The presence of Dirac delta function in differential equation can lead to a discontinuity,which may degrade the accuracy of related numerical methods.To improve the accuracy,a secondorder numerical method for elliptic equations with singular sources is introduced by employing a local kernel flter.In this method,the discontinuous equation is convoluted with the kernel function to obtain a more regular one.Then the original equation is replaced by this fltered equation around the singular points,to obtain discrete numerical form.The unchanged equations at the other points are discretized by using a central difference scheme.1D and 2D examples are carried out to validate the correctness and accuracy of the present method.The results show that a second-order of accuracy can be obtained in the fltering framework with an appropriate integration rule.Furthermore,the present method does not need any jump condition,and also has extremely simple form that can be easily extended to high dimensional cases and complex geometry.
Eddy-dampingquasinormal Markovian(EDQNM)theory is employed to calculate the resolved-scale spectrum and transfer spectrum,based on which we investigate the resolved-scale scaling law.Results show that the scaling law of the resolved-scale turbulence,which is affected by several factors,is far from that of the full-scale turbulence and should be corrected.These results are then applied to an existing subgrid model to improve its performance.A series of simulations are performed to verify the necessity of a fixed scaling law in the subgrid modeling.
