Problem with centrifugal pump calculation

Michiel · September 23, 2009, 06:12

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 can’t 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, 06:22

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, 22:32

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

September 23, 2009, 06:12	Problem with centrifugal pump calculation	#1
Michiel Member Michiel Join Date: Jul 2009 Location: The Netherlands Posts: 42 Rep Power: 17	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 can’t 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?

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September 23, 2009, 06:22		#2
Michiel Member Michiel Join Date: Jul 2009 Location: The Netherlands Posts: 42 Rep Power: 17	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.

June 17, 2012, 22:32		#3
yuchuan19831021 New Member Wang Yuchuan Join Date: May 2012 Posts: 1 Rep Power: 0	I have met the such problem, when i generate the finer grids, the convegence shows good.