[Nek5000-users] Low Mach configuration in Nek5000

[nek5000-users at lists.mcs.anl.gov]

Marco, 

>	- the low Mach does not seem to work for PnPn-2 formulation. Following this remark, what would be the correct set up with the low Mach approach to >compute the full stress tensor with variable viscosity?

       You will have to use the Pn-Pn formulation with IFSTRS set to true.

>	- the user manual reads 'The implementation of the equation if state for the Low Mach formulation is for the moment hard-coded to be the ideal gas >equation of state p = ρRT. This allows for both variable density and variable viscosity.’ Does that mean the density is always computed using the ideal gas >equation of state? What does happen when the density is specified in uservp?

       For variable density, the RHS of the velocity constraint is non-zero, i.e. div u = -1/rho (D rho/D t) .  This was implemented in Nek5000 assuming an ideal gas equation of state regardless of what you prescribe in uservp.  You will need to modify qthermal.f to account for whatever equation of state you need.

-Dillon



-----Original Message-----
From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov
Sent: Friday, May 19, 2017 2:51 PM
To: Nek5000-users at lists.mcs.anl.gov
Subject: [Nek5000-users] Low Mach configuration in Nek5000

Hello,

I am trying to simulate two membranes that produce a synthetic jet with Nek5000. I have been using the low Mach configuration in Nek5000 (the flow conditions are low Mach). The low Mach set up in the low_mach example was helpful but I still have a few questions:

	- the low Mach does not seem to work for PnPn-2 formulation. Following this remark, what would be the correct set up with the low Mach approach to compute the full stress tensor with variable viscosity?

	- the user manual reads 'The implementation of the equation if state for the Low Mach formulation is for the moment hard-coded to be the ideal gas equation of state p = ρRT. This allows for both variable density and variable viscosity.’ Does that mean the density is always computed using the ideal gas equation of state? What does happen when the density is specified in uservp?

	- since I have a moving boundary condition ‘mv’ and I solve the heat equation, what would be a good boundary condition for the temperature at the membranes? I do not think ‘mv’ boundary type is supported for the heat equation. I have tried with ’t’ and ‘I’ without noticing any significant differences in the numerical solution.

Thanks,

Marco

	
	
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