Computational study of the effect of sweep on the performance and flow field in an axial flow compressor rotor

Abstract

In the recent past, experimental studies have shown some advantages of blade lean and sweep in axial compressors. As most of the experimental results are combined with other features, it is difficult to determine the effect of individual parameters on the performance of the compressor. The present numerical studies are aimed at understanding the performance and three-dimensional flow pattern within and at the exit of swept and unswept rotors. Three rotors, namely, unswept, 20° forward swept, and 20° backward swept rotors, are analysed with a specific intention of understanding the three-dimensional flow pattern within the rotors and also the pattern of the blade boundary layer flow. The analysis was done using a fully three-dimensional viscous CFD code CFX-5. Results indicated a reduction in pressure rise with sweep. Backward sweep adversely affects the stall margin. Forward sweep changes the streamline pattern in such a way that the suction surface streamlines are deflected towards the hub and the pressure surface streamlines are deflected towards the casing. An opposite behaviour is observed in the backward swept rotors. High axial velocities reduce the secondary losses near the hub, resulting in a high pressure rise in forward swept rotor.

Aerodynamic Performance of Low Speed Axial Flow Compressor Rotors with Sweep and Tip Clearance

“…At tip regions, unswept rotor is found to produce more pressure rise. This observation is similar to the one reported by Govardhan, Krishnakumar and Sitaram (2007). This difference in the pressure rise as well as the span over which the unswept rotor produced more pressure rise from the tip are found to increase with the introduction of τ/ch = 0.007 clearance.…”

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.…”

“…Based on the results from the literature [4][5][6]13], it was contemplated that better 3D stacking scheme would be the combination of forward tip chordline sweeping and positive dihedral, which turns out to be "axial sweeping". Thus, the 3D blade stacking schemes chosen for the present study are shown in Table 1.…”

“…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].…”

“…Forward sweep modifies the flow structure in low speed axial compressors by the following: (1) Reducing the blade loading in the frontal area near the tip region, which results in flow near the leading edge becoming more tolerant to the changes in incidence and reduced tip leakage in this area. (2) Modification in the movement of centrifuged blade boundary layer which will not result in accumulation of low energy fluid near tip sections to cause separation and formation of stall cells at lower flow coefficients [1,4,5]. Major sweep effects in compressor rotors are thus found above the mid span, particularly near the tip, where the flow leaking from the finite tip gap already has its own influence.…”