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3D Compressible Nozzle Flow Convergence Problem

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Old   July 29, 2013, 11:47
Default 3D Compressible Nozzle Flow Convergence Problem
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Hi, All

I am simulating a steady-state 3d flow through a Venturii there are two inlets (One lnlet at the left hand side, another inlet on top of the Venturii Jet Region, the outlet is at the right hand side)

The inlet boundary conidtion are pressure inlet of 5bar and 0.5bar (on top of jet region) respectively, and outlet boundary condition is pressure outlet with 0bar pressure (since the outlet condition is unknown)

I firstly tested simulation as the flow is incompressible, and calcaluate the Mach Number at the jet region. The results shows the Mach Number reach 0.5. I therefore conclude the flow should be treated as compressible

I then tested my simulation with coupled pressure-based solver (ideal gas law for density), in which i have obtained converged solution (solution is converged at 500 iterations)

However, when I tried the simulation on density-based solver, I am not able to obtain a converged solution.(solution is not converged even at 2000 iterations). I checked my convergence based on net flux imbalance (mass flow rate)

Can anyone give me some suggestion on my simulation and kindly point out the mistakes i have made?

Many thanks
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Old   July 30, 2013, 15:29
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If you got a converged solution using the coupled pressure based, why are you attempting the density based solver?
What is the value of imbalance?

Regards
Luke
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Old   July 30, 2013, 17:09
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Quote:
Originally Posted by delaneyluke View Post
If you got a converged solution using the coupled pressure based, why are you attempting the density based solver?
What is the value of imbalance?

Regards
Luke
I am not sure which solver I suppose to use.

I only have inlet boundary condition for my simulation, i am not sure whether the flow is compressible or incompressible through out the venturii

Thus, I want to check both solvers to find out which one can yield better solution

For density-based solver, i have tried it again today, i run the simulation for more than 7000 iteration, the value of imbalance is around 2%, and the continuity residual is around 10E-3, and the solution shows the flow is reversed at the inlet (the one on top of venturi jet region)

Many thanks
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