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Justin K

Industrial Smoke Plume Help

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Ive been tasked with recreating smoke plooms for a composite.  Im new to pyro, but Im slowly familiarizing myself with the pyro solver for the task at hand--apllied houdini dynamics has been enormously helpful for this.  The best reference for what we are attempting to achieve large scale structure wise is this https://www.shutterstock.com/video/clip-1006794988-chimneys-power-plant-sunset-air-pollution-concept  

Secondary example would be this:


Two issues I am really struggling with are:

1) keeping the structure of the plooms together over time (say 800 frames)--while still moving in the specified direction.   Im referring to this as the large scale shape.  

2)  keep high levels of disturbance and movement within the plume structures even when they get far away from their original vel source.   Small scale detail retention


I have noticed that generally speaking, over time in the pyro simulation, the sim inevitably starts to disperse and smooth out.  I know there could many reasons for this:.  

A few things that could be affecting this as far as I would know: 

1)  temperature diffusion (this could cause smearing)--consequently to counteract this, I have this very low. 

2) turbulence issues: Its needed as far as I can tell to give the plumes variation in structure.   However  turbulence applied globally over a long enough duration with secondary wind force will slowly spread the density  apart in all directions throughout the volume.  This makes sense but is perhaps also a problem.  We need turbulence, but the turbulence cant blow apart the structure with time in this case.    

3)  rules of incompressibility in pyro sims?  --Ive listened to some explanations where this rule is actually somewhat problematic when it comes to something like a smoke plume or an explosion, where the volume of the sim should actually be increasing over time.  I currently am NOT using combustion though....perhaps I should be?  Perhaps a useful question to ask is: When smoke leaves an exhaust pipe is it combusting?  Or simply cooling off very quickly when it interacts with air? --science help! (thx!))

4) Incorrect temperature change?--right now I have it losing temperature very quickly--which I believe is what happens in nature with smoke plumes, but Im not sure.  Im hoping this gives the smoke a heaviness and keeps it from rising--However, the smoke column still needs to be very active within the confines of its own shape.......

5) Incorrect time steps?  Right now I have the timescale of the sim set quite low (.2)  --in hopes of keeping the sim from emitting and blowing apart too quickly--again, not sure though


At any rate, any tips on this stuff would be REALLY appreciated.  I understand on a basic level what the differnet microsolvers are doing, difference between importing volume fields to affect things, as opposed to using  microsolvers, and alternative effectors like wind force, so any tips would be helpful.  


OK, so, the current state of my terrible sim lol:

I have tried a variety of different things to achieve the desired look.  

One of the first things I tried was driving the plumes along a curve.  However, I could not get the sweet spot as it were with this method--

the sweet spot being: the plume followed the curve structure wise, but did not stretch out and loose shape as it followed the curve.  Basically the plume wiould start to smear with the curve if the attraction was too high, or, conversely, if the curve attraction strength was not strong enough, the velocity pushing it along the curve would not be enough to keep the plume from rising into the atmosphere with temperature.  I did try for a while to get the velocity force along the curve and the temperature to play nicely together, but was unsuccessful overall in keeping the plumes from looking like they were being pulled rather than pushed in a direction.  


I gave up on this art directable shape idea, and instead went with a costume wind volume I built in sops.  This is currently pushing the volume in the wind directionx, and there is some slight oscillation in the y values  and the amplitude to give it some visual interest.  A turbulent noise is running with a time offset as well.  

THis velocity volume, I should point out, is NOT being applied globally to the voxels, Im using the density as a mask in hoping of keeping the thing from falling apart--and yet it still is :huh:.. 


One side noteL

As a side note: the intial shape of a pyro sim is different look wise from the look in say 200 frames, where the emission and the general look have become more consistent.  In other words, there is an initial blast structure and then what comes afterwards.  In my case, I dont want the initial blast of plumes, but instead want what the sim looks like when it has achieved some sort of balance.  Is there a way to avoid having to look at this rev up time every time I sim?  I was thinking of saving checkpoints, say to frame 200, then simming from that checkpoint.  I would sett keyframes for everything I was tweaking at frame 200, and then at 210  dialing in new values and see what my sim looks like as the changes evolve?  Is that a common thing.?


Any other questions you have about my set up feel free to ask! Ive provided a scene file--SCENE IMAGE shows the network that is being used for this --everything in the purple background.  Ive attached a flipbook still for whatever reason as well.  Hope this is enough enough here all, 

Any tips or pointers would be greatly appreciated.  

Thank you!





Edited by Justin K

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