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Simulation of a xenon flow in an azimuthal distributor with discharge in vacuum

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Old   December 8, 2021, 21:57
Default Simulation of a xenon flow in an azimuthal distributor with discharge in vacuum
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Francesco
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Hi everyone, I have to simulate a flow of xenon from a single inlet (fixed mass flow rate) into an annular chamber with multiple holes and plenum, which have the function to re-distribuite the gas flow azimuthally. The distributor is shown in figure (note the radial holes after the first plenum). The gas exit the distributor in an annular channel in near vacuum condition.

I Imported the geometry showed in picture in Ansys and then I extracted the interior of the assembly, creating two caps, filling and suppressing the initial components. I'm new to CFD simulation, I tried to start with an auto-generated mesh, with an elements size reasonably small (I hope). I created 3 named selections, 2 for the inlet-outlets sections and one for the walls surface.

In "Fluid flow setup" I changed the following options:

-Models: Energy (on), Viscous (realizable k-epsilon, scalable wall function)

-Materials: I left the standard materials, air (I changed density to ideal gas) and aluminum. I cannot find xenon in the materials database. If you know how to add it, please tell me.

-Boundary conditions: under operating conditions I insert only pressure =0 Pa Inlet surface: 15e-6 kg/s mass flow rate, normal to surface Outlet surface: pressure 10000 Pa Walls: I inserted only their temperature, 700 K

Method: I left all unchanged apart from having increased some options to "second order".

I left the simulation do 600 iterations (it takes 40 minutes). Unfortunately, the solution doesn't converge well. The velocity residual reach 10^-4, k and epsilon 10^-3, continuity and energy 10^-2. The velocity and pressure contours are not realistic.

I'm aware of the problem that a discharge into vacuum involve transitional and molecular regimes but I think that it is possible to obtain a realistic solution for the azimuthal density and velocity distribution of the flow in the distributor even in viscous flow condition (in which I'm hoping to be with an exit pressure of 10000 Pa).

In which way I can modify the problem setup/mesh to obtain a converged solution?
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distributor, gas, orifice, vacuum, xenon

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