基于CFD-DEM耦合数值模拟的全尺寸直升机沙盲形成机理

Formation mechanism of brownout in full-scale helicopter based on CFD-DEM couplings numerical simulation

为了研究直升机发生沙盲时沙尘云在悬停流场中的状态和分布规律,采用基于雷诺平均Navier-Stokes方程和Menter剪切应力输运(SST)k-ω湍流模型的数值模型,通过应用程序编程接口耦合基于Hertz-Mindlin(No Slip)碰撞接触模型的离散元模型,并基于“多球法”构建了更加真实的非球形沙尘颗粒,计算了沙尘颗粒在流场中的运动和分布状态。与可得到的试验结果进行对比,验证了数值方法的有效性,并进行了地效状态旋翼拉力系数、桨尖涡位置以及沙尘云形成的宏观轮廓图的计算。应用所建立的方法,对不同悬停高度的直升机地效流场进行了计算,给出了流场的涡量以及速度云图,着重对比了不同悬停高度下沙尘云中沙尘颗粒速度和分布情况,分析了地效流场对沙尘颗粒状态的影响及沙尘云的形成机理,并计算出了沙尘云宏观分布图。结果表明:流场中大部分沙尘颗粒只能在地表随流场扩散而并不能形成沙尘云;沙尘云中外层空间的沙尘浓度比内层高;位于桨盘平面下层区域的沙尘颗粒以径向运动为主,切向速度较小,而位于桨盘平面上层的沙尘颗粒速度方向各异,速度大小接近。

To study the state and distribution of dust cloud in the hovering flow field of helicopter brownout,a numerical model based on Reynolds-averaged Navier-Stokes equations and Menter Shear Stress Transport(SST)k-ωturbulence model and a discrete element model based on Hertz-Mindlin(No Slip)contact model are coupled through the application programming interface.A more realistic model is constructed based on the multi-sphere method,and non-spherical dust particles are used to calculate the motion and distribution in the flow field.The effectiveness of the approach is verified by comparing the numerical results with the available experimental results.The drag coefficient of the rotor in the in-ground effect,the position of the tip vortices and the macroscopic outline of the dust cloud are calculated.By using the established method,the inground effect flow field of helicopters at different hovering altitudes is calculated.The vorticity and velocity contour of the flow field are obtained.The velocity and distribution of dust particles in dust clouds at different hovering altitudes are compared.The influence of ground effect flow field on the state of dust particles and the formation mechanism of dust clouds are analyzed.The macroscopic distribution of dust clouds are also obtained.The results show that most of the dust particles in the flow field can only diffuse with the flow field on the ground,but can not form dust clouds.The concentration of dust in outer space is higher than that in inner space.The dust particles located in the lower region of the rotor disk move mainly in the radial direction with smaller tangential velocity,while the velocity of the dust particles located in the upper region of the rotor disk are different in direction and close in magnitude.