以局部流體加速提升Savonius轉子於水流中發電效率之研究

Abstract

本實驗主要探討在矩形流道中加裝加速物體於Savonius轉子上游時對增加其發電效率的可行性。在部分遮蔽的流道中，加速物體會增強和導引水流至凹面葉片同時減弱衝擊凸面葉片的水流。在實驗中，轉子皆放置於流道的寬度15公分及高12公分的位置。實驗測試的水流速範圍是每秒0.1到0.8公尺，流道當中分別加裝不同的加速物體。除了平行流道外，同時也探討加速物體裝置於15度和30度漸擴流道當中的影響。實驗的參數包括水流速度、轉子在流道當中的位置、加速物體的形狀和大小以及流道的漸擴角度。 由實驗得出之能量轉換效率可以發現，在平行流道當中，經由選擇適當的加速物體以及轉子位置的組合後，其能量轉換效率最高可以從完全沒裝任何加速物體的0.04增加到0.43，約10倍以上。但是在漸擴流道當中加裝加速物體的增強狀況都不是非常明顯。而由結果可以發現，轉子的發電效率和所有的實驗參數都有關係，無法單純就單個變數討論。而使用軟體模擬加裝加速物體但沒有轉子的流道可以大致推測出適合的轉子與加速物體配置。總結來看，流道中加裝加速物體基本上能夠對轉子於水流中的發電效率能夠有所幫助。

In this study an experiment is conducted to investigate the possibility of improving the efficiency of extracting kinetic energy from water flow in a rectangular-channel by a Savonius rotor through installing a block upstream of the rotor in the channel. The channel is only partially blocked. The partial channel blockage intends to direct and strengthen the water flow toward the advancing blade of the rotor and meanwhile weaken the flow hitting the returning blade. A small-scale laboratory experimental system is established to test this concept. The rectangular channel is 15 cm wide and 12 cm high. In the experiment the mean water speed is varied from 0.1 to 0.8 m/s and four blocks with different shape and size are tested. To further augment the turbine rotation, the rotor is placed in a diverging section of the channel with a side wall of the channel inclined outward at angle of 15 and 30 . The experimental parameters include the water speed, rotor location, shape and size of the flow acceleration block, and diverging angle of the channel wall. The measured data for the efficiency of the power generation from the hydrokinetic energy indicate that in the straight channel the rotor performance can be increased more than 10 times by a suitable choice of the block and rotor location. Specifically, the power generation efficiency can be increased from 0.04 to 0.42. But in the side wall-diverging channel the installation of the blocks does not result in significant improvement of the rotor performance. Besides, it is noted that the rotor performance varies nonmonotonically with all experimental parameters. It is difficult to provide a simple criterion for choosing the optimal block. However, based on the streamline patterns in the channels affected by the blocks, which can be calculated numerically where there is no rotor in the channel, a suitable choice of the experimental parameters to substantially improve the rotor performance is possible. It can be concluded that the use of a flow acceleration block is effective in improving the performance of a Savonius rotor for harvesting the hydrokinetic energy.