數值模擬探討幾何參數對Savonius風力機氣動力性能的影響

Numerical Study of the Effect of Geometric Parameters on Dynamic Performance of a Savonius Wind Rotor

林晉生(Jin-Sheng Lin)

指導教授 ： 黃博全

國立臺北科技大學/機電學院/能源與冷凍空調工程系碩士班/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00617

摘要

由於能源危機、氣候變遷、世界油價的不穩定，綠色能源中的風能再一次受到重視。其中Savonius風力機擁有噪音小、構造簡單、成本低、不受風向影響等優點，預期阻力型風力機未來將會穩定快速成長，並逐漸扮演著重要的能源角色。
本研究利用計算流體力學之數值方法模擬分析阻力型風力機之氣動力特性，再藉由改變幾何設計參數，包括重疊比、分離間距、葉片數、葉片形狀等，探討其對風力機氣動力的影響，進而提出效能較高的阻力型風力機的造型。
研究結果顯示：(1)隨著尖端速度比的增加，轉子中心處的迴流變大、變強，但葉片尖端的渦流則是變小、變弱，而造成氣動力性能下降；(2)阻力型風力機葉片間的重疊間隙，可以平衡葉片凹面的低壓，同時也縮小迴流的區域，而提升風力機的氣動力性能；(3)減少分離間距可以提升分離點的壓力，但平衡葉片凹面低壓的能力卻變弱，故改變分離間距對風力機的氣動力性能沒有幫助；(4)3葉片的阻力型風力機之扭力變化的幅度較平緩； (5)採用重疊比為0.15、Bach type的葉片形狀之阻力型風力機，在尖端速度比為1.25時有最大的輸出功率係數0.3186。

關鍵字

Savonius風力機 ； 計算流體力學 ； 氣動力特性 ； 幾何參數

並列摘要

Wind energy have once again sparked the discussion of the use of green energy because of energy shortage and climate anomalies and recent price increases on the petroleum. Savonius wind turbine has the advantages of low noise, simple structure, low cost and didn’t influence by wind direction, etc. Forecasting the drag type wind turbine will gradually become the mainstream in wind power generation.
In this work, a numerical study has been carried out for analyzing the aerodynamic performance of drag type wind turbine. The study discussed about variation of aerodynamic performance of drag type wind turbine by the variation of different governing parameters, including the overlap ratio, the separation gap, the number of buckets, and the cross-section profile. Based on the above parametric analysis, this paper provides the best profile for Savonius wind turbine.
The results show that (1) as the tip speed ratio increases, the recirculating flow located at rotor center becomes larger and stronger, but the vortex near the blade tip becomes more weaken and small, which leads to the reduce in aerodynamic performance of Savonius wind turbine; (2) the overlaps of the rotor can balance the low pressure appearing on concave of blades, which will decrease recirculating region and increase aerodynamic efficiency; (3) as the separation gap decreases, the low pressure located at separation point becomes larger. This results in the lessening in ability of balancing the low pressure at concave of blades, which cannot promote aerodynamic performance; (4) the torque change in Savonius wind rotor with three blades is less than that with two blades; (5) the Savonius wind rotor with Bach-type blades and 0.15 overlap radio will have maximum power coefficient under the condition of tsr=1.25.

並列關鍵字

Savonius wind rotor ； Computational fluid dynamics ； Aerodynamic performance analysis ； Geometric Parameters

參考文獻

[3] B. F. Blackwell, R. E. Sheldahl, L. V. Feltz, Wind tunnel performance data for two- and three-bucket Savonius rotors, Journal of Energy, Vol. 2, 1987.

[4] N. Fujisawa, and F. Gotoh, Visualization study of the flow in and around a Savonius rotor, Experiments in Fluids, Vol. 12, pp. 407-412, 1992.

[5] M. Nakajima, S. Iio, T. Ikeda, Performance of double-step Savonius rotor for environmentally friendly hydraulic turbine. Journal of Fluid Science and Technology, Vol. 3, 2008.

[9] M. S. U. K. Fernando, V. J. Modi, A numerical analysis of the unsteady flow past a Savonius wind turbine, Journal of Solar Energy Engineering, Vol. 111, 1989.

[10] J. Menet, A double-step Savonius rotor for local production of electricity: a design study, Renewable Energy, Vol. 29, pp. 1843-1862, 2004.