1977-02-01

An Innovative Approach to the Design of a Durable Scavenge System for a Gas Turbine Engine Integral Particle Separator 770967

Gas turbine engine inlet particle separators requiring a positive extraction means subject the scavenging element to an extremely high concentration of sand and dust particles. Conventional bladed fans, if used as the scavenge means for the engine particle separator, degrade rapidly in performance and mechanical reliability and are thus limited in operational life.One solution to this problem is to design a scavenge blower such that the rotating component is afforded protection from erosion damage by means of an inertial separator incorporated into the blower inlet section. This concept, termed “self-bypassing”, diverts a fraction of the total flow into the scavenge system past the rotor. That fraction contains the majority of the particles scavenged, from the separator. Downstream of the rotor, the two flows rejoin at the mixing point of a concentric annular ejector. Thus, the exhaust from the rotor is used to expel the highly concentrated bypass stream from the system via an ejector.A prototype of this design, configured for 1.0 lb/sec airflow, 25 inches of water total pressure rise, and 50,000 rpm operating speed was tested at a sand ingestion rate of 400 gm/ hr using MIL-E-5007C type sand, 200 micron mean particle diameter. The initial design objective was 50 hours of operation with no more than 10 percent loss in airflow, simulating approximately 1000 hours of intermittent usage in hostile gas turbine environments.The initial 50-hour test showed no appreciable change in performance. A total of 120 hours of test time was required before the system flow capacity was reduced by 5 percent.A “self-bypassing” scavenge blower is applicable to installations requiring exceptional durability and compactness at modest levels of power consumption. The degree of durability achieved in this type of design is a function largely of the amount of air which is caused to bypass the rotor. Application of this versatile concept requires a tradeoff analysis between the operational life desired versus the increase in power consumption as the degree of protection is increased.

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