# undstaedy boundary

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 July 16, 2012, 07:15 undstaedy boundary #1 Member   hayder Join Date: Jan 2012 Posts: 32 Rep Power: 7 Sponsored Links I Make simulation for the wind flow above house and to show the effect of changing winds direction with time ,for this purpose it need to continuous change of the boundary (e.g. inlet to outlet) with time. So I will be grateful to any one show me a way to do this with star ccm+ .

 July 16, 2012, 16:51 #2 Senior Member   Join Date: Oct 2009 Location: Germany Posts: 637 Rep Power: 14 To change the boundary type is only possible by using a Java macro. But I think, you don't need to change the boundary type, but just change the condition (e.g. inlet velocity). When the inlet velocity changes with time, you will have the same effect. You just need to make sure, your fluid is SLIGHTLY compressible and your geometry allows this change. hyderkhan74 likes this. __________________ We do three types of jobs here: GOOD, FAST AND CHEAP You may choose any two!

 July 18, 2012, 05:17 #3 Member   hayder Join Date: Jan 2012 Posts: 32 Rep Power: 7 Dear Abdul thank you for your help ,but can you explain what you mean by (SLIGHTLY compressible and your geometry allows this change) ? With regards

 July 28, 2012, 05:23 #4 Senior Member   Join Date: Oct 2009 Location: Germany Posts: 637 Rep Power: 14 When your domain is cylindrical (vertical axis) and the house resides in the center, you can set the total lateral surface to be a velocity inlet with a specified flow direction. This will allow an easy change of the flow direction just by changing the direction, but you don't need to touch the boundary type. This is not possible when you have a box-shaped domain, that's what I mean with "your geometry allows this". But in this case, you would have only one boundary with a fixed volume flow rate at every face of the boundary. Therefore the solver will struggle to get the continuity equation to converge due to rounding errors, cpu accuracy etc.. Therefore it's best to set the fluid to be slightly compressible, so the solver has an additional degree of freedom to reduce the mass imbalance without violating the volume flow rate of the boundary condition. hyderkhan74 likes this. __________________ We do three types of jobs here: GOOD, FAST AND CHEAP You may choose any two!

 July 28, 2012, 05:27 #5 Member   hayder Join Date: Jan 2012 Posts: 32 Rep Power: 7 It`s clear now ,thank you

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