The use of 90° elbows upstream of a pump inlet can distort the approach flow resulting in spatial and temporal velocity variations and swirling flow that negatively affect pump performance and increase maintenance requirements. In order to attend these flow conditions, pumps have to be installed according to generally accepted standards such as ANSI/HI 9.8. (American national standard for rotodynamic pumps for pump intake design, Hydraulic Institute, Parsippany, 2012). However, in these standards, there is little information about the minimum distance between single and double 90° elbows and a pump. Therefore, this paper presents results for the pipe flow downstream of 90° elbows and its attendance to the standards at the inlet of pumps using Computational Fluid Dynamics (CFD). Prior to its application, the CFD model was validated by comparing the computed velocity profiles with experimental results downstream of a 90° elbow. It is found that it is necessary 3 to 16 pipe diameters from the elbow in order to reduce the swirling flow. The velocity distribution at a cross section was never uniform up to 50 pipe diameters downstream of the elbows. The temporal velocity fluctuation was always low. It is concluded that the specifications of downstream pipe lengths in the current inlet pipe flow standards are not sufficient to achieve the desired flow at the pump inlet.

中文翻译：

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90°弯头对泵入口流量条件的影响

在泵入口的上游使用90°弯头可能会使进场流量变形，从而导致时空速度变化和旋流，这会对泵的性能产生负面影响并增加维护要求。为了满足这些流动条件，必须根据公认的标准（例如ANSI / HI 9.8）安装泵。（用于泵进气口设计的旋转动力泵的美国国家标准，液压研究所，Parsippany，2012年）。但是，在这些标准中，关于90°单弯头和双弯头与泵之间的最小距离的信息很少。因此，本文介绍了使用计算流体力学（CFD）对90°弯头下游的管道流动的结果及其在泵入口处的标准要求。在应用之前，通过将计算出的速度曲线与90°弯头下游的实验结果进行比较来验证CFD模型。已经发现，从弯头开始需要3到16个管径，以减少旋流。在弯头下游直至50个管径处，横截面的速度分布永远不会均匀。时间速度波动始终很小。结论是，当前入口管道流量标准中的下游管道长度规格不足以在泵入口处实现所需流量。在弯头下游直至50个管径处，横截面的速度分布永远不会均匀。时间速度波动始终很小。结论是，当前入口管道流量标准中的下游管道长度规格不足以在泵入口处实现所需流量。在弯头下游直至50个管径处，截面的速度分布永远不会均匀。时间速度波动始终很小。结论是，当前入口管道流量标准中的下游管道长度规格不足以在泵入口处实现所需流量。