Development of Reduced Order Strain Model for Life Assessment of a Gas Turbine Rotor Blade

Compressor rotor blades of Gas Turbine Engines are critical components in the flow path. Their durability is determined by Life and integrity at different operating conditions. These blades experience stresses due to body loads and complex bending stresses due to the aerodynamic work done. While it is essential to establish adequate safety margins in the rotor blade during the design phase, it is equally important to monitor the life that is being consumed in actual operation at different combinations of mass flow rate, pressure and speeds depending on the aero-thermodynamics at various altitudes and manoeuvre conditions. A Meta model is developed with strain as the response surface in terms of mass flow rate and rotational speed as the controlling parameters. Design of Experiments using FEM is conducted for nine combinations of these parameters from which a generic strain model is constructed. This model is capable of predicting the strain in the rotor blade for any engine operating point which in this case is essentially a function of the mass flow and rotational speed of the rotor blade. At the same time, few of these rotor blades have been strain gauged during developmental engine tests for strain/health monitoring. Strain data obtained from engine testing at various operating points is utilized to correlate the aforementioned response model developed wherein good correlation is observed and the error is within 5%. Strain responses predicted from the meta model at respective engine operating points are then used to arrive at the strain ranges the blade would encounter during operation. Rain flow cycle counting method in conjunction with life models are used to arrive at the damage fraction in the rotor blade during each engine test cycle. Damage is cumulated over repeated usages in the engine to arrive at residual life of the rotor blade.