Learning Forum

[sandeepjaggarapu]

Hello Ansys Community,

I am solving a DPM steady state as well as unsteady state simulation with unsteady particle tracking of lubricating-oil with the unsteady continuous fluid as air.

I am trying to simulate a two-phase flow(air and oil) in a circular pipe (Dia. 5mm and length 20mm) using DPM. Can anyone please address the following problem?

1. I have extracted the particle data (reports -> Discrete Phase -> sample -> outlet) both in a steady and transient state. The main aim of this simulation is to get the mass flow rate of the particles at the outlet. I got the mass flow rate results for the respective particle size is obtained. But in the case of transient state simulation, the mass flow rate data is not getting saved.
2. From the console panel, it shows that the particles trapped were 137 out of the injected 20k particles. Is it possible to get data on the different sizes of particles that are trapped on the wall? If yes, can you suggest a solution on how to obtain the data?

Here is my setup:

Time-> Steady

Gravity-> Y: -9.81 m/s^2

Viscous-> Laminar

Discrete Phase (uncoupled and no forces are added except drag force)

Discrete phase on (rosin rammler particle distribution with surface injection)

Boundary Conditions: Inlet & outlet DPM: escape

Wall DPM: trap

Methods -> Simple

Residuals -> 1e-6

Initialize: Standard

Run Calculation: No. of iterations: 1000

Time -> Transient (The same procedure as that of steady but the transient conditions were considered)

DPM (uncoupled and no forces are added except drag force)

Type-> Fixed

Number of Time Steps: 1000

Time Step Size: 1e-5

Max Iterations: 20

Reporting interval: 1

Profile update interval: 1

I have attached the picture of the sample data collected.

Steady:

[Surya Deb]

Hello, n1.) Yes, it is slightly different when using unsteady vs steady state tracking for DPM. For unsteady particle tracking, particles or rather parcels are tracked in a time accurate manner and so particles might not cross the entire domain in the time specified depending on the velocity and other flow properties involved. Please check this link to find more information on this. https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v211/en/flu_ug/flu_ug_sec_discrete_file_props.html. You can make use of the Histogram in Fluent by reading back the sample DPM file. n2.) I think you can make use of DEFINE_DPM_BC UDF to customize your trap conditions as well as writing out selective information to external files. Please check a few examples in this link. https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v211/en/flu_udf/flu_udf_sec_define_dpm_bc.html?q=DEFINE_DPM_BC. You will need to modify and test the UDF according to your needs.nI hope this helps.nRegards,nSDnn

[sandeepjaggarapu]

Hello,Thank you for your reply. nSir, do you know any UDF that writes the sampling trajectories data? So that I could edit that.n

[Surya Deb]

Hello, nYou could try using DEFINE_DPM_OUTPUT UDF to write out particle data when it crosses a sample plane or surface. You can also add levels of customization to this UDF for your purpose. You will find more information here.nI hope this helps.nRegards,nSDn

[ai0013]

Fluent has a built in option to sample particles from a surface. What comes to my mind is to select your outlet as sampling surface. In transient, click start and continue simulating. Once that you ran your case sufficiently long, click stop and post process your data.