Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK.
Philos Trans A Math Phys Eng Sci. 2013 Jan 14;371(1985):20120299. doi: 10.1098/rsta.2012.0299. Print 2013 Feb 28.
This paper explores the influence of blockage and free-surface deformation on the hydrodynamic performance of a generic marine cross-flow turbine. Flows through a three-bladed turbine with solidity 0.125 are simulated at field-test blade Reynolds numbers, O(10(5)-10(6)), for three different cross-stream blockages: 12.5, 25 and 50 per cent. Two representations of the free-surface boundary are considered: rigid lid and deformable free surface. Increasing the blockage is observed to lead to substantial increases in the power coefficient; the highest power coefficient computed is 1.23. Only small differences are observed between the two free-surface representations, with the deforming free-surface turbine out-performing the rigid lid turbine by 6.7 per cent in power at the highest blockage considered. This difference is attributed to the increase in effective blockage owing to the deformation of the free surface. Hydrodynamic efficiency, the ratio of useful power generated to overall power removed from the flow, is found to increase with blockage, which is consistent with the presence of a higher flow velocity through the core of the turbine at higher blockage ratios. Froude number is found to have little effect on thrust and power coefficients, but significant influence on surface elevation drop across the turbine.
本文探讨了阻塞和自由表面变形对通用海洋对转涡轮水动力性能的影响。在现场测试叶片雷诺数 O(10(5)-10(6))下，对具有 0.125 稠度的三叶涡轮机进行了模拟，阻塞比分别为 12.5%、25%和 50%。考虑了两种自由表面边界表示：刚性盖和可变形自由表面。阻塞比的增加被观察到会导致功率系数的大幅增加；计算出的最高功率系数为 1.23。两种自由表面表示之间仅观察到微小差异，在考虑的最高阻塞比下，变形自由表面涡轮机的功率比刚性盖涡轮机高出 6.7%。这种差异归因于自由表面变形引起的有效阻塞增加。发现水动力效率，即产生的有用功率与从流动中去除的总功率之比，随阻塞比的增加而增加，这与在较高阻塞比下涡轮机核心的流速更高相一致。发现弗劳德数对推力和功率系数的影响很小，但对涡轮机表面上升降的影响很大。
