propagating internal waves when ω/ N < 1; the direction of the group velocity is observed to be given by the angle sin −1( ω/ N) to the horizontal axis, in accord with linear theory. A nondiffusive numerical model is developed to investigate the flow behavior during the initial stages of the cylinder oscillations. The large-scale motion features obtained from the numerical model for the early flow development of the various flow regimes are found to compare well with those of the laboratory experiments.