Hello there I am simulating cavitation for a Francis turbine. Francis turbine is rotating with 826 rpm. I have two questions; 1- Vapor pressure for my case is 2100 Pascal, and Temperature is 25 Celsius, now for the "water vapor" how should I find density and viscosity? is there any table for this? Is this table based on VAPOR pressure or temperature? Or should I use the Fluent default values?(plz see Figure 1) 2- Second problem is that when I use Upwind schemes, I got fairly ok values(not accurate enough though), and also my cavitation has a weird part too. when I switched to second order schemes, then cavitation disappears, but I got better results(shaft output, mass flow rate, ...). What should I do? (plz see figure 2)
Thanks,
Farzad
Cavitating liquid is a two-phase flow with gas-liquid mass transfer. Are you using a single-fluid or two-fluid model in simulating this flow?
I am using mixture model in fluent where it solve just one momentum equation for the mixture(both gas and fluid);
https://www.afs.enea.it/project/neptunius/docs/fluent/html/th/node309.htm
In this case, you have a fluid mixture for which the density should be calculated as a function of the volume fraction of each phase using thermostatic laws. You have furthermore, to define an equivalent viscosity for the mixture using an additional empiric correlation, which also is a function of the volume rate. There are several such correlations in the literature. You may find some on:
Presentation TPTF-Chapitre 4 : Pertes de charge dans les écoulements diph...
See Also:
Article Modelling gas–liquid flows in degassing risers used in extra...
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Jamel Chahed Thanks dear Chahed. I used ideal gas relation and the density I found was very close to literature. But I still have problem in finding answer for viscosity. According to formula 24, we still need dynamic viscosity(where I need only dynamic viscosity of water vapor at T=25 Celcius and P=2100 Pascal. Where can I find dynamic viscosity of water vapor?
Thanks,
Farzad
Farzad Farajidizaji See for example https://www.engineeringtoolbox.com/steam-viscosity-d_770.html
Thanks a lot dear Chahed, engineering toolbox is really helpful. Just one last question, when I use ideal gas relation, I got different results(60% different from what openFoam document has given(please see attached figure).
https://github.com/OpenFOAM/OpenFOAM-6/blob/master/tutorials/multiphase/interPhaseChangeDyMFoam/propeller/constant/transportProperties
So I think ideal gas relation has lots of error for my case. I searched engineering toolbox, there is a table for steam density, but it is more than 100 Celcius where my case is at 2100 Pascal and 20-25 degree celcuis;
https://www.engineeringtoolbox.com/densities-specific-volumes-dry-air-water-vapor-d_1575.html
Do you know any other table for water vapor density for room temperature?
Thanks,
Farzad
No worries, I find the steam-density table, and it is fairly close to what I have calculated using ideal gas relation. Thanks a lot.
Now I have to deal with second order discretization problem, where omit cavitation in my simulation.
Thanks,
Farzad