not getting Mach no 1 at throat
 

hi guys
i am using fluent for supersonic nozzle design..
but some how i am get mach number is one at throat section,
i used k-e model,segregated solver,boundary condition is given mass flow rate inlet and pressure outlet,in result i get constant density throughout nozzle.please help me.my outlet pressure is 0.80 bar and mass flow rate inlet is 11.11 kg/s.