Why am I getting negative pressure head of the Centrifugal Pump through CFD?

raza48919 · January 17, 2021, 22:14

Hello,

I'm working on the CFD analysis of a centrifugal pump (basically a left ventricular device, LVAD) having an impeller diameter of 31 mm only.

I've modelled the problem on Fluent and using k-epsilon (realizable) turbulence model. Moreover, I am employing the MRF (multiple reference frame) technique to give a rotation to the impeller of the pump. I'm using following conditions:

1) Inlet: mass flow inlet (0.04375 kg/sec)

2) Outlet: Pressure outlet (0 Pa)

3) Impeller Speed: 1000 RPM (Given to the impeller zone and walls)

Moreover, I've also tried moving mesh technique and checked the model for transients analysis as well but the resulting pressure head of the pump is negative (the pressure at the inlet of the pump is higher than that at the outlet). Hence, the pump is not creating the suction. I've tried different set of boundary conditions and different turbulence models, but I am getting the same problem again and again.

The results of the simulation with 0.04375 kg/sec flowrate (mass flow inlet), outflow outlet and the impeller speed of 1000 RPM are given below.
I am achieving a good convergence:

The mass flow at the outlet is:

The pressure at the inlet is:

The pressure at the outlet is:

Hence, the resulting differential pressure head is -1697-19=1716 Pa (which is against my expectation of getting the suction at the inlet). The model is doing good at higher speeds but at the impeller speed less than or equal to 1000 RPM it doesn't produce any suction. I've checked many times for the possible errors and everything seems fine.

If anyone can identify the cause of the problem and provide any assistance regarding its solution, it would of a great help for me.

Thank you!

Regards,

Ahmad

lampfall90@icloud.com · June 11, 2021, 15:23

Hello dear, Did you find why you outlet pressure was negative? If yes , please heal me out I am facing the same problem. Thanks so much in advance

pakk · June 12, 2021, 05:23

Flow goes from high pressure to low pressure, so it is completely normal that the pressure at the inlet is higher than at the outlet...

lampfall90@icloud.com · June 12, 2021, 06:15

Quote:

Originally Posted by pakk

Flow goes from high pressure to low pressure, so it is completely normal that the pressure at the inlet is higher than at the outlet...

Thanks my Dear, But in pump we need to gain pressure like low pressure to high pressure to gain head

pakk · June 13, 2021, 07:28

O I see, this is the inside of a pump. I thought it was about the outside effects of a pump.

(don't call people "dear" on the Internet. It sounds belittling and insulting. I assume you were not aware and did not mean to.)

Vestdam · June 16, 2021, 05:37

Hi,
Can you post some figures of contours through the pump? Like pressure and velocity? Do you have backflow? Is the impeller turning the right direction? Is it the static pressure, you are monitoring? In that case, the outlet should be 0 Pa and this indicates that it has not yet converged.

Ahmed Abotayel · April 26, 2023, 15:11

Hi Muhammad
I am facing the same problem
Can you give me any advice to solve it?

January 17, 2021, 22:14	Why am I getting negative pressure head of the Centrifugal Pump through CFD?	#1
raza48919 New Member Muhammad Ahmad Raza Join Date: Jan 2021 Posts: 1 Rep Power: 0	Hello, I'm working on the CFD analysis of a centrifugal pump (basically a left ventricular device, LVAD) having an impeller diameter of 31 mm only. I've modelled the problem on Fluent and using k-epsilon (realizable) turbulence model. Moreover, I am employing the MRF (multiple reference frame) technique to give a rotation to the impeller of the pump. I'm using following conditions: 1) Inlet: mass flow inlet (0.04375 kg/sec) 2) Outlet: Pressure outlet (0 Pa) 3) Impeller Speed: 1000 RPM (Given to the impeller zone and walls) Moreover, I've also tried moving mesh technique and checked the model for transients analysis as well but the resulting pressure head of the pump is negative (the pressure at the inlet of the pump is higher than that at the outlet). Hence, the pump is not creating the suction. I've tried different set of boundary conditions and different turbulence models, but I am getting the same problem again and again. The results of the simulation with 0.04375 kg/sec flowrate (mass flow inlet), outflow outlet and the impeller speed of 1000 RPM are given below. I am achieving a good convergence: The mass flow at the outlet is: The pressure at the inlet is: The pressure at the outlet is: Hence, the resulting differential pressure head is -1697-19=1716 Pa (which is against my expectation of getting the suction at the inlet). The model is doing good at higher speeds but at the impeller speed less than or equal to 1000 RPM it doesn't produce any suction. I've checked many times for the possible errors and everything seems fine. If anyone can identify the cause of the problem and provide any assistance regarding its solution, it would of a great help for me. Thank you! Regards, Ahmad Ahmed Abotayel likes this.

June 11, 2021, 15:23	Negative outlet pressure	#2
lampfall90@icloud.com New Member Lamp Join Date: Sep 2020 Posts: 11 Rep Power: 6	Hello dear, Did you find why you outlet pressure was negative? If yes , please heal me out I am facing the same problem. Thanks so much in advance Ahmed Abotayel likes this.

June 12, 2021, 05:23		#3
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	Flow goes from high pressure to low pressure, so it is completely normal that the pressure at the inlet is higher than at the outlet... __________________ "The UDF library you are trying to load (libudf) is not compiled for parallel use on the current platform" is NOT the error after compiling. It is the error after loading. To see compiler errors, look at your screen after you click "build".

June 13, 2021, 07:28		#5
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	O I see, this is the inside of a pump. I thought it was about the outside effects of a pump. (don't call people "dear" on the Internet. It sounds belittling and insulting. I assume you were not aware and did not mean to.) __________________ "The UDF library you are trying to load (libudf) is not compiled for parallel use on the current platform" is NOT the error after compiling. It is the error after loading. To see compiler errors, look at your screen after you click "build".

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June 16, 2021, 05:37		#6
Vestdam Member Vestdam Join Date: Nov 2017 Posts: 44 Rep Power: 9	Hi, Can you post some figures of contours through the pump? Like pressure and velocity? Do you have backflow? Is the impeller turning the right direction? Is it the static pressure, you are monitoring? In that case, the outlet should be 0 Pa and this indicates that it has not yet converged.

April 26, 2023, 15:11		#7
Ahmed Abotayel New Member Ahmed Join Date: Apr 2023 Posts: 8 Rep Power: 3	Hi Muhammad I am facing the same problem Can you give me any advice to solve it?