直昇機的彈性葉片與非穩態空氣動力環境耦合在一起時，彈性葉片上的空氣動 力在不同的尾流振動頻率下之變化及分析將分成頻域及時域加以探討之。本文所考慮的是一 個具鉸接的四片彈性葉片之旋翼做拍撲運動，其中空氣動力模式是由非穩態翼剖面理論及葉 片元素理論推導而成，尾流模式則利用動力尾流理論修改而成。葉片振動模式是利用鄧肯多 項式模擬之。結果顯示由於誘導尾流頻率和葉片的各項頻率共振，會造成升力減少，而尾流 層的影響仍存在於前飛時。
This paper studies the interaction of a blade-and-wake coupled system of a helicopter rotor in both frequency and time domain. The lift response due to a unit step collective pitch control input of a four-elastic-hinged-bladed lifting rotor coupled with a three-dimensional-wake model in frequency domain has been investigated. An advanced dynamic wake theory is used as the wake model. Unsteady airfoil theory is applied to formulate the blade lift function. The Galerkin's method and modified Duncan polynomials are used as the solution procedures. The Eigen-analysis has also been studied to gain insight into the rotor-wake coupling system. The Floquet theory is employed for solving the time domain eigen-problems. Results from the frequency analysis show that the higher elastic modes can be excited to make larger lift drops in resonant areas. The results from the eigen-analysis demonstrate the importance of wake layering effects. The regressing flapping mode has less damping than the other flapping modes due to its tendency to couple with the wake modes.
Journal of the Chinese Society of Mechanical Engineers 20(4), pp.399-408