MICROBUBBLE DRAG REDUCTION.

Photographic and optical surveys of microbubble boundary layers are presented. The results show that the outer edge of the bubble cloud diffuse away from the wall as the bubbles are swept downstream. The plate-on-bottom orientation contains a bubble-free region near the wall that cannot be discerned for the plate-on-top configuration. Skin friction measurements made when the bubble-free region extends to y** plus equals 100 show there is no longer any C//f reduction present suggesting bubbles are not effective when they are in the outer portion of the boundary layer. Bubble size measurements show sizes from 200 to 1100 mu m. Bubble size increases with airflow and decreases with freestream velocity. Bubble coalescence with distance from the injection section appears to be significant.