The Effect of Ultrapolish on a Transonic Axial Rotor

Back-to-back testing was done using NASA fan rotor 67 in the Glenn Research Center W8 Axial Compressor Test Facility. The rotor was baseline tested with a normal industrial root-mean-square (RMS) surface finish of 0.5 μm to 0.6 μm (20 microinches to 24 microinches) at 60, 80, and 100% of design speed. At design speed the tip relative Mach number was 1.38. The blades were then removed from the facility and ultrapolished to a surface finish of 0.125 μm (5 microinch) or less and retested. At 100% speed near the design point, the ultrapolished blades showed approximately 0.3% to 0.5% increase in adiabatic efficiency. The difference was greater near maximum flow. Due to increased relative measurement error at 60 and 80% speed, the performance difference between the normal and ultrapolished blades was indeterminate at these speeds.