A Numerical Design Space Investigation of Low-Speed Axial Compressor Stages Using Single-Row and Tandem Bladings

The present article numerically investigates the design space of an axial, low-speed compressor stage using tandem and single aerofoil configurations. The investigated rotor and stator designs follow a coupled throughflow and blade-to-blade design approach and will yield quasi-3D designed compressor stages with either single-rotor single-stator or tandem-rotor tandem-stator configurations. In past studies, tandem aerofoil configurations have shown a potential for increasing stage working coefficients, while maintaining their efficiency compared to their single aerofoil reference configuration. However, it was also shown that tandem configurations are able to reduce efficiency due to an increase of secondary flow caused by the higher loading and introduction in the second aerofoil. Currently, there is no clear design guideline on when tandem aerofoil configurations should be preferred over single ones, and under which circumstances they should be avoided. To answer this question, the present article will attempt to create a “Smith chart” for tandem aerofoil stages and compare them to their single aerofoil counterparts. Originally intended for use with turbine stages, the Smith chart maps out the potential efficiencies of turbomachinery designs. It plots the working coefficient (Ψ) over the throughflow coefficient (⁠$φ$⁠), which gives a direct indication of the shape of velocity triangles in the stage. However, the Smith chart has been well investigated for single aerofoil stages, both numerically and experimentally, as well as for low- and high-speed applications, and this is not the case so far for tandem configurations. The current work presents a fast Q3D design and analysis procedure used on a low-speed axial compressor stage and will yield quasi-3D efficiencies for a large number of different design coefficients. The findings of this work will enable future research to identify preferred combinations of design coefficients for tandem aerofoil configurations, which can then be further analyzed in 3D investigations at a higher fidelity level.