Response of Large Turbofan and Turbojet Engines to a Short-Duration Overpressure

The influences of thrust setting and overpressure level on engine operating characteristics have been obtained for two different high-thrust engines. The thrust setting was varied from engine-off to take-off rated thrust (TRT) and the overpressure was varied from 6.9 kPa (1.0 psi) to 19.4 kPa (2.8 psi). The specific engines under consideration were the Pratt/Whitney TF33 low bypass ratio turbofan and the Pratt/Whitney J57 turbojet. The experimental results suggest that overpressure has little influence on either the HP compressor speed or the exhaust gas total temperature. However, the magnitude of the overpressure has a large influence on turbine exhaust total pressure and on the inlet casing and the diffuser casing radial displacements. The J57 turbine casing was significantly influenced by the overpressure, whereas the TF33 turbine casing was relatively insensitive. The J57 inlet casing radial displacement was noticeably greater than the corresponding turbofan displacement. Even though the component radial displacements for the TF33 exceeded the steady-state red-line limit by more than 300 percent, the engine did not sustain any permanent damage. The J57 did, however, experience an internal rub at an overpressure of about 14.5 kPa (2.1 psi).