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-   -   DOES ASPECT RATIO PLAY A PART IN CFD RESULTS? (http://www.cfd-online.com/Forums/main/14586-does-aspect-ratio-play-part-cfd-results.html)

RIF January 4, 2008 01:58

DOES ASPECT RATIO PLAY A PART IN CFD RESULTS?
 
Hi, I'm running a simulation on aerofoil flows. i cannot seem to match the Cp from my simulations with that from the Cp i found in books. Is this something to do with my mesh? i have changed alot of parameters in my boundary conditions. does the aspect ratio play a big part in the results? does the aspect ratio between the mesh of boundary layers of the aerofoil and the mesh immediately after it play a part in the results at all?

Cheerios Rif

ag January 4, 2008 15:48

Re: DOES ASPECT RATIO PLAY A PART IN CFD RESULTS?
 
The aspect ratio can play a huge role in the results you get. At a minimum understand that 1) gradients can occur in the tangential direction and the mesh needs to be able to resolve them, and 2) sudden changes in grid spacing can have a strongly negative impact on algorithm accuracy, rendering the formal order of accuracy of your algorithm null and void.

In my experience, an aspect ratio of 1000:1 in a viscous layer is about the largest I've ever used (and I didn't like it). You also need to make sure that the tangential grid spacing does not change suddenly. Of course, the best way to determine the answer to your question is to change the grid and re-run the solution. By experimenting you will learn more about how your flow solver behaves.

Balduin Bankerotti January 5, 2008 14:14

Re: DOES ASPECT RATIO PLAY A PART IN CFD RESULTS?
 
If you want to avoid the large aspect ratios next to the wall the following might be interesting:

http://www.gridpro.com/Tutorials/Nest%20Tutorial/nest.pdf


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