Fluid Simulation in Blender: Smoke, Fire, and Cache Settings

What will you learn in this guide?

When setting up a fluid simulation in Blender, you need to work with both the Flow object that brings fluid into the scene and the domain where the calculations take place. Flow settings determine whether you create smoke, fire, or liquid, and whether the fluid is added, removed, or treated as geometry. The Cache panel stores the simulation result, reducing the need to recalculate the same motion every time.

This guide explains how to create a Flow source, choose its type and behavior, set the simulation’s time range, and bake the simulation. According to the Blender manual, baking can require significant computing power and time, depending on the scene.

Requirements

• Software: Blender. The source guides do not specify a particular version number.

• Account: The guides do not mention any account or sign-in requirements.

• Scene: You need a domain and a Flow object positioned within its boundaries.

• Storage and time: Baked data is written to the folder specified as the Cache Directory. The Resumable option saves additional data so you can continue a paused bake; as a result, it can generate more disk writes during high-resolution bakes.

The sources do not recommend a particular hardware level or specify how much storage is required. Bake time also depends on the scene, so the information in the sources is not enough to determine exactly in advance how long a large simulation will take.

Step-by-step: creating a Flow source

1. Position the domain and source. Define the domain where the simulation will take place, then move the mesh object you intend to use as the source inside the domain’s Bounding Box. The Blender manual states that Flow objects must be within these boundaries.

2. Set the object to Flow. Enable Fluid physics in the source mesh object’s Physics properties and set Type to Flow. Then choose the fluid to generate using Flow Type: Smoke produces smoke only, Fire + Smoke produces both, Fire produces fire only, and Liquid is for liquids.

3. Choose how the fluid behaves. Inflow makes the object add fluid to the domain, so it can be thought of as a continuously flowing source. Outflow removes fluid from the domain when it enters the object’s Bounding Box; when used with an Inflow, it can prevent the entire area from filling up. With Geometry, the parts of the object inside the domain are treated as fluid in the simulation. You can add multiple Geometry sources; make sure their surface normals point outward.

4. Set which parts of the source emit fluid. The Mesh option in the Flow Source section generates fluid from the object’s mesh. Is Planar lets you define the flow source as a planar structure, such as a plane, or as a non-manifold mesh. If you are using Smoke or Fire, Volume Emission determines the amount generated inside the mesh. Volume-based emission can produce unpredictable results with non-manifold geometry. With Surface Emission, the emission distance is calculated in voxels, so the result can vary with the domain resolution.

5. Review motion and density settings. Sampling Substeps can help reduce gaps in the emission of fast-moving sources. Substeps are applied during simulation steps, not on every frame; the number of steps is controlled by adaptive time stepping. The amount of smoke is controlled by Density, while Fuel controls the amount of fire fuel. Enable Initial Velocity if you want the source’s motion to be transferred to the fluid. When Source is set to 1, the fluid moves at the source’s velocity.

6. Set the simulation range and directory. Choose where bake files will be saved in the Cache Directory field in the Cache panel. Frame Start and End define the frames where the simulation begins and ends; baking covers the first and last frames within this range. The calculation only takes place on positive frames between Start and End. Increase End if you need a longer simulation than the default range.

7. Choose a cache type and bake. Replay bakes while the simulation plays in the viewport and requires Playback Sync to be set to Play Every Frame. If you want to use Frame Dropping or Sync to Audio, the manual recommends considering Modular or All. Modular distributes bake steps across different panels; for example, the mesh bake tool is in the Mesh panel. All processes the selected settings in a single bake operation. Once baking is complete, the simulation data is stored in the cache.

Common mistakes

• Leaving the source outside the domain: Check that the Flow object is inside the domain’s Bounding Box.

• Using Replay with an incompatible sync setting: Replay only works with Play Every Frame. If you need another Playback Sync method, consider Modular or All.

• Setting an incomplete frame range: Baking is limited by the Start and End values in the Cache panel. Check End to make sure it covers the final frame needed for the simulation.

• Seeing gaps in the emission of a fast-moving source: If the source moves quickly, review the Sampling Substeps setting; it is intended to reduce gaps in the emission.

• Long bake times with heavy mesh settings: If the mesh has a modifier, render settings are used when the mesh is passed to the fluid solver. The Blender manual notes that a high Subdivision Surface level on a moving obstacle can increase calculation time. Once the setup is working correctly, you can increase the settings for more realistic results.

• Enabling Resumable indiscriminately at high resolutions: This option saves additional data so you can continue a paused bake. The manual recommends avoiding it at high resolutions because more data will be written.

Next steps

Start with a short time range and check the source type, fluid behavior, and position within the domain. Then determine the required simulation duration, adjust End, and choose a suitable cache method. Uni Cache and OpenVDB formats are available for smoke or fire data. OpenVDB can be saved using Zip, Blosc, or no compression; precision can be set to Full (32-bit), Half (16-bit), or, where appropriate, Mini (8-bit). Binary Object and Object formats are listed for liquid mesh caches. The source guide does not identify a single option as superior in quality or file size regardless of project requirements.

Sources and license

This guide has been adapted into Turkish from the “Flow” and “Cache” pages of the Blender Manual. Both sources are published under the CC BY-SA 4.0 license.