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Mass transfer studies across ventilated hydrofoils: A step towards hydroturbine aeration

机译:通风水翼的传质研究:迈向水轮机通气的一步

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The water discharged by hydropower facilities is a matter of increasing concern due to poor downstream water quality. The use of auto-venting hydroturbines has been suggested as one of the best ways to mitigate low dissolved oxygen levels in the downstream water. Much of the design of auto-venting hydro-turbines is currently performed with computational fluid dynamics (CFD) simulations. However, there is little information available to test and verify the performance of these simulations regarding gas transfer and bubble size distribution. This paper investigates the performance of a water tunnel test-bed for CFD simulations of an auto-venting hydroturbine through the use of a ventilated hydrofoil. Bubble size distributions are measured by a shadow imaging technique and found to have a Sauter mean diameter of 0.9 mm for a reference case. Higher liquid velocities, a lower airflow rate and a higher angle of attack all resulted in a greater number of small bubbles and a lower weighted mean bubble size. Bubble-water oxygen transfer is measured by the disturbed equilibrium technique. The gas transfer model of Azbel (1981) is utilized to characterize the liquid film coefficient for oxygen transfer, with one scaling coefficient to reflect the fact that characteristic turbulent velocity is replaced by cross-sectional mean velocity. The value of the coefficient is found to stay constant at a particular hydrofoil configuration while it varied over a narrow range of 0.52-0.60 for different hydrofoil angles of attack. This suggests that it is an appropriate coefficient for flow over a ventilated hydrofoil and possibly other flow situations. These results can be used by investigators to test and verify their CFD model against known bubble size distributions and gas transfer in a water tunnel flow that has important similarities to an auto-venting hydroturbine.
机译:由于下游水质较差,水电设施排放的水越来越引起人们的关注。已经建议使用自动排气水轮机作为减轻下游水中低溶解氧水平的最佳方法之一。目前,自动排气水轮机的大部分设计都是通过计算流体动力学(CFD)模拟进行的。但是,几乎没有可用的信息来测试和验证这些关于气体传输和气泡尺寸分布的模拟性能。本文研究了通过通风的水翼对CFD模拟自动排气水轮机的水隧道试验台的性能。气泡尺寸分布是通过阴影成像技术测量的,发现参考案例的索特平均直径为0.9毫米。较高的液体速度,较低的气流速率和较大的迎角都导致大量的小气泡和较小的加权平均气泡尺寸。气泡-水的氧转移通过扰动平衡技术进行测量。利用Azbel(1981)的气体传输模型来表征用于氧气传输的液膜系数,其中一个比例系数反映了特征湍流速度被横截面平均速度所代替的事实。发现该系数的值在特定的水翼构造下保持恒定,而对于不同的水翼迎角,其值在0.52-0.60的窄范围内变化。这表明对于通风的水翼上的流量以及其他可能的流量情况,它是一个合适的系数。研究人员可以使用这些结果来测试和验证他们的CFD模型是否与已知的气泡大小分布和水隧道流中的气体转移相对应,该过程与自动排气水轮机具有重要的相似性。

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