### 11.6.2. Full Model Simulation versus Reduced Geometry Simulation (Pitch Change Models)

To reduce costs (CPU & memory) of a transient blade row simulation, you can model a turbomachinery flow on a small sector of the machine and apply a pitch change model (such as Profile Transformation, Time Transformation or Fourier Transformation) to account for the difference in pitch between blade rows.

In general, the transient blade row simulation becomes more efficient on the small sector model with respect to the full wheel model as the number of blade counts in the original machine increases. For example, in some cases it is better to do a transient blade row simulation on a full wheel rather than a reduced geometry with pitch change models if the blade count is very small. Axial machines can have a large number of blades per row (for example, 100 blades or more) so the cost savings with transient blade row methods can be very large (of the order of 100x for such a machine). For radial machines, the blade count is typically much smaller (for example, 5-20 blades) resulting in reduced potential cost savings for the pitch change models.

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