抬升角对食蚜蝇飞行动稳定性的影响

抬升角的存在对昆虫飞行时的气动力会产生不同程度的影响，其对昆虫飞行动稳定性的影响也非常值得探索。首先，求解Navier-Stokes方程得到了有抬升角时食蚜蝇的纵向与横向稳定性导数；然后，用特征模态分析法研究其动稳定性。结果表明:有抬升角时，在侧向来流作用下食蚜蝇的滚转力矩对应的导数比无抬升角时明显减小，而其余导数无明显变化，导数减小是由于抬升角的存在使得有侧向来流时因左右翅举力不同产生的正向滚转力矩数值明显减小，而由侧向力产生的负向滚转力矩数值略有增大，从而使得其总的负向滚转力矩数值增大；但有侧向来流时滚转力矩所对应导数的减小并未引起食蚜蝇飞行动稳定性的改变，其纵向和横向的特征模态仍与无抬升角时相同。 

Effects of stroke deviation on flight stability of true hoverfly

The aerodynamic performance of insect can be affected by wing stroke deviation, which may also influence the flight stability. The longitudinal and lateral non-dimensional stability derivatives of hoverfly with stroke deviation are obtained by solving Navier-Stokes equation, and then the natural modes of motion analysis method is used to analyze the flight stability. The results show that, when stroke deviation exists, the stability derivative of the rolling moment induced by the side motion velocity decreases significantly, while the other derivatives have little difference by comparing the situation with no stroke deviation. The reason why the existence of stroke deviation causes the decrease of the derivative is that the positive rolling moment of the left and right wings declines obviously under lateral wind circumstance, while the negative rolling moment caused by the lateral force increases slightly, which makes the total negative rolling moment increase. However, the decrease of the derivative of the rolling moment caused by the lateral flow does not alter the flight stability of hoverfly, and the longitudinal and lateral characteristic modes of motion are still the same as those without stroke deviation.