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Convergence issues for a 3D Centrifugal pump simulation using ANSYS CFX

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Old   February 28, 2014, 04:00
Default Convergence issues for a 3D Centrifugal pump simulation using ANSYS CFX
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Venkat
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Am currently solving a steady state 3D Centrifugal pump problem using ANSYS CFX.

Objective:

To validate the performance curve of pump based on experimental inputs

Domain decomposition:

Stationary domain: Inlet, Outlet and Casing (1 Body)

Rotating domain: Impeller fluid volume surrounding the solid impeller. But solid impeller trace is left within the impeller fluid volume

Domain interface: Between Stationary domain and rotating domain.

Method: SRF and Frozen Rotor with no pitch change

Mesh:

Fine On curvature with skewness of 0.92 and Aspect ratio of 60

Boundary conditions used:

Domain ref pressure = 1 bar.

Inlet: Total pressure = 0 bar

Outlet: Mass flow rate = 0.065 kg/s or 3.9 lpm.

Turbulence intensity: Medium

Heat transfer: none

Rotating domain: 3100 RPM about Global Y

Issues:

Convergence beyond 1E-3 seem to be impossible with lot of wiggles Number of iterations: 700; Criteria: Want to set 1E-6 but I set it to default for first run.

If I consider the heat transfer, I get similar behavior. My idea is to consider the temperature later when I get the desired pressure rise.

I tried various combinations of BCs. Gone through previous threads.

It was so tricky to get the solution converged even if I use thumb rule of 1/2w , 1/4w....as physical timescale. Checked with automatic timescale in the beginning.

After 290 iterations, flow is getting blocked at inlet and outlet with changes in block % ranging from 0.5 % to 67%

Any suggestions or discussions related to this matter is highly appreciated.

Please find attached the current status as images:


Attached Images
File Type: jpg Mass and momentum.jpg (42.7 KB, 27 views)
File Type: jpg Turbulence.jpg (39.9 KB, 16 views)
File Type: jpg User points.jpg (39.8 KB, 15 views)
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Old   February 28, 2014, 04:46
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