@BlenderBiker (BlenderBiker) posted a new topic, subject "Gravity off, no luck, how do I stop the smoke from rising?". It read:

   Is it possible? I know I can mess with the temp dif, but it's still moving up, just less. I want it to come out straight. Is there some setting that I am missing? It seems like with the gravity off it should not rise.

After which, @Star_Ranger4 (Star Ranger4) added

    the whole POINT of the smoke sim is to have it rise ‘realistically'. just exactly what effect are you trying to create? perhaps smoke is not the way to go. besides, hasn't anyone ever told you smoking is bad for you?

After which, @Storrboy (Storrboy) added

    Even in the real world, gravity has little visual effect on smoke, vapors etc. It's all about density - which is directly related to temperature. Even if it did, turning gravity off would allow those things to rise faster, not slower. I didn't have the success I wanted either when I tried to get non-rising smoke working, but I did get close by spending a lot of time changing the density and temp settings. If I remember right, having high-density and low temp diff values on both the flow object and domain object got me close. However, this made moving the smoke in any direction very slow. You may be able to work around that by having the particles live longer and control their movement more. Alternatively, if it fits what you're trying to do, do what they do in the movies and film from a different angle. Looking down or up on an explosion makes it look spherical, rotate the camera onto it's side and rising smoke will appear to move left or right.

To which @BlenderBiker (BlenderBiker) replied

    The reason real smoke rises IS gravity. Take out the gravity, and there is no up, so density will not make it go up, since there is no up.
    
    My goal is to simulate a gas plume in space. So there is no up in space, and various densities wouldn't cause it to go up, because there is no up.
    
    If I just rotated my whole model so the plume is pointing up would not work either, because I have plumes in multiple directions for attitude control (steering), so if one is pointed up, then the rest can't be, and so they would look goofy.

Then @BlenderBiker (BlenderBiker) said

    I should also mention that I do want it to flow, and am using a wind force to flow the direction I want. Pretty good results, but not great, and when I change anything else then I have to tweak the temps and densities to get it back again, and with higher resolution smoke I'm finding that I can't completely stop the rising even with tweaking temp/dens.

@BlenderBiker (BlenderBiker) replied

    I've found by trial and error that I was able to get a pretty good effect, hopefully I can duplicate it. Part of it was to shrink the domain more, duh…plus some other stealthy settings I don't remember now.

Then @Storrboy (Storrboy) said

    BlenderBiker:
    
    > The reason real smoke rises IS gravity. Take out the gravity, and there is no up, so density will not make it go up, since there is no up.
    
    I'm glad you got something satisfactory, but I'm a little baffled by this statement. Gravity makes thing rise?
    
    I did a simple test when I got home, and regardless of the gravity setting, if I made density and temp 0, the smoke didn't move. If I made density a negative number, it sank. I added a wind force and the non-moving smoke moved in the direction of the wind. It did get a bit puffy as you'd expect, but it didn't rise.

To which @BlenderBiker (BlenderBiker) replied

    Right, I was talking about real world physics, when there no gravity there is no up. I'm a noob when it comes to blender, and I was wondering if I was missing a setting somewhere, or maybe a bug, or maybe just a software limitation, not to pick on the software, I think it's awesome. BTW, I have a strong solidworks background, so I have a 3d mind, but this is greatly different in so many obvious ways.

After which, @BlenderBiker (BlenderBiker) added

    I just redid it from scratch. Made a domain, made a flow, added wind force along x, scene-gravity off, domain dens/temp=0, smoke still floats to the top of the domain. Tried switching flow d/t=0, similar upward. Switched domain off zero, similar. Seemed to be getting the same results on my work pc too.
    
    Which density number do you mean you set to zero, for domain or flow?

@BlenderBiker (BlenderBiker) replied

    Even if I adjust the density either way + or -, I can get it to start by dropping, but then it still swerves to the top.
    
    Is it possible to align the smoke to a part instead of the world, so if I rotate the part 90, then the smoke will rise sideways? EDIT: Rotating the domain didn't do it for me.

Then @Storrboy (Storrboy) said

    It might have been on both the flow and domain but I can double check tonight when I get home. For me it just produced a ball of unmoving smoke unless something acted on it.

