# Negative temperature

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 October 27, 2003, 04:34 Negative temperature #1 Oleg Melnik Guest   Posts: n/a Dear All! I need some help. I try to calculate shock tube problem when the high pressure chamber is filled with gas-particle dispersion. I use Mac-Cormack method with implicit account of interaction terms. When I've used isothermal approach everything worked fine. When I've added energy equation I got negative temperatures and pressures after the shock wave at the beginning. Later on proper shock wave forms. Additionally I need very small CFL numbers ~ 0.05 whereas for isothermal case 0.2-0.3 was good. I am trying to simulate high pressure drops – 20-40 MPa. Any suggestions? Oleg

 October 28, 2003, 13:37 Re: Negative temperature #2 T. Pallidum Guest   Posts: n/a What kind of artificial viscosity are you using?

 October 29, 2003, 05:08 Re: Negative temperature #3 Oleg Melnik Guest   Posts: n/a I use the term eps*(V_i+1 - 2*V_i + V_i-1) in momentum equation and play with eps. V is gas velocity. Oleg

 October 29, 2003, 12:18 Re: Negative temperature #4 Oleg Melnik Guest   Posts: n/a The problem is solved now. I've added TVD to Mac-Cormack method and temperature behaves properly. Now there is one more issue. I have a closed end of the high pressure chamber. The material of the wall is metal with high conductivity. The behaviour of the pressure at the wall (which we measure) strongly depends on temperature BC. I've tried constant temperature and adiabatic wall. The real one should be in between. Could you help me with a proper BC for the temperature? Best regards, Oleg

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