Gas turbine rotors are high speed rotating components which operate under high temperatures. These turbine rotors undergo repeated cycles of low speeds to high speeds and therefore low stresses to high stresses which lead to low cycle fatigue failure. This low cycle fatigue leads to initiation of cracks at high stress areas like bolt holes, blade slots or disc bore. During design the life obtained through numerical methods is verified by cyclic spin tests. This particular paper talks about the spin testing of turbine rotor assembly of a turbo-shaft engine to validate its low cycle fatigue life obtained through analysis. These three stage turbine rotors were indigenised for cost savings. The life of the indigenously designed rotors were required to be the same as the turbine rotors being supplied by the engine OEM’s. Since the test rig which was used to validate the life of the rotors had a limitation of applying uniform temperatures, there was a need to develop a test schedule that simulates the operating conditions of the actual engine rotors.
The work was carried out in two phases. In the first phase FEA tools were utilised to find out stress and strain levels of the turbine rotors by applying actual engine load conditions. Since rotor assembly was tested under uniform temperature in the test rig a combination of centrifugal load and temperature that would result in the same factor of safety levels of the rotors as in the actual engine conditions was arrived at in an iterative manner. Once the right combination was achieved the life of the engine rotors under test conditions was estimated numerically. In the second phase cyclic spin test was carried out on the turbine rotor assembly at equivalent load conditions. At regular intervals dimensional and NDT checks were carried out on the rotor assembly to find out crack initiation. The life of the rotor assembly which was estimated with the help of FE tool was validated through spin test.