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Flow Simulation - Centrifugal Pump - Solver Abnormally Terminated

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Old   July 12, 2022, 12:05
Default Flow Simulation - Centrifugal Pump - Solver Abnormally Terminated
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Plevik
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Hello for everyone,


I want to perform CFD analysis of centrifugal pump to find the performance of pump. I have the tested data for this pump.


Definition of the BCs (see Figure 1):

Internal Volume Flow Rate on INLET

Environment Pressure on OUTLET

Real wall (Stator) - marked as blue in the Figure 1

Local Rotating (Averaging) Region 2950 RPM. Rotating region is defined by the outer shape of the impeller (marked as green*in the Figure 1)


Surface Goals:

Mass Flow Rate Inlet

Mass Flow Rate Outlet

Av. Static Pressure Inlet

Bulk Av Static Pressure Outlet (at the point of the discharge flange)

Torque on impeller


Equation Goals:

Pressure Drop* { Av Static Pressure Outlet}-{Av Static Pressure Inlet}

Efficiency {Pressure Drop}*{Inlet Volume Flow 1:Volume flow rate:5.000e-003}/{Rotating Region 1:Angular velocity:3.089e+002}/{SG Torque on Impeller}



Most of the time I got an error "Solver Abnormally terminated" after going circa 300 iterations.

If it got solved, I observed that Mass Flow Rate at inlet and outlet were not equal.

They had a huge difference in value.

The pressure difference and torque value were also very high (Figure 2.).


Kindly suggest and help me out what changes I should make in the set up to achieve the required results.


Thanks in advance.


Stan K.
Attached Images
File Type: png Figure 1. Definition of the BCs.PNG (103.0 KB, 16 views)
File Type: png Figure 2. Goal Plot.PNG (18.7 KB, 8 views)
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Old   October 26, 2022, 16:19
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Matt
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I've been running a lot of centrifugal blowers in Flow Sim lately. Some things I've learned:
1.It's VERY sensitive about the clearances around the rotating region. It doesn't like the RR to be coincident with walls, with preferably several cells of clearance between the RR and any solids. If you need to model a very small clearance, you either need a ridiculously fine mesh or just let an axisymmetric portion of the casing/volute/whatever rotate with the RR (not strictly correct, but at least it lets you run a simulation). Otherwise, you can just artificially increase the clearances until it will run
2.It's sensitive about inlet mass/volume flow boundary conditions. I usually initialize it with a total pressure inlet BC, then iterate the inlet P0 manually until I get the correct mass/volume flow. Once you are in the ballpark, you can usually restart with a volume flow BC, however. But it really struggles with the startup transient with centrifugal turbomachines combined with mass/volume flow BCs.

The issues with #1 usually cause the solver the terminate before the first iteration, so that may not be your main concern. But try running with a total pressure inlet BC and see if it converges.

For any turbomachine, looking at relative streamlines in the rotating reference frame will tell you a lot about what's going on in your simulation. Unfortunately, Flow Sim doesn't let you monitor these during a run, so you have to save the results and inspect periodically. If the blade incidence is really high or low, you probably aren't near the design condition for that rotor.
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