Newly developed zonal method using the interface scheme based on the Fortified Navier-Stokes concept is applied to steady and unsteady flow problems. Two computational results are shown as application examples to unsteady flow problems. One problem is a train moving into a tunnel and the other problem is a blast wave propagation. These problems require the accuracy enhancement and the problem adaptability, both of which are important obstacles of the current CFD technology. The computed result indicates that the present method alleviates the difficulty with simple modification of the existing codes. Steady flow problems include supersonic intake flow simulation and three dimensional simulation of the complex body configuration. The results indicate that the present method alleviate the difficulty of the simulation of complex flow configuration. In general, it is shown that several types of zonal approach such as overlaid, overlapped, and multi-block methods are treated in the same manner under this concept, and that the present zonal method can make a conventional program to be an effective CFD tool for the analysis of complex flow configuration.