The Influence of Reynolds Number and Roughness on the Efficiency of Axial and Centrifugal Fans—A Physically Based Scaling Method

There is a technical and economical need for a correction method to scale model test data, which fulfills five tasks: It should be (i) physically based, (ii) understandable and easy to apply, and (iii) universal, i. e., applicable to centrifugal as well as to axial machines of different specific speed. Moreover, the method should (iv) account for the aerodynamic quality of the machine and should (v) be reliable not only at peak efficiency, but also at off-design condition. Up to now, no method meets all five tasks. To fill that gap, a method developed at Technical University Darmstadt together with Forschungsvereinigung fur Luft- und Trocknungstechnik e. V. (FLT) is introduced in this work. The method consists of three steps: Assuming the so-called master curve, scaling the efficiency itself and shifting the best efficiency point to a higher flow coefficient. For each step, a simple physical explanation is given. The validation of the method is done with test data of two axial fans with four different stagger angles and two centrifugal fans. In spite of its simplicity, the method shows a good agreement to test data compared with traditional and most recent scaling methods. A short overview about the advantages and disadvantages of compared methods and a conclusion is given at the end of this work.