A method of connecting three-dimensional structured meshes to form a conformal mesh, for solutions of flow problems, including: forming an interface by overlaying surfaces of two structured meshes; defining an interface set of mesh points in the interface; merging mesh points in the interface set that are within a predetermined distance of each other and projecting mesh points of one mesh in the interface that are within a predetermined distance of a line of the other mesh; generating an interface layer in the form of an unstructured mesh; and inserting a node at the center of each hexahedra, and producing an unstructured layer of cells between the two structured meshes by joining the nodes to the mesh points of the interface layer.