The Effect of Leading-Edge Geometry on Wake Interactions in Compressors

The effect of leading-edge geometry on wake/boundary-layer interaction was studied in a low-speed single-stage HP compressor. Both a 3:1 elliptic and circular leading-edge were tested on a Controlled Diffusion (CDA) stator-blade. Experiments were undertaken on the stator suction-surface, these included hotwire boundary-layer traverses, surface hotfilm measurements and high resolution leading-edge pressure measurements. Steady CFD predictions were also performed to aid the interpretation of the results. The two leading-edge shapes gave rise to significantly different flows. For the blade with the elliptic leading-edge (Blade A), the leading-edge boundary-layer remained attached and laminar in the absence of wakes. The wake presence led to the formation of a thickened laminar boundary-layer in which turbulent disturbances were observed to form. Measurements of the trailing-edge boundary-layer indicated that the wake/leading interaction for Blade A raised the suction-surface loss by 20%. For the blade with the circular leading-edge (Blade B) the leading-edge boundary-layer exhibited a separation bubble, which was observed to reattach laminar in the absence of wakes. The presence of the wake moved the separation position forwards whilst inducing a turbulent reattachment upstream of the time-average reattachment position. This produced a region of very high momentum thickness at the leading-edge. The suction-surface profile loss was found to be 38% higher for Blade B compared to Blade A. The total loss (suction-surface and pressure-surface) for Blade B was measured to be 32% higher than that of Blade A.