Aircraft Gas Turbine Blade - Coursework Example

Aircraft Gas Turbine Blade Section A) Review the function of your selected component and describe how it operates within the system of which it is apart Function The aircraft engine has a complex combustion system that applies both air and fuel mixture in a balance that enables the attainment of the required temperatures of about 1350˚C to run the engine (O’Donoghue, 1). To achieve this, there must be an efficient system that enables the appropriate supply of both the air and the fuel that contribute to constant supply of the desired mixture. Perhaps the most important aspect of the gas turbine variously referred to as the jet engine is this specificity of combustion parameters. A series of blades are aligned along the length of the jet gas turbine in order to facilitate the achievement of the high energy output required for the engine. Aircraft gas turbine blade is a component of the internal combustion engine which plays an important role; turning the air or gas that enters into the engine for mixing with fuel. After turning the gas stream in preparation for mixing with fuel, the gas turbine blade also propels and accelerates the gas into the fuel mixing phase of the engine. It is important to highlight the functions of the gas turbine blades in the jet engine with the specialized nature of the engine coming into focus. The turning of the air or gas needed in the combustion chamber must be ensured in order to facilitate compression of the air entering into the engine for mixture with the fuel. This set of blades in the series of turbine blades are referred to as compressor blades. Operation The gas turbine blades rotate with a high speed of spinning in order to carry out the above mentioned functions. The air entering the engine from the atmosphere through the sucking force created by the turbine is spun and compressed for mixing with the fuel. In he combustion chamber, the exhaust gas obtained is passed on to the turbine section of the engine and expelled on the turbine blades through a nozzle system. The turbine is powered by the energy obtained from temperature and pressure changes that the end products of combustion experience in form of exhaust gases. Propulsion from the engine is therefore in form of shaft power thrust force as well as compressed air. Compressor blades are aligned at the entrance of the engine and they also facilitate in the sucking in of air. Positioning of the compressor turbine blades at the entrance of the engine with regard to the flow of materials is important since it enables sucking in of air from the atmosphere without difficulties (O’Donoghue, 1). The other set of turbine blades is the inner blades that facilitate mixture of fuel with gas. The motion of the blades facilitates an even mixture of fuel and gas in order to supply the combustion process with the appropriate raw materials. A different type of such inner blades is also present in the combustion chamber which is turned due to the combustion process. Stator and rotor blades play different roles in the gas turbine. Section B) Describe both the operational requirements and in-service conditions for your component and relate them to the material properties required Operational Requirements In order for the gas turbine blade to be of use in the engine operations, it must meet certain requirements that meet the conditions of the combustion processes environment. While it could be difficult for several parts of a system to remain functional under high speeds of rotation as well as very high temperatures, the gas turbine cannot afford to bend the physical needs in such environment. It is therefore expected that the most appropriate design of a gas turbine blade be capable of overcoming the harsh conditions inside the gas turbine that is almost synonymous with the high efficiency combustion requirement mentioned earlier (about 1350˚C). The blades must be maintained in good shape to ensure that the functions mentioned earlier are met. Without the expected shape and condition, the various material movements could be compromised and hence the propulsion functions of the engine. In-Service Conditions Material used in the manufacture of the various blades needed in the engine must meet the high pressure and temperature that the gas turbine rotation is supposed to operate in. It is expected that material of choice is capable of withstanding deformation likely to occur due to these harsh conditions. Stresses and deformation forces must be anticipated and therefore contemplated during the design and manufacture of the gas turbine blades (Jazayeri, Naeem and Rezamahdi, 2). The blades must also be resistant to wear and corrosion as the gases brush by them at high speeds. Due to the variations in the effective stresses at the different stages of blade series along the turbine, it is important that various types of blades are used at the appropriate instances. Stress types at different stages of the engine usually give different needs for the design shapes and material for improved efficiency. For instance, a different turbine blade is required for the exhaust gas manipulation and