Novel Compressor Blade Design Study

Jet engine eciency goals are driving compressors to higher pressure ratios and engines to higher bypass ratios, each one driving to smaller cores. This is leading to larger tip gaps relative to the blade height. These larger relative tip clearances would negate some of the cycle improvements, and ways to mitigate this eect must be found. A novel split tip blade geometry has been created which helps improve the eciency at large clearances while also improving operating range. Two identical blades are leaned in opposite directions starting at 85% span. They are cut at mid chord and the 2 halves then merged together so a split tip is created. The result is similar to the alula feathers on a soaring bird. The concept is that the split tip will energize the tip ow and increase range. For higher relative tip clearance, this will also improve eciency. The 6th rotor of a highly loaded 10 stage machine was chosen as the baseline for this study. Three dimensional CFD simulations were performed using CD Adapco\’s Star-CCM+ at 5 clearances for the baseline and split tip geometry. The choking ow and stall margin of the split tip blade was higher than that of the baseline blade for all tip clearances. The pressure ratio of the novel blade was higher than that of the baseline blade near choke, but closer to stall it decreased. The sensitivity of peak eciency to clearance was improved. At tight clearances of 0.62% of blade height, the maximum eciency of the new design was less than the baseline blade, but as the tip clearance was increased above 2.5%, the maximum eciency increased. Structural analysis was also performed to ascertain the feasibility of the design.