Comprehensively considered the calculation accuracy and cost, the 2mm structured hexahedral mesh is adopted for the porous media, and 1 mm unstructured tetrahedral mesh is used for the other parts. As shown in Fig. 2, there is the mesh model with 0.41 million cells in total. Fig. 2a shows the Z = 1 direction view of the model which is perpendicular to the air inlet velocity direction and Fig. 2b shows the space location view.