INFLUENCE OF PRESSURE AND TEMPERATURE ON FLOW PAST A HYDROPHOBIC CYLINDER AT HIGH REYNOLDS NUMBERS
K. G. Dobroselsky
Kutateladze Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences (KIT SB RAS), Novosibirsk, Russia
Keywords: hydrophobic cylinder, PIV, near wake, drag coefficient, Reynolds stress
Abstract
We investigate the effects of the Reynolds number, static pressure, and flow temperature on the evolution of vortex structures in the turbulent wake of a circular Teflon cylinder. Velocity fields are measured using particle image velocimetry (PIV) in a hydrodynamic facility for Reynolds numbers in a range of 1.75 · 105 ÷ 2.84 · 105. The hydraulic drag coefficient of the cylinder, together with time-averaged wake characteristics, indicates an earlier onset of the drag crisis, similar to that observed for rough, non-hydrophobic surfaces. It is shown that a reduction in the freestream pressure leads to both an increase in the wake size and the hydraulic drag. Furthermore, an increase in the flow temperature leads to a decrease of the hydraulic drag of the cylinder, despite larger wake dimensions. This reduction is attributed to a possible decrease in Reynolds stresses on the cylinder surface and the associated frictional drag component.
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