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-   -   tricky flat plate laminar flow (http://www.cfd-online.com/Forums/fluent/37840-tricky-flat-plate-laminar-flow.html)

sarat September 8, 2005 14:24

tricky flat plate laminar flow
 
hi all,

I have done the simulation of laminar flow over a flat plate but the results are very weird.

i gave the BCs:

1. velocity inlet at the entry & freestream(inx-direction)

2. pressure outlet at the outlet with 0 gauge pressure

3. wall with no slip condition

only the flow equations were solved but the cf values along the wall as compared to the blasius solution are highly ridiculous. besides, the velocity at some points exceeds the freestream velocity....I know this is very basic...

please help.... thanx in advance.............sarat


wei September 8, 2005 22:50

Re: tricky flat plate laminar flow
 
1. Grid may need more refinement , cf is easily to match where first grid y+ less than 5.

2. Overshooting is duo to your grid quality, espicilly aspect ratio that results in numerical diffusion.Kind of a paradox to the refined requirment. Has to trade off. Do not remember in fluent manual what is the recommended aspect ratio.

sarat September 9, 2005 01:07

Re: tricky flat plate laminar flow
 
hey..i think i found the tutorial for the simulation. following the steps as in it, i find that the BL thickness is higher tahn predicted..... also, the BCs of 'outflow' at the top and te outlet of the plate is different than that I have used...i.e. the pressure-outlet condition...

I would use a refined grid and then check it.

I think the recommended aspect ratio is 1.07

thankx...sarat

wei September 9, 2005 10:08

Re: tricky flat plate laminar flow
 
I do not know where you got the number 1.07. Anyway it is unrealistic. 1.07 meant you have to always keep the cell squre. I thought AR less that 5 should be OK.

wei September 9, 2005 18:35

Re: tricky flat plate laminar flow
 
I tried myself a flat plate solution with fluent, I got good match on cf and Nu near the wall, but the match with Blasius solution is not good.

Anybody know of why?


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