This paper describes the development and the validation of two computational fluid dynamics (CFD) frameworks for multidisciplinary and multi-scale simulations. The first framework is an overset grid topology with a six-degree of freedom rigid body dynamics library for both structured-grid and unstructured-grid approaches. This framework will enable the CFD flow solver to simulate the problems involving relative motions between multiple bodies such as the stage/store separation process, etc. The second framework is a hybrid scheme that integrates a direct simulation Monte-Carlo (DSMC) method for rarefied gas flows and a Navier-Stokes (NS) solver for continuum flows. The hybrid DSMC-NS numerical framework can greatly improve the computational efficiency for simulation of problems with disparate length scales or a wide range of Knudsen numbers. A density-based Navier-Stokes flow solver, HYB3D, and a pressure-based Navier-Stokes flow solver, FDNS, were employed in this study to demonstrate the capability, strength, and accuracy of these two frameworks. Numerical simulations of benchmark test cases were conducted as the preliminary evaluation for these two frameworks, and the numerical results are presented. © 2006 IMACS.