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Re: [sparta-users] Boundary condition, pressure drops drasticaly around the outlet
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From: <geo...@dl...> - 2023-06-13 14:08:17
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But that does seem consistent – you get an error (i.e. drop) only near the edge of the simulation domain where an inconsistency between the BC and actual flow is present – thus extending the body will shift the pressure drop point to the edge of the new (extended domain). The rapid drop in pressure seems logical to me – at the very edge, particles that are reflected into the outflow have no impact on the flow, whereas in a subsonic regime you would have particles colliding with each other and propagating upstream as well, leading to higher pressure values. As for the appropriate BC function, I am not sure, as you need a mix of supersonic/subsonic, with a varying subsonic pressure, if I understand correctly... Perhaps you could simulate some part of the wake flow after the body? Mit freundlichen Grüßen Dr. Georgii Oblapenko Postdoctoral Researcher Alexander von Humboldt Stiftung Fellow Institut für Aerodynamik und Strömungstechnik Deutsches Zentrum für Luft- und Raumfahrt (DLR) ________________________________ From: Vahid Jafari <ja...@hs...> Sent: 13 June 2023 15:34:33 To: Oblapenko, Georgii Cc: spa...@li... Subject: Re: [sparta-users] Boundary condition, pressure drops drasticaly around the outlet Hey Georgii, thank you so much for your answer. That was also my first thought, but as you can see from the pictures below, if I extend the half body and the computational dmoain correspondingly, the pressure drop will be postponed furthire doenstream near the outlet boundary again. [cid:168...@hs...] [cid:168...@hs...] And even if there is an effect of boundary layer (or even boundary layer separation) don't you think the pressure should remain constant and not fall drastically? And How should I define in SPARTA the outflow at xhi? Thank you very much and Beste Grüße, Vahid Jafari Am 2023-06-13 13:12, schrieb geo...@dl...: Dear Vahid, On first thought, it seems to have to do with the boundary layer and outflow condition: you have a supersonic outflow at xhi, but the boundary layer is not necessarily supersonic. For smaller values of the accommodation coefficient you have (mostly) specular reflection, which given the relatively small angle of the body still retains enough velocity in the x direction to provide a supersonic flow in the slip layer. Mit freundlichen Grüßen Dr. Georgii Oblapenko Postdoctoral Researcher Alexander von Humboldt Stiftung Fellow Institut für Aerodynamik und Strömungstechnik Deutsches Zentrum für Luft- und Raumfahrt (DLR) ------------------------- From: Vahid Jafari <ja...@hs...<mailto:ja...@hs...>> Sent: 12 June 2023 12:57:47 To: spa...@li...<mailto:spa...@li...> Subject: [sparta-users] Boundary condition, pressure drops drasticaly around the outlet Deal all, I am a Ph.D. student researcher at Helmut-Schmidt university in Hamburg, working with SPARTA for hypersonic flow purposes. However, I am having some issues with the boundary condition at outlet. I have a 2d axisymmetric flow filed around a half body like in the picture below. We evaluate the data along the white line in the picture below. The problem is that the pressure drops drastically (which is unrealistic) around the outlet as seen in the picture below. It happens for an accommodation coefficient of 1. By decreasing the accommodation coefficient, this vanishes such that for an accommodation coefficient smaller than 0.2 it completely disappears. Do you have an explanation for that or do I configure something wrong here. Enclosed you can also find the input files Thank you for your help in advance. Kind Regards, Vahid Jafari -- -- M.Sc. Vahid Jafari -- Chair for High Performance Computing -- Helmut-Schmidt-Universität Hamburg -- Holstenhofweg 85/ Postfach 70 08 22 -- 22043 Hamburg/Germany -- -- Phone: +49 40 6541-3382 -- E-mail: ja...@hs...<mailto:ja...@hs...> -- URL: www.hsu-hh.de/hpc<http://www.hsu-hh.de/hpc> [1<http://www.hsu-hh.de/hpc>] Links: ------ [1] http://www.hsu-hh.de/hpc |
