3D Finite Element Vibrational Analysis of T385 Turbine Rotor BLISK Using SAFE Diagram

Abstract

Integrally bladed rotors (BLISK) are most stressed part of aircraft engines due to high rotational speeds, elevated temperatures and pressures. Turbine blades fail mainly due to fatigue under alternating stresses resulting from vibration of rotor systems. Non-uniform pressure field is experienced by turbine BLISK due to interaction of stator and rotor blades which acts as a source of excitation during turbine operation. The number of stator blades dictates the occurrence of resonance in the rotor BLISK during steady-state operation. Therefore, it is necessary to design a mechanically feasible rotor with respect to stator and verify its modal and harmonic response to ensure its resonance-free operation. Design and development of T385 turbine stage for 1 kN small gas turbine engine are carried out in Propulsion Division, CSIR-NAL. The dynamic behaviour of T385 turbine rotor BLISK is evaluated for vibration reliability. This paper presents vibrational analysis of the T385 turbine rotor BLISK using finite element technique to evaluate critical nodal diameter, critical frequencies and response in engine environment. The turbine speed is 50,500 rpm at the engine design point based on the inlet temperature. Detailed vibration analysis of T385 turbine is carried out using FEA to plot Campbell and SAFE diagrams. The critical nodal diameter extracted from plotted SAFE diagram is 19, which is very well agreeing with Bertini analytical formulae. The Campbell diagram is plotted for T385 turbine at critical nodal diameter of 19. The obtained critical speed from this Campbell diagram is 33,000 rpm, which ensures the rotor is safe in the operating conditions.