The IDDES(Improved Delayed Detached Eddy Simulation) turbulence modeling is validated with the flat plate boundary layer and is used to investigate the stall flows of NACA0012 airfoil. The spatially filtered unsteady 3D Navier-Stokes equations are solved using a 5th order WENO reconstruction with a low diffusion E-CUSP scheme for the inviscid fluxes and a conservative 4th order central differencing for the viscous terms. Validation and comparison of 3D flat plate flows are conducted at different Mach numbers, Reynolds numbers and mesh sizes using the Spalart-Allmaras(S-A) model, DES97, DDES and IDDES. The study indicates that the IDDES is accurate to predict the velocity profile in the turbulent boundary layer regardless of the mesh size, whereas model stress depletion and log layer mismatch are observed in the DES97 and DDES computations. Stalled flows of the NACA0012 airfoil at four different angle of attacks of 5°, 17°, 45°, 60° are simulated to investigate the capability of the IDDES to resolve massive separated turbulent flow structures. At high angle of attack(AoA), the airfoil lift and drag coefficients calculated by IDDES are much more accurate than those of the URANS results using S-A turbulence model. The S-A model over-predicts the drag coefficient by about 30%, whereas the IDDES accurately predicts the drag coefficient. For the massive separated flows, more realistic voritcal and spanwise flow structures are resolved by the IDDES simulation.