[Gorz]

Good evening,

For my final year group project I am modelling rotor-stator side wall gaps in multi-stage centrifugal pumps.

So, I am modelling a 12th of the problem which has been split into fluid regions (see attached) and periodic zones assigned to the corresponding faces - each region connected via interface BC. Inner impeller is rotating at 3000RPM, and all applicable walls are assigned as rotating.

I am using k-e RNG model std wall functions, and have a nice structured mesh in all zones except the radial annulus and axial outlet, however I'm not particularly interested in the flow here, more so on the impeller faces and shroud face.

I can achieve convergence on all residuals but continuity. Mass flow monitors at inlet and outlet converge (velocity inlet, pressure outlet), but my average impeller and shroud pressures continue to slowly creep up with 1000s of iterations. This also applied to my inlet pressure value.

I have tried to reduce the relaxation factors and do get a slight drop in the continuity residual, but not enough to get below 10-3.

y+ is between 30-300 on all but 1 of 18 walls. On that wall the majority lie above 30, with maybe 8 cells below.

Any advice on how to proceed/speed up convergence/achieve continuity convergence?

Note that I am using an academic license with a cell limit of 512000.

Also, the pressure profile down on the impeller wall looks is in reasonable agreement with an analytical model I am working from.

P.s. There is minimal skewness in the mesh - no cells above 4 aspect ratio, majority of cells about 0.85 quality, with about 1% of no less than 0.6.

[Gorz]

Still having problems with this...

Refined the mesh and y+ is less acceptable and the pressure is lower at stability.

Made another mesh with perfect y+ and the inlet pressure solves higher.

Seems like the mesh sensitivity is all over the place...