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Structural design of aircraft engines: Key obectives and techniques article pay-per-view 25€/article

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The continuous trend in weight reduction together with novel engine architectures results in large structural and thermal loads, with narrower security margins. The lecture note on aircraft engine reviews the main challenges of structural design of an aircraft engine, and the associated certification constraints. The first part of these proceedings addresses the engine behaviour (whole engine dynamics, impacts, and thermal loads). Whole Engine dynamics overviews how to model the different elements of the engine to study the dynamic behaviour of the assembled system while respecting design criteria. Foreign object damage and fan blade out describes the methodologies currently used to perform simulations in compressor blades to predict the integrity of the structure.

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The continuous trend in weight reduction together with novel engine architectures results in large structural and thermal loads, with narrower security margins. The lecture note on aircraft engine reviews the main challenges of structural design of an aircraft engine, and the associated certification constraints. The first part of these proceedings addresses the engine behaviour (whole engine dynamics, impacts, and thermal loads). Whole Engine dynamics overviews how to model the different elements of the engine to study the dynamic behaviour of the assembled system while respecting design criteria. Foreign object damage and fan blade out describes the methodologies currently used to perform simulations in compressor blades to predict the integrity of the structure.

Another set of notes is focussed on bladed disk design, from the standard aeromechanical design practices to more complex problems such as aeroelastic stability. The aeromechanical design of bladed disks explains the iterative process to find the optimum compromise between aerodynamic performance and structural strength. Forced response prediction proposes an alternative approach to mitigate the development risk by estimating the forced response early before the engine testing. The lecture note on flutter presents a description of the steps in the design analysis process, with examples in fans and low pressure turbines. Comparisons are given of 2D/3D, inviscid/viscous, linear/nonlinear, and single blade row/multi-stage methods. The airfoils of bladed disks and blisks vary due to manufacturing processes and field usage. This condition is known as “mistuning” and has the potential to affect significantly flutter and forced response.

The third part addresses high cycle fatigue, design strategies to mitigate forcing and the state of the art on aeroelasticity research. The non linear dynamics lecture note discusses the damping properties caused by friction, aerodynamic viscous and hysteretic dissipation effects on the alternating stresses. The Harmonic Balance Method used for the linearization of friction forces, and the physical interpretation of blade vibrations with friction dissipation at shrouds and on dampers are taken into consideration. A major goal in the development process of rotating turbomachinery turbine blades is to prevent them from high cyclic fatigue (HCF) failure. The Stress-Life method, are discussed in relation to Goodman’s, Soderberg’s, Morrow’s, Gerber’s and Bagaci’s equations. Essential information about the linear and non-linear hypotheses for the prediction of the cumulative damage is reminded briefly. The evaluation of stochastic vibrations is analyzed considering engineering needs. Design strategies to mitigate unsteady forcing presents a successful example of resonant-stress reduction through mitigation of unsteady forcing during the aerodynamic design of turbine components. This includes a discussion of techniques for appropriate code validation and assessment of the quality of time-resolved fluid-dynamic analyses used to predict resonant stresses during the design cycle. Experimental research on aeroelasticity elucidates possible methods for the experimental investigation of aerodynamic damping and forcing as well as discuss relevant measurement techniques. It concludes with giving an overview of testing facilities in aeroelasticity research.

The last part is focussed on the mechanic behaviour of material and life estimation. A global overview on material science is given. Then the process and rules to estimate the life of components versus fatigue and creep is presented. Two consecutive lecture notes on materials associate the temperatures of different engine parts with material alternatives from polymer matrix composites in the front end of the engine to the superalloys - carbon matrix composites in the rear parts. The limits related to various parameters are analyzed: microstructures, grain boundary weakness, and especially the catastrophic influence of stress/strain assisted grain boundary oxidation on hold time fatigue life. The lecture continues with a description of the general failure mechanisms, fatigue failure mechanisms and mechanical testing to allow life predictions. Creep life prediction and TMF life prediction in turbines cover the fundamentals of creep and fatigue behaviour from a material point of view. Assess these behaviours and the methods used, followed by examples of this behaviour and problems.

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