DPM problems

katia · January 23, 2013, 08:17

Hi all!
i'm new in using fluent and i need a big help about modelling a dpm simulation.

I run an unsteady 3D simulation where water droplets are being injected into turbulent airflow (std k-e model) with an uncoupled approch. so i run the continuous before and i injected the particles in a second step. i used a surface injection and i specified velocity and mass flow rate of every single point of injection of that surface and diameter and density of the particles.

But:
problem1: when the particles are injected there is a change of the residuals that let me think that the continuous is affected by the droplets. what can i do to set up in a right way an uncoupled simulation?

problem2: i specified density and diameter of the particles and mass flow rate of each point of injection. but at each time step fluent injects a particle for each point of injection (about 51000) so i have a very big number of particles injected. This fact let me think that dansity or diameter setting weren't respected. maybe i have to change the type of injection. is there an injection in which u can set up a total mass flow rate of the whole area?

many thanks!!

mattyg101 · January 29, 2013, 11:27

If you have ticked the 'interaction with continuous phase' this will be a coupled calculation. This wasnt clear to me at first either. You can run a DPM simulation without this option ticked, just have a suitable injection.

As for your second problem, i have a similar issue. When using a surface injection + uncoupled, the mass flow rate is ignored. If you want a particular flow rate (kg/s) you must adjust your time step so that the number of particles injected per second is equivalent to what you want.

January 23, 2013, 08:17	DPM problems	#1
katia New Member Join Date: Jan 2013 Posts: 1 Rep Power: 0	Hi all! i'm new in using fluent and i need a big help about modelling a dpm simulation. I run an unsteady 3D simulation where water droplets are being injected into turbulent airflow (std k-e model) with an uncoupled approch. so i run the continuous before and i injected the particles in a second step. i used a surface injection and i specified velocity and mass flow rate of every single point of injection of that surface and diameter and density of the particles. But: problem1: when the particles are injected there is a change of the residuals that let me think that the continuous is affected by the droplets. what can i do to set up in a right way an uncoupled simulation? problem2: i specified density and diameter of the particles and mass flow rate of each point of injection. but at each time step fluent injects a particle for each point of injection (about 51000) so i have a very big number of particles injected. This fact let me think that dansity or diameter setting weren't respected. maybe i have to change the type of injection. is there an injection in which u can set up a total mass flow rate of the whole area? many thanks!!

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January 29, 2013, 11:27		#2
mattyg101 New Member Matty Join Date: Nov 2011 Posts: 5 Rep Power: 14	If you have ticked the 'interaction with continuous phase' this will be a coupled calculation. This wasnt clear to me at first either. You can run a DPM simulation without this option ticked, just have a suitable injection. As for your second problem, i have a similar issue. When using a surface injection + uncoupled, the mass flow rate is ignored. If you want a particular flow rate (kg/s) you must adjust your time step so that the number of particles injected per second is equivalent to what you want.