Hi, i am doing the compressible flow analysis. In the model, one region is having the rectangular diverging duct. end of the duct is having porous medium. velocity inside the duct is low, average is around 8-10m/s. But in the diverging duct total pressure is increased by small amount(20-30Pa). According theory, total pressure remains constant in the diverging duct. i checked the velocity inside the duct at different location to conform whether is there any problem in mesh, but velocity inside the domain is not above the max. vel of the whole domain. What is the problem, how to over come from this? Thanks in advance

It's likely to be discretization or convergence error. The total pressure should tend to the physical bounds as the mesh is refined and the residuals reduced.

problem is solved using MARS scheme. for MARS scheme residuals of momentum and turbulence equations are 1.1e-4, Pr and Temp is 1e-6. I ran the solution for another 5000 iteration after achieving the above mentioned convergence, residuals are not converging but oscillating within that value. so i thought the solution is converged and also mass flow is remain constant.

That may be true, but it only addresses convergence error. To address discretization error you would have to refine your mesh until the solution is mesh-independent.