Pump's Torque in CFD simulation is higher than experience.

ngoc_tran_bao · May 31, 2016, 01:23

Dear All, I have a challenge with the torque in my pump simulation. At Design Flow rate, the torque calculated on impeller of pump in CFD simulation is much higher than torque measured by experiment, 90Nm compared with 73 Nm. It is obvious that in simulation we can not account for all factors as reality, so I believe that because of lower resistance, torque in CFD should be lower than that of experiment. In my simulation, impeller consists of Hub, Shroud and 7 blades and I calculate torque on impeller for Z axis (used both monitor point in Solver and Function calculator in Post). Does anybody have ideas to explain me why there is an existence of unreasonable result? Thank you in advance.
impeller.png

urosgrivc · May 31, 2016, 01:33

inappropriate boundary conditions, or mesh, or other setings
In cfd it is almost always the user`s fault as computer is just a number crunching machine it can only do what you say it to do.

More details will be needed to figure out what is wrong

-Maxim- · May 31, 2016, 01:58

That's quite interesting because in my simulations, the calculated CFD torque is always lower from what we would expect.
Maybe you can share more information about your setup so that we can have a look?

ngoc_tran_bao · May 31, 2016, 02:03

Thank for your replies,
As for BC, I set total Pressure at Inlet = 0.1 Mpa;
Variable Mass Flow rate at Outlet From 60 - 180 m3/h (Q design =120);
Rotation = -1750 RPM (Z axis)
Smooth wall for all suction, discharge walls;
Reference Pressure =0 atm;
Physical time step =1/W.
I hope those Information useful.

-Maxim- · June 1, 2016, 02:36

can you please post your ccl and/or out file?
Have you checked the typical questions such as:
Has your simulation converged? Are the imbalances under 1%? Etc.

ngoc_tran_bao · June 1, 2016, 03:27

centrifugal pump 1.txt
this is CCL file. As for convergence and imbalance, both are satisfied. The simulation gets convergence at timestep of 150, and imbalances at all domain are under 1%.

ngoc_tran_bao · June 6, 2016, 23:00

Hello, do you have any suggestion about very high torque in this CFD simulation? A higher torque in simulation results in a lower pump effeciency compared with experiment efficiency. That is not reasonable. I am looking forward to hearing opinions from you.

May 31, 2016, 01:23	Pump's Torque in CFD simulation is higher than experience.	#1
ngoc_tran_bao Member ngoc tran bao Join Date: Jan 2016 Posts: 35 Rep Power: 10	Dear All, I have a challenge with the torque in my pump simulation. At Design Flow rate, the torque calculated on impeller of pump in CFD simulation is much higher than torque measured by experiment, 90Nm compared with 73 Nm. It is obvious that in simulation we can not account for all factors as reality, so I believe that because of lower resistance, torque in CFD should be lower than that of experiment. In my simulation, impeller consists of Hub, Shroud and 7 blades and I calculate torque on impeller for Z axis (used both monitor point in Solver and Function calculator in Post). Does anybody have ideas to explain me why there is an existence of unreasonable result? Thank you in advance. impeller.png

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May 31, 2016, 01:33		#2
urosgrivc Senior Member urosgrivc Join Date: Dec 2015 Location: Slovenija Posts: 365 Rep Power: 11	inappropriate boundary conditions, or mesh, or other setings In cfd it is almost always the user`s fault as computer is just a number crunching machine it can only do what you say it to do. More details will be needed to figure out what is wrong

May 31, 2016, 01:58		#3
-Maxim- Senior Member Maxim Join Date: Aug 2015 Location: Germany Posts: 415 Rep Power: 12	That's quite interesting because in my simulations, the calculated CFD torque is always lower from what we would expect. Maybe you can share more information about your setup so that we can have a look?

May 31, 2016, 02:03		#4
ngoc_tran_bao Member ngoc tran bao Join Date: Jan 2016 Posts: 35 Rep Power: 10	Thank for your replies, As for BC, I set total Pressure at Inlet = 0.1 Mpa; Variable Mass Flow rate at Outlet From 60 - 180 m3/h (Q design =120); Rotation = -1750 RPM (Z axis) Smooth wall for all suction, discharge walls; Reference Pressure =0 atm; Physical time step =1/W. I hope those Information useful.

June 1, 2016, 02:36		#5
-Maxim- Senior Member Maxim Join Date: Aug 2015 Location: Germany Posts: 415 Rep Power: 12	can you please post your ccl and/or out file? Have you checked the typical questions such as: Has your simulation converged? Are the imbalances under 1%? Etc.

June 1, 2016, 03:27		#6
ngoc_tran_bao Member ngoc tran bao Join Date: Jan 2016 Posts: 35 Rep Power: 10	centrifugal pump 1.txt this is CCL file. As for convergence and imbalance, both are satisfied. The simulation gets convergence at timestep of 150, and imbalances at all domain are under 1%.

June 6, 2016, 23:00		#7
ngoc_tran_bao Member ngoc tran bao Join Date: Jan 2016 Posts: 35 Rep Power: 10	Hello, do you have any suggestion about very high torque in this CFD simulation? A higher torque in simulation results in a lower pump effeciency compared with experiment efficiency. That is not reasonable. I am looking forward to hearing opinions from you.