HYDRAULIC FORCES ACTING ON A CIRCULAR-CYLINDER WITH SURFACE SOURCE OFMINUTE AIR BUBBLES AND ITS CAVITATION CHARACTERISTICS

Experiments are performed by using two circular cylinders made of poro us filter material that is, bronze sintered compact, with a different filter size, respectively, in a water tunnel. The effects of minute ai r bubbles injected from the surface of the circular cylinder into its boundary layer on its hydraulic force characteristics are investigated over the Reynolds number (1.2 approximately 4.2) x 10(5), changing th e airflow rate of bubble injection. The pressure distributions on the porous cylinders are also measured. Their cavitation characteristics a re studied, too. Compared with a smooth-surface cylinder, the critical Reynolds numbers of the porous cylinders decrease owing to the increa se in the surface roughness caused by the bronze particles which compo se the sintered compact. The effects of the bubble injection on the hy draulic force characteristics are different according to the size of t he bronze particles. Though a little difference is recognized, the hyd raulic force characteristics show a similar tendency in both cases of bubble injection and cavitation occurrence.