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Buoyant environmental flow including salinity in OpenFOAM 

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July 4, 2019, 02:26 
Buoyant environmental flow including salinity in OpenFOAM

#1 
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Jost Kemper
Join Date: Apr 2018
Location: Kiel, Germany
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Dear All,
I am still fairly new to this forum so please do not get mad if I am doing this all wrong…. I am working on a project including the simulation of a jet (velocity 2[m/s]) of cold depth water (temperature=10[°C], salinity 35.4 [g/kg]) into the ocean surface region (temperature=25[°C], salinity 36.1 [g/kg]). After some research in this forum, I found a few threads asking questions about salinity induced buoyant flow in OpenFOAM. However, no solutions have been presented so far. For this reason, I would like to put together this thread in order to concentrate the efforts in this field and, if possible, derive general instructions on how to model salinity induced buoyant flow in OpenFOAM. First, I will give a short summary on what has been said in this forum so far. Since there is a high probability that will forget important statements on this matter, I kindly ask all of you to help put together this review. [1] Incompressible isothermal buoyancy is on isothermal salinity induced buoyant flow. There is a Suggestion to develop a solver based on the buoyantBoussinesq solvers, using a passive scalar transport equation for salinity, which is inspired by the temperature equation implemented in those solvers and calculate a density change and corresponding Buoyancy from this. [2] Introducing a scalar field for buoyancy production in kepsilon is on buoyancy driven production of turbulence induced by salinity (if I understand correctly). [3] add concentration states that temperature and salinity can be modeled using the same equations. However, it is said that modeling salinity is computationally more demanding due the small diffusion coefficients. It is further suggested to model the influences of temperature and salinity in two separate simulations. We can conclude from this that:
A passive scalar can easily be introduced into a solver (e.g. following this tutorial https://www.youtube.com/watch?v=L94iYGvZr9Q). However, we will need a more sophisticated transport equation for salinity, which might be very similar to buoyantBoussinesqPimpleFoams Teqtn. Modifying buoyantBoussinesqPimpleFoams linear Boussinesq approximation, we can introduce a term for the salinity influence on density. Seems easy so far... However, Ferziger and Peric state that, in water Boussinesqs linear approximation for the temperature density coupling does merely hold for temperature differences up to 2[°C], which is by far not enough for many environmental flows (including mine see above). Even though a higher order polynomial for the temperature density coupling can easily be derived (e. g. based on TEOS10 http://www.teos10.org) and implemented, it appears to me that buoyantBoussinesqPimpleFoam is not applicable to problems with large temperature differences, since
A short description of the theory is given here: https://caefn.com/openfoam/solversbuoyantpimplefoam . Using the icoPolynomial equation of state, buoyantPimpleFoam can be used in “incompressible mode” (i.e. density is only depended on temperature not on pressure), which seems appropriate. But, how do we implement the density salinity coupling now? Do we:
Also, not only the density is salinity dependent. Especially the heat capacity Cp, but also thermal conductivity and dynamic viscosity show some (minor) dependence on salinty. I will thus stop my monologue here and give the ball to you. Maybe more of a coding question at this stage but I am sure we will face many more challenges on our way towards a solver for buoyant environmental flow including salinity in OpenFOAM. Best regards from Kiel(Germany), Jost 

July 4, 2019, 14:55 

#2 
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Michael Alletto
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This paper may help https://www.researchgate.net/publica..._the_ke_Model


July 24, 2019, 08:08 

#3  
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Jost Kemper
Join Date: Apr 2018
Location: Kiel, Germany
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Dear Mr. Alletto,
thanks a lot for your input! Having moved forward a bit on the problem of implementing the density salinity coupling, I now see that turbulence modeling is definitely a big topic when dealing with buoyant environmental flow. Also based on recent progress, I have to revise a statement I made on buoyantBoussinesqPimpleFoam. Quote:
I use the following polynomial: where: is Temperature. is absolute salinity, which is modeled as a passive scalar. is the standard density. and the are scalar coefficients. This approach delivers good results. However, the problem that buoyantBoussinesqPimpleFoam does not have a real thermophysical model, to account for viscosity and thermal conductivity changes due to temperature and salinity, does still remain. It thus still seems attractive to use the solver buoyantPimpleFoam for my simulations. I have implemented a new salinity dependent thermophysical model based on OpenFOAMs polynomal based thermophysical models. The polynomials I implemented are similar to the ones shown above. The code structure of the new thermophysical model is shown in the attached pdf (salineThermoProperties.pdf), which is derived from this schematic. With this recent progress, I now have two solvers for buoyant flow including salinity. However my transport equation for salinity is still very basic. I would really appreciate if anyone could give me some input on a proper passive scalar transport equation for salinity. Cheers, Jost 

July 24, 2019, 15:58 

#4 
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Michael Alletto
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Turbulent diffusion in rans models are usually modelled assuming gradient diffusion. The ratio between mass and momentum diffusivity is described by the turbulent Schmidt number which is a function of stratification. See e.g. https://agupubs.onlinelibrary.wiley....9/2008GL036056. So using a similar equation as for the temperature equation will be OK.
Best Michael 

May 9, 2020, 03:36 
Densitysalinity relationship

#5 
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Join Date: Oct 2010
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Dear Jost,
I was interested on how you programmed the polynomial densitysalinity reltionship in OpenFOAM. Would it be possible to advise how you went about this? Also, where does this densitysalinity reltionship come from? Thanks. Tom www.mtscfd.com 

July 8, 2020, 07:54 
New equation of state

#6 
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Namagambe Aidah
Join Date: Jun 2020
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Greeting, am kindly requesting for your help. I have been modifying the boussinesq equation of state to add in the salinity in openfoam7. But am failing can you please advice


