Design and off-design behavior of a tandem rotor stage

Abstract

With an ever-increasing focus on clean and sustainable energy for transport and power, aero-engine designers need to come up with engine designs that can meet the efficiency and thrust requirements. In this aspect, compressor/fan designers always aim at designs that can result in higher pressure ratios and maximum possible efficiency with a fewer number of stages. Compressor blades, which are designed for higher diffusion, have an inherent risk of flow separation. This, therefore, fixes the upper permissible limit in terms of diffusion. If the suction surface adverse pressure gradient can be efficiently managed to avoid flow separation, it would be possible to target higher diffusion factors. One such concept for achieving this is using tandem blading. In the present computational study, a conventional low-speed compressor stage performance is compared with a tandem stage. Both designs attempt similar levels of targeted diffusion. The computational results are simulated at the design and the off-design conditions. The computational results are validated with experimental data. A high percentage pitch and low axial overlap configuration are finalized for the design of the tandem rotor based on existing literature as well as initial parametric analyses. The study shows that it is possible to achieve higher diffusion for the tandem rotor in comparison to a single rotor. The behavior of the gap-nozzle, interaction of the tip leakage with the gap-nozzle, blockage due to the tip leakage vortex, performance of stator, and performance of both stages are discussed in detail in this paper.