maneuver when compared to the rotor blades at the entrance of the engine due to the temperature conditions and roles played. The blades need to have high impact strength, and resistant to creep. Section C): From a consideration of the required material properties outlined in part a), justify a material for your selected component based on maximizing functionality and minimizing weight and cost. Relevant performance indices should be used to justify material selection. Maximizing Functionality To ensure that the gas turbine blades meet the highest possible efficiency in dispensation of its expected service, various elements need to be considered the most important of which entails material selection. In the earliest days after discovery of the gas turbine, various materials were applied in the manufacture of the blade parts. However, with advancement in technology and knowledge, the most efficient material has been sought to deliver maximum performance by the blade obtained from such material. To meet the high temperature requirement that the gas turbine blade requires, it is important to use materials that can withstand high temperatures for the blades involved in the stages where the turbine involves very high temperatures. High temperature resistant materials such as nickel-based alloys have been applied in the manufacture of the gas turbine blades. However, the upper temperature limits that these alloys can withstand are slightly below the range of temperatures that the jet engine is expected to produce for full operations. For instance, the ordinary temperature that the engine is expected to operate in is around 1350˚C while the range of nickel-based allows resistance to temperatures between 1200˚C and 1315˚C. Generally, there is another challenge that faces the gas turbine blades in form of corrosion due to the harsh conditions of the turbine. To overcome the corrosion and temperature challenges that the blades experience, there are additional modifications that the nickel-based alloys and other super-alloys used to manufacture the blades are subjected to (Blackford, 15). One of the modifications of the turbine engine is its design such that air is introduced into the turbine and allowed to flow on the blade on specific cooling channels thereby reducing the effective temperatures to below the melting temperatures of the alloy. Other modifications include introduction of specified coatings that can withstand higher temperature than the alloy. Other coatings that can overcome the corrosive conditions that the gas turbine exposes the blade to are effected on the blade to facilitate improved functionality. Various elements have been used to facilitate high temperature and corrosion resistance in gas turbine blades. Aluminades and aluminides are the commonest type of coatings that are applied onto gas turbine blades to improve functionality against oxidation and corrosion. Other coatings are ceramic materials such as zirconia that are used in conjunction with other alloys to reduce heat deformation. Minimizing Weight and Cost Perhaps the most conspicuous feature of the gas turbine that has improved its operation while retaining its operation needs is the reduction in size. Such reductions in size not only reduce the cost of materials that the turbine blades require but also reduce the mount of materials needed for the rest of the turbine. Reduction in size and material subsequently translates into reduced costs of manufacture and maintenance. This is particularly the case due to the need to increase efficiency of the turbine and maximize its operation life through reduced maintenance. The use of superalloys and coatings in conjunction with other cooling techniques eliminates the need of more the expensive procedure of maintenance and replacement of blades (Sourmail, 1). If higher efficiency is achieved on the blades operation, it is expected that the fuel consumption will also go down thereby reducing the cost of operating the gas turbine. Section D) Assuming that your selected component is required in a large batch quantity (10,000), justify and explain a manufacturing route. Manufacturing Route There are a number of procedures that can be employed in the manufacture of gas turbine blades. The most basic one is referred to as the investment casting which involves the liquefaction of the particular material for use in the manufacture of the gas turbine blade (Deepaksibudhi, 18). Liquefaction of the alloy requires the thermal conditions specified by the physical attributes of the alloy in order to achieve the threshold temperatures. Meanwhile, a mould made of ceramic material is prepared and heated in order to enable the development of the desired design upon pouring the molten alloy. For the mould to achieve the function that it is intended, it must be place on a cold chill plate that is made of copper immersed in water for cooling purposes. This process is done in a manner that enables the formation of thin layers after every pour of the molten alloy on top of the cooled down layer. A thermal gradient is established between the containing material that the molten alloy is poured onto, that is the copper chill