Smith diagram for Low Reynolds number axial fan rotors

Authors

Raul Corralejo - Dyson Ltd
Peter Harley - Dyson Ltd

Abstract

Compressor operation at low Reynolds numbers is commonly associated with a loss increase. A semi-analytical approach was used to investigate this region of the design spectrum. To do this, an axial rotor with constant diameter endwalls was non-dimensionalised to understand the influence of different design parameters independently. Smith diagrams showing contours of efficiency on a plot of flow coefficient versus stage loading coefficient were produced at low and high Reynolds numbers. The results showed not only lower levels of efficiency at low Reynolds numbers but a much narrower high efficiency island, with losses rapidly increasing as the design moved away from the high efficiency region. Several points in the Smith diagram were selected, dimensionalised and simulated using CFD with and without a transition model. Good agreement between the CFD and the model was found, with discrepancies increasing towards low efficiency regions. Meanline correlations for the low Reynolds number regime were also provided.