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Old   October 3, 2010, 02:37
Default Savonius sliding Mesh
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Hi everyone,
i am studying a 2D Unsteady Flow around a VAWT (Savonius).
I'd like to use the sliding mesh tecnique and i have made the tutorial about the axial compresor stage.I also have read the topic about "Setting condition on a VAWT"here, but there are some things i am doing in the wrong way, so I'd like to receive some help.
My steps:
1)I have created 2 different mesh geometries : a small circle with my profile inside of it and a big rectangle with a hole inside which fits the circle.Then i have set the inner circle of the rectangle and the edge of the small circle as interface boundary with gambit.Then with Tmerge i have merged the 2 geometries and read the mesh with Fluent.
2)With Fluent i have defined the grid interface,choosing the 2 interface boundaries made with gambit and set them as periodic.Then i have setted as boundary condition that the fluid zone around the profile is moving (moving mesh) but i must set the angular velocity of blades and mesh.
I want to know how to let that the wind makes move the turbine, because another boundary condition is one of the edge of the rectangle setted as velocity inlet (at 20 m/s).So i don't know how to relate velocity of the wind and blade velocity.
3)When i try to initialize Fluent said that there are no periodic zone near the interface,so i made by Fluent console "Grid-Modify Zones-List Zones-Make Periodic".
Now i have to choose a zone and a shadow zone.Have i to set the 2 interface zones?and why if i set them ,Fluent delete one of these zones (the second)?
4)After this have i to set timestep and number of time steps and iterate or there is some more?
Thx for readingsand please if you have any suggestions answer me.
Best regards,
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Old   October 4, 2010, 02:29
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Maxime Perelli
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*I don't see the purpous of using tmerge (and also periodic option for interfaces)

* As far as I understand you don't want to set the rotationnal velocity of impellers, but you want them to rotate as a result of flowfiled, right?

Then you need a udf, which computes the pressure force (moments) on the impellers, and set the rotation speed for the sliding mesh ( as result of Newton 's law)
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Old   October 4, 2010, 04:00
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Hu Max.thx for answering!
I used tMerge but it's true i could easily make the geometry and se t the innterface zones,but anyway i don't think it will affect my study,or at least i hope.
I have solved my problem with sliding mesh using the moving mesh for the fluid zone and making the blades move with it.
Now i am waiting results!
best regards as ever
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Old   October 6, 2010, 06:20
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Dear Richard

Could you let me know how you get on with trying to make the fluid drive the turbine, as opposed to setting a fixed angular velocity? I am trying to do a similar thing (well will be when we get the software). did you write a udf in the end, or did you do it an alternative way?

Best regards

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Old   November 1, 2010, 22:29
Default fluent with sliding mesh
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i read thru the thread and i am looking at a similar problem with a rotating mixing paddle in a flowing tank (inlet velocity on one end and outlet on the opposite).

i can get mrf to work ok but i don't believe the interaction with the oncoming stream and the rotating flow(zone) is simulated correctly because mrf essentially is for mixed out flows.

the mixing paddle wall sits inside a cylindrical zone which is point to point conformally matched to the outer zone, that is the cylindrical zone outer is the box zone inner face.

if i set the grid interface boundary to periodic it barfs in running saying there are no periodic faces or ??. (this may be due to the ends of the cylinder but they are still point to point match). if i leave the interface type blank, fluent creates 2 new walls which fluent documentation says for non periodic boundaries to set to something other than 'wall'. i can't get fluent to accept any other bc for these walls.

i am not sure if they are empty walls or not, that is if they impede flow across the zonal interface or not but i want flow to be able to pass through the boundary freely which is the reason for sliding mesh in the first place.

anyone here know how to approach this.


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