This paper presents the experimental studies of the efficiency of open and ducted contra-rotating propeller systems operating in the low Reynolds number range. Eight off-the-shelf propellers were selected with a diameter in the range from 139 mm to 377 mm and seven ducts were built with the duct length of 0.28–0.53 the propeller diameter. Static and wind tunnel experiments were conducted. The maximum increase in the static thrust coefficient and power loading for the ducted contra-rotating propeller systems over the open systems was found to be 25% and 50%, respectively. This performance improvement for the medium size ducted systems is smaller than that observed in previous studies for ducts longer than the 0.8 propeller diameter but greater than for ducts shorter than the 0.15 propeller diameter. The thrust coefficient decreases with an advance ratio increase. The power loading of both open and ducted systems drops dramatically after reaching maxima.

中文翻译：

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涵道对转螺旋桨推进的特性

本文介绍了在低雷诺数范围内运行的开式和涵道对转螺旋桨系统效率的实验研究。选择了直径在 139 毫米到 377 毫米之间的 8 个现成螺旋桨，并建造了 7 个管道，管道长度为螺旋桨直径的 0.28–0.53。进行了静态和风洞实验。与开放系统相比，涵道对转螺旋桨系统的静态推力系数和功率负载的最大增加分别为 25% 和 50%。中型管道系统的这种性能改进小于先前研究中观察到的大于 0.8 螺旋桨直径的管道，但大于小于 0.15 螺旋桨直径的管道。推力系数随着提前比的增加而减小。在达到最大值后，开放式和管道式系统的功率负载都会急剧下降。