[NikhilMakan02]

Hi Everyone,

I'm still working my way around Star but I would like to run an analysis on a steam silencer.

The construction of the steam silencer is merely just 2 reducers on top of each other. 12/16 then 16/20. At the start of the first reducer I have an orifice plate, while at the middle and the end I have a diffuser plate with different number of holes and sizes.

The silencer bolts onto a turbine blow off line were the turbine takes in HP steam at 360 Degrees Celsius at 31 Bar. Now I know the blow off line won't necessarily be at these conditions as the steam passes through multiple smaller lines until they all meet in the header and out the blow off line. But lets assume as a worst case scenario that these are the conditions at the blow off line. The mass flow through the blow off line is 10 tons/hour.

All I would like to know is what the pressure at the outlet would be. As I am looking for a substantial pressure drop through the silencer. I have some hand calcs that I can do to check for sonic velocity through the orifice and diffuser plates so using a velocity scalar in star I can check I haven't gone into sonic velocity anywhere by choking the flow.

Now the part that is confusing me is what to use as boundary conditions. I understand that Star does not allow you to specify Pressure and Mass Flow at the inlet as it calculates one from the other. I would assume I would use a Stagnation Inlet as the pressure and temperature of the steam entering the silencer are far more *important* parameters than the mass flow. Would this be correct?

For the outlet I would like to use a pressure outlet and set the pressure to 1 atm. Though I am having doubts on this reading through other threads where I'm thinking I'm suppose to model the air space outside the silencer as well. However I am not really interested in seeing how the pressure waves expand in the air and how this effects the acoustics at this point. I would like to just model the pressure drop across the silencer.

Any help would be much appreciated.

Thank you.

[marmot]

sounds like a cool problem,

for the pressure boundary under physics condition --> pressure outlet option you can set a target mass flow, so you can run pressure-pressure,

keep in mind you set the relative pressure, so if reference pressure is 1 atm you would specify 0 for the outlet condition,

[NikhilMakan02]

Thanks Marmot

I have set up the simulation however I seem to be running into reverse flow at inlet and outlet.

Error:
Inlet: reversed flow on 372 faces
Outlet: reversed flow on 755 faces
Inlet: reversed flow on 372 faces
Outlet: reversed flow on 755 faces

Bi-Conjugate Gradient Stabilized solver did not converge !
* CFL 5 -> 0.5...

Bi-Conjugate Gradient Stabilized solver did not converge !
A floating point exception has occurred: floating point exception [Divide by zero]. The specific cause cannot be identified. Please refer to the troubleshooting section of the User's Guide.
Context: star.coupledflow.CoupledImplicitSolver
Command: RunSimulation
CompletedCommand: RunSimulation
error: Server Error


Any tips you could possibly offer? I have attached an image of the mesh scene for some visual aid as well as the summary report.

[marmot]

some suggestions, set an initial velocity in the z-direction, perhaps what you got from your hand calculation,

with pressure boundaries it is typical to have reverse flow in the beginning

convergence issues
try constant material properties first or simple ideal gas
lower relaxation factors, time step
run 1st order first, switch later to higher order