The impact of boundary layer suction on the aerodynamic performance of bowed compressor cascades is discussed in this paper. Preliminary studies are conducted in the context of a highly loaded compressor cascade with peak diffusion factor of 0.60 and camber angle of 60 degrees. Comparison between numerical simulation results and experiment data shows that blade bowing may well help to modify the radial migration of flow features and prevent the blade suction surface boundary layer from separating. It is noteworthy that there exists an optimum blade bowing design with different operating conditions to increase the incidence range and reduce the loss over the incidence range.
With the introduction of the boundary layer suction, the blade design becomes more complicated. This paper, therefore, conducts a thorough numerical study on design parameters including bowed blade geometry, aspirated flow fraction, and aspiration slot location based on mechanical simplicity and fabrication constraints. For a better understanding of the flow physics, the aspiration slot and plenum are included as part of the computational domain. The aspirated fluid passes into the plenum and is removed through both the hub and the shroud of the blade. From there it can be dumped overboard or carried to another point in the engine to be used as cooling air. Without considering the stagnation pressure loss of the aspirated flow, the blade lose can be sustainably decreased with the growing aspirated flow fractions from 0.5% to 2.5% of the inlet mass flow. However, when the aspirated flow’s effect on stagnation pressure loss is properly quantified, the blade’s loss decreasing trend will be relatively stable or even reversed with the aspirated flow fraction increasing.
The calculations show that the application of aspiration on the flow path needs to be investigated and combined with blade bowing to partly counter the negative impacts with the application of aspiration. The application of blade bowing on aspirated blade makes it possible to achieve the same loss reduction by using lower amounts of aspirated flow. In other words, the increase in spanwise pressure gradient near the endwalls can be further utilized to reduce the effects of secondary flow by bowed blade with the same aspirated flow fraction.
Aspiration should not be isolated from blade bowing, the optimum blade bowing angle is different on the basis of different aspirated flow fraction and aspiration slot location. The aspiration slot location is determined by the flow phenomena such as the three-dimensional separation in the cascade corner. In consideration of the stagnation pressure loss from the aspirated flow, aspiration inside of the three-dimensional separation region has a beneficial impact on the blade loss. Conversely, it will quickly lose its effectiveness, or even lead to slight deterioration of the aerodynamic performance if aspiration location is in the midspan, outside the three-dimensional separation region.