The subsonic/transonic stall flutter characteristics of the Pratt & Whitney PW1120 Low Pressure Compressor (LPC), recently have been defined through fan rig tests and a full-scale engine test. Flutter data analyses, based on both empirical and analytical methods, have shown excellent correlations between test results and predictions. While the LPC was demonstrated to be flutter-free over its entire flight envelope, the study indicates the need for continued research in transonic unsteady aerodynamics, particularly, the effects of passage shocks and large leading edge incidence.
Vibratory stress characteristics of the low pressure compressor in the Pratt & Whitney Aircraft PW1120 turbojet engine recently have been evaluated during full-scale engine testing at the United States Air Force’s Arnold Engineering Development Center. A description is presented of the approach used to evaluate the vibratory characteristics of the new three stage low pressure compressor. Results are presented showing the effects of simulated altitude conditions, inlet pressure distortion, and off-schedule variable vane operation. Strain gage data is compared to case-mounted light probe data, and the levels of system damping and mistuning are discussed. Predicted vibratory response is compared to test results showing the new compressor to be free of destructive vibration.
The development of gas turbine engines has been keyed primarily to increases in thrust-to-weight ratio and to greater demands for structural durability. In fewer than 20 years, the thrust-to-weight ratio of turbine engines has doubled, as demonstrated by the F100-PW-100 engine compared to the J75. Also, a new engine life parameter, low cycle fatigue, was recognized. This new parameter results from stress variations in the engine hardware during thrust level excursions and is now included in the latest engine Military Specification (MIL-E-5007D). Since current projections of propulsion systems for the next decade show a continuing trend of increases in thrust-to-weight ratio and required durability, highly sophisticated time-phased structural analysis and verification methodology is being developed [Reference 1] for future engine development programs. This methodology is intended to ensure that the risk of structural distress, which is a primary cause of “high-costs” during system development and after deployment is minimized, and to provide a reliable understanding of the systems structural capability to facilitate expansion of the overall weapons systems to counter new “threats.” The following discussion describes the principal features of the methodology developed.
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