Numerical Studies on Aspirated Axial Compressor Stator Cascade for Improved Aerodynamic Performance

Owing to adverse pressure gradient in an axial compressor, the blade surface boundary layers become thicker and are prone to separation. Boundary layer suction technique has been widely investigated to reduce the boundary layer growth on compressor blades. However, most of the research is limited to low Mach number compressor cascades. In the present study, aspiration, or blade boundary layer suction, has been numerically investigated on a high inlet Mach number, high deflection linear compressor cascade. The cascade comprised the stator blade mean section of the NASA 37 transonic compressor stage. Aspiration or suction slots were introduced on the blade suction surface and CFD simulations were carried out for two cases of single suction slot at two different chordwise positions and one case with the two suction slots together. Studies were undertaken for two different suction mass flow rates at design and off-design incidence angles. The density based implicit solver of the commercial CFD code ANSYS FLUENT was used for all simulations. The results of the present studies have clearly indicated that aspiration through the suction slot near the trailing edge (SS1) is very effective in reducing the boundary layer separation at high incidence angles. The suction slot at mid-span (SS2) is effective to ingest the boundary layer upstream of the slot (i.e. near the leading edge); however it affects the downstream flow adversely and increases the spanwise boundary layer growth in the core region. Also, an increase in the suction mass flow rate does not improve the overall cascade performance for the selected suction slot positions and slot geometry. However, the chosen aspiration scheme on this blade section was able to reduce the endwall recirculation with consequent reduction in endwall losses. The reasons for the suction slot position and change in mass flow rate for being not so effective are attributed to the suction slot inlet angle and the flow behaviour within the suction slot cavity at high inlet Mach numbers.