[Saturne 6.0.6] Particles are accelerated by head loss

[Antech]

Thanks for your explanation and support! I see that it's more numeric thing... Resistance zones are not simple for the universal representation as distributed pressure drop / heat transfer. We use this approach intensively for boiler heating surfaces and heat exchangers (in Ansys CFX/Fluent) and I can say that there is no "distributed approach" that can represent real object reasonably well in all cases even with user-defined expressions for heat transfer or resistance coefficient. So it's normal that Saturne will not describe real objects perfectly with distributed resistance/porosity/heat transfer. No any program can do that. Regarding resistance area, it will be enough if program will physically just retain particle forces that are accounted for in entire domain. If porosity is less than 1, fluid will accelerate and so particles (due to drag force). CFX also has option to enable heat transfer with porous solid material (that is stationary) via simple correlations like q=HTC*DeltaT. Also, if you want to implement near most detailed resistance model, you may add porous resistance option (porous resistance is proportional to velocity, inertial one - to velocity^2, there is only inertial resistance in Saturne GUI for now in version 6.3). Although we never used porous resistance, there may be users interested in it.

[Antech]

Hello. May I know if there is some progress in resolving particle acceleration issue?

[Yvan Fournier]

Hello,

No, not to my knowledge. Looking at the code (analyzing another possible issue), I see that in src/lagr/cs_lagr_sde.c,
after the call to cs_user_lagr_ef, there are expressions using "grav" and "gradpr" (both with and without added mass).

The gradpr (pressure gradient) is probably influenced by the head loss, and thus related to the issue. It would be interesting to replace this by a constant value in a test to confirm this avoids the incorrect behavior.

If this is the case, pending a clean solution, adding an artificial "compensation" external force (which ideally would be "pressure gradient without head loss - pressure gradient with head loss") with the user function would probably be a working solution.

Best regards,

Yvan