Initialize flow from different geometry

B.Axel · January 24, 2018, 05:43

Hello there,
I am currently doing simulations of a nozzle flow for my master's thesis with Fluent 18.2.
I want to create a steady state result for a particular mesh and BC setup (which I have already done) and then use this steady result to initialize a transient simulation in a nozzle with slightly different geometry, and subsequently different mesh.

I have tried to use the 'Interpolate' function in Fluent to initialize the flow and even though I don't recieve any errors, the flow is completely wrong, very patchy and coarse. It seems to import some sort of data, however, as some flow features can be found, altough with bad resolution.

Is it actually possible to interpolate data onto a different geometry, or is that feature only meant to be used for different meshes with the same geometry?

Thanks a lot in advance,
Axel

LuckyTran · January 24, 2018, 13:27

The interpolator does 0th order interpolation (it finds the nearest data) and that's why it gets really wonky on different geometry and even on the same geometry but different mesh.

If you want a better transfer, you would have to do the interpolation from the old grid onto the new grid yourself using some other tool. In my opinion Fluent would do well to at least smooth the data and do some laplacian blending or something (some sort of 1st order interpolation) but even that is not implemented yet (or maybe it has in the newer versions).

You are right, interpolate is meant for transferring data on different meshes within the same geometry. But of course this gives many people the idea to transfer data from one geometry to another. This was never the intent because in general, what logic do you use to assign values in the parts where the geometry is different?

B.Axel · January 24, 2018, 14:15

Thanks a lot for the response!
It's unfortunate that the initialization won't work as intended. I will try to find a workaround.

January 24, 2018, 05:43	Initialize flow from different geometry	#1
B.Axel New Member Axel B Join Date: Jan 2018 Location: Munich Posts: 2 Rep Power: 0	Hello there, I am currently doing simulations of a nozzle flow for my master's thesis with Fluent 18.2. I want to create a steady state result for a particular mesh and BC setup (which I have already done) and then use this steady result to initialize a transient simulation in a nozzle with slightly different geometry, and subsequently different mesh. I have tried to use the 'Interpolate' function in Fluent to initialize the flow and even though I don't recieve any errors, the flow is completely wrong, very patchy and coarse. It seems to import some sort of data, however, as some flow features can be found, altough with bad resolution. Is it actually possible to interpolate data onto a different geometry, or is that feature only meant to be used for different meshes with the same geometry? Thanks a lot in advance, Axel

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January 24, 2018, 13:27		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	The interpolator does 0th order interpolation (it finds the nearest data) and that's why it gets really wonky on different geometry and even on the same geometry but different mesh. If you want a better transfer, you would have to do the interpolation from the old grid onto the new grid yourself using some other tool. In my opinion Fluent would do well to at least smooth the data and do some laplacian blending or something (some sort of 1st order interpolation) but even that is not implemented yet (or maybe it has in the newer versions). You are right, interpolate is meant for transferring data on different meshes within the same geometry. But of course this gives many people the idea to transfer data from one geometry to another. This was never the intent because in general, what logic do you use to assign values in the parts where the geometry is different?

January 24, 2018, 14:15		#3
B.Axel New Member Axel B Join Date: Jan 2018 Location: Munich Posts: 2 Rep Power: 0	Thanks a lot for the response! It's unfortunate that the initialization won't work as intended. I will try to find a workaround.