The mechanism of bubble entrance to a capillary needle is studied numerically by using boundary integral method in this paper. A concurrent flow surrounding the bubble, which is activated by the suction flow in the capillary, is found to be the primary factor that makes the entrance happen. An artificial repulsive force is introduced to form a thin layer of liquid around the bubble surface inside the capillary needle to subdue the numerical instability. With this scheme, it is possible to simulate bubble motion both outside and inside the capillary. Computed bubble shapes are found to be in very good agreement with limited experimental results. This study is motivated by the possibility of using capillary needle to remove bubbles under micro-gravity conditions.
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