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The final scene consists of the following elements:

1. A shelled Poly Plane used as the source geometry for Smoke, Fuel and Temperature. An animated Noise modifier is applied to the plane to break-up the emission and produce interesting swirls.
2. A Phoenix FD Fire/Smoke Source with the Poly Plane in its Emitter Nodes list. The Source is in Volume Inject mode and Noise is enabled for extra randomization.
3. A Phoenix FD Fire/Smoke Simulator with some tweaks in the Grid, Dynamics, Fuel and Rendering roll-outs. It's note-worthy that with this setup Burning is enabled under the Fuel roll-out.
4. A 3ds Max Vortex force responsible for creating the funnel. The position of the vortex force is animated which gives the tornado a more chaotic appearance.
5. A Phoenix FD Turbulence force to break-up the fire and smoke even further. As the purpose of the turbulence is to create large-scale motion, its Size parameter is set to a rather high value and the Fractal Depth is reduced to 0 so the noise field has only 1 layer of details.
6. A V-Ray Physical camera with minor tweaks for final rendering.

Set the Time Configuration → Animation Length to 200 so that the Timeslider goes from 0 to 200.

Apply a Shell modifier to the plane to give it some thickness and set the Outer Amount to 5.

Create a Phoenix FD Fire/Smoke Simulator and set the Grid → Cell Size to 4.

Set the Size X / Y / Z to 150 / 150 / 40 respectively.

Set the Boundary Conditions: Z to Jammed ( - ). When a wall is Jammed (closed off, basically) the velocities inside the simulator are calculated differently than in the situation where the wall is considered open. The emitted fluid will also collide with Jammed walls.

Create a Space Warps → Forces → Vortex force. Phoenix FD will automatically recognize and use it during the simulation unless you choose to put it in the Simulator → Scene Interaction → Exclude List.

Set the Time Off to 200, or however many frames your simulation length is.

Set the Taper Length parameter to 0 - this parameter can be useful for controlling the height of the vortex but it tends to be easier to only use the options in the Capture and Motion section.

Set the Axial Drop and Orbital Speed parameters to 6.
Set the Radial Pull to 1.5.

To produce a funnel shape that doesn't spin outwards uncontrollably or collapse in on itself, you need to find a balance between the Radial Pull and the Orbital Speed. The provided values work for this example but if you are using a different setup, you may need to tweak the parameters until you get the desired shape.

Make sure to rotate the Vortex force gizmo 180 degrees in Y such that the arrow is pointing up in the +Z direction.

Here's how the simulation looks after the animation on the Vortex force.

We are trying to make a Fiery Tornado simulation but fire is only present right at the bottom of the simulator. To deal with this, we will use the Phoenix FD Fire Source to emit Fuel. Once Fuel is present in the Simulator, we can enable burning which will consume the emitted fuel and produce more fire.

Select the Phoenix FD Source and enable the emission of Fuel.

Fuel is a required component for the simulation of burning. Once it comes into contact with the Temperature channel, it will ignite and produce more temperature and smoke based on the settings specified in the Fuel tab of the Simulator.

Here's the simulation with Fuel emission and Burning enabled.

To deal with the uniform appearance, we'll make a few changes to the Phoenix FD Source and the Phoenix FD Simulator.

Add a Noise modifier to the shelled Poly Plane.

Set the Scale to 134, and the X/Y/Z Strength to 456 / 127 / 77.

Enable Fractal and leave the Roughness to 0 and the Iterations to 6.

Make sure to Enable the Animate Noise option.

You may also open the Graph Editors → Track View - Curve Editor and set the tangents for the Phase parameter to Linear.

Here's how the simulation looks with those changes.

Setting the mode to Volume Inject instead of Surface Force allows the fluid to follow the vortex force more closely. Notice how the twisting of the smoke at the top of the simulator is more pronounced now.

Now that we've got Fuel, Temperature and Smoke injected into the simulation and carried by the Vortex force, the fiery tornado is finally starting to take shape.

One major issue to address is that the smoke can be clearly seen travelling straight up. This is caused by the Gravity setting in the Dynamics tab. With Fire/Smoke Simulations, cold smoke (Temperature lower than 300 Kelvin) falls down and hot smoke rises up. This is causing the funnel of the tornado to break-up in an unnatural way. There are 2 ways to go about fixing this:

1. You can try increasing the Axial Drop / Orbital Speed / Radial Pull parameters on the Vortex Force to counteract gravity. This would likely be the 'physically correct' way to go about doing this - the vortex should be strong enough to have full influence over the trajectory. However, this could also turn into a time-consuming endeavor
2. You can simply disable Gravity.

We go with the second approach.

Uncheck the tickbox to the left of Gravity to disable it.

Lastly, open the Output roll-out of the Simulator and enable the export of Velocity.

The Velocity channel is required when rendering with Motion Blur so V-Ray knows in what direction to 'stretch' the fluid.

Let's make some tweaks to the Volumetric Shader before proceeding with the rest of the tutorial.

Open the Phoenix FD Simulator → Rendering roll-out and click the Volumetric Options button. The Volumetric Options contain the shading parameters for rendering fire and smoke. You can think of that window as the Phoenix FD Volumetric Shader.

In the Smoke Opacity roll-out, set Based on to Smoke. The Opacity Diagram below should now become active - it is used to control the thickness of the smoke.

The difference between the Smoke and Simple Smoke option is that when the Opacity is set to use the Smoke channel, the Opacity Diagram below can be used to make changes to the way the Smoke is rendered by using the opacity curve. With Simple Smoke, you get a single Simple Smoke Opacity multiplier that acts as if the Based on was set to Smoke and the curve below was completely straight, going from (0, 0) on the left to (1, whatever value Simple Smoke Opacity is ) on the right. To summarize: Based on: Smoke gives you access to a curve which can be used to control the thickness based on the value of the Smoke channel for a given voxel while the Simple Smoke provides a single uniform multiplier only.

The Opacity Curve in the diagram below is tweaked as follows:

Point 1: (0.1, 0)
Point 2: (0.95, 0.08)
Point 3: (1.0 , 0.3)

This change is essentially removing all the sparse smoke. If you want to get a clean preview of what your changes are doing to the Smoke, you can go to the Fire roll-out and set the Based on option to Disabled to isolate the Smoke.

Here's the entire 200 frames of the simulation with all the tweaks we've done so far:

Create a Helpers→ Phoenix FD → PHXTurbulence.

Set the Strength to 250 and the Size to 914.

Reduce the Fractal Depth to 0.

The Turbulence is used to break-up the fire even further. Please check the comparison images below.

Without turbulence

With turbulence

This section of the tutorial is optional. You may skip to the Rendering section below if you're not interested in re-creating the effect to the right.