A Low Speed Axial Compressor With a Cascade of Magnus Rotors to Replace the Aerofoils of the Stator

Abstract

The low speed axial research compressor ‘Rheinfall’ in the Turbomachinery Labs at ETH Zu¨rich has been modified to include a novel stator row. The conventional stator’s vanes have been replaced with a cascade of rotating cylinders or ‘Magnus Rotors’. The initial aim was to demonstrate that such a cascade could reproduce the effect of the aerofoils. This paper gives an overview of the design, experimental results and conclusions drawn from simple modeling of the experiment. The behaviour of the compressor is essentially preserved; the conventional rotor stalls at a slightly higher flow coefficient (φ = 0.4). The pressure rise across the compressor is a function of the cylinder rotational speed. The pressure recovery coefficient Cpr across the stator can be increased by up to 60% compared to the conventional aerofoils with high rotational speed. The stator pressure rise is maintained at much lower flow coefficient (φ = 0.23). Lift coefficients of up to 7.0 have been stably demonstrated. The stator is capable of very high turning (>60°), to axial and beyond. From simple flow modeling the aerodynamic efficiency appears to be about the same as the conventional machine. However, the parasitic losses in the high-speed Magnus spindles double the power absorbed. The recorded characteristics show strong hysteresis across the whole flow range.