地面效应中前飞旋翼的自由尾迹计算

发展了一种自由尾迹模型，用于对地面效应状态下的旋翼前飞流场进行数值模拟，并求解该状态下的旋翼气动特性.为了扩大模型的适用范围，使用了面元法模拟地面对流场的影响.为提高尾迹迭代的收敛性和精度，在计算模型中引入了地下尾迹等比例修正、环式地面面元分布等改进措施.结果显示：前进比增加，地面附近的旋翼流场由环流模式转变为地面涡模式.在前飞速度很小时出现的环流，对旋翼前缘的轴向下洗速度影响十分强烈，导致此时出现随前进比增加，旋翼拉力减小、需用功率几乎不变的特殊现象.将得到的旋翼气动特性参数随前进比变化情况同实验值进行了对比，证实了新构建模型的准确性.

Calculation of free-wake of forward flying rotor in ground effect

A free-wake based model was developed to predict the flow field and performance of a forward flying rotor in ground effect.In order to expand the application range of the model,the ground was modeled using surface panel method to simulate the influence of ground upon the flow field.For further improving the prediction convergence and accuracy,modification measures such as rectifying the wake vortices below the ground plane proportionally and distributing the ground panels circularly were incorporated into the model.The prediction results show that as the advance ratio increases,the flow regime below the rotor changes from recirculation to ground vortex mode.When rotor gets into the recirculation regime at extremely low advance ratio,the downwash velocity across rotor leading edge is very large.Which leads to an unexpected phenomenon that the rotor thrust decreases and the required rotor power almost keeps constant while the advance ratio increases.The predicted characteristic values of rotor aerodynamics at different advance ratios were then compared with experimental results and conformed well,proving the accuracy of the newly founded model.