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Large eddies at top of building using FLAIR

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Old   April 18, 2007, 08:42
Default Large eddies at top of building using FLAIR
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I'm using the Pheonics FLAIR to model the wind flow within urban area. For a certain model setup with unobstructed wind flow of 10m/s, the wind speed increase drastically to more than 30m/s after flowing across the top of one of the buildings under one particular wind direction. The wind speed of 30m/s is so high that it does not seem realistic. Does anyone know if we can change any of the model setup, say KE model setup, limit of values for parameters etc, that can eliminate such unrealistic ocurrance of eddies in the FLARE model? Is this pheonomenace related to the fact that the building details inputted to the FLARE model being too fine when compared with the model grid and cause strange response in the FLAIR model?

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Old   April 26, 2007, 11:18
Default Re: Large eddies at top of building using FLAIR
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Lack of convergence may result in unrealistic velocities, as can inadequate cut-cell resolution of the building geometry if PARSOL is being used to represent curved surfaces on the background Cartesian mesh. Another possible cause is an inappropriate choice of boundary conditions for momentum on the fixed pressure conditions applied to the side and top boundaries. The solution fields should be examined in detail to see if the pressure field reflects the observed flow acceleration.
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Old   April 28, 2007, 06:07
Default Re: Large eddies at top of building using FLAIR
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Thanks Mick for your suggestions. I've not use PARSOL in my case. With regards to the choice of boundary conditions, in FLAIR, I set up the surfaces of the domain with object types like 'wind profile', 'opening', and 'plate' etc in accordance with the FLAIR manual tr313. Pls advise how I can input the boundary conditions for momentum in FLAIR, or should I restict the limits of variables for ambient wind flow simulation?


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