Experimental Investigation of the Bubbly Drag Reduction in the Presence of Axial Flow in a the Couette-Taylor System

Modification of frictional drag reduction due to the presence of small bubbles and axial flow is investigated experimentally using a Couette-Taylor system. Flow condition between concentric cylinders is fully turbulent and Taylor vortices are appeared into flow when rotational Reynolds number is changed from 5000 to 70000. Torque acting on rotating inner cylinder and bubble behavior are measured while air bubbles and axial flow are injected constantly from the bottom of the system into annulus gap. Pure water is used to avoid the uncertain interfacial property of bubbles and to produce nearly mono-sized bubble distributions. Bubble diameter is measured by image processing method. The result showed that in the absence of small bubbles, axial flow reduces the friction drag. Moreover, it is observed that axial flow improves positive effect of bubbles on drag reduction. In this case, a drag reduction of 28% is obtained which is decreased by increasing the rotational Reynolds number.