The Impact of Forward Swept Rotors on Tip Clearance Flows in Subsonic Axial Compressors

Abstract

This paper presents an experimental and analytical study of the impact of forward swept rotors on tip-limited, low-speed, multistage axial compressors. Two different configurations were examined, one with strong tip-clearance flows and the other with more moderate levels. Evaluations were done at multiple rotor tip clearances to assess differences in clearance sensitivity. Compared to conventionally stacked radial rotors, the forward swept blades demonstrated improvements in stall margin, efficiency and clearance sensitivity. The benefits were more pronounced for the configuration with stronger tip-clearance flows. Detailed flow measurements and three-dimensional viscous CFD analyses were used to investigate the responsible flow mechanisms. Forward sweep causes a spanwise redistribution of flow toward the blade tip and reduces the tip loading in terms of static pressure coefficient. This results in reduced tip-clearance flow blockage, a shallower (more axial) vortex trajectory and a smaller region of reversed flow in the clearance gap.

Experimental Investigation of a Forward Swept Rotor in a Multistage Fan with Inlet Distortion

“…The trend in using aerodynamic sweep to improve the performance of transonic blading [1][2][3][4][5][6][7][8] has been one of the most significant technological evolutions for compression components in turbomachinery. Wadia et al in [2] reported on the experimental evaluation and the subsequent analytical assessment of both aft and forward sweep compressor rotor technology with respect to aerodynamic performance and stability in a single-stage environment.…”

Study of Sweep and Induced Dihedral Effects in Subsonic Axial Flow Compressor Passages—Part I: Design Considerations—Changes in Incidence, Deflection, and Streamline Curvature

“…Theories based on infinite span blades would invariably be different in such cases. Streamline twist [8,9] and spanwise redistribution of flow [4,7] are reported with sweep in such low aspect ratio configurations. Starting from lifting line theory, nearly all the blade design procedures (axisymmetric flow assumption followed by finding a blade-to-blade solution for each axisymmetric stream surface) are not legitimate when the blades are swept.…”

“…Three dimensional forward sweep designs have shown increased compressor efficiency and operating range [1][2][3][4][5], higher pressure rise with moderate sweep angles [4], suppression of secondary losses [1,5,6], reduced blade loading near the tip leading edge portions [4,6], and low tip clearance flow blockage [7]. Deliberate use of sweep in subsonic blade rows is found to improve the operating range and efficiency characteristics, while in transonic environment it is due to significant changes in the shock structure to reduce shock-related losses [2,3].…”

Investigation of the Hydrodynamics of Sweep Blade in Hi-Speed Axial Fuel Pump Impeller

“…Results by Li et al [2], Vad [4], and McNulty et al [5] show that sweep blade can improve the aerodynamics performance of fans and compressors, including increasing total-pressure peak value, enhancing efficiency, and widening no-stall range. By both CFD simulations and experiments, Gallimore et al [1,3] investigated sweep blade in hi-speed axial compressors.…”

“…Aerodynamics of sweep blade had been investigated and analyzed by many researchers [2][3][4][5]. Results by Li et al [2], Vad [4], and McNulty et al [5] show that sweep blade can improve the aerodynamics performance of fans and compressors, including increasing total-pressure peak value, enhancing efficiency, and widening no-stall range.…”