A problem with particle tracking!

sina_mech · October 22, 2016, 20:14

Hi,

I have a weird issue with particle tracking in Fluent. I have a stationary huge tank of water , and I want to inject particles (heavier than water, rho = 2500 kg/m3) from the surface of the tank.

in my experience with Fluent, having gravity on, and pressure gradient and drag forces on, when I inject particles bigger than d= 0.005m, the particles settle, and when the particle is smaller than that size, they don't settle at the bottom of the tank (which they technically should!)

Does anybody have any clue that why this happens?

Thanks

pakk · October 24, 2016, 10:21

What do they do instead of settling at the bottom?

sina_mech · October 24, 2016, 12:09

they pretty much stay at the surface! with random superficial motions.

pakk · October 25, 2016, 03:03

If you take a ball at 1m above earth and let go, it will fall on the floor.
If you take dust at 1m above earth and let go, it will float around in the air.

I think there is nothing wrong with your simulation. You just found that for particles smaller than 0.005m, drag forces are dominant, and for particles larger than 0.005m, gravity is dominant.

October 22, 2016, 20:14	A problem with particle tracking!	#1
sina_mech Senior Member SinaJ Join Date: Nov 2009 Posts: 136 Rep Power: 16	Hi, I have a weird issue with particle tracking in Fluent. I have a stationary huge tank of water , and I want to inject particles (heavier than water, rho = 2500 kg/m3) from the surface of the tank. in my experience with Fluent, having gravity on, and pressure gradient and drag forces on, when I inject particles bigger than d= 0.005m, the particles settle, and when the particle is smaller than that size, they don't settle at the bottom of the tank (which they technically should!) Does anybody have any clue that why this happens? Thanks

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October 24, 2016, 10:21		#2
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	What do they do instead of settling at the bottom?

October 24, 2016, 12:09		#3
sina_mech Senior Member SinaJ Join Date: Nov 2009 Posts: 136 Rep Power: 16	they pretty much stay at the surface! with random superficial motions.

October 25, 2016, 03:03		#4
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	If you take a ball at 1m above earth and let go, it will fall on the floor. If you take dust at 1m above earth and let go, it will float around in the air. I think there is nothing wrong with your simulation. You just found that for particles smaller than 0.005m, drag forces are dominant, and for particles larger than 0.005m, gravity is dominant.