[MITgcm-support] Inviscid fluid modeling

[Павел Лобовиков]

Thanks for reply, Martin!

I guess I didn't quite correctly ask a question.
So, if I'll use  inviscid boundary conditions (free-slip) + I'll disable
viscosity ( implicitViscosity=.FALSE.) - will the liquid be considered
inviscid in this case?

ср, 14 авг. 2019 г. в 11:45, Martin Losch <Martin.Losch at awi.de>:

> Hi Pavel (?),
>
> by default, the MITgcm code solves the Reynolds-averaged hydrostatic,
> Boussinesq Navier-Stokes equations on the sphere, additional assumptions
> make this the so-called Primitive Equations (PE). There are flags that can
> turn on different parameterisations of the turbulent eddy viscosity, and/or
> non-hydrostatic dynamics. You can also interpret the equations as pure
> Navier-Stokes with molecular viscosity. On a cartesian grid some of the PE
> assumptions are not necessary (e.g. thin-shell approximation) and you can
> use the code for LES or DNS type Navier-Stokes simulations.
>
> As far as I understand the viscosities are also required for numerical
> stability reasons. Therefore, from a numerical points of view you’ll need a
> different numerical scheme to solve the inviscid Euler equations. This
> scheme needs to be unconditionally stable (which will involve some implicit
> viscosity). In the same way, reducing the explicit viscosities towards zero
> will recover the Euler equations, but at the cost of numerical instability.
>
> I am not sure what you mean by changing the boundary conditions. An
> inviscid boundary conditions (free-slip, v.Neuman) would be consistent with
> vanishing viscosity. The no-slip boundary condition (Dirichlet with
> tangential velocity =0 on the boundary) parameterizes a viscous boundary
> layer, but does not require viscosity outside of this boundary layer. Both
> options are available with the MITgcm code.
>
> Martin
>
> > On 14. Aug 2019, at 09:42, Павел Лобовиков <plobovikov at gmail.com> wrote:
> >
> > Hi folks!
> > I have one theoretical question regarding the equations underlying
> MITgcm.
> > If we are dealing with the movement of a viscous fluid it's obvious that
> we are solving the Navier-Stokes equations.
> > But if I want to simulate the motion of an inviscid fluid I have to go
> back to Euler equations.
> > The question is: how is viscosity deactivation implemented in MITgcm?
> >
> > I have two assumptions:
> > 1. We need to go back to Euler equations and change the boundary
> conditions.
> > 2.  We remain within the framework of the Navier-Stokes equations and
> just transit to the limit ViscocityCoefficient -> 0
> >
> > Thanks!
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> > MITgcm-support at mitgcm.org
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>
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