viscosity input for single phase flow
hello,
some of the tutorials I have gone through uses the alpha co efficient value and not direct input of the viscosity in physical unit (e.g. in poinse or pa.s). How do we make sure that the alpha value has recovered the correct physical viscosity? the Run.out file did not mention the physical viscosity being calculated by the simulation.
Is there any documentation on different ways of assigning viscosity in the _Def.xml file? The above discussion is related to using artificial viscosity I suppose as in section 3.2.1 eqn (8) in documentation. There is some discussion on laminar viscous stress calculation as well. But apart from theory, is there guidelines on setting viscosity or recovering actual fluid viscosity after using the alpha co efficient? Is using the alpha coefficient the only way to manipulate viscosity for single phase flow in the released version 5.0?
Also, i was testing the inletoutlet tutorial 01_flow_around a cylinder. I was trying to increase the Reynolds number by increasing the velocity, but it gave some error. But the tutorial recommendation was to change the viscosity (alpha) in order to change the reynolds number. Is there a reason changing the velocity in place of the viscosity might cause issue?
Comments
The only way to use physical viscosity is to use laminar viscosity since artificial viscosity is just a numerical trick to dissipate energy.
Last version 5.0 using new density difussion term (Fourtakas et al., 2019) and new mDBC (English et al., 2021) should give proper results using only laminar viscosity + SPS turbulence model.
In addition, please start using the full package instead of DesignSPHysics. In this way you can experience and use all latest functionalities implemetned in DualSPHysics.
Regards
So on the tutorials I mentioned above, I was modifying the _Def.xml files supplied with the tutorial. I did not create any case with designSphysics. How can we use laminar viscosity in physical units directly in the _Def.xml file? Is there provision for that? Is there any tutorial which shows where is it input in the parameters list?
Any comment on the 2nd portion of my inquiry on the Reynolds number manipulation?
I see these options:
<parameter key="ViscoTreatment" value="2" comment="Viscosity formulation 1:Artificial, 2:Laminar+SPS (default=1)" />
<parameter key="Visco" value="" comment="Viscosity value" /> % Note alpha can depend on the resolution. A value of 0.01 is recommended for near irrotational flows.
I have put "2" for ViscoTreatment now.
What physical unit is for Visco value? do i need to put dynamic or kinematic viscosity in the value field?
Kinematic Viscosity, 1e-6 for water, SI units
You can check the list of examples we provided in the full package and follow an example with laminar viscosity.
The way to do this is to open the Examples*.pdf files in DualSPHysics_v5.0\examples where you can find the definition of the main feature of the cases.
For example if you open "Examples_main.pdf" you can read that a case in 12_FLOATINGWAVES include this
Regards
hello,
I have a question regarding your comment "Last version 5.0 using new density difussion term (Fourtakas et al., 2019) and new mDBC (English et al., 2021) should give proper results using only laminar viscosity + SPS turbulence model."
Does it mean I have to use new density difussion term (Fourtakas et al., 2019) and new mDBC (English et al., 2021) when I use laminar viscosity + SPS turbulence model.? I can't use DBC with it for example?
I am looking into other tutorials to find answer to the above questions I posed.
Tutorials are not updated to use v5.0
Please follow the examples we have in the full package you can donwload from our website
Regards
That link is for you... the idea is to monitor the downloads, so better if you do not share the link here, please
Regards
sorry, thanks for taking it out from here on behalf of me.