Abstract
The phenomenon of skin friction reduction with micro bubble has been studied experimentally. We reveal the relation between drag reduction and the bubble size, using two different types of bubble. One is large bubble of millimeter order by porous plate ; and the other is small bubble of micrometer order made by mixing air and water under high pressure. Bubble diameter is calculated from images captured by high speed camera and the shear stress is measured by shear stress sensor. The experiments have been carried out for large bubble flow conditions with Reynolds number ranging from 10,000 to 50,000 ; void fraction up to 0.04 and small bubble flow with Reynolds number ranging from 30,000 to 50,000 ; void fraction less than 0.01. In the case of large bubble flow for Re>30,000, drag has been reduced up to 10%. In contrast, small bubbles hardly contribute to reduce shear stress due to dispersion of bubbles in turbulent channel flow.
