01-09-2012, 04:54 PM
Analysis of Gas Turbine Blades with materials N155 & INCONEL718
Analysis of Gas Turbine.pdf (Size: 765.3 KB / Downloads: 89)
Abstract
The analysis of Stress values that are produced while the turbine is running are the key factors of study while designing the gas turbines. A gas turbine Rotating system is loaded with time by the changes in stress levels as a result of start up and shut down procedures. Hot section blades typically fail because of creep, oxidation, low cycle fatigue and High cycle fatigue.
Therefore this report has primarily focused on heat transfer characteristics, centrifugal and thermal stresses in the blade. The maximum stresses obtained from different analysis by using innovative high heat resistant material N155 are found to be within the yield strength of the material. Results are obtained interms of thermal stresses,Vonmisses stress are compared with high heat resistant material INCONEL 718.Inspite of all operating conditions the blade with material INCONEL 718 is expected to perform well .The object is to improve the life and efficiency of future generation of engines.
Introduction
The purpose of turbine technology are to extract the maximum quantity of energy from the working fluid to convert it into useful work with maximum efficiency by means of a plant having maximum reliability, minimum cost, minimum supervision and minimum starting time.
The gas turbine obtains its power by utilizing the energy of burnt gases and the air which is at high temperature and pressure by expanding through the several rings of fixed and moving blades to get a high pressure of order 4 to 10 bar of working fluid which is essential for expansion. The pressure and Speed required at the inlet is very high so a centrifugal or axial compressor is required at the inlet. The turbine drives the compressor so it is coupled to the turbine shaft. If after compression the working fluid were to be expanded in a turbine, then assuming that there were no losses in either component, the power developed by the turbine can be increased by increasing the volume of working fluid at constant pressure or alternatively increasing the pressure at constant volume. Either of these may be done by adding heat so that the temperature of the working fluid is increased after compression. To get a higher temperature of the working fluid a combustion chamber is required where combustion of air and fuel takes place giving temperature rise to the working fluid.
Finite Element Modeling
The finite Element model used in this analysis. The time steps are varied and the results are stored in load step files.ANSYS allows the thermal analysis to be conducted first and then the results are automatically transferred to the structure model.
For the finite element representation of a problem the nodal values of the field variable become the unknowns. Once these unknowns are found, the interpolation functions define the field variable throughout the assemblage of elements. Clearly, the nature of the solution and the degree of approximation depend not only on the size and number of the elements used but also on the interpolation functions selected. As one would expect, we cannot choose functions arbitrarily, because certain compatibility conditions should be satisfied. Often functions are chosen so that the field variable or its derivatives are continuous across adjoining element boundaries. These are applied to the formulation of different kinds of elements. Thus far we have briefly discussed the concept of modeling an arbitrarily shaped solution region with an assemblage of discrete elements, and we have pointed out that interpolation functions must be defined for each element. We have not yet mentioned, however, an important feature of the finite element method that sets it apart from other numerical methods. This feature is the ability to formulate solutions for individual elements before putting them together to represent the entire problem. This means, for example, that if we are treating a problem in stress analysis, we find the forceādisplacement or stiffness characteristics of each individual element and then assemble the elements to find the stiffness of the whole structure. In essence, a complex problem reduces to considering a series of greatly simplified problems.
Conclusions
The results and conclusions are presented for a study concerning the durability problems experienced with gas turbine engines. The investigation encompassed the design and failure history of hot gas path components in the engines. The maximum operational Vonmises Stresses are within the yield strength of the material but the deformation is comparatively better for material INCONEL 718.
The present study has conducted detailed heat transfer analysis on the blade using different materials. This study has primarily focused on the centrifugal and thermal stresses arising in the blade for two materials. From the results obtained it is noted that the values are in tolerance limit for material INCONEL 718