---
title: "Phoenix FD Force operator"
canonical: "https://documentation.chaos.com/space/PHX4MAX/124528505/Phoenix%20FD%20Force%20operator"
format: markdown
---
This page provides information on the Phoenix FD Force operator for Particle Flow.

## **Overview**

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This Particle Flow operator affects the movement particles using the velocity from a Phoenix simulation.

It requires the simulator's cache to contain the grid **Velocity** channel.

You can improve the viewport performance of this operator by increasing the **PFlow Cached Frame Count** option in the [Phoenix FD Global Preferences](https://docs-chaos.atlassian.net/wiki/spaces/PHX4MAX/pages/125311186), However, this will increase the memory usage.

> Macro (ui-text-box)
> 
> When doing Liquid simulations, Phoenix populates the grid **Velocity** channel only for cells / voxels inside the liquid volume - empty (air) voxels contain no velocity information. To generate velocity information for the empty voxels, enable **Simulate Air Effects** under the [Dynamics](https://docs-chaos.atlassian.net/wiki/spaces/PHX4MAX/pages/124628691) rollout of the simulator and re-run the simulation.


## **Parameters**

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