Bubble Drag Reduction Requires Large Bubbles

Drag reduction by compressible bubbles.

Drag reduction by bubbles in stationary turbulent flows is sensitive to the compressibility of the bubbles. Without this dynamical effect the bubbles only renormalize the fluid density and viscosity, an effect that by itself can only lead to a small percentage of drag reduction. We show in this paper that the dynamics of bubbles and their effect on the compressibility of the mixture can lead to...

Simulations of Turbulent Drag Reduction Using Micro-Bubbles

Acoustic einstein-hopf drag on a bubble

Theoretical results show that the drag on a bubble can be modified by the presence of isotropic, homogeneous, broadband acoustic noise, when the band overlaps the bubble's resonance width. While these results constitute an acoustic analog to the Einstein-Hopf drag on an oscillating dipole in the presence of electromagnetic fluctuations, an important difference is that band-limited acoustic nois...

Large-area superhydrophobic nanofiber array structures for drag reduction

Surface with a static contact angle (CA) greater than 150° are in general defined as superhydrophobic surfaces. Superhydrophobic surface have great potentials in fundamental research,[1-5] and also wide practical applications in the production of textile, microfluidics, self-cleaning surfaces, building glass, windshields of cars, ships hulls, pipes and the satellite antenna surfaces.[6] Superhy...

Large Trucks Drag Reduction Using Active Flow Control

Aerodynamic drag is the cause for more than two-thirds of the fuel consumption of large trucks at highway speeds. Due to functionality considerations, the aerodynamic efficiency of the aft regions of large trucks was traditionally sacrificed. This leads to massively separated flow at the lee side of truck trailers, with an associated drag penalty: roughly a third of the total aerodynamic drag. ...