Fluid Simulation in Blender: Setting Up Smoke and Baking the Cache

What will you learn in this tutorial?

This guide covers how to define the role of a Flow object in Blender fluid simulations, understand the key settings that control smoke and fire emission, and cache the result. A fluid source object can add fluid, like a faucet, remove it, like a drain, or use its own geometry as fluid in the simulation. The right behavior depends on the effect you want to create in your scene.

This overview is limited to the Flow and Cache settings described in the Blender 5.2 LTS manual. Rather than providing a start-to-finish recipe for an entire simulation, it explains the key options for getting a source object to work correctly and storing the calculation in a manageable way.

Requirements and setup

The reference used is the Blender 5.2 LTS manual. The manual pages provided do not specify minimum hardware requirements or user account requirements for running a simulation. Therefore, no specific graphics card, memory capacity, or account requirement should be assumed. The manual notes that fluid simulations require computing power and time, and recommends allowing enough time for caching, depending on the scene.

The scene should contain a domain object and a Flow object within the domain’s boundaries. According to the manual, the Flow object must be inside the domain’s Bounding Box. Prepare a mesh object to use as the fluid source. You’ll choose the Flow Type and Flow Behavior based on the intended effect, such as liquid, smoke, or fire.

1. Define the Flow object

Select the mesh object you want to use as a fluid source. Add Fluid physics under Properties > Physics, then set the Type to Flow. This makes the object one of the sources in the fluid simulation. Make sure the object is inside the domain’s Bounding Box; a source outside it may not work as expected.

Next, choose a Flow Type:

• Smoke: Generates smoke only.

• Fire + Smoke: Generates both fire and smoke.

• Fire: Generates fire only.

• Liquid: Generates liquid flow.

Flow Behavior determines what the source does to the simulation. Inflow continuously adds fluid, like a water outlet or fire source. Outflow removes fluid that enters its own bounding box from the domain. With Geometry, the parts of the object within the domain boundaries are used directly as fluid. You can use multiple fluid objects with Geometry; their surface normals must point outward.

2. Adjust emission and motion

Use the Use Flow setting to switch the source object’s fluid emission on or off during the animation. If the source moves quickly, consider increasing Sampling Substeps to reduce gaps that can appear during emission. These substeps are applied at simulation steps, not every frame; the number of simulation steps is controlled by adaptive time stepping.

The Smoke Color, Density, and Initial Temperature options also affect the appearance of smoke. Density controls how much smoke is generated at a time. Initial Temperature determines how much hotter or colder the generated smoke is than the domain’s ambient temperature; its effect depends on the domain’s Heat Buoyancy setting. You can also adjust Absolute Density, which changes how smoke or fire accumulates around the source, according to the scene.

When emitting from a source mesh, you can use the Mesh option in the Flow Source settings. Surface Emission defines emission within a specified voxel distance from the mesh surface; the result may vary depending on the domain resolution. Volume Emission applies only to fire or smoke. If the mesh is non-manifold, estimating emission through its volume can produce unpredictable results. When using these options, consider the mesh structure and domain resolution together.

Enable Initial Velocity if the source’s motion needs to be transferred to the fluid. The Source value sets the factor of the source’s velocity transferred to the fluid; a value of 1 means motion at the same speed. The Normal setting adds velocity along the surface normals. Since normals point in different directions on a closed mesh, emission may move in multiple directions. If you want the initial velocity to travel in one direction, using a plane as the source is one option mentioned in the manual. Initial X, Y, and Z can be used to define additional velocity in world coordinates.

3. Choose a cache type and calculate the simulation

In the domain’s Cache panel, set the directory where the simulation will be stored, along with the start and end frames. The calculation is limited to this frame range; if the simulation needs to run longer, adjust the End value accordingly. Choose a cache type to suit your workflow:

• Replay: The simulation is cached as it plays in the viewport. Playback Sync must be set to Play Every Frame.

• Modular: The calculation is carried out in stages using the tools in the relevant panels.

• All: The selected settings are calculated with a single tool.

Baking can take time and computing power, depending on the scene. If the mesh has modifiers, render settings are used when they are passed to the fluid solver; higher settings can increase calculation time and memory use. The manual notes that once the setup is correct, you can increase the settings later for a more realistic result. So, verifying the scene setup first and then increasing quality settings provides a more controlled workflow.

For volumetric simulation data—that is, grids and particles—you can choose Uni Cache or OpenVDB format. OpenVDB offers Zip, Blosc, or uncompressed storage, as well as Full, Half, and Mini precision levels. According to the Blender manual, Zip is slower than Blosc, which uses multithreaded compression. Half provides 16-bit precision, Full provides 32-bit precision, and Mini uses 8-bit where possible, switching to 16-bit for data that requires it. Consider your output requirements and available storage when choosing these options.

Common mistakes and next steps

If the Flow object is outside the domain boundaries, the simulation may not behave as expected. In Geometry mode, surface normals pointing inward can also cause problems. If gaps appear in the emission from a fast-moving source, check Sampling Substeps. If the Replay cache does not work, confirm that Playback Sync is set to Play Every Frame.

When choosing a cache directory, remember that separate folders can be created for different types of simulation data. The Resumable option writes additional data to support continuing a paused calculation; because high-resolution calculations write more data to the drive, the manual recommends leaving this option disabled. Bake All can be canceled with Esc after it starts; it cannot be paused and resumed.

In architecture, interior design, and archviz workflows, these settings can be used to control source behavior in scenes featuring fountains, pools, smoky atmospheres, or fire. For animated sources in particular, substeps, geometry structure, and cache settings all affect the result. Since the manual does not provide numerical hardware requirements, assess calculation time by testing with your scene and settings. A practical next step is to run a low-cost test first, then increase the resolution and other settings if needed.

Sources and license

This article is based on the Fluid, Flow, and Cache sections of the Blender 5.2 LTS Manual. The Blender manuals are licensed under CC BY-SA 4.0; the material has been adapted into Turkish and retold.