The influence of the different finite difference schemes on the transmission of T-S waves in flat plate boundary layers and free shear flow was studied.The results show that if 2nd order scheme is used

the T-S waves always decay in the flat plate boundary layer.Although the T-S wave grows in the free shear flow

no three dimensional structures appear.If high order scheme is used

the T-S wave grows in the plate boundary layer.The results obtained by DNS agree well with linear stability theory.In the free shear layer

not only the T-S wave grows quickly in the free shear flow

but also three dimensional waves appears evidently and three dimensional structures are excited.