Set up and boundary conditions for vacuum cleaner

Potato765 · September 13, 2024, 02:51

Hello,
I am trying to set up a CFD Simulation of a lower end of a vacuum cleaner, to optimize its shape for a better and more consistant suction power at the bottom.

What I got:
I have the volume flow in the pipe going up to the motor, and I think, the absolute Pressure is about 0.7 Bar (so 30% less than atmosphere) but this value is more of a quess. I have also set up a virtual Room around the Vacuum cleaner.

Whats my question:
I don´t know where and how to set my boundary conditions, because I learnd, to set up a velocity, Mass-/Volume flow inlet and a pressure outlet.
But in my case the pump is sucking air, so I would guess, that I would have to set a volume flow outlet in the pipe to the motor with the direction up; and a pressure inlet at the outer walls of my room, with 0 Pa relative pressure.
This doesn´t seem to give my right results and I also don´t account for the 0.7 Bar presssure in the tube.

At the moment I just want to simulate air without dirt, I might add this later.
I would greatly appreciate any help.
Thanks in advance.

Hamidzoka · September 13, 2024, 05:14

Hi,
The virtual walls can be set to opening boundary type instead. This allows inlet and outlet flows through that freely. Since it is not possible to distinguish exactly the inlet and outlet parts of it.
Vacuum cleaner can be asumed as a fan with inlet and outlet boundaries. But these boundaries are merged into its sorroundings and there is not separate boundary for that. remember that it sucks the air from sorrunding and discharge it again to that sourrunding at a different position. So practically there is no explicit inlet or outlet boundaries for that. You can model the fan in your domain and perform steady state simulation using a stator-rotor interface for that. So, tehcnically you have opening boundaries on virtual walls, solid walls of fans, chambers and pipes and also rotor-stator interface to dvide the domain into stationary and rotating parts.

Regards

Potato765 · September 13, 2024, 08:56

Hey,
thanks for your answer. But as I said, I really just care about the lower part of the vacuum. Not the motor or fan. I don´t really want to model and simulate those rotating parts. I was hoping to just set a volume flow in the hose and my walls to opening boundary. How do I account for the vacuum pressure?

LuckyTran · September 15, 2024, 10:23

Pressure inlet and outlet is fine

0.2 bar is a common vacuum spec so 0.3 is not too terrible a guess. However, the maximum vacuum pressure occurs at deadflow of 0 m^3/s. At maximum flow, the suction is nearly 0 bar. Pumping/vacuum power is roughly W = Q*dp and the pumping power is nominally constant, forming the vacuum curve. The vacuum power is roughly 1/4 to 1/3 of the electric motor capacity for a typical household vacuum. I.e. 300 W vacuum capacity for a 1200 W electric motor.

When you do CFD of the brush head only, you will see that the static pressure at the outlet decreases as you increase flowrate, which can be counter-intuitive but that is because you don't have a pump. You need to find the intersection of your head-curve and pump curve for it to make sense.

mikethe1wheelnut · September 16, 2024, 09:24

Quote:

Originally Posted by Potato765

Hello,
I am trying to set up a CFD Simulation of a lower end of a vacuum cleaner, to optimize its shape for a better and more consistant suction power at the bottom.

What I got:
I have the volume flow in the pipe going up to the motor, and I think, the absolute Pressure is about 0.7 Bar (so 30% less than atmosphere) but this value is more of a quess. I have also set up a virtual Room around the Vacuum cleaner.

Whats my question:
I don´t know where and how to set my boundary conditions, because I learnd, to set up a velocity, Mass-/Volume flow inlet and a pressure outlet.
But in my case the pump is sucking air, so I would guess, that I would have to set a volume flow outlet in the pipe to the motor with the direction up; and a pressure inlet at the outer walls of my room, with 0 Pa relative pressure.
This doesn´t seem to give my right results and I also don´t account for the 0.7 Bar presssure in the tube.

At the moment I just want to simulate air without dirt, I might add this later.
I would greatly appreciate any help.
Thanks in advance.

..this sounds like a question I might actually know the answer to.. https://www.youtube.com/watch?v=Er2j5Kq17as .. and see the section on inlet boundary conditions in blazek.., and my comment on said video, if you happen to notice and recognize it..

