Erosion of T56 5th Stage Rotor Blades Due to Bleed Hole Overtip Flow

Severe trailing edge erosion of ALLISON T56 gas turbine 5th and 10th stage compressor blades has been observed in Field Service Evaluations and sand ingestion tests. The erosion typically occurs within 3 mm of the blade tip and has been attributed to overtip flow produced by the bleed holes present over the 5th and 10th stage rotors. The overtip flow through the 5th stage bleed holes of an operating T56 has been surveyed with a laser two-focus (L2F) velocimeter in order to identify the features of the flow field responsible for the tip erosion. Two-dimensional measurements were made at 4 spanwise locations in the outer 25 percent of the span. Three-dimensional measurements were made at three spanwise stations within 7 mm of the blade tip (15 percent of span). The flow was found to be unaffected by the bleed holes beyond 3-4 mm from the blade tip. This result is consistent with erosion patterns observed on service-exposed blades and blades subjected to accelerated erosion in sand ingestion tests.