On the figure of merit and streamwise flow of a propulsive rotor with synthetic jets
On the figure of merit and streamwise flow of a propulsive rotor with synthetic jets
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DOI：
10.1016/j.ast.2021.106712
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发表时间：
2021-04
影响因子：
5.6
通讯作者：
V. Maldonado;N. Peralta;Serdar Gorumlu;Wolduamlak Ayele
中科院分区：
文献类型：
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作者：
V. Maldonado;N. Peralta;Serdar Gorumlu;Wolduamlak Ayele
提高垂直起降(VTOL)飞行器推进旋翼的优值系数是提高旋翼机悬停效率和飞行耐力的关键。本文提出了一种新的流动控制方案，在大型推进转子上使用60个合成射流激励器，并使射流速度从叶片根部向叶尖递增，以保持每个叶片模块的动量系数水平不变。三叶片旋翼直径2.58米，包含一个NACA 0012翼型，叶片扭转分布为零。转子的测试速度分别为每分钟250、500、750和1000转(RPM)，叶片俯仰角分别为2、5和8度。利用大容量称重传感器和电流传感器测量了旋翼的推力和功率，并在翼型吸力面附近的叶片根部和叶尖附近的两个测量平面上用激光多普勒测速技术测量了流向流动。对两种流动控制方案进行了测试和比较：新的恒定动量系数(恒定Cμ)和非恒定Cμ，其中合成射流速度在整个转子叶片内保持恒定。当每个叶片的所有20个合成喷嘴都被激活时，发现恒定Cμ改善了低速转子的优值系数、调频和推力系数，当转速为250rpm时，恒定Cμ改善了低速转子的性能，而在较高转速下，非恒定C JPM略有改善。当两种流量控制方案仅应用于叶片根部模块时，在750和1000转/分的转子速度下，与基线相比，性能有所提高，但每种方案获得的Fm和CT值不同。在叶片尖端附近，边界层经历了向湍流的转变，并伴随着随着转子转速和叶片俯仰角的增大而增加的逆压梯度。在这些条件下，归一化的流向速度分布在近壁流动中显示出显著的速度亏损，合成射流为延迟分离提供了一些动量，如边界层形状因子所量化的那样。
Increasing the figure of merit of propulsive rotors for vertical takeoff and landing (VTOL) vehicles is critical to improving the hover efficiency and flight endurance of rotorcraft. In this paper, a new flow control scheme is proposed where 60 synthetic jet actuators are utilized on a large-scale propulsive rotor and the jets' velocity is increased from the blade root to the blade tip in order maintain constant levels of momentum coefficient per blade module. The three-bladed rotor measures 2.58 m in diameter and contains a NACA 0012 airfoil with zero blade twist distribution. The rotor was tested at speeds of 250, 500, 750 and 1,000 revolutions per minute (RPM) and blade pitch angles of 2, 5, and 8 degrees. Rotor thrust and power were measured using a high-capacity load cell and current sensor, and the streamwise flow was measured using phased-locked laser Doppler velocimetry (LDV) techniques at two measurement planes near the blade root and near the blade tip along the suction surface of the airfoil. Two flow control schemes were tested and compared; the new constant momentum coefficient (constant C μ) and non-constant C μ where the synthetic jet velocity is held constant throughout the rotor blade. When all 20 synthetic jets per blade are activated, it was found that constant C μ improves low-speed rotor performance in terms of figure of merit, FM and thrust coefficient, C T at 250 RPM, while non-constant C μ is marginally superior at higher rotor speeds. When both flow control schemes are applied for just the blade root module, an increase in performance compared to the baseline is observed at rotor speeds of 750 and 1000 RPM, however different values of FM and C T are achieved for each scheme. Near the blade tip the boundary layers undergo transition to turbulent flow combined with an increasing degree of adverse pressure gradient with rotor speed and blade pitch angle. Under these conditions where the normalized streamwise velocity profiles show significant velocity deficit in the near-wall flow, synthetic jets provide some momentum to delay separation as quantified by the boundary layer shape factor.