Abstract: 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.

Key words: tidal power, horizontal axis turbine, yawed flow, hydraulic performance, entropy production