Abstract
In this study the main causes of the failure of a GE-F9 second stage turbine blade were investigated. The stress distribution of the blade which has 6 cooling vents in three modes (with full cooling, closure of half of the cooling channels, and without cooling) was studied. A three dimensional model of the blade was built and the fluid flow on the blade was studied using the FVM method. The stress distribution due to centrifugal forces applied to the blade, temperature gradients and aerodynamic forces on the blade surface was calculated by the finite element model. The results show that the highest temperature gradient and as a result the highest stress value occurs for the semi-cooling state at the areas near the blade root and this status is true for the full cooling mode for the regions far from the root. However, the field observations showed that the failure occurred for the blade with the semi-cooling state (due to closure of some of the channels) at areas far from the root. It is discussed that the main factor of the failure is not the stress values being maximum because in the state of full cooling mode (the state with the maximum stress values) the temperature of the blade is the lowest state and as a result the material properties of the blade show a better resistance to phenomena like hot corrosion and creep.
Highlights
One of the important components of gas turbines is their moving blades which are under mechanical and thermal stresses due to high-speed rotation and exposure to high temperatures
In the sight of theory, the thermal stresses, static and dynamic forces that affect the performance of the turbine blades are as follows: – the aerodynamic forces of flow; – the stresses resulting from temperature gradient; – forces due to centrifugal effect
In order to find the temperature distribution and Stress caused by temperature gradients in the blade, 4 sections are considered with similar distances in the blade according to Figure 9 for all three cooling modes
Summary
One of the important components of gas turbines is their moving blades which are under mechanical and thermal stresses due to high-speed rotation and exposure to high temperatures. In recent years, many studies have been done to estimate temperature and stress distribution of the turbine blade [3], turbulence intensity of the streamline [4,5], the Reynolds number and Mach number [6,7], to experimentally study the effect of cooling temperatures and mass flow on the heat transfer distribution on the turbine blades [8], swirl effects of unsteady vortices [9,10] as well as the tip and shape of the blade [11,12] In addition to these experiments, numerical studies have been carried out using CFD codes developed based on the Navier-Stokes equations and boundary layer.
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