Cavity separations and associated impulsive pressures around a cavitating circular cylinder. 1st report: Vortex cavitation in the wake and attached cavitation

Abstract

The flow pattern and the fluctuating pressure are systematically studied around a cavitating circular cylinder, especially about the wake and the attached cavity separation in the supercritical region where Re is greater than 4 x 10(exp 5) and less than 7 x 10(exp 5) in the closed-type cavitation-tunnel, by means of highspeed photography and time series analyses. The impulsive pressures of about -70kPa in amplitude and of 4 ms in half width duration originate within the core of the vortex cavitation, which occurs frequently in the turbulent wake. The attached cavitation is intermittently resulted by the alternately fluctuating pressures from the Karman vortices and its inception point locates within the turbulent transition region where the fluctuating pressures of about 7kHz are predominant. In the attached cavitation, the Brennen waves expectedly appear at the boundary between the clear- and the cloud-cavity, from which a lump of bubbles separate, leaving the clear cavity.

キャビテーションする円柱のまわりの流れパターンと変動圧力の系統的測定を行なった。特に4×10{5}<Re<7×10{5}の超臨界領域での伴流と付着キャビティ剥離を、閉流型キャビテーションタンネル中で高速度写真と時系列解析法により調べた。振幅-70kPa,持続時間の半値幅4msのインパルス圧力が渦キャビテーションの内部で生じており、乱流伴流中で頻発していることを示す。付着キャビティは間欠的にKarman渦により交互に発生する変動圧力により発生し、その発生位置は変動圧力が約7kHzの乱れた過渡領域内にあることがわかる。付着キャビテーションにおいてはBrennen波が透明および不透明キャビティの間の境界で予想通り発生し、これより気泡の塊が発生し、透明なキャビティを放出する。