CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Pre-Processing

alphaEff

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree5Likes
  • 1 Post By alexeym
  • 4 Post By pmdelgado2

Reply
 
LinkBack Thread Tools Display Modes
Old   June 22, 2015, 22:44
Default alphaEff
  #1
New Member
 
zahra
Join Date: Jun 2014
Location: Iran-Tehran
Posts: 28
Rep Power: 4
zahraa is on a distinguished road
Hello foamers,
I would like to find the difinition of alphaEff() wich is used in hEqn.H in following form :

fvm::laplacian(turb.alphaEff(), h)


Does anyone know where "alphaEff()" is defined?
zahraa is offline   Reply With Quote

Old   June 23, 2015, 02:27
Default
  #2
Senior Member
 
Alexey Matveichev
Join Date: Aug 2011
Location: Nancy, France
Posts: 1,438
Rep Power: 25
alexeym will become famous soon enoughalexeym will become famous soon enough
Hi,

I guess, turb in your message is compressible turbulent model, so for RAS alphaEff is defined as

Code:
virtual tmp<volScalarField> alphaEff() const
{
    return thermo().alphaEff(alphat());
}
for LES it is

Code:
virtual tmp<volScalarField> alphaEff() const
{
    return thermo().alphaEff(alphaSgs());
}
and finally thermo.alphaEff() is http://foam.sourceforge.net/docs/cpp...b7cebc3adf4b1d
zahraa likes this.
alexeym is online now   Reply With Quote

Old   August 19, 2016, 12:47
Default
  #3
New Member
 
Paul
Join Date: May 2012
Posts: 23
Rep Power: 6
pmdelgado2 is on a distinguished road
It took me a very long time to figure this one out. The reason why it took me (and probably you) so long is because of the complicated structure of openFoam's thermophysical classes.

As alexeym indicates, no matter which type of turbulence model you choose (RAS or LES), the turbulence model will have a call to a thermophysical model. Searching through the various files, i figured out that in

/src/thermophysicalModels/basic/heThermo/heThermo.C

you will find a line that says something along the lines that

alphaEff = CpByCpv* (alpha + alphat)

I haven't found any other thermophysical model that also says this (if anyone discovers another one like this, please post a reply!!)

Note: alpha is defined in the

/src/thermophysicalModels/basic/basicThermo/basicThermo.H

as having the units kg/m/s. This probably looks strange to you knowing that thermal conductivity (kappa) usually has units of kg*m/s^3/k, where k is the degrees in kelvin.

In effect, alpha is known as the thermal diffusivity for the enthalpy of a mixture, where as kappa is the thermal diffusivity for temperature. The relation between the two is that

kappa = alpha * Cp,

where Cp is the specific heat capacity at constant pressure.

You may also notice that the definition of alphaEff above is also scaled by a factor of CpByCpv. CpByCpv = Cp/Cpv, where Cpv is the specific heat capacity at constant pressure/volume.

Depending on which energy model you use, e.g. sensibleEnthalpy, then

cpbycpv = 1

since it is assumed that cp=cpv.

If you use sensibleInternalEnergy, then

cpbycpv = Cp/Cv,

where cv is the specific heat capacity at constant volume.

The different types of energy models can be found in the directory

src/thermophysicalModels/specie/thermo

However, keep in mind that some solvers limit which of these energy models that you can use.
Mojtaba.a, vasava, alexj and 1 others like this.
pmdelgado2 is offline   Reply With Quote

Old   September 1, 2016, 06:37
Default
  #4
Senior Member
 
Paritosh Vasava
Join Date: Oct 2012
Location: Lappeenranta, Finland
Posts: 682
Rep Power: 15
vasava will become famous soon enough
Quote:
Originally Posted by pmdelgado2 View Post
In effect, alpha is known as the thermal diffusivity for the enthalpy of a mixture, where as kappa is the thermal diffusivity for temperature.
Did you mean, alphaEff is known as the thermal diffusivity for the enthalpy of a mixture, where as kappaEff is the thermal diffusivity for temperature?

Quote:
Originally Posted by pmdelgado2 View Post
where as kappa is the thermal diffusivity for temperature
You mean that kappa is the thermal conductivity, right?
vasava is offline   Reply With Quote

Old   December 8, 2016, 17:13
Default
  #5
New Member
 
Hasan Celik
Join Date: Sep 2016
Posts: 10
Rep Power: 2
PositronCascade is on a distinguished road
Dear Paritosh,

kappa is thermal diffusivity in OpenFOAM, isn't it correct? And I think it is Alpha / Cp as OpenFOAM SIMPLE solvers neglect the rho.
PositronCascade is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Fixed heat flux BC in buoyantPimpleFoam bhh OpenFOAM Running, Solving & CFD 36 November 27, 2016 06:06
Heat flux calculating with wallHeatFlux utility and alphaEff tanshihaj OpenFOAM Post-Processing 0 March 12, 2014 06:55
Wall with fixed heatFlux boundary condition Martin Lorenz (Lorenz) OpenFOAM Running, Solving & CFD 31 December 31, 2013 06:35
Accessing fields and dictionaries from within a BC implementation alberto OpenFOAM Running, Solving & CFD 12 December 6, 2011 10:30
alphaEff scalarField deji OpenFOAM 1 July 29, 2010 14:12


All times are GMT -4. The time now is 16:20.