# Smoke doesn't seem to have initial velocity

I've been following this tutorial on how to make a simple explosion, I am using the same values, but I don't get the same effect.

It seems like my particles have no initial velocity.

Do you know what could cause this problem?

Updated .blend file:

His explosion:

My explosion:

My explosion after James' tips:

[Edited per our conversation below]...

I think blender is indeed having a problem with its cache.

Aside: I see you have disk cache vs. memory cache for Plane.001 vs Plane.002; perhaps your just trying various combinations.

Try:

1. deleting your 'blendcache_smoke_test' and 'cache_fluid_4b85f272' cache folders
2. In scripting, click on New and cc/paste and run the following script (also in the attached blend file) that should create things in the correct order (finding and running all PS sims before Fluid sims).
import bpy
import time

bakedItemCount=0
startTime=time.time()
for scene in bpy.data.scenes:
for object in scene.objects:
for modifier in object.modifiers:
if modifier.type == 'PARTICLE_SYSTEM':
print("Baking particles for ", object.name)
override = {'scene': scene, 'active_object': object, 'point_cache': modifier.particle_system.point_cache}
bpy.ops.ptcache.free_bake(override)
bpy.ops.ptcache.bake(override, bake=True)
bakedItemCount+=1
for object in scene.objects:
for modifier in object.modifiers:
if modifier.type == 'FLUID':
if modifier.fluid_type == 'DOMAIN':
print("Baking fluid for ", object.name)
object.select_set(True)
bpy.context.view_layer.objects.active = object
bpy.ops.fluid.bake_data()
bakedItemCount+=1
elif modifier.type == 'CLOTH':
print("Baking cloth for ", object.name)
override = {'scene': scene, 'active_object': object, 'point_cache': modifier.point_cache}
bpy.ops.ptcache.free_bake(override)
bpy.ops.ptcache.bake(override, bake=True)
bakedItemCount+=1

endTime=time.time()
duration = int((endTime - startTime)+.999)
print( bakedItemCount, ' items baked over ', duration, ' seconds')


Frame 16 rendered with max samples = 16 to reduce render time:

• Hi James, I've tried your suggestions, but it still looks almost the same. The smoke that the particles spawn don't seem to have any velocity, and are just a puff of fire and smoke. I have no idea what could cause this. I've updated the post with a new image and the new blend file. (now on Blend-Exchange) Dec 26, 2021 at 13:11
• I actually think that this is a bug, I've been doing some tests. Here is my test scene. If you bake the weird domain first, both simulations will have no initial velocity, but if you bake the correct one first, both will look good. The difference between the two is the flow source of the cube, the incorrect is from the volume and the correct is from the surface. Do you think I should report this somewhere? Dec 26, 2021 at 13:33
• @Matthias -- you would certainly have to bake the PSs first, as then the PS drives the position of the particles that the fire'n'smoke are based upon. I do not think that is a bug per se: it is a procedural workflow that is perhaps a bit arcane. Have you reviewed the tutorial to see if you had missed a step or if that was not covered? Does my video look anything like what you are expecting? Dec 26, 2021 at 15:51
• Yes, I've baked the PSs, I changed all the thing that you've suggested. And also yes, I've reviewed the tutorial step by step. And the problem is that I can't really see, because my video looks the same at 32 resolution divisions. I think that if you'd render one frame at like 192, you'd get the same effect as me. Like the smoke that the particles spawn don't have velocity and are technically just a static sphere with a geometry inflow, not like in the tutorial. Dec 26, 2021 at 19:56
• If you don't know what I could do to change this, maybe I'll follow the tutorial again tomorrow, but with an older version of blender. Maybe that'll help to discover the root of the problem. Dec 26, 2021 at 19:58