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I've been following an explosion tutorial. Blender's quick smoke results are very impressive but I'm trying to mimic artillery explosions I've seen on youtube in several places. In particular, I've noticed that the blender quick smoke simulation seems to put smoke first and has a rounded outer edge rather than ragged, spiky flame. I've experimented a little and, even with high particle velocities, the outer puffs of smoke look a bit like fragments of cauliflower or broccoli. Here's my explosion:

enter image description here

Having carefully studied that second video I linked above, I've identified these distinct stages, the first of which is not provided by the Blender quick smoke simulation:

Stage 1: Extremely fast, bright, symmetrical initial flash of flame, like a white-hot blob of plasma with spiky outer edge. Dust instantly kicked up from ground for some distance (fast shock-wave? vibrations passing through the earth?) enter image description here

Stage 2: Initial flash burns off almost instantly, often rising very quickly and sometimes leaving thin vertical column of wispy smoke. Secondary billowing, expanding cloud of black smoke appears. In a lot of these videos, you can see an expanding outer shockwave like an optical distortion in otherwise clear air. enter image description here

Stage 3: Black billowing smoke ignites, filling with billowing, globular flames which cause a rapid second expansion emanating sparks. Sometimes additional, assymetric reignitions/expansions occur. Fragments and chunks appear, flying radially outwards. This additional burning usually reinvigorates the explosion, giving additional outward impetus to fragments and chunks of detritus, propelling them through the air with renewed speed. This is the main fiery body of the explosion. enter image description here

Stage 4: Secondary ignition completes, burning itself out and leaving mixture of black/gray/white smoke clouds. Many more fragments and chunks now visible flying outward. enter image description here

Stage 5: Aftermath. Flames gone. Chunks and fragments fly outward, falling to earth. Smoke dissipates.

QUESTIONS: It looks like I'll need to do some kind of combination of two explosions but I'm confused about some things:

  • Why create a plane below the explosion and then on the physics tab choose collision? Why is this necessary? What does it do?
  • When you select some emitter and add object->quick effects->quick smoke, does this generate smoke from all the particles emitted inside its domain volume? Is it possible to have one domain nested inside another and each of the two smoke domains connected to different, non overlapping particle emitters?
  • Does a quick smoke+fire simulation act as a light source? In my picture here, the shadows of the two columns are totally unaffected by the explosion. I'm hoping to render a night scene where the explosion is the only source of light. If I need to create a light source inside my explosion, it should clearly be a point light source. How would I make the intensity and size of this light change over time?
  • Is there some way to generate random fragments/chunks flying outward that are leaving a trail of smoke? These should be pointed and not cauliflower/broccoli shaped. The space shuttle explosions come to mind.enter image description here

Any assistance would be much appreciated!

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  • $\begingroup$ i am pretty sure that you cannot nest domains. $\endgroup$
    – Chris
    Apr 15 at 3:48
  • $\begingroup$ Perhaps 'nesting' is the wrong word. In this video, Iago discusses adding an additional domain at around 12:20 (without providing sufficient detail for a slow noob like me). His explosion at 13:00 is a LOT like what I'm trying to do. $\endgroup$
    – S. Imp
    Apr 15 at 8:24
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    $\begingroup$ In the Domain properties there is a Collections section where you can specify which collection acts as Flow and which acts as Effectors. Setting this for a domain restricts that domain to only take notice of those collections. $\endgroup$ Apr 16 at 8:21
  • $\begingroup$ @RichSedman that's just it. I've been unable to locate any property or sub-property of the Smoke Domain to specify which emitters for which it smokes. I do see on my emitter's physics tab that it has its own ParticleSettings specified as the flow source, but I cannot find any reference to my emitter in Smoke Domain nor to Smoke Domain in my emitter. If you have additional information, I'd greatly appreciate it. $\endgroup$
    – S. Imp
    Apr 16 at 17:20
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    $\begingroup$ Regarding your question for the light emision of the explosion: yes, it emits light in Cycles - but regarding your image with the two columns, the scene light seems to be pretty bright while the explosion's fire is not. So there might be an effect but it's hardly visible. If you turn off all scene suns, lamps and environmental light you will see how much light your explosion actually emits and turn that up. $\endgroup$ Apr 17 at 11:35
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Why create a plane below the explosion and then on the physics tab choose collision? Why is this necessary? What does it do?

The plane below the explosion will prevent explosion products (ie, the smoke and flames) as well as particles from moving below the floor. (As commented by @vklidu the 'ground collider' doesn't need to be flat if the ground is uneven - for more realistic ground collision - or, if flat, you can actually use the boundary of the domain itself.)

When you select some emitter and add object->quick effects->quick smoke, does this generate smoke from all the particles emitted inside its domain volume? Is it possible to have one domain nested inside another and each of the two smoke domains connected to different, non overlapping particle emitters?

By default, the smoke domain will act on all smoke emitters and effectors. However, within the Domain properties there is a Collections setting that lets you set the Collection used for Flow and Effectors. Leaving these blank will use all Flow and Effectors in the scene for this Domain. However, setting it to a specific Collection will restrict it to using only that Collection.

smoke domain collections

Note that if you have multiple domains you should ensure that they are at slightly differing locations/scales so as to avoid z-fighting issues at their boundary faces.

Does a quick smoke+fire simulation act as a light source? In my picture here, the shadows of the two columns are totally unaffected by the explosion. I'm hoping to render a night scene where the explosion is the only source of light. If I need to create a light source inside my explosion, it should clearly be a point light source. How would I make the intensity and size of this light change over time?

This depends on your render engine. For Cycles, yes - it will act as a light source by default. For Eevee you need to enable volumetric emission by way of the Irradiance Volume Light Probe.

Is there some way to generate random fragments/chunks flying outward that are leaving a trail of smoke? These should be pointed and not cauliflower/broccoli shaped. The space shuttle explosions come to mind.

You can model the fragments and use Rigid Body or particle system to eject them from the explosion. Making them emit smoke should leave suitable trails if you have sufficient timesteps to give sufficient precision for their velocity.

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    $\begingroup$ +1 BTW To collide smoke with flat ground doesn't has to be necessarily Plane object, you can also use Domain it self ... Just enable collision with bottom side of domain. $\endgroup$
    – vklidu
    Apr 17 at 8:10
  • $\begingroup$ @vklidu - good point. I've updated the answer. $\endgroup$ Apr 17 at 8:17

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