Effects of Inlet Ramp Surfaces on the Aerodynamic Behaviour of Bleed Hole and Bleed Slot Off-Take Configurations

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Bleed off-take air pressure and the interaction of the off-take with the primary flow through the blade passage is determined by: (1) the location of the bleed off-take at the endwall relative to the blade passage; (2) the bleed flow rate; and (3) the off-take geometry. In the companion paper (Leishman et al., 2004) the effect of bleed rate and endwall location was investigated using a circular hole bleed off-take configuration; the circular hole was tested at three endwall locations and for bleed flow rates between zero and 9 percent of the primary (core) flow through the blade passage. The effects of bleed off-take geometry are presented in this paper by comparing the aerodynamic behaviour of a number of generic bleed off-take configurations. Using results from low-speed cascade experiments and three-dimensional numerical calculations, the off-take configurations are compared with respect to the requirement to maximise bleed off-take air pressure and minimise loss generated within the blade passage. The off-take geometry, and especially the introduction of contoured inlet ramp surfaces to guide flow into the off-take for high bleed pressure, has a strong effect on its aerodynamic behaviour because it determines the extent to which flow within the off-take is coupled to the primary flow through the blade passage. In this paper, the off-take configurations that give the highest bleed pressure generally cause the highest levels of loss in the blade passage.