Hello Everyone,
I am running Rayleigh Benard natural convection case with Rayleigh number to be 630000 and Pr as 0.71. I am using AFM as turbulent heat flux model. For boussinesq implementation, I am adding boussiesq(rho*beta*(Tt_ref)*g) source term in momentum equation.
I am facing an unusual problem regarding the turbulent heat flux magnitude. The turbulent heat fluxes for this case are incredibly low value(1e38 to 1e36). Whereas the temperature profiles are predicted well when compared to DNS results.
Also the turbulent kinetic energy (i.e. rij values) is also incredibly low.
Code_saturne v 5.1.3.
Turbulence model : RSMEB
turbulent heat flux model : AFM
Kindly suggest few changes.
Regards
Kunal
Low value of Turbulent heat fluxes in Natural convection
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Low value of Turbulent heat fluxes in Natural convection
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 63e4_afm_data0.csv
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Re: Low value of Turbulent heat fluxes in Natural convection
Hi,
May I asked how did you implement Boussinessq?
i.e cs_user_source_terms.f90 under ustsnv or cs_user_physical_properties.f90 under usphyv?
Cheers,
Costas
May I asked how did you implement Boussinessq?
i.e cs_user_source_terms.f90 under ustsnv or cs_user_physical_properties.f90 under usphyv?
Cheers,
Costas
Re: Low value of Turbulent heat fluxes in Natural convection
Hello,
I used ' cs_user_source_terms.f90' under ustsnv for Boussinesq approximation.
Regards
Kunal
I used ' cs_user_source_terms.f90' under ustsnv for Boussinesq approximation.
Regards
Kunal
Re: Low value of Turbulent heat fluxes in Natural convection
Hello,
I have started a case with natural convection under 6.0beta, RijSSG + AFM, the temperature / turbulent heat fluxes have a very high amplitude, 10e50. Switch back to 5.0 if you need results quickly. Otherwise, wait for fixes.
P.S.: tests performed with the temperature flagged as buoyant in cs_user_parameters.c and the SIMPLEC time scheme. Switching to PISO and nterup = 3 did not improve the situation.
Best regards,
Cédric
I have started a case with natural convection under 6.0beta, RijSSG + AFM, the temperature / turbulent heat fluxes have a very high amplitude, 10e50. Switch back to 5.0 if you need results quickly. Otherwise, wait for fixes.
P.S.: tests performed with the temperature flagged as buoyant in cs_user_parameters.c and the SIMPLEC time scheme. Switching to PISO and nterup = 3 did not improve the situation.
Code: Select all
void
cs_user_parameters(cs_domain_t *domain)
{
/* Declare the temperature as a buoyant scalar */
cs_field_set_key_int(cs_field_by_name("temperature"),
cs_field_key_id("is_buoyant"),
1);
}
Cédric

 Posts: 8
 Joined: Fri Apr 27, 2018 2:33 pm
Re: Low value of Turbulent heat fluxes in Natural convection
Thank you for your feedback on the AFM model. Your temperature profile looks good probably because the GGDH part of the AFM works well whereas the additional terms ( bouyancy, velocity gradient,...) might be bugged.kunalck wrote: ↑Mon Apr 08, 2019 3:23 pmHello Everyone,
I am running Rayleigh Benard natural convection case with Rayleigh number to be 630000 and Pr as 0.71. I am using AFM as turbulent heat flux model. For boussinesq implementation, I am adding boussiesq(rho*beta*(Tt_ref)*g) source term in momentum equation.
I am facing an unusual problem regarding the turbulent heat flux magnitude. The turbulent heat fluxes for this case are incredibly low value(1e38 to 1e36). Whereas the temperature profiles are predicted well when compared to DNS results.
Also the turbulent kinetic energy (i.e. rij values) is also incredibly low.
Code_saturne v 5.1.3.
Turbulence model : RSMEB
turbulent heat flux model : AFM
Kindly suggest few changes.
Regards
Kunal
Can you post your test case so that I can have a look ?
Re: Low value of Turbulent heat fluxes in Natural convection
Hi,
Thanks for the clarification. Another question if you do not mind. If you use Boussinesq through cs_user_source_terms.f90 under ustsnv what did you do with the gravity vector in the generation rate of turbulence (Gk)?
Cheers,
Costas
Thanks for the clarification. Another question if you do not mind. If you use Boussinesq through cs_user_source_terms.f90 under ustsnv what did you do with the gravity vector in the generation rate of turbulence (Gk)?
Cheers,
Costas
Re: Low value of Turbulent heat fluxes in Natural convection
Hello JeanFrancois,JeanFrancois Wald wrote: ↑Tue Apr 09, 2019 12:54 pmThank you for your feedback on the AFM model. Your temperature profile looks good probably because the GGDH part of the AFM works well whereas the additional terms ( bouyancy, velocity gradient,...) might be bugged.kunalck wrote: ↑Mon Apr 08, 2019 3:23 pmHello Everyone,
I am running Rayleigh Benard natural convection case with Rayleigh number to be 630000 and Pr as 0.71. I am using AFM as turbulent heat flux model. For boussinesq implementation, I am adding boussiesq(rho*beta*(Tt_ref)*g) source term in momentum equation.
I am facing an unusual problem regarding the turbulent heat flux magnitude. The turbulent heat fluxes for this case are incredibly low value(1e38 to 1e36). Whereas the temperature profiles are predicted well when compared to DNS results.
Also the turbulent kinetic energy (i.e. rij values) is also incredibly low.
Code_saturne v 5.1.3.
Turbulence model : RSMEB
turbulent heat flux model : AFM
afm_dns.png
63e4_afm_data0.csv
Kindly suggest few changes.
Regards
Kunal
Can you post your test case so that I can have a look ?
Thank you for your feedback. I have also run the same case with unsteady solver(CS_v4.0) and I could not prevent the laminarization. Although, temperature profile was like previous case(predicting well compared with DNS).
Re: Low value of Turbulent heat fluxes in Natural convection
Hello,
I gave the value of gravity as a negative vector in GUI. And when using Boussinesq through cs_user_source_terms.f90, then the I would use gy for gravity.