Negative Temperature

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Hi,

How can we overcome on an  Negative temperature error.

I put an initial condition with 298K and all my BC are correct and in K.

Idan

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Sounds like you are trying to use the ideal gas density model.  In this case, the solver is computing density based on rho= P/(R*T).  So, a negative absolute temperature will produce a negative density, which is obviously impossible.  More often than not this issue is caused by improper initial conditions and boundary conditions for pressure or temperature.  It is important to ensure that you have reasonable temperature AND pressure initial conditions (and boundary conditions).  Make sure your outlet pressure and initial pressure is specified in an absolute scale (i.e. 101325 Pa instead of 0), or that you provide an absolute pressure offset of 101325 Pa if you assign pressures as gage.  Providing a developed velocity field will also help produce better initial conditions as well. You may want to run the simulation with constant density for a few time steps to establish the initial field, then restart with variable density.

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Sounds like you are trying to use the ideal gas density model.  In this case, the solver is computing density based on rho= P/(R*T).  So, a negative absolute temperature will produce a negative density, which is obviously impossible.  More often than not this issue is caused by improper initial conditions and boundary conditions for pressure or temperature.  It is important to ensure that you have reasonable temperature AND pressure initial conditions (and boundary conditions).  Make sure your outlet pressure and initial pressure is specified in an absolute scale (i.e. 101325 Pa instead of 0), or that you provide an absolute pressure offset of 101325 Pa if you assign pressures as gage.  Providing a developed velocity field will also help produce better initial conditions as well. You may want to run the simulation with constant density for a few time steps to establish the initial field, then restart with variable density.

Does this means that for environment condition, the setting can be either these 2 options:

1. Abs. pressure offset = 0 Pa; nodal initial condition = 101325 Pa; and pressure outlet = 101325 Pa.

or

2. Abs. pressure offset = 101325 Pa; nodal initial condition = 0 Pa; and pressure outlet = 0 Pa.

Both are correct, am I right?

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Correct.  Both of the settings described above should produce identical results.

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Hello I have the problem with the negative absolute pressure of the model material and can't understand where is my mistake. My model is like the "cavity rotating" from examples of Acusolve help, but with inflow and outflow. I have the Mass Flux and Pressure in the inlet. When I use the constant model of the material it work, but I need to use the ideal model of air.

zazor-1k1-hm.acs

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IIdar, since you have reported this in the other thread, we will follow it up there.

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