Blender Smoke and Fire Simulation: How to Set Up a Flow Source

What will you learn in this guide?

In Blender, Flow is a source type that defines how an object interacts with a liquid, smoke, or fire simulation. Setup involves two separate decisions: Flow Type selects what will be generated, while Flow Behavior determines the source’s role in the simulation domain. You can then adjust details such as emission density, motion, and area.

These steps are based on the Fluid and Flow documentation in the Blender 5.2 LTS Manual. The guide focuses on smoke and fire sources. The documentation also includes a Liquid option, but other liquid simulation settings are not covered here. Test how the settings behave in a specific scene alongside the domain and object geometry.

Requirements

The Blender scene needs a Flow source and a domain object for it to operate in. Keep the Flow object within the domain’s Bounding Box; according to the manual, this placement is required for the source to work properly. With the Geometry behavior, mesh sections inside the domain box are used in the simulation.

Add Fluid physics to the source object and set its type to Flow. The manual describes this process under Physics in the Properties section. In addition to mesh sources, a particle system can be used to generate smoke or fire; only particle systems of the Emitter type can add smoke, according to the documentation.

This guide follows the setting names in the Blender 5.2 LTS manual; the sources do not specify hardware requirements or a separate account requirement. If you are using another Blender version, check the setting names and available options against the documentation for that version.

Set up a Flow source step by step

1. Place the source inside the domain and set it to Flow

Place the object that will generate the flow within the domain’s Bounding Box. Add Fluid physics to the object and set the Type option to Flow. The object can then serve as a flow source; the other Flow settings determine what it generates and how.

When choosing the source’s purpose, don’t confuse the content type with the behavior type. For example, Smoke specifies what will be generated, while Inflow describes how that content is added to the domain. Keeping these choices separate makes it easier to test the settings in order.

2. Choose what to generate

The Flow Type field has four options: Smoke, Fire + Smoke, Fire, and Liquid. Choose the appropriate option to generate smoke, fire and smoke, fire only, or liquid. The manual notes that even when Fire is selected, the domain can automatically create smoke left behind by burned fuel.

3. Set the source behavior

Flow Behavior selects the object’s role in the simulation:

• Inflow: The source adds the selected content to the simulation domain. Use this behavior when continuous emission is needed.

• Outflow: Flow entering the object’s Bounding Box is removed from the simulation. Used with an Inflow source, it can help prevent the entire domain from filling up. The Outflow object can be animated, and the removal area follows its position.

• Geometry: Parts of the mesh within the domain boundaries are used as flow. Multiple flow objects can exist in the same domain. Surface normals should point outward for this method; reversed normals can prevent the simulation from working properly.

You can enable or disable the Use Flow feature to selectively start or stop emission or flow removal during animation.

4. Adjust mesh emission and quantity

For mesh sources, set Flow Source to Mesh. Is Planar indicates whether the source is a planar surface or a non-manifold mesh; the manual says this option can help improve simulation accuracy for these types of sources.

Surface Emission limits the distance around the mesh surface where emission occurs, measured in voxels. As a result, the same value may produce different results at different domain resolutions. Under Fire or Smoke Only, Volume Emission sets the amount generated from inside the mesh: 0 means no emission, while 1 represents the full amount. The documentation notes that volume-based emission can produce difficult-to-predict results with non-manifold meshes.

Density adjusts the amount of smoke generated at a time; increasing it produces denser smoke. Fuel sets the amount of fuel burned per second and affects flame size. Initial Temperature sets the emission temperature relative to the domain’s ambient temperature; its effect on smoke depends on the Heat Buoyancy setting.

5. Control motion and the emission area

If gaps appear between emissions from a fast-moving source, consider adjusting Sampling Substeps. This value determines the number of substeps used to sample emission from the flow source more frequently. Substeps are applied per simulation step, not per frame; the number of simulation steps is controlled by adaptive time stepping.

When Initial Velocity is enabled, the flow can inherit velocity from the source’s movement. The Source value sets the proportion of this transfer; 1 means the flow moves at the same speed as the source. Normal controls the velocity applied along the surface normals. On closed meshes, normals point in different directions, so velocity may be applied in multiple directions. If velocity in only one direction is needed, the normals must all point the same way. Initial X, Y, and Z define additional velocity components in world coordinates.

A Vertex Group can be used to restrict where emission occurs. When texture-based control is enabled, Texture limits the emission areas on the mesh. You can choose Generated UVs or manual UV mapping; Size sets the texture scale, while Offset adjusts its position along the Z axis. These texture options do not affect Outflow behavior. Smoke Color sets the color of the emitted smoke; smoke with different colors blends as it mixes. If Absolute Density is enabled, the source emits when there is room in the emission area; if disabled, emission continues and accumulates.

Common issues

• The source has no effect: Check whether the Flow object is inside the domain’s Bounding Box.

• Problems with a Geometry source: Check the mesh’s surface normals and the parts inside the domain.

• Gaps in emission during fast movement: Try adjusting Sampling Substeps; this setting affects sampling during simulation steps, not the number of frames.

• Unexpected volume emission: Check whether the mesh is non-manifold; the manual notes that results with this geometry can be unpredictable.

• Difficulty adjusting smoke spread or appearance: Test Density, Smoke Color, Absolute Density, and, if needed, Vertex Group or Texture options separately.

What does this mean for architecture and archviz workflows?

These controls let you determine where and how a source emits in architectural visualization work that calls for smoke or fire effects in Blender scenes. For emission tied to a specific area in an interior scene, you can explore the Mesh, Vertex Group, or Texture options. Artists working with moving sources can also consider velocity transfer and Sampling Substeps together.

The documentation does not provide hardware requirements, simulation times, performance gains, licensing costs, or compatibility information for other software for these features. Therefore, don’t make assumptions about project schedules or hardware needs based on these settings. A sound approach is to test source behavior in a small scene and check the documentation for the Blender version you’re using before production.

Next steps

For an initial test, choose Flow Type and Flow Behavior and observe the result; then change density, velocity, or emission area settings one at a time. This makes it easier to identify which change affects the appearance. Keep in mind that Surface Emission values depend on domain resolution, and that the effect of Initial Temperature is related to Heat Buoyancy.

Before putting a scene into production, check the source object’s position, the normals if you’re using Geometry, and whether emission occurs in the intended area. Also note that texture settings do not affect Outflow. The manual does not guarantee a specific final appearance or performance result beyond these points; test the results with your scene settings.

Source and license

This guide is adapted into Turkish from the “Fluid” and “Flow” sections of the Blender Manual. Both sources are published under the CC BY-SA 4.0 license.