The effect of bubbles on the wall drag in a turbulent channel flow -: art. no. 095102

The effect of a few relatively large bubbles injected near the walls on the wall drag in the minimum turbulent channel is examined by direct numerical simulations. A front-tracking/finite-volume method is used to fully resolve all flow scales including the bubbles and the flow around them. The Reynolds number, using the friction velocity and the channel half-height, is 135 and the bubbles are 54 wall units in diameter. The results show that deformable bubbles can lead to significant reduction of the wall drag by suppression of streamwise vorticity. Less deformable bubbles, on the other hand, are slowed down by the viscous sublayer and lead to a large increase in drag. (c) 2005 American Institute of Physics.