October 11, 2023 at 12:58 amAayushya AgarwalSubscriber
I'm trying to simulate a multi phase flow of the following geometry, where discrete particles are being injected from the surface on the left
I have inserted a Rosin-Rammler distribution of particle diameters with anywhere from 100-100000 streams and randomized the initial starting point. However, when I plot the particle trajectories, they seems to be non-continuous. Below I've attached two examples of the particle traces near the outlet. The two examples are of 1000 streams and 100,000 streams
When I sample the dpm on the outlet boundary, the plot looks like particles are clumped rather than spread evenly. This geometry models a printer where I expect the particles to deposit in all regions of the outlet (however with a distribution). I see in the simulation that even with more streams I am getting the same areas with no particles depositing. I'd appreciate the help. Thanks
October 11, 2023 at 9:12 amRobForum Moderator
Have a look at the flow field. Is gravity on, and are you modelling 3d, 2d or 2d axisymmetric?
October 11, 2023 at 11:27 am
October 11, 2023 at 3:10 pmRobForum Moderator
OK. Now, if particles are funnelled to the axis through the domain, why would they not remain in the centre?
October 11, 2023 at 4:04 pmAayushya AgarwalSubscriber
I agree the particles should remain in the center. My question is regarding the discrete nature of where the particles land. You can notice that there are gaps between where the particles land, as shown in the figure below. And no matter how many particles I inject, or I randomize the initial starting points on the surface, this gap remains. I would expect with a large number of particles there should be a continuous deposition
October 11, 2023 at 4:14 pmRobForum Moderator
Please can you overlay the particle tracks with velocity contour and mesh? You may need two images, one with contour node values on, and a second with them off.
October 11, 2023 at 8:52 pm
October 12, 2023 at 12:49 pmRobForum Moderator
Thanks. It looks like you've got some particles outside of the jet core, the remainder are not seeing enough radial force (or stocastic kick) to spread out.
October 12, 2023 at 4:01 pmAayushya AgarwalSubscriber
Would the answer then to be have a higher fluid flow rate, or maybe a better initial velocity for the particles?
October 12, 2023 at 4:18 pmRobForum Moderator
To spread the particles out?
Initial velocity may not do much as their trajectory by the outlet is pretty much entirely determined by the nozzle and entrainment inlet.
I would check the flow near the outlet in more detail - in the two velocity images it looks like the fluid jet is very diffuse. Is that mesh or convergence related? How "good" are the backflow conditions?
October 16, 2023 at 7:45 pm
October 17, 2023 at 1:05 pmRobForum Moderator
Try "neighbouring cell" on the backflow direction. The radial velocity looks very odd on the last image.
To clarify, you're running 100k particle tracks and displaying those? Have you got stochastic tries turned on?
October 17, 2023 at 7:41 pmAayushya AgarwalSubscriber
I have tried making the backflow direction specification method as "From Neighboring Cell". Here is the particle trajectories and radial velocity contour now:
Also yes I am displaying the 1000 particle tracks. I have the randomize starting points on, but I don't have turbulent dispersion so I'm not able to do the stochastic tries
October 18, 2023 at 11:41 amRobForum Moderator
October 18, 2023 at 11:11 pm
October 19, 2023 at 9:30 amRobForum Moderator
OK, no turbulence so no stochastic tracking: it uses the turbulent values to kick the trajectories in a random way.
In your case the streams are released from the inlet face,and will then follow the flow. I'd then expect some discrete particle tracks. Remember we're tracking parcels rather than particles.
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