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Ramu August 5, 2003 09:06

Problem with interpolation
Hi every body, i have a cylidrical domain( axis symmetric), I want to interpolate this data to the cartessian grid, can any body help me in this problem, i will be very greatfull, if u tell at lease some good reference books on interpolation techniques..

thankyou in advance

Kevin August 5, 2003 09:26

Re: Problem with interpolation
I'm not sure I've fully understood your question. If you're talking about your mesh, since your problem is cylindric, it's straight forward : it's a rectangle. If you're talking about the equations, you must add some (source) terms (arising from the change of coordinates from xyz to r theta z) to be able to compute axisymmetric flow on bidimensionnal mesh.

Hope it helps

Ramu August 5, 2003 11:47

Re: Problem with interpolation
Hi Kevin, thankyou for ur reply, my problem is not simply convertion of data from cylidrical to cartessian. I will explain my problem clearly.

I have a cylidrical domain(which is for LES of the round jet), I want to DNS of this round jet.if i increase my grid ressolution with this cylindrical domain for doing DNS, time step is becoming very low(NAN), it is due to the very small mesh size around the axis of the jet, now i want to replace this cylindrical system with carstessian grid, but here what i need is i am doing the DNS from (domain in axial direction)3d to 20d where d is the nozzle diameter.for this i am taking the LES (cylidrical domain) data at 3d of jet as inlet B.C for my DNS(this is cartessian grid just superimposed on cylidrical gird of the LES domain at inlet plane), now i want to inerpolate this LES cylidrical domain data to my cartessian grid.. I think now u can understand my problem very clearly,please let me know ur suggestions

Thankyou in advance

Kevin August 7, 2003 15:34

Re: Problem with interpolation
I'm not at all familiar to DNS or LES calculation so I can't undersatand your problem. I hope someone here will help you. Good Luck.

Rami August 8, 2003 07:32

Re: Problem with interpolation
Hi Ramu,

To be honest, I had never done this exact type of interpolation - only some tasks of similar principle.

To my opinion, it is most important to make the interpolation conservative. In the following, suppose we wish to interpolate quantities of energy (as a representative example). The conserved entity then should be the local energy (or power). Now, the energy in each cell of the original (cylindrical) grid is given. You also know the geometry of the target (Cartesian) grid. You can therefore find what parts (volume) of the original grid contribute to each target grid cell. If you assume contant energy per volume in each original cell, you can calculate the sum of contributions from each of the original cells to the target cell total energy. You may also wish to verify that the contribution of the partial volumes sum up to the target cell volume. If you need the energy per volume in the target grid, it may now be readily calculated.

You may visually inspect the interpolation by plotting contours of the energy per volume on both grids and see how similar the look. You should also inspect that the total energy was conserved exactly in the process.

This idea should be applied to any consered entity (e.g., mass, force components, species mass, etc.).

I hope it helps, Rami

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