After which, @Storrboy (Storrboy) added

    I retried it, with the same results. Yesterday was with gravity off, today with it on.  
    I kept all settings simple since I really don't know what your scene requires, but I don't think things like HiRes would affect the movement much, just the quality. The pictures are all after 100 frames, from the same file, and the same objects. Only the smoke settings changed.
    
    Particle Settings (All other settings than these left unchanged from defaults)  
    Emission Group:  
    Number: 1  
    Start: 1  
    End: 10  
    Lifetime: 1
    
    Flow Object (same in all three tests)  
    Absolute Denisty: True  
    Denisty: 1  
    Temp Diff: 1
    
    Test 1 (unchaged settings)  
    Domain Object  
    Denisty: -0.00100  
    Temp Diff: .10000  
    [ATTACH=CONFIG]195359[/ATTACH]
    
    Test 2 (unmoving)  
    Denisty: 0  
    Temp Diff: 0  
    [ATTACH=CONFIG]195360[/ATTACH]
    
    Test 3 (falling smoke)  
    Denisty: -.1  
    Temp Diff: 0  
    [ATTACH=CONFIG]195358[/ATTACH]
    
    I think I kind of understand what you mean by no gravity - no up, but in real world physics, it is the density of the medium (gases, smoke, dust, whatever) that matter most. Lighter, less dense gases rise above the heavier denser ones, because they are being “pushed” upward. Yes, if you turn gravity off, smoke shouldn't rise (assuming all surrounding medium being of equal density and not moving either), but then it would just be a bland cloud with no shape as it tries to find a balance in all directions. There would be no swirling or eddies or anything to make it look like smoke. If you want to simulate smoke, you need something to apply those dynamics against so that it looks like smoke. Even in space, gases mix, mingle and push against each other randomly depending on their densities, velocities and the local gravity (even a gas cloud exerts gravity). Look at a nebula, yes - all directions are up, but they swirl and condense in beautiful patterns based on density, temperature and speed.
    
    I didn't get time to show the wind test, but it was just an empty placed accordingly to move the smoke emitted from the “unmoving” test. It puffed a little opposite the wind source, but it traveled only in the x axis.

To which @BlenderBiker (BlenderBiker) replied

    Thanks for the in-depth response.
    
    The way space works is there is no surrounding gas to be denser. So a cold gas thruster fires (spray paint can), and it's gas under pressure escaping into virtually no surrounding gas nor detectable gravity, so if no momentum then the propellent only expands in a sphere. But it has momentum, so it expands in a turbulent cone in whatever direction that the thruster is pointed. It never rises, because there is no up, and also no surrounding denser gas, it's a vacuum. Now reality is there are no complete vacuums, but look up torr maybe on wikipedia and see that space is an extreme vacuum, so the propellant doesn't interact with a surround gas, it just expands equally in all directions, taking into account it's initial velocity coming out of the thruster.
    
    At my workplace, we have a bunch of high speed vacuum tanks for simulating space, high speed, in order to hold the vacuum even while a thruster is rapidly expanding gas being fed in and burned as plasma. I get to see all kinds of small thrusters firing in those now and then, Pretty cool stuff.
    
    I'd be curios to see the wind test pics, as that's what I'm not being able to handle as I want, but sounds like you are, and great too if more people did the same test and gave feedback.

@Storrboy (Storrboy) replied

    This one adds a wind force and uses the same settings as the “unmoving” smoke previously shown. Notice the slight puffiness I mentioned.
    
    [ATTACH=CONFIG]195388[/ATTACH]
    
    This one changed a few things. Removed the wind force and I did disable gravity's effect in the particles Field Weight tab. I also changed particle velocity as shown so that they travel left and live a little longer. This removes the plume, and you could probably better control spread with a curve guide, or one of the other forces. If the particles die to quickly, the smoke stops generating and remains still where it is. It would require an external force to act on them. This may be your best method of making a jet, but will likely require some playing around with speeds and dissolve times etc.  
    [ATTACH=CONFIG]195389[/ATTACH] [ATTACH=CONFIG]195391[/ATTACH]
    
    Is this what you're trying to make?  
    http://m.static.newsvine.com/servista/imagesizer?file=http3A2F2Fwww.newsvine.com2F_vine2Fimages2Fusers2Fboyle2F6515167.jpg&width=600

To which @BlenderBiker (BlenderBiker) replied

    Yes that's exactly what I'm trying to make. If the plumes are curved at all, it looks very fake.


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