Unsteady Flow Characteristics in a 90 Degree Elbow Affected by Developed, Undeveloped and Swirling Inflow Conditions
Unsteady Flow Characteristics in a 90 Degree Elbow Affected by Developed, Undeveloped and Swirling Inflow Conditions
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发达、未发达和旋流流入条件影响下90度弯头的非定常流动特性
DOI：
10.1299/jfst.7.315
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发表时间：
2012
影响因子：
0.8
通讯作者：
H. Yamano
中科院分区：
文献类型：
--
作者：
Y. Iwamoto;Manabu Kondo;Hirotaka Minamiura;Masaaki Tanaka;H. Yamano
采用激光多普勒测速（LDV）技术，在曲率半径与内径重合的90度弯头条件下，对长管、短管和旋流发生器的流入进行了测量。基于内径和体速的雷诺数为320000时的总体平均流动分布表明，上游管道长度缩短至4。9d从10d引起弯头下游的流动分离。详细观察表明，上游管道的缩短削弱了第一类普朗特二次流。根据管内直径和体速计算，涡流发生器产生了一个无量纲角动量为0.12的旋流流入。在弯头进口处，周向速度分布呈朗肯组合涡状，涡中心处轴向速度加速。而在弯头后半部分，轴向速度分布与非旋流流入情况基本相同。频率分析表明，除了长管外，在弯头内侧发生边界层涡脱落的斯特劳哈尔数为0.6。斯特罗哈尔数的变化可能与边界层宽度和局部流速有关。
Laser Doppler Velocimetry (LDV) measurements in a 90 degree elbow of which the curvature radius coincides with its inner diameter were examined for the cases of inflow from a long pipe, short pipe and swirl generator. Ensemble averaged flow distribution at the Reynolds number of 320000 based on the inner pipe diameter and bulk velocity shows that shortening the upstream pipe length to 4 . 9 D from 10 D induces the flow separation downstream of the elbow. Detailed observation suggests that shortening upstream pipe weakens the Prandtl’s secondary flow of the first kind. Our swirl generator induced a swirling inflow with the non-dimensional angular momentum of 0.12 based on the inner pipe diameter and bulk velocity. The circumferential velocity distribution formed a shape like a Rankine combined vortex at the elbow inlet, and the acceler-ated axial velocity was observed at the vortex center. The axial velocity distribution however was found to be almost the same as that of the non-swirl inflow case in the latter half of the elbow. Frequency analyses showed that the Strouhal number by vortex shedding from the boundary layer occurring at the inner side of the elbow become except for 0.6 in the case of the long pipe. The change of the Strouhal number is probably related with the boundary layer width and the local flow velocity.