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In a horizontal flow channel an experimental study was made on the effects of a small amount of air bubbles on the performance of a circular cylinder at a critical flow range where the drag coefficient of the test model decreased as Reynolds number increased. The measurements of the pressure distribution and fluid forces on the cylinder, the longitudinal turbulence level in water phase and the bubble size distribution in a free stream were taken. The results indicated that a large reduction in the drag coefficient and a change of the pressure distribution around the test model were caused at the low critical flow range by introducing a very small quantity of air bubbles such as 0.05 percent, though the turbulence level in water phase did not increase.

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