考虑遮蔽区影响的旋翼三维水滴撞击特性计算新方法

针对直升机旋翼三维黏性流场特有的复杂环境,建立了一种基于欧拉法的旋翼三维水滴撞击特性计算的新方法。首先,在旋翼桨叶嵌套网格的基础上,发展了一套用于预测旋翼绕流流场的计算流体力学(CFD)模拟方法。然后,为克服传统直升机旋翼二维水滴撞击特性计算方法的不足,充分考虑旋翼流场的三维效应,在嵌套网格中基于欧拉法求解旋翼三维水滴撞击流场。其中,为解决尾流等区域的密度脉冲现象所引起的稳定性和收敛性问题,提出并建立了遮蔽区扩散模型。该模型通过判断遮蔽区变量,在计算域中动态生成遮蔽区域,并随迭代步数逐渐扩散。最后,通过与NACA0012翼型及国外UH-1H桨叶的试验和计算结果的对比,验证了旋翼三维水滴撞击特性计算新方法的可靠性,并进行了温度和水滴当量直径(MVD)对旋翼三维水滴撞击特性的影响分析。结果表明:遮蔽区扩散模型的加入,使二维情况的计算时间减少了22%,并增加了三维情况的计算稳定性,显著提高了旋翼三维水滴撞击特性的计算效率;沿着旋翼桨叶展向位置增大的方向,旋翼桨叶剖面水滴撞击范围有所增大,最大水滴局部收集系数呈先增加后减少再增加的变化趋势,其变化幅度接近50%;旋翼桨叶表面的水滴撞击区域和水滴局部收集系数随水滴当量直径的增加而增加。

New method for predicting 3-D water droplet impingement on rotor considering influence of shadow zone

For the complex 3-D viscous flowfield of the helicopter rotor,a new 3-D Eulerian method is established for calculating the droplet impingement on the rotor.The Computional Fluid Dynamics (CFD) simulation method for predicting the rotor flowfield is developed based on the embedded grid method.Considering the 3-D effect of the rotor fully,the 3-D flowfield of droplets on the same embedded grids is solved by the Eulerian method to overcome the defects of the traditional 2-D calculation method.To overcome the problem of numerical stability and convergence by the density impulse in the wake area,a shadow zone dispersion model is proposed.In the model,a shadow variable is used to control the generation and dispersion of the shadow cells.The new Eulerian method is validated by comparing the calculation and experiment results of NACA0012 airfoil and UH-1H rotor in hover.In addition,the effects of the atmospheric temperature and Median Volumetric Diameter (MVD) of the droplet on the droplet impingement on the rotor are calculated and analyzed.Results show that the computation time of the 2-D droplet impingement property is reduced by 22％ and the calculation stability of 3-D droplet impingement property is improved by using the shadow zone dispersion model.The droplet impingement area increases with the spanwise distance on the rotor blade.The maximum droplet local collection efficiency presents the change tendency of 'increase-decrease-increase',and the variation amplitude is close to 50％.The droplet impingement area and the collection efficiency increase with the increase of the MVD.