Acceptance tests for large turbomachines are carried out with the help of small-scaled models on standardized test rigs. This non-similarity, e.g. in Reynolds and Mach number between model and prototype causes an efficiency change. Therefore, the prediction of efficiency change is done by scaling methods. Darmstadt Scaling Method is extended to consider different stagger angles and different blade numbers for axial fans. The method is validated with experimental data and shows good agreements in the stagger angle range from -18° to +12° and Reynolds number ranges of Re = 2.2E6 … 6.5E6 for half- and full-equipped rotors with respect to blade number.

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