{"action":"created","issue":{"url":"https://api.github.com/repos/mostaphaRoudsari/Butterfly/issues/55","repository_url":"https://api.github.com/repos/mostaphaRoudsari/Butterfly","labels_url":"https://api.github.com/repos/mostaphaRoudsari/Butterfly/issues/55/labels{/name}","comments_url":"https://api.github.com/repos/mostaphaRoudsari/Butterfly/issues/55/comments","events_url":"https://api.github.com/repos/mostaphaRoudsari/Butterfly/issues/55/events","html_url":"https://github.com/mostaphaRoudsari/Butterfly/issues/55","id":172077548,"number":55,"title":"Boundary Conditions for external flows","user":{"login":"kostnermo","id":1919773,"avatar_url":"https://avatars.githubusercontent.com/u/1919773?v=3","gravatar_id":"","url":"https://api.github.com/users/kostnermo","html_url":"https://github.com/kostnermo","followers_url":"https://api.github.com/users/kostnermo/followers","following_url":"https://api.github.com/users/kostnermo/following{/other_user}","gists_url":"https://api.github.com/users/kostnermo/gists{/gist_id}","starred_url":"https://api.github.com/users/kostnermo/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/kostnermo/subscriptions","organizations_url":"https://api.github.com/users/kostnermo/orgs","repos_url":"https://api.github.com/users/kostnermo/repos","events_url":"https://api.github.com/users/kostnermo/events{/privacy}","received_events_url":"https://api.github.com/users/kostnermo/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/mostaphaRoudsari/Butterfly/labels/discussion","name":"discussion","color":"d4c5f9"}],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":2,"created_at":"2016-08-19T08:12:09Z","updated_at":"2016-08-23T07:08:34Z","closed_at":null,"body":"Hello everyone,\r\n\r\nI recently came across the [proposed BCs for external flows](https://github.com/mostaphaRoudsari/Butterfly/blob/master/etc/OpenFOAM_Sample_Files/SolvingTheCase/BoundaryConditions/Boundary%20conditions%20external%20simulation.pdf) mentioned in the repository.\r\n\r\n1. Is there a reason why you are using _zeroGradient_ for _k_ and _epsilon/omega_ on the ground instead of _wallFunctions_?\r\n2. What is the benefit of having a _slip_ condition over a _symmetry_ condition on the side/sky? [Here](http://www.cfd-online.com/Forums/openfoam-solving/149691-slip-vs-symmetry-boundary-condition.html) it is mentioned that it should be treated identically, the results however seem to be different.\r\n\r\nAre those BCs a best practice from other proprietary software or is this based on validation against some measured data?\r\n\r\nBest,\r\n\r\nPatrick"},"comment":{"url":"https://api.github.com/repos/mostaphaRoudsari/Butterfly/issues/comments/241645921","html_url":"https://github.com/mostaphaRoudsari/Butterfly/issues/55#issuecomment-241645921","issue_url":"https://api.github.com/repos/mostaphaRoudsari/Butterfly/issues/55","id":241645921,"user":{"login":"kostnermo","id":1919773,"avatar_url":"https://avatars.githubusercontent.com/u/1919773?v=3","gravatar_id":"","url":"https://api.github.com/users/kostnermo","html_url":"https://github.com/kostnermo","followers_url":"https://api.github.com/users/kostnermo/followers","following_url":"https://api.github.com/users/kostnermo/following{/other_user}","gists_url":"https://api.github.com/users/kostnermo/gists{/gist_id}","starred_url":"https://api.github.com/users/kostnermo/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/kostnermo/subscriptions","organizations_url":"https://api.github.com/users/kostnermo/orgs","repos_url":"https://api.github.com/users/kostnermo/repos","events_url":"https://api.github.com/users/kostnermo/events{/privacy}","received_events_url":"https://api.github.com/users/kostnermo/received_events","type":"User","site_admin":false},"created_at":"2016-08-23T07:08:34Z","updated_at":"2016-08-23T07:08:34Z","body":"@TheodoreGalanos Thank you for your input on this!\r\n@mostaphaRoudsari I read a couple of papers by Blocken which are, indeed, quite sophisticatedly investigating the atmospheric boundary layer. Most of the research is done with Fluent though. \r\n\r\nIn addition, I found [this paper](http://repository.tudelft.nl/islandora/object/uuid:1cd14ecd-984a-47bb-9f26-93b59a166bcf/datastream/OBJ/download) by DE Dwyer, which in essence uses the same approach as posted above. \r\n\r\nThe official tutorial _windAroundBuildings_ uses a _wallFunction_ for k and epsilon, although, unlike other tutorials, it merely seems to show what is possible with OpenFOAM. \r\n\r\nCurrently, I am doing some validation of different boundary conditions as well as turbulence models (kOmegaSST) against measured data. I am happy to share the results once I finished that."}}
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