Flow over a backward step

The problem of the flow over a backward step was simulated using Converge CFD. The problem was simulated as a 2D flow problem with the top and bottom boundaries as the wall. Three base grid sizes were selected: 2mm, 1.5 mm and 1mm. The maximum velocity was found to be varying from 16 m/s to 15 m/s for 2mm to 1 mm base grid. A flow recirculation was found at the point where cross-section increases. Inlet pressure was 1.1 bar and outlet pressure 1 bar. Air was taken as the working medium. Turbulence model was RNG-K-e. The simulation was run for 15000 cycles.