July 8, 2020, 12:30 

#7  
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Jost Kemper
Join Date: Apr 2018
Location: Kiel, Germany
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Hi,
what problems exactly do you run into? Quote:
The code looks like this Code:
rhok = ( C_0 + CT_1 * T + CT_2 * T*T + CT_3 * T*T*T + CSA_1 * salinity ) / rho_0; In my case, they look like this Code:
//Coeffeicients for density approximaton dimensionedScalar C_0("C_0", dimless, laminarTransport); dimensionedScalar CT_1("CT_1", dimless/dimTemperature, laminarTransport); dimensionedScalar CT_2("CT_2", dimless/(dimTemperature * dimTemperature), laminarTransport); dimensionedScalar CT_3("CT_3", dimless/(dimTemperature * dimTemperature * dimTemperature), laminarTransport); dimensionedScalar CSA_1("CSA_1", dimless, laminarTransport); //Reference temperature for rho_0 in K dimensionedScalar T_0("T_0", dimTemperature, laminarTransport); //Reference salinity for rho_0 dimensionedScalar SA_0("SA_0", dimless, laminarTransport); //Calculate reference density dimensionedScalar rho_0 ( "rho_0", dimless, C_0.value() + CT_1.value() * T_0.value() + CT_2.value() * T_0.value() *T_0.value() + CT_3.value() * T_0.value() *T_0.value() *T_0.value() + CSA_1.value() * SA_0.value() ); Maybe someone in this forum knows a nicer way program this... I hope this helps with your problem. Cheers, Jost 

July 11, 2020, 02:18 

#8 
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Namagambe Aidah
Join Date: Jun 2020
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Thanks alot dear,
Am working on problem involving heattransfer within a solarpond and am using buoyantpimplefoam in openfoam7. The openfoam7 comprise of boussinesq equation of state rho = rho0 = 1  beta*(T  T0) but depends on only temperature. The problem am working on assumes that the density follows boussinesq approximation rho0 = rhoO*( 1  beta*(T  T0) + betas*( S  So)) where S is the salinity and the So is the reference salinity depending on both temperature and salinity. On trying to modify the boussinesq equation of state within the openfoam7 adding in salinity and on compling am obtaining an error of S not declared within the scope. How can I declare S within my equation of state. Will be grateful for your help 

July 11, 2020, 03:52 

#9 
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Michael Alletto
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Did you include a field for the salinity in the file creatFields


July 11, 2020, 04:33 

#10 
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Namagambe Aidah
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Yes I did within the solver but the error is appearing in the compling of the thermophysicalModel under specie directory.


July 11, 2020, 06:26 

#11 
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Michael Alletto
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In the solver you are using the thermodynamic package is responsible for updating the density.


July 11, 2020, 13:22 

#12 
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Michael Alletto
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the function which calculates rho for compressible pressure based solvers is in the equation of state class.
 $FOAM_SRC/thermophysicalModels/specie/equationOfState/ 

July 11, 2020, 15:18 

#13 
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Namagambe Aidah
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Thanks Alletto,
$FOAM_SRC/thermophysicalModels/specie/equationOfState  this is true. In $FOAM_SRC/thermophysicalModels/specie/equationOfState/boussinesq is what I modified and renamed it myBoussinesq and I modified rho0 = 1  beta*(T  T0) to rho0 = rhoO*( 1  beta*(T  T0) + betas*( S  So)). And on compling in the $FOAM_SRC/thermophysicalModels/specie/, it's when the error S is not declared in the scope of the myBoussinesq equation of state appears. Is it that I didn't define S with in EOS. 

July 12, 2020, 04:46 
Densitysalinity relationship

#14 
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Hi Aidah,
Please find attached my coding for this which I hope will help. "C" corresponds to salinity. Regards, Tom www.mtscfd.com 

July 12, 2020, 05:22 

#15 
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Namagambe Aidah
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thanks Tom
but am using buoyantPimpleFoam which involues the energy equation not temperature equation and the rho is coded in the Equation of state files. please see the added file of my solver and the EOS( where i include in salinity S which am denoting with C). but when i compile in $FOAM_SRC/thermophysicalModels/basic/  the error In file included from /home/aidah/OpenFOAM/root7/run/src/thermophysicalModels/specie/lnInclude/myBoussinesq.H:243:0, from rhoThermo/rhoThermos.C:33: /home/aidah/OpenFOAM/root7/run/src/thermophysicalModels/specie/lnInclude/myBoussinesqI.H: In member function ‘Foam::scalar Foam::myBoussinesq<Specie>::rho(Foam::scalar, Foam::scalar) const’: /home/aidah/OpenFOAM/root7/run/src/thermophysicalModels/specie/lnInclude/myBoussinesqI.H:96:51: error: ‘C’ was not declared in this scope return rho0_*(1.0  beta_*(T  T0_) + betas_*(C  C0_)); ^ /opt/openfoam7/wmake/rules/General/transform:25: recipe for target 'Make/linux64GccDPInt32Opt/rhoThermo/rhoThermos.o' failed 

July 12, 2020, 05:33 

#16 
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Namagambe Aidah
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sorry i had not attached the files but for the solver i have excluded the pressure and velocity equation files (UEqn.H and PEqn.H)
myBoussinesq.zip solver.zip 

July 12, 2020, 05:37 

#17 
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Michael Alletto
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Not declared in this scope means that your field c is not seen where you want to use it


July 12, 2020, 05:55 

#18 
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Namagambe Aidah
Join Date: Jun 2020
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Am not so good at programming, How can I really declare it in my file


Tags 
buoyancy driven flow, environmental flow, heat and mass transfer, passive scalar, salinity 
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