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Old   May 13, 2005, 07:01
Default why H-energy ??
  #1
Alex
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Dear experts...

I'm dooing a CHT simulation where the fluid has constant properties (air at 25C) and I've activated Boussinesq model for the buoyancy.

The flow is turbulent.

I use the thermal energy model.

So I can say : h_tot=h_stat=c_p*dT

Dooing so, I suppose that in the energy equation the pressure's work (-dP/dt) will be neglected.Isn't it ??

If I rewrite the Reynolds averaged energy equation with an eddy viscosity model I should say (eq 32 solver theory ):

rho*c_p*dT/dt+c_p*rho*div*(U*T)=div*(lambda*grad T+c_p*mu/Pr*gradT)

So I have only the temperature!

When I run my simulation I see that an H-energy equation is still solved: WHY ??

One last question...

When I activate the buoyancy the pressure in the momentum equations excludes the hydrostatic gradient. So if I have an incompressible fluid, can I say that the modified pressure due to turbulence effects (solver theory pag 67) will be as follow?

p'=p+2/3*rho*k-rho_ref*g*(r-r_ref)

where r_ref is a reference location.

Thanks you all

Alex
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Old   May 13, 2005, 14:21
Default Re: why H-energy ??
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Robin
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Did you select Total Energy or Thermal Energy?
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Old   May 13, 2005, 15:52
Default Re: why H-energy ??
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Alex
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Hi Robin

Maybe you didn't see....no problem!

I selected Thermal Energy

Thanks
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Old   May 13, 2005, 17:10
Default Re: why H-energy ??
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Juan Carlos
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Dear Alex,

The ANSYS CFX solver always solves either the Static Enthalpy (Thermal Energy) or the Total Enthalpy (Total Energy). Your equations imply that the Specific Heat Capacity does not change throughout the domain.

In either case, H-Energy means solving for some kind of enthalpy..

Hope this clarify your concerns, Juan Carlos
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Old   May 14, 2005, 05:54
Default Re: why H-energy ??
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Alex
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Hi Juan Carlos

Thanks for your reply.

Maybe I realize ! Please correct me if I'm wrong:

in my simulation I have a constant Specific Heat Capacity and density. So the enthalpy (static because of the thermal energy model )depends only by temperature.

In any case the solver compute the enthaply,isn't it?

Thanks

Alex
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