大口径・高流速配管の流力振動特性試験(2) エルボ部の流況と圧力変動特性

Flow-induced Vibration Tests of Large Diameter and High Velocity Piping (2) Flow Pattern and Pressure Fluctuation Behaviors of Elbow

藤井 正; 近澤 佳隆  ; 此村 守

Fujii, Tadashi; Chikazawa, Yoshitaka; Konomura, Mamoru

実用化戦略調査研究で概念設計を進めているナトリウム冷却大型炉では、建設コスト削減の観点から、冷却系ループ数を2ループに削減している。これに伴い、薄肉構造の1次冷却系配管は大口径化(ホットレグ配管:外径1.27m)するとともに、管内の平均流速は9m/s台に高速化される。そこで、1次系配管設計の成立性を確認するため、実機ホットレグ配管を1/3縮尺で模擬した水流動試験装置を製作し、配管エルボ部での流動特性やエルボの乱れに起因する振動特性を把握する試験を開始した。今回、アクリル製試験体を用いた可視化試験を実施し、以下の結果を得た。(1)全体流況や管内の速度分布には、レイノルズ数依存性が見られない。また、エルボ部の最大流速は、平均流速の約1.5倍となった。(2)従来の試験範囲を超える高レイノルズ数条件(3.3106まで)でのエルボ部の全圧力損失係数は1.3程度となり、エルボでの剥離を伴う管内流れから与えられる乱れのエネルギは小さい。(3)圧力変動特性に関しては、剥離域での圧力変動が支配的となる。また、剥離域の境界における圧力変動パワースペクトルには、ストローハル数0.45での卓越ピークが現れる。(4)実機のランダム振動応答評価に適用する圧力変動パワースペクトル密度、相関長については、剥離による乱れの度合いに応じて領域区分を設定した。

A conceptual design study of the sodium-cooled fast reactor (JSFR) is in progress in the Feasibility Study on Commercialized Fast Reactor Cycle Systems (F/S). The cooling system of the reactor is composed of two loops in order to reduce construction cost. According to reduction of loop number, large diameter pipings are adopted in the primary cooling system (for example, outer diameter of a hot leg piping is 1.27m). And the mean velocity in the piping increases to 9 m/s level. Then, flow visualization and flow-induced vibration tests using 1/3 scale water test facility, which simulates a hot leg piping, have been started in order to confirm the realization of the piping design for primary cooling system. As a first step of the test series, flow visualization test was conducted using acryl model piping, following results are obtained. (1)Flow pattern and velocity distributions in the model piping are independent of Reynolds number. The maximum velocity in the elbow is about 1.5 times of the mean velocity. (2)Total pressure loss coefficients of the elbow under high Reynolds number conditions (up to 3.3106), which are exceeded from past test condition, are about 1.3. According to this, the turbulence energy given from flow separation of the elbow is small. (3)As for pressure fluctuation behaviors, pressure fluctuations of the region of flow separation are dominance in the model piping. An eminent peak in the power spectrum densities of pressure fluctuations at the border of region of flow separation is revealed at 0.45 of Strouhal number. (4)According to extent of the turbulence caused by flow separation of the elbow, the power spectrum densities of pressure fluctuations and the correlation lengths, which are applied in random vibration response evaluation for actual plant pipings, are classified into some sections.