Experiments on gas entrainment phenomena due to free surface vortex induced by flow passing beside stagnation region

よどみ部と周辺流れの間に発生する自由表面渦ガス巻込みに関する実験研究

江連 俊樹 ; 伊藤 啓; 田中 正暁  ; 大島 宏之; 亀山 祐理*

Ezure, Toshiki; Ito, Kei; Tanaka, Masaaki; Ohshima, Hiroyuki; Kameyama, Yuri*

本論文では、よどみ領域周辺のせん断流により発生する自由表面渦型のガス巻込みに関する実験結果を報告する。実験では、水平方向流速および吸込み速度を数条件変化させ、液面のくぼみ形状と渦周囲の速度分布の関係を、可視化と粒子画像流速測定法により同時に把握し、液面直下と液面と吸込みノズル中間断面の速度分布から循環と鉛直速度勾配を評価した。ガス巻込みの評価手法開発の基礎的なデータとして、循環、鉛直速度勾配、およびガスコア長それぞれの時間発達の関係を定量的に取得した。その上で、渦モデルに基づくガス巻込み評価が有効であることを確認した。

This paper reports the results of an experiment on surface vortex-type gas entrainment, which occurs in a shear flow area where flow passes besides the stagnation region. The relationship between the free surface dimple shape and the velocity distribution around the free surface vortex was simultaneously grasped under several horizontal and suction velocity conditions by a combination of visualization and particle image velocimetry measurements. The circulation and the vertical velocity gradient were also evaluated from the velocity distributions at a plane just below the free surface and the middle plane between the free surface and suction nozzle. Quantitative relationships between the circulation, vertical velocity gradient, and gas core length were obtained in time-trends as fundamental data to develop the evaluation method of gas entrainment. Furthermore, it was confirmed that the evaluation method based on a vortex model was an effective way to evaluate gas entrainment.