Drag reduction via microbubble injection in boundary layer of channel flows
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An investigation of turbulent structure modification of fully developed channel flow by microbubble injection close to the upper wall was studied. Two-dimensional velocity components at Reynolds number of 5128 based on the half height of the channel and bulk velocity were measured. The particle image Velocimetry technique (PIV) was utilized to obtain the two-dimensional velocity fields of the fluid an the microbubbles. Microbubbles with an average diameter of 30 um were injected into the buffer layer. Various values of void fractions were used to evaluate the effects of microbubble concentrations on the drag reduction. Modifications in the lenght and time scales were detected by calculating two-point correlation coeffiecient and Wavelet maps. The energy spactra were calculated. It is interesting to note a shift from large frequency domain to lower low frequency structure.
