並列タイトル等開放クロスフロー水車の性能に関する実験的および数値的研究
一般注記The flow and torque mechanisms of an open cross-flow hydraulic turbine in underflow and waterfall conditions are investigated through experiments and numerical simulations. The unsteady flow fields around a hydraulic turbine are measured by a phase-averaged particle image velocimetry in an open-circuit water tunnel, and the results are compared with those of a two-dimensional numerical simulation using the volume of fluid method for two-phase flow analysis. The experimental and numerical results of the flow fields generally agree well with each other in both operating condition, suggesting the validity of the two-dimensional numerical simulation for open cross-flow hydraulic turbines. In underflow operating condition, the experimental and numerical results indicate that both the accelerated flows over the downstream blade and through the bottom spacing between the turbine and channel wall yielded the positive torque generation of the cross-flow turbine. It is discovered that these flow features improved by decreasing the bottom spacing, and that they contributed to the local torque generation; consequently, the torque performance and efficiency of the cross-flow turbine improved. However, very small bottom spacing may not be effective for improving the efficiency. The maximum efficiency attains 39%, when the bottom spacing is optimized. In waterfall operating condition, the experimental and numerical results indicate that the flow and torque mechanisms of the cross-flow hydraulic turbine studied are explained by stagnation pressure on the concave side of blades and a Coanda-like flow on the convex side of the blades at small angle of blade position, followed by the formation of a high-velocity region within the turbine and flow impingement on the downstream blades at large angle. These flow field variations generated an increased local torque at small angle and a moderate torque at large angle, and the maximum efficiency reached approximately 60%, which is higher than that of the underflow operating condition. The improved efficiency was obtained by optimizing the off-axis distance to the waterfall and the tip-speed ratio of the hydraulic turbine, which were verified by a visualization of the flow through the turbine and the local torque distribution with respect to the angle of blade position, respectively.
新大院博(工)第524号
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受理日（W3CDTF）2022-08-08T06:02:54+09:00
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