Commercial sand media filters adopt different underdrain designs, with pod, wand and spike designs being the most common. Studies about the consequences of using these configurations are often not conclusive since auxiliary elements and dimensions vary between filters. Here computational fluid dynamics (CFD) simulations were carried out comparing underdrain designs in filters with equal sized diffuser plates and same inlet, inner and outlet diameters. Seven underdrain pod-type designs were analysed ranging from a market model to one with more than 50% of pods. Designs with equal number of pods but with different spatial distributions were investigated. Two wand- and two spike-type underdrain models were also evaluated. The main variables analysed were pressure and volumetric flowrate. Results confirmed that the flow uniformity through the filter was crucial to achieve low pressure drop values. Pressure losses through the sand were the most important contribution to the filter pressure drop for all cases. The water-only region at the inlet had low relevance in terms of pressure losses. All underdrain designs had similar pressure drops at the exit collector chamber (pod-type) or pipe (wand- and spike-type). Pod-type designs with the same slot open area as wand- and spike-type configurations clearly had a better efficiency since wand- and spike-type designs had faces opposing the incoming flow. Pod- and spike-type designs with similar horizontal projected upward slot areas behaved alike in both filtration and backwashing modes, with a better performance for the spike-type configuration. Recommended spike-type designs should cover most of the filter cross-sectional area.

中文翻译：

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加压砂滤池中荚状、棒状和尖刺型暗渠系统影响的数值研究

商业砂介质过滤器采用不同的暗渠设计，最常见的是吊舱、棒状和尖刺设计。关于使用这些配置的后果的研究通常不是结论性的，因为辅助元件和尺寸因过滤器而异。这里进行了计算流体动力学 (CFD) 模拟，比较了具有相同尺寸扩散板和相同入口、内径和出口直径的过滤器中的暗渠设计。分析了七种暗渠吊舱类型设计，从市场模型到具有 50% 以上吊舱的设计。研究了具有相同数量的豆荚但具有不同空间分布的设计。还评估了两个棒状和两个尖峰型暗渠模型。分析的主要变量是压力和体积流量。结果证实，通过过滤器的流动均匀性对于实现低压降值至关重要。在所有情况下，通过沙子的压力损失是对过滤器压降的最重要贡献。入口处的纯水区域在压力损失方面的相关性较低。所有暗渠设计在出口收集器室（荚型）或管道（棒型和尖刺型）处都有相似的压降。具有与棒型和尖刺型配置相同的槽开口面积的荚型设计显然具有更好的效率，因为棒型和尖刺型设计具有与流入流相反的面。具有相似水平向上投影槽区域的荚型和尖峰型设计在过滤和反冲洗模式中表现相似，尖峰型配置具有更好的性能。