Experimental and Numerical Investigations of Inlet Circumferential Fluctuations in Swept Compressor Cascades

Abstract

Swept blades have been widely used in the transonic fan/compressor of aircraft engines. However, because of the gap in knowledge regarding the change of the inlet flowfield by sweeping, design deviations are often produced. This study used experimental and numerical simulation methods to investigate the inlet circumferential fluctuations (CF) generated by the sweep. The results indicate that the CF source terms induced by the inviscid blade force cause a negative pressure gradient ahead of the leading edge of the forward sweep blade. This pressure gradient results in a spanwise migration of the inlet flow from the hub to the shroud, which redistributes the axial velocity across the entire spanwise range. As a result, there is a reduction in the incidence angle at the tip of the forward-swept blade, whereas an increase is observed at the root. This effect increases with increasing sweep angle. The influence of the CF stress terms starts at approximately 30% of the chord length upstream of the leading edge and the values of the axial component UU and tangential component WW are maximum. CF source terms are physical quantities that quantitatively describe the effect of the sweep, which can help quantify the mechanism of sweep and can play an important role in the design of sweep blades. Swept blades are extensively used in modern transonic fans and compressors to reconcile the conflict between high efficiency, high load, high through-flow, and wide stable operating range. However, there is more qualitative understanding of the mechanism of swept blades and less quantitative design theory. In this work, a method for quantitatively describing the flow mechanism of swept blades was proposed, using a reduced-dimension spanwise force balance analysis of experimental and numerical results. The effect of swept blades on the incoming flowfield is simplified as the action of the circumferential fluctuation source terms. The source terms induce a spanwise migration of the incoming flowfield, which results in a spanwise redistribution of the incidence angle of the swept blades, even under uniform inflow conditions. The circumferential fluctuation source term force can aid in quantitatively understanding the mechanism of swept blades, and enhance the precision and efficiency of swept blade design.