用于非定常粘性流动计算的无网格算法(英文)

把无网格算法发展用于求解涉及动边界的非定常粘性流动问题。在处理粘性流动的布点问题时,通过在远离物面的区域采用无粘流动计算时所用的各向同性点云,而在物面附近引入各向异性点云,从而在保证物面法线方向布点较密以准确模拟边界层的同时,有效控制了布点总量,减少了计算时间。对于动边界问题,本文在上述方法获得的初始布点的基础上,采用基于扰动衰减规律的点云移动技术,快速得到物面运动到其他位置时流场求解所需点云。在所获得的点云上,采用一种带权系数的二次极小曲面逼近方法来离散Navier-Stokes方程的空间导数,权系数的引入使得流场求解时对各向同性点云和各向异性点云无需分开考虑,而是采用统一的求解方法,从而简化了编程求解。用发展的无网格算法,结合Navier-Stokes方程求解双时间推进方法,并耦合Spalart-Allmaras湍流模型,先成功地模拟出NLR7301翼型后缘摆动诱发的非定常流,并通过与实验比较,验证了本方法.接着进行了NACA0012失速模拟,给出了动态失速过程,展示出用本文方法处理复杂动边界问题的效果。

GRIDLESS METHOD FOR UNSTEADY VISCOUS FLOWS

Gridless method is developed for unsteady viscous flows involving moving boundaries.The point distribution of gridless method is implemented in an isotropic or anisotropic way according to the features of viscous flows.In the area far away from the body,the traditional cloud of isotropic points is used,while in the adjacent area,the cloud of anisotropic points is distributed.In this way,the point spacing normal to the wall can be small enough for simulating the boundary layer,and meanwhile,the total number of points in the computational domain can be controlled due to large spacing in other tangential direction through the anisotropic way.A fast moving technique of clouds of points at each time-step is presented based on the attenuation law of disturbed motion for unsteady flows involving moving boundaries.In the mentioned cloud of points,a uniform weighted least-square curve fit method is utilized to discretize the spatial derivatives of the Navier-Stokes equations.The proposed gridless method,coupled with a dual time-stepping method and the Spalart-Allmaras turbulence model,is implemented for the Navier-Stokes equations.The computational results of unsteady viscous flows around a NLR7301 airfoil with an oscillating flap and a pitching NACA0012 airfoil are presented in a good agreement with the available experimental data.