Damageability of Gas Turbine Blades – Evaluation of Exhaust Gas Temperature in Front of the Turbine Using a Non-Linear Observer

Abstract

A turbine is a fluid-flow machine that converts enthalpy of the working agent, also referred to as the thermodynamic agent (a stream of exhaust gas, gaseous products of decomposition reactions or compressed gas) into mechanical work that results in the rotation of the turbine rotor. This available work, together with the mass flow intensity of the working agent, define power that can be developed by the turbine and subsequently used to drive various pieces of equipment (e.g. compressors of turbojet engines). The basic advantages of gas turbines include: possibility to develop high power at rather compact dimensions and low bare weight, relatively high efficiency of the energy conversion process, simple design and high reliability of operation (Blachnio, 2004, 2007; Kroes et al., 1992; Sieniawski, 1995). On the other hand, the drawbacks are: high operating temperatures of some components, sophisticated geometrical shapes of the components, e.g. blades and vanes, which makes the manufacturing process difficult, as well as high working speeds of rotors that impose the need to apply reduction gears, e.g. when turbine-power receivers show limited rotational speeds. Because of the direction of flow of the exhaust gas, turbines are classified as axial-flow and radial-flow systems. Each turbine is made up of two basic subassemblies that compose the turbine stage.  A stationary rim with profiled vanes fixed co-axially (axial-flow turbines) or in parallel (radial-flow turbines), i.e. the so-called turbine nozzle guide vanes, or shortly, the stator;  A moving rim (one or several ones) with profiled blades fixed circumferentially (axialflow turbines) or on the face surface (radial-flow turbines) of a rotating disk seated on the shaft, i.e. the turbine blade rim.  Depending on the distribution of the inlet energy of exhaust gases among basic subassemblies, turbines are classified as:  action (impulse) turbines, the exhaust gases are subject to decompression exclusively in turbine nozzle guide vanes,  reaction turbines the exhaust gases are decompressed by both the guide vanes (stator vanes) and in the turbine rotor.