Bubble path in the wake of a cavitating propeller

Abstract

Propellers that operate underwater at high rpm's cavitate at the tip. The tip cavitation creates air bubbles that are then swept downstream by the motion of the surrounding fluid. In this paper, a theory is presented to predict the local velocity and the path of the bubble. The bubble motion is assumed to be governed by a group of terms due to the acceleration of the displaced fluid, the convective term, and the drag due to the cross‐sectional area of the bubble. At very low and very high Reynolds numbers, the equations have been solved in closed form. Results are presented for the bubble velocity and path for the following flow fields: (a) uniform axial flow field and (b) uniform flow field with an axially decaying swirling component. In all cases presented the bubble axial velocity component asymptotes to the free stream velocity; the manner in which it asymptotes is exponential at very low Reynolds numbers and algebraic at high Reynolds numbers. Bubble helical paths and velocity patterns are shown for different bubble sizes.