# why H-energy ??

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 May 13, 2005, 07:01 why H-energy ?? #1 Alex Guest   Posts: n/a Dear experts... I'm dooing a CHT simulation where the fluid has constant properties (air at 25°C) 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

 May 13, 2005, 14:21 Re: why H-energy ?? #2 Robin Guest   Posts: n/a Did you select Total Energy or Thermal Energy?

 May 13, 2005, 15:52 Re: why H-energy ?? #3 Alex Guest   Posts: n/a Hi Robin Maybe you didn't see....no problem! I selected Thermal Energy Thanks

 May 13, 2005, 17:10 Re: why H-energy ?? #4 Juan Carlos Guest   Posts: n/a 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

 May 14, 2005, 05:54 Re: why H-energy ?? #5 Alex Guest   Posts: n/a 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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