# low pressure at front of buildings

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 March 1, 2010, 02:26 low pressure at front of buildings #1 New Member   CFT Join Date: Mar 2009 Posts: 15 Rep Power: 9 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

 March 1, 2010, 12:55 Convergence criteria, wall fuction vs enhanced Wall treatment #2 New Member   Join Date: Nov 2009 Posts: 22 Rep Power: 8 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

 March 5, 2010, 05:37 low pressure at front of building #3 New Member   CFT Join Date: Mar 2009 Posts: 15 Rep Power: 9 Hi I checked my residuals and are all below 1e-6. Also the yplus is in the range of 0

 March 7, 2010, 18:25 #4 New Member   Join Date: Nov 2009 Posts: 22 Rep Power: 8 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

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