• Author / Uploaded
• Sahil Jawa

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Workshop: Mixing Tank

ANSYS Fluent Watertight Geometry Workflow Release 2019 R1

Introduction • This workshop demonstrates the use of the Watertight Geometry workflow in Fluent Meshing to mesh a mixing tank • All steps are not shown explicitly in the slides – please watch the video for complete details

Geometry Topology Not Shared – requirement for BOI Shared Topology – shared items highlighted in graphics

Visibility of BOI bodies is off in this picture

BOI Bodies

Visibility of BOI bodies is on in this picture They are copies of the MRF volumes (with name "fluid" in the structure tree) but they are excluded from shared topology Using copies of MRF volume to define the BOIs is not required, just convenient in this case

Named Selections (NS)

NS assigned to faces of BOI bodies Turn off visibility of MRF bodies to ensure the correct faces are being selected Confirm faces (and not bodies) are selected by checking in the border below the graphics window

Import Geometry

Use mm for Units

The name of the workshop input file is mt-2i.scdoc

Add Local Sizing

Size Control Type: Body of Influence

Size Control Type: Face Size

Target Mesh Size = 10 mm

Target Mesh Size = 4 mm

Face Zone Labels: boi-lower & boi-upper

Face Zone Labels: wall-impeller-lower wall-impeller-upper

Create Surface Mesh The default values are acceptable. Min. size is much smaller than any feature and it is unlikely curvature and proximity settings will result in overrefinement. Based on size preview boxes, max. size is suitable for this problem. Use clipping plane to examine mesh near impellers Baffles are expected so the warning message is not a concern

Maximum skewness of ~ 0.4 is good

Describe Geometry

This model contains three fluid regions – the main tank region and one MRF region surrounding each of two impellers. Setting fluid-fluid boundary types to internal is important in this model because these are the boundaries between the MRF regions and the main tank region.

Update Boundaries

Change the boundary types for “sym-top" to “symmetry”. It is common practice in mixing tank simulations to represent the free surface as a symmetry boundary when no surface vortex is present.

Update Regions

"fluid-lower-mrf"

Region names are initially inherited from SpaceClaim part names. They can be changed in this panel but here they already had the desired names. Mousing over the region in the panel will highlight it in the graphics window if the highlight option is active.

"fluid-main-tank"

"fluid-upper-mrf"

Create Volume Mesh

Choose poly-hexcore for the fill method and set the number of buffer layers to 3. Buffer layers control the rate of transition of the hex core cells. A larger number produces a more gradual transition. In this case it will result in a higher number of smaller hex cells close to the impeller and shaft surfaces.

Final Mesh

Orthogonal quality is good.

Notes: For problems with MRF zones, check carefully to make sure boundaries are internal. When zone assignment is correct, there will not be any boundary layer mesh visible, which is the case here. In mixing tank problems, if the top surface of the domain is the liquid surface and not an actual wall, set the boundary type to symmetry during meshing to avoid boundary layer mesh generation. The boundary type can be changed in solution mode if it is desired to define a slip wall as opposed to a symmetry plane

Final Mesh

Clip by Limit in Z and note that the boundary layer mesh is also grown from the baffles. Hint: If you want to use the slider bar to change the clipping plane, movement is faster if you turn off Draw Cell Layer, move slider to desired position, turn Draw Cell Layer back on

Effect of increasing buffer layers can be seen near impeller blades

Switch to Solution

Save mesh file before switching to solution. Workflow tasks and inputs are stored in the mesh file. Or alternatively, save the workflow