Dynamic Behaviour of “Hybrid Composite Shaft Rotor-Bearing System” of an Aero Gas Turbine Engine

Abstract

In the present study, the hybrid composite shaft's dynamic behaviour is evaluated in detail with the primary intention of using it in the high-speed rotor-bearing system of an aero gas turbine engine. In this research work, the top-down research approach is adopted wherein the most appropriate rotor-bearing system for the composite shaft application was first assessed. A preliminary rotor dynamic study was carried out on the three prospective rotor-bearing systems to verify the possibility of using the composite shaft. The preliminary rotor dynamic study indicated that the power turbine rotor-bearing system of a front driving turboshaft engine powering the rotorcraft as the most suitable application of composite shaft. To avoid the gas turbine engine's high temperatures, the composite shaft was proposed to be within the compressor section while the existing steel alloy was retained in the hot section. The hybrid composite shaft made of composite material sandwiched between the steel tubes was envisaged to avoid the direct exposure of composite material to the gas turbine's harsh environment and for the easier interface with the subsequent metallic assembly. A parametric study was carried out to select the right combination of material, thickness, and stacking sequences of the composite laminate layers. The mechanical characterization was carried out to estimate the material strength using a universal testing machine. The damping estimation was carried out using the free vibration and dynamic mechanical analysis techniques. Based on the parametric study and characterization tests, the carbon-epoxy laminate of 10 layers with the stacking sequence of [90, 45, -45, 06, 90] sandwiched by steel was found to be the best material configuration for the hybrid power turbine shaft. Finally, the rotor dynamic analysis of the power turbine shaft was carried out for a couple of variations in the thickness of steel tubes and length of the hybrid shaft to obtain the best configuration in comparison to the existing steel shaft. The results obtained in this work have successfully demonstrated the utility of the hybrid composite shaft in line with the objectives laid down for the thesis work.