Sun Mao, Tang Jian
Institute of Fluid Mechanics, Beijing University of Aeronautics and Astronautics, Beijing 100083, People's Republic of China.
J Exp Biol. 2002 Aug;205(Pt 16):2413-27. doi: 10.1242/jeb.205.16.2413.
The lift and power requirements for hovering flight in Drosophila virilis were studied using the method of computational fluid dynamics. The Navier-Stokes equations were solved numerically. The solution provided the flow velocity and pressure fields, from which the unsteady aerodynamic forces and moments were obtained. The inertial torques due to the acceleration of the wing mass were computed analytically. On the basis of the aerodynamic forces and moments and the inertial torques, the lift and power requirements for hovering flight were obtained. For the fruit fly Drosophila virilis in hovering flight (with symmetrical rotation), a midstroke angle of attack of approximately 37 degrees was needed for the mean lift to balance the insect weight, which agreed with observations. The mean drag on the wings over an up- or downstroke was approximately 1.27 times the mean lift or insect weight (i.e. the wings of this tiny insect must overcome a drag that is approximately 27% larger than its weight to produce a lift equal to its weight). The body-mass-specific power was 28.7 W kg(-1), the muscle-mass-specific power was 95.7 W kg(-1) and the muscle efficiency was 17%. With advanced rotation, larger lift was produced than with symmetrical rotation, but it was more energy-demanding, i.e. the power required per unit lift was much larger. With delayed rotation, much less lift was produced than with symmetrical rotation at almost the same power expenditure; again, the power required per unit lift was much larger. On the basis of the calculated results for power expenditure, symmetrical rotation should be used for balanced, long-duration flight and advanced rotation and delayed rotation should be used for flight control and manoeuvring. This agrees with observations.
利用计算流体动力学方法研究了粗壮果蝇悬停飞行时的升力和功率需求。对纳维-斯托克斯方程进行了数值求解。该解给出了流速和压力场，由此得到非定常气动力和力矩。通过解析计算得到了由于翅膀质量加速产生的惯性扭矩。基于气动力和力矩以及惯性扭矩，得到了悬停飞行的升力和功率需求。对于处于悬停飞行状态（对称旋转）的粗壮果蝇，平均升力要平衡昆虫体重需要大约37度的中风攻角，这与观测结果相符。翅膀在一次向上或向下 stroke 过程中的平均阻力约为平均升力或昆虫体重的1.27倍（即，这种小昆虫的翅膀必须克服比其体重约大27%的阻力才能产生等于其体重的升力）。单位体重功率为28.7 W kg(-1)，单位肌肉质量功率为95.7 W kg(-1)，肌肉效率为17%。与对称旋转相比，采用提前旋转时产生的升力更大，但能量需求更高，即单位升力所需功率要大得多。与对称旋转相比，采用延迟旋转时，在几乎相同的功率消耗下产生的升力要少得多；同样，单位升力所需功率也大得多。基于功率消耗的计算结果，对称旋转应用于平衡的长时间飞行，提前旋转和延迟旋转应用于飞行控制和机动。这与观测结果相符。
