Turbulent drag in a rotating frame

Abstract : What is the turbulent drag force experienced by an object moving in a rotating fluid? This open and fundamental question can be addressed by measuring the torque needed to drive an impeller at constant angular velocity ω in a water tank mounted on a platform rotating at a rate Ω. We report a dramatic reduction in drag as Ω increases, down to values as low as 12% of the non-rotating drag. At small Rossby number Ro = ω/Ω, the decrease in drag coefficient K follows the approximate scaling law K ∼ Ro, which is predicted in the framework of nonlinear inertial wave interactions and weak-turbulence theory. However, stereoscopic particle image velocimetry measurements indicate that this drag reduction rather originates from a weakening of the turbulence intensity in line with the two-dimensionalization of the large-scale flow.
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Antoine Campagne, Nathanaël Machicoane, Basile Gallet, Pierre-Philippe Cortet, Frédéric Moisy. Turbulent drag in a rotating frame. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2016, 794, ⟨10.1017/jfm.2016.214⟩. ⟨cea-01485216⟩

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