CFD Online Discussion Forums - Interface between rotating and static zone

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Interface between rotating and static zone

Hello,

i have a problem regarding the interface between a rotating and static cell zone. Which settings do i need to adjust in Fluent to have a correct simulation? The case is pretty simple. I have a rotationally symmetric fluid zone. There is one inlet at the left side of the model and one outlet on the top of the model. The bottom part of the model rotates and the upper part doesnt. The result i got til now is that the velocity of the fluid at the border between the rotating and static part changes suddenly. I want it to change smoothly. The overall settings are correct. I just dont know the interface thing. Until now i simulated a completely rotating system.

Can you post a picture of your result? There can be a few reasons of your problem. One is that you define velocities in a zone using wrong type (absolute vs. relative). Another reason can be bad mesh at the interface and therefore poor interpolation there. Or, if the discontinuity is not too large, it can be simply because of the way how Fluent postprocess the results. I quote a Fluent Guide:

Quote:

You may instead create zone surfaces for the interface zones. Data displayed on these surfaces will be "one-sided''. That is, nodes on the interface zones will "see'' only the cells on one side of the grid interface, and slight discontinuities may appear when you plot contour lines across the interface. Note also that, for non-planar interface shapes in 3D, you may see small gaps in your plots of filled contours. These discontinuities and gaps are only graphical in nature. The solution does not have these discontinuities or gaps.

Well, i dont really know how to post a picture, because i dont have a URL for it. Thats why i drawed the situation simplified below. Actually you have to imagine the Model 90 degrees turned anticlockwise. the rotating part is at the bottom and the static part above. How do i get a smooth decrease of velocity like i described with 'fast...slow...slower...0' ?

.................................................. .......................
. fast---------------slow ! slower ----------------0 -.
.------------------------ !--------------------------.
. ------- Zone 1 ---------! --------Zone2---------- -.
.------- rotating (300rpm) ! ------static (0rpm) ------.
..............................Border....................................