Air-lubrication in Bubble-Laden Couette Flow: Analysis of Drag Modification Mechanisms
ORAL
Abstract
Air-lubrication systems offer significant potential for marine transport drag reduction, with recent studies demonstrating substantial friction savings (Ceccio, ARFM 2010).
However, the fundamental mechanisms controlling drag modification regimes remain poorly understood. We perform a series of numerical simulations of Couette flow containing a swarm of bubbles to identify key parameters governing drag reduction versus increase.
Numerical simulations were conducted in a 4πδ×δ×2πδ domain with periodic streamwise/spanwise boundaries, a moving bottom wall (u=Uw), and a stationary top wall. Following turbulent flow development, 128 spherical bubbles (radius r=0.2δ, volume fraction 5.4%) are injected in a horizontal plane at the domain center. Density and viscosity ratios of 10 and 55 represent carrier-to-bubble fluid properties. Nine systematic simulations at Re = ρc Uw δ / μc = 5000, based on carrier flow properties, varied Froude (Fr = Uw² / (gδ) = 5, 50, 500) and Weber (We = ρc Uw² δ / σ = 69, 277, 5000) numbers as controlling parameters.
Results reveal that bubble deformability is crucial for effective drag reduction (Verschoof et al.,PRL 2016; Spandan et al., JFM 2018). Low Weber number cases maintain spherical bubbles, causing drag increase at Fr = 50, 500 and minimal reduction at Fr = 5. High Weber numbers enable bubble deformation and streak formation, obtaining drag reduction that reaches a maximum of 40% at Fr = 5, We = 5000.
However, the fundamental mechanisms controlling drag modification regimes remain poorly understood. We perform a series of numerical simulations of Couette flow containing a swarm of bubbles to identify key parameters governing drag reduction versus increase.
Numerical simulations were conducted in a 4πδ×δ×2πδ domain with periodic streamwise/spanwise boundaries, a moving bottom wall (u=Uw), and a stationary top wall. Following turbulent flow development, 128 spherical bubbles (radius r=0.2δ, volume fraction 5.4%) are injected in a horizontal plane at the domain center. Density and viscosity ratios of 10 and 55 represent carrier-to-bubble fluid properties. Nine systematic simulations at Re = ρc Uw δ / μc = 5000, based on carrier flow properties, varied Froude (Fr = Uw² / (gδ) = 5, 50, 500) and Weber (We = ρc Uw² δ / σ = 69, 277, 5000) numbers as controlling parameters.
Results reveal that bubble deformability is crucial for effective drag reduction (Verschoof et al.,PRL 2016; Spandan et al., JFM 2018). Low Weber number cases maintain spherical bubbles, causing drag increase at Fr = 50, 500 and minimal reduction at Fr = 5. High Weber numbers enable bubble deformation and streak formation, obtaining drag reduction that reaches a maximum of 40% at Fr = 5, We = 5000.
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Presenters
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Simone Di Giorgio
Institute of marine engineering - CNR
Authors
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Simone Di Giorgio
Institute of marine engineering - CNR
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Sergio Pirozzoli
Sapienza University of Rome
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Alessandro Iafrati
Institute of marine engineering - CNR