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Michiel September 23, 2009 05:12

Problem with centrifugal pump calculation
 
The idea is to create a predicted pump curve which gives information about the maximum pressure at a fixed flow and a fixed inlet pressure. Based on this information I like to calculate the pump power (mechanic and hydraulic), and the efficiency.

I use Floworks to perform the analysis. The medium is water (pre defined in floworks). First I like to set up a basic calculation method, and then I can analyze some pumps and compare results tot actual test data.



For calculating the maximum outlet pressure at fixed flow and inlet pressure I set the following boundary conditions:
-At inlet a total pressure of 1 bar
-At oulet a outlet volume flow of 2 m3/sec
-The impeller walls which are in contact with the fluid are defined as ideal wall
-The pump casing and the inlet pipe are defined as real wall

I have set the following goals:
-Bulk av static pressure at inlet and outlet
-Equation goal to calculate the pressure drop (used for convergence)
-Inlet volume flow (used for convergence)
-Outlet volume flow (used for convergence)


When I run the calculation I canít get a good result. The most strange is that the inlet flow is not the same as the outlet flow. During the calculation the inlet flow varies from -8 m3/sec up to 12 m3/sec. After 400+ iterations the inlet flow keeps bouncing up and down. This indicates there is something wrong. The inlet and outlet flow should be exactly the same.

When I use the same model to solve the volume flow at fixed inlet and outlet pressure, there is no problem. Also when I solve the inlet pressure at fixed outlet pressure and fixed inlet volume flow, there is no problem.

Does anyone has an idea what is going wrong over here?

Michiel September 23, 2009 05:22

Ow sorry.... I see I forgot to mention some more information.

I use the local rotating region for the impeller. Angular velocity will be around 325 rpm. The numbers i use are normal for this type of pumps, so i am not analyzing something far away from the actual duty point.

yuchuan19831021 June 17, 2012 21:32

I have met the such problem, when i generate the finer grids, the convegence shows good.


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