Internal and External Flow

In a fluid flow simulation, the fluid flow region comprises one or more volume bodies representing a space around and between solid objects through which fluid may flow; that space is filled with a fluid material. There are two types of fluid flow simulations:
  • A simulation that represents internal flow.
  • A simulation that represents external flow.

For internal flow simulations, the motion of the fluid material is constrained by physics conditions to the region by walls representing the bounding solid bodies, and may enter or exit the region through inlets, outlets, and openings that represent conditions outside of the modeled region. Examples of internal flow are fluid flowing through compressors, pumps, fans, and pipes.

In external flow simulations, the fluid material surrounds the body. Examples of external flow are air flow around an airfoil, vehicle, or any object. When simulating external flow around an object, your geometry might not contain a fully defined external flow boundary. You will create an external flow boundary by defining a bounding box that surrounds the relevant aspects of your geometry, such as around a vehicle.

Note: You can set one or more solid bodies as cutter bodies to automatically block the fluid flow, allowing you to experiment with the positions of solid objects within the flow path without needing to geometrically extract overlapping bodies from the fluid.
To model internal or external flow, use one of the QuickStart options in the ribbon of the Simulation tab:
  • Internal Flow: After the internal flow region is defined by the inlets, outlets, and (if relevant) flow caps, the flow volume is extracted automatically. Values for the flow inlet and outlet conditions are shown in the physics tree.
  • External Flow: The enclosure volume is automatically created and values for the flow inlet and outlet conditions can be found in the physics tree. Friction will be included on the ground and model surfaces. No friction will be included for the remaining enclosure surfaces.
Note: The External Flow quick start option is only available when in the Explore stage. It cannot be transferred to Fluent from the Explore stage. To model external flow in Explore and Refine, use the Enclosure tool (accessible from the ribbon of the Prepare tab). In general, the Enclosure and Volume Extract tools (also in the Prepare tab) can be used for more complex geometries and applications to create flow volumes.

This section contains the following topics: