Analysis and design of rotor blades due to the transient thermal and vibratory loads

Abstract

The research work carried out in this thesis deals with the transient thermal and vibratory analysis of a gas turbine rotor blade. The design criteria of a rotor blade is suggested after studying the combined effects of the vibratory and thermal stresses on the turbine blade. -- The non-linear equations for the transient temperature distribution within the airfoil cross-section of the blade are derived using the finite element analysis. The non-linearity in these equations is due to the radiative heat transfer and-also due to the variation of the material properties of the blade with temperature. The non-linear differential equations are transformed to the non-linear algebraic equations in the time domain using a finite difference scheme. The temperature gradients and the thermal stresses are calculated from the transient temperatures obtained from the heat transfer analysis. -- The mathematical model for the vibratory analysis is formulated using solid, quadratic, isoparametric finite element's. The stiffness and mass matrices are integrated using Gaussian quadrature. A dynamic matrix reduction technique is used to condense the global stiffness and mass matrices of the blade. The free vibration analysis of the blade is carried out using the condensed system matrices. The effects of the transient temperature distribution and the angle of pre-twist on the undamped natural frequencies of the rotor blade are studied. -- The vibratory stresses are calculated due to nozzle excitation and centrifugal forces. The nozzle excitation forces are modelled as a series of impulses using the kinematic equations. The principal stresses are obtained from the vibratory stress vector and the design of the rotor blades is based on the distortion energy stress.