Hydrokinetic turbines extract energy from free-flowing water, such as river streams and marine currents. For river applications, the typical deployment location is highly space-constrained due to both the nature of the river (i.e., its natural width and depth) and the other usages of the river. Therefore, a modified design of a conversion device is desired to accommodate these space limitations. The objective of this work is to derive optimum design criteria for a coaxial horizontal axis hydrokinetic turbine system utilizing both numerical and experimental approaches. Single-turbine systems configured with different sizes of untwisted untapered blades were numerically studied to obtain the optimum solidity and to examine the blockage effects on the various-solidity rotors. The numerical modeling was, then, extended to analyze the performance of the coaxial multi-turbine system (equipped with optimum-solidity rotors) and characterize its ambient flow. The numerically predicted power outputs were validated against those measured with torque and rotational speed sensors in a water tunnel for both single-turbine and multi-turbine systems. Particle image velocimetry was also utilized to evaluate the wake structure and validate the numerical results of the flow characteristics. The optimum-solidity for the single-turbine system was found to be 0.222 48. An optimum-solidity three-turbine axial system can increase power output by 47% when compared to an optimum-solidity single-turbine system. Increasing the number of rotors from three to five only enhanced efficiency by about 4%. The study of wake structures behind a three-turbine system showed that the highest velocity deficit occurs behind the second rotor rather than the third rotor.

中文翻译：

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同轴水平轴流体动力涡轮系统：数值建模和性能优化

流体动力学涡轮机从自由流动的水中提取能量，例如河流和洋流。对于河流应用，由于河流的性质（即河流的自然宽度和深度）以及河流的其他用途，典型的部署位置受到空间的高度限制。因此，期望转换设备的修改设计以适应这些空间限制。这项工作的目的是利用数值和实验方法得出同轴水平轴动水力透平系统的最佳设计标准。数值研究了配置有不同尺寸的未加捻的无锥度叶片的单涡轮机系统，以获得最佳的坚固性并研究了对各种坚固性转子的阻塞效应。当时的数值模型是 扩展以分析同轴多涡轮机系统（配备最佳强度转子）的性能并表征其环境流量。针对单涡轮机系统和多涡轮机系统的水通道中使用扭矩和转速传感器测量的功率输出，对数值预测的功率输出进行了验证。粒子图像测速仪还用于评估尾流结构并验证流动特性的数值结果。发现单涡轮机系统的最佳功率为0.22248。与最佳功率的单涡轮机系统相比，最佳功率的三涡轮机轴向系统可将功率输出提高47％。转子的数量从三个增加到五个，仅使效率提高了约4％。