ON ROTOR BLADE LOADING AND TIP LEAKAGE PHENOMENA IN A LOW SPEED AXIAL COMPRESSOR WITH FORWARD BLADE SWEEP

The present numerical work is undertaken to focus on the performance of Tip Chordline Sweeping (TCS) and Axial Sweeping (AXS) of low speed axial compressor rotor blades against the baseline unswept rotor (UNS) performance for different tip clearance levels. This paper presents in detail the trends in blade loading and tip leakage flow as modified by the two rotor sweeping schemes. 15 domains were modeled with 5 sweep configurations (0 degrees, 20 degrees TCS, 30 degrees TCS, 20 degrees AXS and 30 degrees AXS) for 3 clearances (0.0%, 0.7% and 2.7% of the blade chord). CFD simulation and flow analysis are done using commercial CFD package ANSYS (R) CFX 11.0. Turbulence was modeled by standard k-omega model employing automatic wall functions. Results are validated with the experimental data available in the literature. Through the results, 20 degrees AXS rotor is found to be distinctive among all the rotors with highest pressure rise, higher operating range and less tip clearance loss characteristics. TCS rotors produced improved total pressure rise at the low flow coefficients when the tip gap is increased. Observations near the tip reveal that UNS rotor shows very high sensitivity in the static pressure distribution for the tip clearance flows while AXS rotor found to be stable than the other rotors when the tip clearance is increased. Besides, AXS rotor has high loading capability and less tip clearance effect on blade loading at the near stall mass flow. At non-zero clearances, much of the leakage flow exits the clearance gap with a negative axial velocity component, creating vortex related flow blockage. At both non-zero clearance levels, this blockage is highest for the UNS rotor and lowest for the AXS rotor. UNS rotor leakage vortices penetrated more into the passage before the axial velocity deficit getting sufficiently dissolved. This problem is found to be less for the swept rotors.