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Old   June 23, 2005, 07:48
Default Interpolation to Second-Order
  #1
ashish
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Hi, I have a query related to transient results. I have got the first-order upwind result for a transient flow problem. Now i wish to obtain the second-order results quickly from this first order results. Is there any method by which i can interpolate thise first order results and quickly solve/ see second order solution (at the same timesteps)? in other words i have first order results for 1-10 seconds in certain timesteps can i use these results to see the results for 1-10 seconds using second-order scheme quickly? any help thanks ashish
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Old   June 23, 2005, 09:01
Default Re: Interpolation to Second-Order
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Rui
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Hi,

I think what you said doesn't make much sense. It would make sense if you were looking for a steady state solution (only one solution). But in a transient simulation if you used, for each time step, the initial solution as the final solution obtained with the 1st-order upwind scheme, every time you changed to the next time step you would loose the accuracy you have gained with the 2nd order scheme. And, to my knowledge, it's not possible to do that in CFX. So, start the simulation from the biginning, with the 2nd order scheme, and compare the results.

Regards,

Rui
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Old   June 23, 2005, 09:31
Default Re: Interpolation to Second-Order
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stex
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Maybe if you are studing a developed flow simulation (not a simulation like t=o---> velocity=0) you can start from the last timestep 1st order solution to run a 2nd order. But you just increase the velocity of the first iteration, not all the timestep.
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Old   June 23, 2005, 10:46
Default Re: Interpolation to Second-Order
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ashish
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hi all, thanks for reply. i think i will re-run using second order scheme to see any variation.
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Old   June 23, 2005, 19:28
Default Re: Interpolation to Second-Order
  #5
Glenn Horrocks
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Hi,

I think Ashish is confused about what second order timestepping is. Second order timestepping is not equivalent to interpolating a first order timestepping solution, it means the transient terms are evaluated with a second order scheme rather than a first order scheme. The result it gives can be completely different.

You are correct in saying the only way to compare a first and second order simulation is to run both simulations from the beginning.

Regards, Glenn Horrocks
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Old   June 24, 2005, 10:33
Default Re: Interpolation to Second-Order
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Rui
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Hi Glenn,

I think Ashish meant he wants to obtain transient results using a 2nd order <u>advection scheme</u> by interpolating transient results obtained with the 1st order upwind advection scheme, as he mentioned "I have got the first-order upwind result for a transient flow problem".But I think your statement is also valid, as the results obtained with each advection scheme can also be completely different.

Regards,

Rui
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