{"action":"created","issue":{"url":"https://api.github.com/repos/idaholab/moose/issues/7622","repository_url":"https://api.github.com/repos/idaholab/moose","labels_url":"https://api.github.com/repos/idaholab/moose/issues/7622/labels{/name}","comments_url":"https://api.github.com/repos/idaholab/moose/issues/7622/comments","events_url":"https://api.github.com/repos/idaholab/moose/issues/7622/events","html_url":"https://github.com/idaholab/moose/issues/7622","id":173080479,"number":7622,"title":"Sign wrong in INSMomentumNoBCBC.C","user":{"login":"lindsayad","id":10248304,"avatar_url":"https://avatars.githubusercontent.com/u/10248304?v=3","gravatar_id":"","url":"https://api.github.com/users/lindsayad","html_url":"https://github.com/lindsayad","followers_url":"https://api.github.com/users/lindsayad/followers","following_url":"https://api.github.com/users/lindsayad/following{/other_user}","gists_url":"https://api.github.com/users/lindsayad/gists{/gist_id}","starred_url":"https://api.github.com/users/lindsayad/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/lindsayad/subscriptions","organizations_url":"https://api.github.com/users/lindsayad/orgs","repos_url":"https://api.github.com/users/lindsayad/repos","events_url":"https://api.github.com/users/lindsayad/events{/privacy}","received_events_url":"https://api.github.com/users/lindsayad/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/idaholab/moose/labels/C:%20Modules","name":"C: Modules","color":"0052cc"},{"url":"https://api.github.com/repos/idaholab/moose/labels/P:%20normal","name":"P: normal","color":"ededed"},{"url":"https://api.github.com/repos/idaholab/moose/labels/T:%20task","name":"T: task","color":"cccccc"}],"state":"closed","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":12,"created_at":"2016-08-24T23:18:16Z","updated_at":"2016-08-29T16:06:33Z","closed_at":"2016-08-29T15:19:12Z","body":"@jwpeterson Shouldn't the sign [here](https://github.com/idaholab/moose/blob/devel/modules/navier_stokes/src/bcs/INSMomentumNoBCBC.C#L98) be negative? The volume term becomes positive upon integration by parts; the corresponding surface term should be the opposite sign. Otherwise I think the do nothing BC is saying `-_test * _normals * _sigma = + _test * _normals * _sigma`. Changing the sign allows what should be a flow through solution to go from non-converging to yielding very nice results:\r\n\r\nPressure:\r\n\r\n![nobc_sign_fixed_p](https://cloud.githubusercontent.com/assets/10248304/17951256/66c85c10-6a26-11e6-8c66-9ca7c79546a3.png)\r\n\r\nAxial velocity: \r\n\r\n![nobc_sign_fixed_v](https://cloud.githubusercontent.com/assets/10248304/17951259/6ff4cdb4-6a26-11e6-90fd-3f5c1c5e2593.png)\r\n\r\nNote that here I am specifying an inlet profile for the axial velocity and do nothing boundary conditions at the outlet **without** specifying any conditions on the pressure. It should be noted that I only get these nice profiles when I don't integrate the pressure by parts. If I do integrate by parts, then I get oscillations in my radial velocity near the axis of symmetry, and an absolute maximum in the axial velocity near the outlet which makes no sense. I am still quite troubled why I can't get the simulation to look correct with integration_by_parts = true...but that's not the thrust of this issue.\r\n\r\nMight this incorrect sign be the reason why pressure conditions had to be imposed in Martin's open_bc case?\r\n"},"comment":{"url":"https://api.github.com/repos/idaholab/moose/issues/comments/243170182","html_url":"https://github.com/idaholab/moose/issues/7622#issuecomment-243170182","issue_url":"https://api.github.com/repos/idaholab/moose/issues/7622","id":243170182,"user":{"login":"jwpeterson","id":1775907,"avatar_url":"https://avatars.githubusercontent.com/u/1775907?v=3","gravatar_id":"","url":"https://api.github.com/users/jwpeterson","html_url":"https://github.com/jwpeterson","followers_url":"https://api.github.com/users/jwpeterson/followers","following_url":"https://api.github.com/users/jwpeterson/following{/other_user}","gists_url":"https://api.github.com/users/jwpeterson/gists{/gist_id}","starred_url":"https://api.github.com/users/jwpeterson/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jwpeterson/subscriptions","organizations_url":"https://api.github.com/users/jwpeterson/orgs","repos_url":"https://api.github.com/users/jwpeterson/repos","events_url":"https://api.github.com/users/jwpeterson/events{/privacy}","received_events_url":"https://api.github.com/users/jwpeterson/received_events","type":"User","site_admin":false},"created_at":"2016-08-29T16:06:33Z","updated_at":"2016-08-29T16:06:33Z","body":"Specifically the 1/r d(r*u_r)/dr terms in the mass and momentum equations as seen [here](http://ingforum.haninge.kth.se/armin/AR_2000/HL2008/NAVIER_STOKES_EQ.pdf)?"}}
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