Abstract
Aero Gas Turbine engines power aircrafts for civil transport application as well as for military fighter jets. Jet pipe casing assembly is one of the critical components of such an Aero Gas Turbine engine. The objective of the casing is to carry out the required aerodynamic performance with a simultaneous structural performance. The Jet pipe casing assembly located in the rear end of the engine would, in case of fighter jet, consist of an After Burner also called as reheater which is used for thrust augmentation to meet the critical additional thrust requirement as demanded by the combat environment in the war field. The combustion volume for the After burner operation together with the aerodynamic conditions in terms of pressure, temperature and optimum air velocity is provided by the Jet pipe casing. While meeting the aerodynamic requirements, the casing is also expected to meet the structural requirements. The casing carries a Convergent-Divergent Nozzle in the downstream side (at the rear end) and in the upstream side the casing is attached with a rear mount ring which is an interface between engine and the airframe. The mechanical design parameters involving Strength reserve factors, Fatigue Life, Natural Frequencies along with buckling strength margins are assessed while the Jet pipe casing delivers the aerodynamic outputs during the engine operation. A three dimensional non linear Finite Element analysis of the Jet pipe casing assembly is carried out, considering the up & down stream aerodynamics together with the mechanical boundary conditions in order to assess the Mechanical design parameters
Highlights
While operated at maximum material strength limits, Jetpipe is subject to elasto-plastic condition locally at stress concentrated locations and strain based lifing methodology is used for assessing Low Cycle Fatigue (LCF) life cycles
Based on the further investigations, Manson along with Gary Halford proposed a method in the form of Universal slope equations [11] for the estimation on Low Cycle Fatigue behaviour of Materials in 1967
Linear order shell elements with 6 dof/node were used for the Finite Element model as the casing is a thin shell like member
Summary
There has been continued demand worldwide for higher performance lighter fighter aircrafts for various military related missions in defence sector This has led to development of efficient aero engines capable of providing high thrust / weight ratios [1], low specifics fuel consumption as well as improved component lifing. This led to a major shift in current aero engine design and lifing philosophy, especially in military sector – replacing multiple stages of turbine or compressor to a fewer ones but more heavily loaded stages, replacing heavier steels and nickel based super alloys by high strength-low density materials [3-4] such as Titanium alloys in compressor module, replacing solid blades design by more complex hollow ones for achieving higher TET [5] (Turbine Entry Temperature) levels by cooling channels, replacing polycrystalline microstructure to directionally solidified to single crystal for improved high temperature capabilities of materials, requiring development of strategic investment casting technologies in place of conventional wrought ones and replacing Safe life [6] based design philosophy to more advanced ones such as fracture mechanics and damage mechanics
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