plate and the ceramic mould. Several layers of alloy are poured onto the developing grain structure until the mould cavity is filled up while also ensuring that the chill plate is in line with the grain surface. After cooling down, the developed blade is treated with heat to facilitate strengthening of the formed grains. Heat treatments include annealing of the layers, tempering, hardening and case hardening and gas quenching before polishing up on the obtained blades. Besides, the treatment is useful in ensuring that undesirable contaminants such as carbides and borides are eliminated through fractional precipitation along the boundaries of the achieved grains. The next step is forging of the molded blade which happens in a closely monitored range of temperatures to ensure that the structure of the alloy remains in a good condition. Forging is done to enhance the shape of the blade as needed in the turbine design (Moradi and Nayebsadeghi, 19). In addition to forging, several machine stages are carried out on the unfinished design through processes such as profile grinding and cutting, root cutting and hand grinding. Additionally, the blade is subjected to sand blasting which is supposed to enhance the internal bonding of the blade after machining. Alternatively, the blade is passed on to the coating process where various heat and corrosion eliminating treatments are carried out. Inspection is usually finally facilitated on the finished blades read for packaging and delivery to the market. Due to the large number of the large number of units needed through the production process, a simplified process should be outlined. The procedure is expected to capture all the important elements of the necessities that the blade ought to comply with for the conditions it is subjected to. Section E) Explain how your selected manufacturing route influences the microstructure of the material and the consequent affect on properties. Influence on Microstructure As observed in the above investment casting technique, there are a number of treatments that the manufactured blade is subjected to, particularly the heating and the coating procedures. Heat treatments are influential in the atomic structure and state of the material in question in different ways. Features of the blade at the microstructure level can be established to determine if there are changes on the properties of the material used and hence implicate the operation of the gas turbine blade (Slovak Academy of Sciences, 1). It is important to set the treatment temperatures within the optimum temperatures that cannot distort the microstructure features needed for the exhibition of the desired properties such as strength. In the above selected manufacture process, temperatures for the various treatment types will be enhanced within the optimum temperatures that cannot damage the material features at the microstructural level. The alloy to be used in making the blade is annealed to soften it in readiness for cold forging and machining or to relieve residual stresses after casting. The process also refines the grains and makes the structure of the alloy homogeneous. Hardening and quenching on the other hand are done to increase the strength of the metal used. During the quenching process, Pearlite which is a mixture of cementite and ferrite is transformed into martensite with a needle-like, fine grain structure. This process makes the metal resistant to plastic deformation and resistant to wear. Bibliography Blackford, J. “Engineering of Superalloys: Gas Turbines,” n.d. Web. http://www.cmse.ed.ac.uk/AdvMat45/SuperEng.pdf (accessed 8 July 2011) Burns, J., “Gas Turbine Engine Blade Life Prediction for High Cycle Fatigue,” The Technical Cooperation Program (TTCP), P-TP1, 1998. Print Conor, P.C. “Compressor Blade High Cycle Fatigue Life-Case Study,” The Technical Cooperation Program (TTCP), P-TPI, 1998. Print Jazayeri, S. A., Naeem, M. T. & Rezamahdi, N. K. N. “Failure Analysis of Gas Turbine Blades,” 2008. Web. http://www.ijme.us/cd_08/PDF/120,_ENG_108.pdf (accessed 8 July 2011) Moradi, M. & Nayebsadeghi, M. “3D Simulation of the Forging Process of a Gas Turbine Blade of Nickel-Based Superalloy,” Canadian Journal of Mechanical Sciences and Engineering, 2.2(2011):19-22 O’Donoghue, L. “Why Don’t Gas Turbines Blades Burn?” n.d. Web http://www.ul.ie/elements/Issue6/Gas%20Turbine%20Blades.htm (accessed 8 July 2011) Slovak Academy of Sciences “Effect of Heat Treatment on Microstructure and Mechanical Properties of Gas Turbine Intermetallic Ti-46al-2w-0.5si Blades,” (n.d). Web. http://www.umms.sav.sk/index.php?ID=613 (accessed 8 July 2011) Sourmail, T. “Coatings of Turbine Blades,” n.d. Web. http://www.msm.cam.ac.uk/phase-trans/2003/Superalloys/coatings/index.html (accessed 8 July 2011) Subudhi, M. “Manufacture of Aircraft Turbine Blades,” (n.d). Web. http://www.scribd.com/doc/14170736/Manufacture-of-Aircraft-Turbine-Blades (accessed 8 July 2011) Walls, D.P., Delaneuville, R.E., and Cunningham, S.E., “Damage Tolerance Based Life Prediction in Gas Turbine Engine under Vibratory High Cycle Fatigue,” Journal of Engineering for Gas Turbines and Power, 119(1997):143–146. Read More