## Preprocessing

#### Meshing a packed bed of spheres(Fuel elements) in a cylindrical container and fluid domain.

• rogannithin99
Subscriber

Hi there,

As a Novice user of Ansys Fluent, I am currently doing my Research project on Thermal Energy heat storage systems.

The storage system involves a number of spherical balls(fuel elements) filled in a cylindrical container. These balls(Each of size 60 cm in diameter) are arranged in layers and filled up to the brim of the container(at a height of 120 cm and a diameter of 75cm).  The fluid would flow from the inlet to the outlet, submerging the spherical balls periodically.

I've attempted to mesh the balls and define the fluid flow domain(by trying to create a Boolean around the entire cylindrical geometry and subtracting the balls from the cylindrical geometry)  All these attempts failed. I then realized that the balls needed to be distinct without any contact with each other. Thus,i gave a gap of 0.1 mm between each ball.

Now how do I mesh(tetramesh) these balls and define the fluid flow domain accurately?

Ansys Employee

Though geometry looks simple, it has lot of curved faces. This mesh will have much more elements. As student version you can go upto 512K cells.

First of all reduce the problem size. Take only small representative part of the geometry and try to mesh it. Once it is meshed, you can go ahead with reduced problem or you can increse problem size and apply similar geometry/meshing strategy.

Regards,

Keyur

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• rogannithin99
Subscriber

Now as you have told, I have reduce the geometry's complexity. I am now considering only a portion(sector) of my model. please find the images attached.

when I use Boolean combine, the operation works. however, when I try to subtract the tool bodies(spherical balls) from the cylindrical body, it fails to do so. I get this error:

Ansys Employee

still i believe, you need to reduce problem further.

just keep two or three rows of sphere.

to use boolean, make sure that sphere do not have only point contact. they should intersect each other considerably. i am saying considerably because if they intersect only marginally, it will create sharp angles and mesh will have bad elements.

Regards,

Keyur

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• Rob
Ansys Employee

To add non-manifold is the error when volumes try to overlap and create a face area of zero: it's documented online as all CAD tools suffer from this issue.

• rogannithin99
Subscriber

Any solutions to overcome this error?

• Rob
Ansys Employee

Yes, create an overlap. But you then get into mesh quality issues so need to be a bit more creative as Keyur mentions.  Or create a gap, quality issues tend to be reduced but cell count can get very high and conduction between solids doesn't happen as readily.