低速预处理方法在悬停旋翼模拟中的应用

 在可压缩方程的求解当中引入时间导数低速预处理技术，构造了能够同时处理低速和高速流场的统一数值方法，采用该方法对Caradonna-Tung旋翼的亚声速悬停状态进行了模拟，其中方程采用在旋转坐标系下求解,网格采用重叠网格进行模拟。数值结果表明，在加入低速预处理方法以后，流场的收敛速度得到了明显提高，更为适合对下洗速度场等细节的模拟；另外,在加入低速预处理以后，方程的各个特征值都处在同一量级，避开了因特征值差异带来的数值耗散过大的问题，提高了数值计算的精度。

Application of Low Speed Preconditioning to Hovering Rotor Simulation

Low speed time-derivative preconditioning schemes are implemented in the compressible Navier-Stokes code to deal with the low Mach number flows,which makes the methods have unified accuracy and efficiency for computing incompressible and compressible flows.The subsonic hovering flow fields of Caradonna-Tung rotor are simulated by this way,in which the equations are solved on rotating coordinates and the meshes are constructed using overlap grids.The results show that the convergence speed is improved markedly by virtue of low speed preconditioning technique and flow details such as down washing are highlighted.In addition,the preconditioning methods make all the eigenvalues of equations be on the same level,thus avoiding amplifying the numerical dissipation in case of eigenvalue discrepancy,and as a result the accuracy of numerical computation is enhanced.