偏流条件下潮流能水轮机的熵产特性评估北大核心CSCD

部署在开阔水域的潮流能水平轴水轮机经常不可避免处于偏流中并造成一定的负面影响,为了研究其在偏流条件下的熵产及水力特点,通过求解雷诺平均(RANS)方程并结合熵产理论对一水平轴潮流能水轮机进行了三维数值模拟研究。结果表明,随着偏流角的增大,涡轮机的输出功率及推力逐渐减小,最高点所对应的尖速比(TSR)逐渐向低位移动,同时输出功率及推力的波动幅度变大。在相同的偏流角下,熵产随TSR的增大而增大。在不同的偏流角下,熵产在较低的TSR下随偏流角的增大而减小,而在较高的TSR下随偏流角的增大而增大。增加偏流角同样也会导致熵产波动幅度的变大。此外,流场分析表明偏流角决定了下游尾迹的偏转方向并显著改变了尾迹形状。大部分的熵产出现在水轮机的叶尖和轮毂后方,这是因为此处形成了较大范围的流动分离和涡流,这也是导致水轮机出现高熵产的主要诱因。研究结果揭示了水平轴水轮机在偏流条件下的熵产和水力特点并准确定位了熵产集中区域,为水平轴水轮机的优化设计提供了一定的参考依据。

Entropy production evaluation of a tidal turbine under yawed flow condition

Tidal horizontal-axis turbines deployed in open water are often inevitably subject to yawed flow conditions, which can cause negative effects on their performance. The detailed hydraulic performance of such a turbine is investigated by numerically solving the Reynolds-averaged Navier-Stokes equations and a shear-stress-transport turbulence model; its simulated entropy production characteristics are examined. The results show that as the inflow yaw angle increases, the power and thrust are reduced and the optimum tip speed ratio (TSR) declines, while the power and thrust fluctuation amplitudes are increased. At a fixed yaw angle, entropy production increases with TSR; at an increasing yaw, it decreases at low TSRs and then grows at high TSRs. A larger yaw also leads to larger entropy production fluctuation amplitudes. In addition, a flow field analysis reveals that the yaw angle determines the downstream wake deflection direction and alters the wake shape significantly. Most of the entropy production loss takes place behind the blade tip and hub where large scale flow separation and vortices occur; this is naturally the main origin of high entropy production in the turbine. This study demonstrates the hydraulic characteristics, the mechanism of entropy production, and the locations of entropy production in a horizontal-axis turbine, laying a basis for its optimal design.