Learning Forum

[vamshigundla003]

hi,

i am simulating a transonic flow with pressure ratio 0.58 which is the ratio of static pressure at exit to stagnation pressure at inlet.

At inlet the pressure is 1 atm and outlet it is 0.58 atm.

it is a 2D simuation internal flow with density based solver as it is a compressible flow. I am using k-epsilon and K-Omega models but both them are not converging.can anyone please check my mesh and boundry conditions i have doubts with pressure inlet and pressure outlet conditons.i am attaching my screenshots of simulation

ideal gas density and pressure at outlet is 0.58.

[Federico]

First, this is gauge pressure, which is relative to your operating conditions (1atm is the default), so you might not be getting the pressure ratio you expect right now.

Is your inlet supersonic? The static pressure (termed the Supersonic/Initial Gauge Pressure) must be specified if the inlet flow is supersonic or if you plan to initialize the solution based on the pressure inlet boundary conditions.

[vamshigundla003]

No, my inlet is not supersonic the flow is reaching 0.918Mach with this the pressure ratio 0.58 according to isentropic equations which means my inlet velocity is 315m/s.

I have kept 1 atm as supersonic pressure and 0.58 atm as outlet pressure (1 atm as inlet pressure) and tried but still the solution is not converging

[Federico]

Did you check that you are getting those values?

There could be several other reasons for this not to converge. Also, density-based solver is typically used for high Mach numbers. Pressure-based solver should work fine here, even for compressible flow.

[vamshigundla003]

When I keep 1 atm as supersonic initial pressure I am getting 315m/s x velocity which is equal to my mach speed (0.918mach) when I initialiaze from inlet.

But if I keep 0.99 then the x velocity is changing to 45m/s during initialisation.

[Federico]

What are your operating conditions?

[vamshigundla003]

I am keeping 0 in operating conditions 

[vamshigundla003]

I have now used pressure based solver instead of density the residual are much better than density based but no convergence is achieved.

Is this the problem of mesh or setup problem ?

My mesh is a Structured one with inflation layer applied to all walls.

Mass flow rate net is -0.0037

And residuals are fluctuating.

[vamshigundla003]

[vamshigundla003]

[Federico]

aspect ratio from last layer to core mesh appears to be way too large from this last screen capture.

[vamshigundla003]

But how can I have smooth transition in fluent mesh are there any options for smooth transition between inflation layers and core mesh.