Numerical investigation on internal and external flows for axisymmetric convergent-divergent nozzles on over-expansion state

When a axisymmetric convergent-divergent nozzle work at an over-expansion state,the strong shock wave and layer separation appear in the interior of the nozzle and the flow characteristic is very complex.The computed results were compared unfavorably with experimental data when adopting RNG k-ε turbulent model with standard wall functions.A wall treatment that combines a two-layer model with enhanced wall functions was employed in the numerical simulation and it was in good agreement with the experimental data.It is suggested that this enhanced wall treatment is more effective to deal with the problem of severe pressure gradients leading to boundary layer separations.