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Suggested solutions if you run into convergence issues: 1) Make sure that the grid at the interface is not too dissimilar. 2) Grid should ideally be very fine at the wall becoming coarser away from the wall 3) Ensure good grid quality by checking equiangle skew and aspect ratio etc. 4) First obtain converged solution using flow equations only, then solve the flow and energy equations simultaneously 5) Obtain converged first order solution first and then switch to second order solution 6) Use velocity inlet instead of pressure inlet BC. 7) Lower the energy under-relaxation factor. Try 0.98 (don not go lower than 0.95) 8) Use Pressure-based solver with coupled option, lower the Courant number. 9) In Define-> Model-> Solver, select ‘node-based’ for gradient option. 10) If using tetrahedral grid, turn off secondary gradients using the following TUI command: (rpsetvar ‘temperature/secondary-gradient? #f) 11) Change multigrid settings (solve->controls->multigrid) for energy. Set it to W cycle with a termination criteria of 0.01 (or smaller) 12) Increase the upper limits of pressure and temperature in Solve-> Controls->Limits