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

Abstract

Blade tip gap, though finite, has great influence on the performance of a turbomachine. Tilting the blade sections to the flow direction (blade sweep) would increase the operating range of an axial compressor by modifying the pressure and velocity fields on the suction surface. The present paper investigates the combined effect of these two factors on various flow characteristics in a low speed axial flow compressor. For the present study, six computational domains were modeled: two rotor sweep configurations (0° and 20°) and three different clearance levels for each rotor. Commercial CFD package ANSYS® CFX 11.0 is used for the simulations. Results indicated that the effect of tip clearance is more predominant in swept rotor than unswept rotor in terms of change in total pressure rise and efficiency. Traced streamlines indicated that blade sweep guides the suction surface boundary layer fluid towards the trailing edge, preventing it from getting accumulated near the tip. Studies near the tip region showed the pattern of velocity streamlines through the tip gap. Tip clearance vortices are found and their trajectory and effect on the flow are studied. Total pressure rise contours at the rotor exit showed that radial migration of low energy boundary layer fluid towards the tip sections is well prevented with sweep.