The numerical method for solving Navier-Stokes equations is developed based on the SST k-ω turbulence model and the delayed detached-eddy simulation(DDES). Meanwhile, the preconditioning technique coupled with implicit dual time stepping approach is implemented to simulate large separated flows with low speed and high Reynolds number. Low speed flow over a delta wing and separation flows around a 6:1 prolate spheroid are simulated. The simulated complex vortex structures agree well with physical analyzed results and experimental data．