Bypass transition from laminar to turbulent flow in boundary layer of a blunt nose was studied by means of Direct Numerical Simulation(DNS).The full Navier-Stokes equations were numerically solved

using high-order compact finite difference schemes and high-resolution non-reflecting boundary conditions.The local finite amplitude disturbances were directly introduced into the boundary layer of a curved surface.The common calculating methods

i.e.using periodic boundary condition and curved surface replaced by flat plane

were discarded.The present result shows that transition in the flow field is correlated with the appearance of a kind of elongated structure

which is similar to a "hair-pin".This structure has not been found in other literatures.In addition

there are a lot of differences both in the instable process and in the structure pattern.The present results point out the direction of generalization of the observed transition mechanism to localized disturbances in wall bounded shear flow.