### 11.4.1. Frozen Rotor

The Frozen Rotor model treats the flow from one component to the next by changing the frame of reference while maintaining the relative position of the components. Usually, periodicity is used to reduce the number of components to a subset that has approximately the same pitch ratio as the full geometry. To account for differences in pitch ratio between the subset and the full geometry, the flow passing through the interface is scaled according to the net pitch ratio of the subsets.

The Frozen Rotor model must be used for non-axisymmetric flow domains, such as impeller/volute, turbine/draft tube, propeller/ship and scroll/volute cases. It can also be used for axial compressors and turbines. The Frozen Rotor model has the advantages of being robust, using less computer resources than the other frame change models, and being well suited for high blade counts. The drawbacks of the model include inadequate prediction of physics for local flow values and sensitivity of the results to the relative position of the rotor and stator for tightly coupled components.

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