In the variable conditions calculation of thermodynamic calculation for marine steam turbine,it is often for overcritical conditions and overflow conditions to occur.

Based on actual observational data and model tests of downstream slope protection stability for overflow cofferdam, the energy coversion relation of the cofferdam overflow condition is brought out with hydraulic theory of dam engineering and theory of boundary layer, and then a dicriminant for overflow condition is put forward with the condition of slope protection stability.

In the paper, based on reading and studying a great number of references about fluid dynamic technique and numerical computing methods of flow field, 3-D Numerical simulations and visual analysis of the flow field in hydraulic poppet valve with inside flow work condition were obtained by CFD (Computational Fluid Dynamics) software Fluent.