I face a similar situation but instead my Flow is shaded and set to be a horizontal flame generated by a large industrial burner where fuel is spayed out under high pressure into the center of a 60 mph air stream generated by a large fan, creating a 10-foot long by 7-foot diameter flame conical in shape.
The fuel travels about 18" out from the nozzle in a wide-angle cone before combustion begins. As you would expect, the resulting flame is not gentle, with slowly lapping swirls and tongues of flame that Flow does so well, but extremely fast and chaotic.
I am unable to get Flow to simulate this flame, whose entire body is at the same high velocity from source to tip. Instead, the flame starts out at nearly zero velocity then progressively increases to the desired speed at the flame/smoke transition. I know this is due to the logarithmic nature of gravity and buoyancy, so I was hoping setting the flowEmitterSphere’s Velocity to a very high, 4,000 value, the same as Pekka Varis shows in his video above, would make the entire volume move at that speed. Velocity does push the start of ignition farther away from the source, which I like, but the initial flame speed is still nowhere near real world, nor is the entire volume of the flame at the same velocity. Buoyancy has nearly zero affect in the real world, because there’s not enough time for it to act on the flame itself, whereas Expansion is the primary force.
Also, under such extreme parameter settings, the flame becomes unstable, and most times will not reignite after stopping and restarting the simulation.
I have a feeling that the CFD algorithms Flow uses are not designed to create this high-pressure fuel, high-velocity airflow type of flame. Correct me if I’m wrong.
At any rate. I can produce a nice looking and nearly properly-shaped flame, but it plays in slow motion at 1/20th or more real-world “speed” (see video in my next post below). My RTX3090 frame rate is at a respectable 30fps, even though the flame is inside a rough, but reflective metal drum, so LOTS of rays being cast, because I disabled all raytrace options for Flow – seen in reflections, etc.