VOF Simulation for Gas-Liquid Interface Deformation due to Free Surface Vortex

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伊藤 啓; 堺 公明; 大島 宏之; 山口 彰

Ito, Kei; Sakai, Takaaki; Ohshima, Hiroyuki; Yamaguchi, Akira

ナトリウム冷却高速炉の実用化に向けては、物量削減の観点からコンパクト化設計が指向されており、炉上部プレナム内の冷却材流速が比較的大きくなることから、自由液面からのガス巻込み防止が重要である。特にくぼみ渦によるガス巻込みは、その発生条件が未知であるため、現在、実験的・解析的研究が進められている。本報では、容器中のくぼみ渦を対象に、メッシュサイズや境界条件が解析精度に与える影響を調査した。その結果、水平方向メッシュサイズの感度が非常に大きいことが明らかになった。そこで。必要な精度に対するメッシュサイズの指標を決定する観点から、メッシュサイズと解析精度の関係を推定する評価式を導出し、解析結果との比較によって検証を行った。

Gas entrainment due to free surface vortex is one of important phenomena to be solved for its onset condition to design the innovative fast breeder reactor because the reactor has the high coolant velocity. The free surface vortex must be studied in detail by both experiments and numerical simulations to make clear the complicated behavior of the vortex gas entrainment. However, an applicability of a numerical simulation to the free surface vortex has not been clear yet. In this paper, numerical simulation for the free surface vortex was conducted to study the sensitivity of some parameters on the simulation accuracy. Moreover, the effect of the horizontal mesh size on the simulation accuracy is discussed because the effect is important to determine the mesh size for the accurate simulation. As a result of the simulation, it became clear that the horizontal mesh size near the vortex center has a significant sensitivity on the simulation accuracy near the vortex center rather than the vertical mesh size. Agreement of the simulation result with the experimental one is highly improved with the decrease of the mesh size. An equation for evaluating simulation accuracy was derived from the extension vortex theory. The relationship between the mesh size and the simulation accuracy was quantified with this equation. The equation showed good agreement with the simulation results in terms of the effect of the horizontal mesh size on the simulation accuracy and was verified to have capability to evaluate the simulation accuracy.