Hovering efficiency optimization of ducted propeller with large blade tip clearance based on grooved duct configuration.

To achieve a high hovering efficiency of the ducted propeller, a very small blade tip clearance is required. This requires high precision in fabrication and manufacturing, resulting in a substantial increase in cost. To address this issue, the grooved ducted propeller is proposed to improve hovering efficiency under large blade tip clearance. Parametric analysis and aerodynamic shape optimization based on the multiple reference frame model are performed. First, analysis based on the ducted propeller without groove indicates that an increase in blade tip clearance will lead to a significant decrease in hovering efficiency. When the blade tip clearance is four times that of the baseline design, the efficiency decreases by more than 25%. Second, based on the grooved ducted propeller, the impacts of blade tip clearance, blade tip location, groove depth, and groove shape are investigated. The results indicate that hovering efficiency is primarily dependent on the blade tip location. However, reducing blade tip clearance and optimizing groove shape are beneficial in improving hovering efficiency. The results of optimization indicate that there is a best blade tip location such that the impact of the blade tip clearance and the shape of the groove can be minimized. By slightly stretching the blade tip into the groove, the hovering efficiency can be improved by 5%, although the blade tip clearance is six times greater than the baseline design. Finally, verification experiments are conducted with grooved ducted propellers with very large fabrication and manufacturing errors. The results of the experiment indicate that the grooved ducted propeller can effectively handle the problems caused by manufacturing errors. Consequently, the cost of manufacturing and maintenance can be significantly reduced. [ABSTRACT FROM AUTHOR]

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