Learning Forum

[ganesh2516822]

I'm trying to find out the thrust generated by an air bearing that I've designed. For that I need to know the pressure drop across the porous graphite. Below figure shows the inlet portion of the graphite section (porous media).

[Rob]

How well resolved is the mesh? Please plot a velocity contour across the device so we can see what's going on.

[ganesh2516822]

Thank you for your response
I'll give you some mesh metrices Aspect ratio: 1.82
Orthogonal quality: 0.78
Skewness: 0.22

The velocity contours are given below I've a hard time believing these results since there is zero velocity throughout the entire porous medium and also the residuals starts to diverge after about 350 iterations

[Rob]

I don't like the streaking in the lower image. Please zoom in on one of the narrow sections in the top image and replot with node values off.

[ganesh2516822]

You mean like this ? I don't know how to turn off the node values

[Rob]

More or less. Zoom in more on the higher velocity region. Top left of the contour panel you'll see an option for node values, deselect it.

[ganesh2516822]

There is no option to toggle node values. Or Is it the Vertex value/ face value option as seen below ? I tried to export only the cell centre values from Fluent, but unfortunately that option is also not available there.

[Rob]

OK, that's the image I want, but do the post processing in Fluent.

[ganesh2516822]

Alright. Turned off nodal values in fluent's post processor and this is what I got
Do I need to refine the mesh at the top and send another plot ?

[Rob]

That looks like you have only two cells across the high(er) velocity region. You want at least 6, possibly more depending on the flow.

[ganesh2516822]

Here you go

[Rob]

Better. How's the solver behaving now?

[ganesh2516822]

The convergence plot follows this trend

[Rob]

That's a weird looking convergence plot. Try with a velocity inlet and see how it behaves.

[ganesh2516822]

Tried it already - yielded more or less the same plot

[Rob]

What are you using to initialise the model? I think you've got energy on; what is the gas density and how does the temperature field look?

[ganesh2516822]

I do have energy turned on. I'm using a density based solver, because the inlet air is actually from a compressor - (60psi , 450K compressed air) and I assumed the density is going to change further in its flow. I'll attach the temperature and density contour plot