### 5.6.2. Using Multiple Domain Interfaces

A given simulation can make use of multiple domain interfaces. Each `Fluid Fluid` interface can use a different frame change model. For example, two domains can be connected by a `Fluid Fluid` interface without a frame change; one of these domains might also contain a rotationally periodic interface to define a blade passage. Finally, there might be another `Fluid Fluid` interface between the first two domains and a third domain that uses a frame change model. A four stage axial compressor, consisting of four stators and four rotors, might contain seven `Fluid Fluid` interfaces with a `Frozen Rotor` frame change model (one at each frame change interface between components).

It is possible to have a combination of frame change models within a single problem definition. For example, in a stator/rotor/stator configuration, the first `Fluid Fluid` interface could be a `Stage` or `Frozen Rotor` interface, and the second interface could be a `Transient Rotor-Stator` interface. This might make sense if you are only interested in accounting for the transient conditions between the rotor and the downstream stator.

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