{"id":42275,"date":"2020-03-31T09:40:14","date_gmt":"2020-03-31T09:40:14","guid":{"rendered":"\/forum\/forums\/topic\/gas-model-change-hypersonic\/"},"modified":"2020-03-31T09:40:14","modified_gmt":"2020-03-31T09:40:14","slug":"gas-model-change-hypersonic","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/gas-model-change-hypersonic\/","title":{"rendered":"Gas Model Change (Hypersonic)"},"content":{"rendered":"

Hi all! I´m having issues right with switching the gas-model. I have attached 3 screenshots so you can observe the problem. The first one is my “initialization” which is the ideal-gas solution.<\/span><\/span><\/p>\n

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As soon as I switch the gas model, the residuals jump sudently and the simulation does not diverge because I have set pressure and temperature limits based on the ideal-gas solution (assuming that the flow field will not change dramatically with the real gas model), and the residuals keep almost constant through the iterations, they don´t converge. The Mach number contour after 1 single iteration looks very scattered, I had to clip the contour for Mach number between 0 and 10 because at the inlet the Mach number increased up to Mach 630. I have been trying many solver configurations to continue the calculations from the ideal-gas solution (i.e. explicit\/implicit modes, multigrid levels, low Courant and Under-relaxation factors…) but none of them seem to work properly.<\/span><\/span><\/p>\n

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At the inlet I am applying pressure-inlet. Since the temperature is lower than 500 Kelvin, the model is solving the flow using the Ideal-gas formulation which should give the same exact solution in that region. I tried to use a user-defined ideal gas model (the same model that is available at fluent but programmed as an external model) and I had the same issue. Therefore I believe that the problem is how the solver handles the gas-model change.<\/span><\/span><\/span><\/p>\n

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Does anyone know any efficient way to perform this sudden gas-model change?<\/span><\/span><\/p>\n

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This is my initial solution with ideal-gas:<\/span><\/span><\/p>\n

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These are my residuals once I switch the gas models:<\/span><\/span><\/p>\n

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And this is the Mach number contour 1 iteration after the change:<\/span><\/span><\/p>\n

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\"\"<\/span><\/span><\/p>\n","protected":false},"template":"","class_list":["post-42275","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t