Learning Forum

[Jasper Gollwitzer]

I am using Ansys Fluent 2024R1.

I tested the porous jump model in the following simple setup:

• Geometry: pipe (L=15m, D=2.5m) followed by a nozzle (L=2m, contraction ratio=4.3)
• Flow model: incompressible (density=const.) /RANS SST kw / steady
• Boundary conditions: inlet: velocity=6m/s, outlet: static pressure=0Pa
• Porous jump (5m after the inlet): alpha=1e12m^2,delta m = 1.5e-3m and C2 = 660.5m^-1

The solution converges in terms of residuals. However, I observe a rise in both static pressure and total pressure across the porous jump, whereas I would expect the porous jump to introduce a pressure loss, particularly a decrease in total pressure.

Is there a known explanation for this behavior? 

Any suggestions on additional quantities or settings I should check would be appreciated.

[Rob]

Can you check what else is going on in the flow, and post some images. If the nozzle is the primary pressure drop in the domain, is the PJ doing anything much with the flow? 

[Jasper Gollwitzer]

[Jasper Gollwitzer]

This example is with two screens (int_*)  and some planes for evaluating the flow.

[Jasper Gollwitzer]

I also tried the mass flow outlet condition, using the same mass flow as at the inlet. In this case, I see a pressure drop across the screens (same settings). However, in my final setup, this boundary condition is not an option.

[Rob]

Mass in & mass out is also a bad combination as any small difference will result in either vacuum or infinite pressure in a steady model. Velocity in & pressure out are generally best. 

I can only see the contour plot, but that looks odd. I don't think the model is converged, but can't see if that a flow or mesh problem. How does the mesh look on the centre plane?