Efficient aerodynamic prediction method of contra-rotating propellers in axial flight
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摘要:
提出了一套适用于共轴对转螺旋桨轴流状态的高效气动性能预测方法。为消除大入流角状态下小角度假设引入的误差,应用了精确的气动力分解模型与Prandtl桨尖损失函数;根据对转系统的桨尖涡演化规律,发展了轴流状态的尾迹叠加模型,构建了考虑前后桨之间轴向相互气动干扰和前桨对后桨的周向诱导的干扰模式;进而建立起了基于入流角求解的共轴对转螺旋桨的气动性能预测方法。使用该方法计算了对转螺旋桨在不同前飞速度下气动性能随前进比的变化,结果表明非失速段的拉力和功率消耗的预测结果与试验值一致性良好,整体推进效率与试验值吻合。通过对孤立高速螺旋桨、共轴双旋翼以及对转螺旋桨气动性能的评估,表明与采用小角度假设、忽略双桨间的部分干扰并基于入流比求解的常规气动模型相比,该方法对共轴对转螺旋桨的拉力、功率消耗和推进效率的预测更可靠。
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关键词:
- 对转螺旋桨 /
- 气动性能 /
- 动量—叶素理论(BEMT) /
- 尾迹叠加 /
- 气动干扰
Abstract:An efficient aerodynamic prediction method applicable for contra-rotating propellers in axial flight was developed based on Blade Element Momentum Theory. Firstly, the accurate decomposition of aerodynamic forces and Prandtl tip loss were employed to eliminate errors introduced by the small angle assumptions at high inflow angles. Secondly, based on the helical tip vortex evolution of the contra-rotating system, a wake superposition model was developed, and the interaction pattern was built, which took into account the axial aerodynamic interactions and circumferential aerodynamic interference that the front propeller exerted on the rear propeller. Finally, the aerodynamic model of contra-rotating propellers in axial flight was established based on inflow angle solutions. The method was applied to predict the aerodynamic performance variation with advance ratio for a contra-rotating propeller under different flight speeds. The calculated thrust and power in non-stall conditions were consistent with the measurements, and the whole propulsive efficiency agreed well with measurements. Aerodynamic prediction comparisons of the single propeller, the coaxial rotor and the contra-rotating propeller revealed that the established model can provide more reasonable performance predictions including thrusts, powers and efficiencies for contra-rotating propellers compared with conventional BEMT models, which assume small angles, neglect some of the interactions in contra-rotating system and rely on inflow velocity solutions.
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表 1 有无应用小角度假设下的叶素项对比
Table 1. Comparison of blade element terms with and without small angle assumptions
性能 大角度假设
(真实情况)小角度假设 30°入流角
示例误差/%$ {\mathrm{d}}T $ $ {\mathrm{d}}L\cos\; {\phi} - {\mathrm{d}}D\sin \;{\phi} $ $ {\mathrm{d}}L $ 16.0 $ {\mathrm{d}}Q $ $ ( {{\mathrm{d}}L\sin \;{\phi} + {\mathrm{d}}D\cos\; {\phi} }) r $ $ ( {{\phi} {\mathrm{d}}L + {\rm{d}}D} ) r $ 4.9 $ {\phi} $ $ {\mathrm{arc}}{\tan} ( {{{{V_{\text{0}}}} / {{W_{\text{e}}}}}} ) $ $ {{{V_{\text{0}}}} \mathord{\left/ {\vphantom {{{V_{\text{0}}}} {{W_{\text{e}}}}}} \right. } {{W_{\text{e}}}}} $ 10.3 -
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