In the present study, the effectiveness of passive structures called tubercles on an axial compressor blade row is studied experimentally. Tubercles are the modifications to the leading edge of an airfoil in the form of blunt wave-like serrations. Although several studies on the effect of tubercles on isolated blades are available in literature, detailed study of their effect on a cascade of blades, such as in the case of an axial flow turbo-machine is lacking. Such an application in an axial compressor will result in a significant increase in the stall margin. Presently, experiments have been performed on a linear compressor cascade with a blade height of 0.15 m and mean chord of 0.06 m, on a NACA 65209 airfoil profile. The plain and modified blades are fabricated using rapid prototyping to ensure conformity to the required geometry. The cascade is designed in such a way that the incidence (angle of attack) and the stagger can be changed easily. The measurements are taken at the exit plane using a five-hole Pitot probe to obtain three-components of velocity and static pressure data over fine measurement grids. The effect is determined in terms of lift and drag coefficients, lift-to-drag ratio and total pressure loss coefficient. Experiments have been carried out for different pitch and amplitude (serration depth) of tubercles to understand their effect. The stall incidence angle for the best performing blade is found to increase up to 8.6° from that of the unmodified blade of 6.0°. Application of such structures in axial compressor blades may well be adequate to prevent stalling in axial compressors over a wide operating range.
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