Strength calculation of gas turbine engine main elements

Strength calculation of HPT 1st stage rotor blade

During engine operation static, dynamic and temperature loads act on a turbine rotor blade. Dynamic and temperature loads are not taken into account because of their analytical determination complexity, but they are assigned by statistical experimental data or considered for a strength safety factor selection.

Such operational static loads are the centrifugal forces of blade weights caused by rotor rotation, gas forces caused by action of gas flow around a blade airfoil and a difference of a gas pressure before and after a blade.

The centrifugal forces cause blade tensile deformations, its bending and torsion, and gas forces cause bending and torsion of the blades. For strength calculations the most loaded details of a gas turbine engine (GTE) rotor are selected. Such details are the elements of a high pressure (HP) rotor. Therefore the rotor blades and shafts of high pressure turbines (HPT) are selected as the objects for strength calculations.

The tensile stresses are largest in turbine rotor blades. The bending stresses are considerably smaller and make approximately 20…30 % of tensile stress value.

The given technique allows making a strength calculation of a turbine rotor blade in its root section at static loading caused by gas forces and owning centrifugal forces of profile part and shrouding cap. Other types of loads are not taken into account in view of their small values. The maximum stresses determine by toting of tensile and bending stresses in three points A, B and C of blade section, most remote from main axes of inertia.

Calculation will be finished by determination of blade function-ability with the help of long-term strength safety factor.

At blade strength calculation it is necessary to allow following:

·          it is necessary to recalculate the parameters of velocity triangle in blade mean radius for contouring of blade root section;

·          the material of rotor blade is selected according to a design temperature of a blade;

·          for simplification of blade strength calculations the area of cooling channels is not taken into account;

·          the total stresses in each point A, B and C are compared to a  long-term strength of a selected material on the basis of 100 hours for a design value of blade temperature.

·          The strength calculation of turbine rotor blade includes:

·          determination of gas flow parameters in blade root section for its contouring;

·          construction of an profile of blade root section and definition of its geometrical characteristics;

·          determination of tensile stresses in blade root section caused by centrifugal forces;

·          determination of bending stresses in specific points of blade root section caused by gas forces;

·          determination of total stresses in these three points of a profile;

·          determination of long-term strength safety factors in each of three specific points of blade root section;

·          conclusions about strength of a blade