Experimental Study on the Flow Past Sinusoidal Leading Edge Serrations in a Compressor Cascade

The leading edge serrations are a type of passive flow control techniques in a compressor cascade. They are particularly attractive as they have been observed to increase the stall angle. This stall postponing character of the serrations is helpful in preventing compressor surge and widens the operational window of the compressor. Due to the simpler geometry of the serration type used in this study, it can be easily implemented onto the existing compressor blades. An experimental study on the flow modifications and losses due to these serrations are conducted in a linear cascade tunnel. The experiments are conducted on blades of NACA 65209 airfoil with and without leading edge serrations at Re of 120,000. Four serration profiles of various width and amplitude are compared. End plane measurements taken with 5-hole probe are studied for the better serration profile and surface flow visualizations are conducted to study the variation in the surface flow pattern on the suction side. The surface flow visualization reveals the presence of local recirculation zones and stream wise vortices created from each wave of the serration leading to flow attachment. These serrated blades have higher losses at 0 deg incidence; the reason for the same is found to be the flat leading edge surfaces formed from serration.