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Old   March 1, 2010, 02:26
Default low pressure at front of buildings
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Dear all

I am simulating flow over a small low rise building. When I look at the dynamic pressure at the front of the building center, i get very low velocity and dynamic pressure. However this is contrary to experimental reults. Any suggestions as to why ?

I am using a k epsilon rng with wall functions, hexahedral grid, double digit precision.

Any help is much appreciated


regards

CFT
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Old   March 1, 2010, 12:55
Default Convergence criteria, wall fuction vs enhanced Wall treatment
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Hi,
two recommendations:
1) maybe this is a silly question but, are you sure your simulation is converged?
I know you might be expert and know it but someone else might find this useful.
The default convergence criteria set by Fluent are not sufficient and maybe misleading.
I recommend to get rid of the residual checking:
solve-> monitors->residuals->convergence criterion: NONE.
Create a couple of points in your domain where you monitor a significant quantity, this could be pressure or velocity component in the prevailing direction of your flow.
I would consider the simulation converged when the residuals are 10^-4 AND the monitored pressure or velocity components are independent of the iteration.

2) If you are using k-epsilon with STD wall function check the y+ on the walls: 30 <y+<300. If you are using k-epsilon with Enhanced Wall treatment y+<5 and ideally y+~1.

Good luck
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Old   March 5, 2010, 05:37
Default low pressure at front of building
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Hi

I checked my residuals and are all below 1e-6. Also the yplus is in the range of 0<yplus<300 for wall functions.

I compare the pressure coefficent and compare with experiemntal results and get less than 0.3. Which cannot be right ?

Is it something to do with my reference pressure location ? I place it at 0,0,0 as recommended in manual.


Any other suggestions


thanks

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Old   March 7, 2010, 18:25
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Hi Have you done this?

1) Create a couple of points in your domain where you monitor a significant quantity, this could be pressure or velocity component in the prevailing direction of your flow.
I would consider the simulation converged when the residuals are 10^-4 AND the monitored pressure or velocity components are independent of the iteration.

2) this is the correct range of y+ for wall functions: 30<y+<300 instead of 0 <y+<300.
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