Unsteady RANS simulations were conducted in order to understand the physics of vortex flow over a delta wing at a high angle of attack. The feasibility and the accuracy of computational results were assessed through comparative study between computational and experimental data for ONERA 70-degree delta wing. Unsteady flow analysis showed a good agreement with experimental data in axial velocity and vorticity distributions. The vortex breakdown can be successfully traced by using the unsteady RANS simulation.