Do thermodynamic quantities scale correctly in cosmological simulations?

From: Leonard Romano <>
Date: Sat, 15 May 2021 14:40:28 +0200

Dear gadget-list,

I keep wondering, whether or not there is an inconsistency with how
certain thermodynamic quantities like pressure, entropy and the sound
speed scale in cosmological simulations with the scale factor. In
particular, expressions where sound speed and velocity both contribute
as a sum, like artificial viscosity it seems obvious that the sound
speed has to scale like a velocity, i.e. "cs_code = a^-1 cs_physical".
In order for this to be the case, the pressure would need to scale as
P_code = a P_physical since cs² ~ P / rho. However since entropy seems
to be set not to scale at all, pressure scales as P_code = a^(3*GAMMA)
P_physical, potentially causing an inconsistency.
Is this a misunderstanding on my side, or is there indeed an inconsistency?

Best regards,

Leonard Romano, B.Sc.(レオナルド・ロマノ)
Physics Department
Technical University of Munich (TUM), Germany
Theoretical Astrophysics Group
Department of Earth and Space Science
Graduate School of Science, Osaka University, Japan
he / him / his
Received on 2021-05-15 14:40:40

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