Potato765 · Today, 08:03

Thanks everyone.
At the moment I belive, that I can just set the Volume Flow/ Mass Flow at the pipe up to the motor and the opening boundary at the walls of my virtual room. Can I put 2 boundary conditions at the same Face? I think about setting the pressure of around 0.8 Bar Absolute on the Outlet face in the pipe up to the Motor as well as the Mass flow.

LuckyTran · Today, 09:18

specifying pressure and mass flow is ill-posed, there is no solution. Technically yes you can set it, but it is guaranteed to crash and diverge.

September 13, 2024, 02:51	Set up and boundary conditions for vacuum cleaner	#1
Potato765 New Member Join Date: Sep 2024 Posts: 3 Rep Power: 2	Hello, I am trying to set up a CFD Simulation of a lower end of a vacuum cleaner, to optimize its shape for a better and more consistant suction power at the bottom. What I got: I have the volume flow in the pipe going up to the motor, and I think, the absolute Pressure is about 0.7 Bar (so 30% less than atmosphere) but this value is more of a quess. I have also set up a virtual Room around the Vacuum cleaner. Whats my question: I don´t know where and how to set my boundary conditions, because I learnd, to set up a velocity, Mass-/Volume flow inlet and a pressure outlet. But in my case the pump is sucking air, so I would guess, that I would have to set a volume flow outlet in the pipe to the motor with the direction up; and a pressure inlet at the outer walls of my room, with 0 Pa relative pressure. This doesn´t seem to give my right results and I also don´t account for the 0.7 Bar presssure in the tube. At the moment I just want to simulate air without dirt, I might add this later. I would greatly appreciate any help. Thanks in advance.

September 15, 2024, 10:23		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,737 Rep Power: 66	Pressure inlet and outlet is fine 0.2 bar is a common vacuum spec so 0.3 is not too terrible a guess. However, the maximum vacuum pressure occurs at deadflow of 0 m^3/s. At maximum flow, the suction is nearly 0 bar. Pumping/vacuum power is roughly W = Q*dp and the pumping power is nominally constant, forming the vacuum curve. The vacuum power is roughly 1/4 to 1/3 of the electric motor capacity for a typical household vacuum. I.e. 300 W vacuum capacity for a 1200 W electric motor. When you do CFD of the brush head only, you will see that the static pressure at the outlet decreases as you increase flowrate, which can be counter-intuitive but that is because you don't have a pump. You need to find the intersection of your head-curve and pump curve for it to make sense. Potato765 likes this.

September 13, 2024, 05:14		#2
Hamidzoka Senior Member Hamid Zoka Join Date: Nov 2009 Posts: 288 Rep Power: 18	Hi, The virtual walls can be set to opening boundary type instead. This allows inlet and outlet flows through that freely. Since it is not possible to distinguish exactly the inlet and outlet parts of it. Vacuum cleaner can be asumed as a fan with inlet and outlet boundaries. But these boundaries are merged into its sorroundings and there is not separate boundary for that. remember that it sucks the air from sorrunding and discharge it again to that sourrunding at a different position. So practically there is no explicit inlet or outlet boundaries for that. You can model the fan in your domain and perform steady state simulation using a stator-rotor interface for that. So, tehcnically you have opening boundaries on virtual walls, solid walls of fans, chambers and pipes and also rotor-stator interface to dvide the domain into stationary and rotating parts. Regards

September 13, 2024, 08:56		#3
Potato765 New Member Join Date: Sep 2024 Posts: 3 Rep Power: 2	Hey, thanks for your answer. But as I said, I really just care about the lower part of the vacuum. Not the motor or fan. I don´t really want to model and simulate those rotating parts. I was hoping to just set a volume flow in the hose and my walls to opening boundary. How do I account for the vacuum pressure?

Today, 08:03		#6
Potato765 New Member Join Date: Sep 2024 Posts: 3 Rep Power: 2	Thanks everyone. At the moment I belive, that I can just set the Volume Flow/ Mass Flow at the pipe up to the motor and the opening boundary at the walls of my virtual room. Can I put 2 boundary conditions at the same Face? I think about setting the pressure of around 0.8 Bar Absolute on the Outlet face in the pipe up to the Motor as well as the Mass flow.

Today, 09:18		#7
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,737 Rep Power: 66	specifying pressure and mass flow is ill-posed, there is no solution. Technically yes you can set it, but it is guaranteed to crash and diverge.