Characteristics of flow field and pressure fluctuation in complex turbulent flow in the third elbow of a triple elbow piping with small curvature radius in three-dimensional layout

3次元レイアウトで小さな曲率半径を有する3段エルボ配管の第3エルボにおける複雑乱流の流れ場および圧力変動の特徴

江原 真司*; 高村 宏行*; 橋爪 秀利*; 山野 秀将   

Ebara, Shinji*; Takamura, Hiroyuki*; Hashizume, Hidetoshi*; Yamano, Hidemasa

本研究では、約1,000,000までの高レイノルズ数領域を扱う日本のナトリウム冷却高速炉のコールドレグ配管の1/7縮尺モデル試験体を含む実験装置を用いて流動可視化及び圧力測定を実施した。流れ場に関して、流動はく離が第3エルボ内側に現れた。しかしながら、そのはく離域は、第1エルボのそれより主流方向と垂直な方向には小さく、周流方向には大きかった。これは、第2エルボ下流で形成される旋回流が多少減衰しつつも第3エルボに流れ込むからであると考えられる。圧力変動試験から、エルボ下流0.0D0.4D(Dは配管直径)の領域において、無次元周波数であるストローハル数が約0.4で圧力変動の卓越周波数が現れることが分かった。また、出口側下流の0.75Dの領域では、ストローハル数が約0.7で弱いピークが見られた。

In this study, a flow visualization and pressure measurement were conducted by using an experimental setup including test sections of 1/7-scale models of the cold-leg piping of Japan sodium-cooled reactor with high Reynolds number region up to about one million. Regarding the flow field, flow separation appeared in the intrados of the third elbow. However, the separation region was smaller than that observed in the first elbow in the direction normal to the mean flow and was larger in the streamwise direction. This can be considered because of the swirling flow generated downstream of the second elbow which flowed into the third elbow with a little reduction. From the pressure fluctuation test, it was found that prominent frequencies of the pressure fluctuation appeared at about 0.4 in Strouhal number, which corresponds to a nondimensional frequency, in the region from 0 D to 0.4 D downstream of the elbow outlet, where D is the diameter of the piping. And weak peaks of about 0.7 in Strouhal number were observed in the region far 0.75 D downstream of the outlet.