{"id":356328,"date":"2024-03-11T11:21:55","date_gmt":"2024-03-11T11:21:55","guid":{"rendered":"\/forum\/forums\/topic\/high-unphysical-pressure-fluctuations-in-an-unsteady-simulation\/"},"modified":"2024-03-11T11:21:55","modified_gmt":"2024-03-11T11:21:55","slug":"high-unphysical-pressure-fluctuations-in-an-unsteady-simulation","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/high-unphysical-pressure-fluctuations-in-an-unsteady-simulation\/","title":{"rendered":"High unphysical pressure fluctuations in an unsteady simulation"},"content":{"rendered":"<p>Hello,<\/p>\n<p>I am simulating a flow around a three-component wing. The flow is compressible (inlet uniform velocity 61.5 m\/s), I am considering periodic BCs (spanwise), outler pressure 1 bar, operating pressure 0 bar, and non-reflecting BCs for inlet and outlet.<\/p>\n<p>Although it does not fully converge (expected), the RANS solution seems fine. However, when I switch to unsteady mode with the DDES turbulence model and the BCD scheme for the momentum equation (second order upwind for the rest of the equations, second order for pressure), I get into trouble. After many time steps simulated, the instantaneous vleocity contour is as follows:<\/p>\n<p><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/03\/11-03-2024-1710155572-blobid0.png\" alt=\"imagen\"><\/p>\n<p><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2024\/03\/11-03-2024-1710155595-mceclip0.png\"><\/p>\n<p>As you can see, there are velocity (and pressure) oscillations that are completely unphysical. I would like to confirm the following:<\/p>\n<ul>\n<li>I have tried other models such as SBES, even URANS, with different BCD scheme boundedness values, and the problem persists (even with URANS). With 1 (maximum possible value) is what you see in the pictures.<\/li>\n<li>If I use second order upwind scheme for the momentum equation, then this problem related with the oscillations dissappears. But I canot follow this path because DDES needs at least BCD to be useful.<\/li>\n<li>I have verified that the pressure fluctuations are some order of magnitude higher than those I should get.<\/li>\n<li>As expected, removing the non-reflecting BCs does not help.<\/li>\n<li>The maximum Courant number is 0.25.<\/li>\n<li>The convergence is excelllent. For example, the Continuity equation passes from 1e3 (first iteration) to 1e-4 (last iteration).<\/li>\n<li>I have tried a coarser and a finer mesh without success.<\/li>\n<li>The minimum orthogonal quality of the mesh is 0.45. It is a fine mesh, with around 1000 cells along the profile, and 20 elements in the normal direction of the boundary layer, with the wall y plus equal to 1.<\/li>\n<li>It is a compressible flow with the ideal gas equation (air). If I simulate the case in incompressible, then the problem dissappears.<\/li>\n<\/ul>\n<p>Could you please provide me some help related to this issue?<\/p>\n<p>&nbsp;<\/p>\n<p>Thank you<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"template":"","class_list":["post-356328","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"Hello,I am simulating a flow around a three-component wing. 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The flow is compressible (inlet uniform velocity 61.5 m\/s), I am considering periodic BCs (spanwise), outler pressure 1 bar, operating pressure 0 bar, and non-reflecting BCs for inlet and outlet.Although it does not fully converge (expected), the RANS solution seems fine. 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