Structures performance, benefit, cost-study

New technology concepts and structural analysis development needs which could lead to improved life cycle cost for future high-bypass turbofans were studied. The NASA-GE energy efficient engine technology is used as a base to assess the concept benefits. Recommended programs are identified for attaining these generic structural and other beneficial technologies

Nonlinear dynamics of turbine bladed disk with friction dampers: Experiment and simulation

Accurately predicting the nonlinear dynamic response of aero-engine components is critical, as excessive vibration amplitudes can considerably reduce the operational lifespan. This paper compares experimental and numerical nonlinear dynamic responses of an industrial aero-engine, specifically focusing on the first stage turbine bladed disk with under-platform dampers (UPDs). The friction forces between UPDs and blades result in a strongly nonlinear dynamic response, influenced by stick, slip and separation contact states at the interfaces. These contact states, and the resulting global dynamic responses, are predicted with an advanced industrial modelling approach for nonlinear dynamics. The predictions are compared, updated and validated against measurement data from an operational engine test. Results highlight the importance to validate models against industrial data and show that realistic contact pressure distributions are required for increased prediction reliability. The novelty of this work includes (1) the use of unique industrial experimental data from a fully operational aero-engine, (2) the observation, at the end of engine testing, of real contact conditions in blade/UPD interfaces, (3) detailed modelling of these contact conditions with high-fidelity finite element representations in nonlinear dynamic solvers. Based on this unique industrial validation work, guidelines are proposed to improve the state-of-the-art modelling of nonlinear dynamics in structures with friction contacts

Aeronautical Engineering: A special bibliography with indexes, supplement 55

This bibliography lists 260 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1975

Turbomachinery Clearance Control

Controlling interface clearances is the most cost effective method of enhancing turbomachinery performance. Seals control turbomachinery leakages, coolant flows and contribute to overall system rotordynamic stability. In many instances, sealing interfaces and coatings are sacrificial, like lubricants, giving up their integrity for the benefit of the component. They are subjected to abrasion, erosion, oxidation, incursive rubs, foreign object damage (FOD) and deposits as well as extremes in thermal, mechanical, aerodynamic and impact loadings. Tribological pairing of materials control how well and how long these interfaces will be effective in controlling flow. A variety of seal types and materials are required to satisfy turbomachinery sealing demands. These seals must be properly designed to maintain the interface clearances. In some cases, this will mean machining adjacent surfaces, yet in many other applications, coatings are employed for optimum performance. Many seals are coating composites fabricated on superstructures or substrates that are coated with sacrificial materials which can be refurbished either in situ or by removal, stripping, recoating and replacing until substrate life is exceeded. For blade and knife tip sealing an important class of materials known as abradables permit blade or knife rubbing without significant damage or wear to the rotating element while maintaining an effective sealing interface. Most such tip interfaces are passive, yet some, as for the high-pressure turbine (HPT) case or shroud, are actively controlled. This work presents an overview of turbomachinery sealing. Areas covered include: characteristics of gas and steam turbine sealing applications and environments, benefits of sealing, types of standard static and dynamics seals, advanced seal designs, as well as life and limitations issues

Self-excited vibrations controlled by damping at blade root joints of turbine disks

The purpose of this thesis is the development of a methodology for the calculation of the non-linear aero-elastic behavior of a bladed disk to be used in an industrial process. The non-linear aero-elastic phenomena of a bladed disk for aeronautical applications are studied in the presence of friction contacts using a one-way coupled method. The calculation is performed using a method based on the Harmonic Balance Method (HBM) and the balance between the energy introduced by the unsteady aerodynamics on the blade airfoil and the dissipative energy. The HBM method is preferred with respect to the Direct Time Integration (DTI) for the strong reduction of the computation time that HBM technique allows in spite of an acceptable level of approximation when nonlinearities are introduced and the response is periodic. The nonlinearity is introduced by purposely developed contact elements, placed at the blade root-joints, that produce additional stiffening and damping in the system due the introduction of contact stiffnesses and friction forces based on Coulomb’s law. The aero-elastic equilibrium will be investigated through a Parameter variation of the Limit Cycle Oscillations (LCO) of the system using two different approaches: the physical approach and the modal approach. The effect of such variations will be highlighted in order to demonstrate what are the parameters that influence most the blade amplitude, both for the CFD and the mechanical simulation. In particular, the uncertainty in the definition of the contact parameters at the blade root will be taken into account by varying the friction coefficient and the normal force distribution on the blade root joint. Finally, the results of the analysis will be compared with the experimental data produced with a cold-flow test rig to verify if the sensitivity study associated to the simplifications introduced in the method are compatible with the measured response

Aeronautical engineering: A continuing bibliography with indexes (supplement 223)

This bibliography lists 423 reports, articles, and other documents introduced into the NASA scientific and technical information system in January, 1988

Annual Report of the National Advisory Committee for Aeronautics (42nd), Administrative Report without Technical Reports

No abstract availabl

Recent Progress in Some Aircraft Technologies

The book describes the recent progress in some engine technologies and active flow control and morphing technologies and in topics related to aeroacoustics and aircraft controllers. Both the researchers and students should find the material useful in their work

Aeronautical Engineering: A continuing bibliography, supplement 120

This bibliography contains abstracts for 297 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1980

The concept of nonlinear modes applied to friction-damped systems

[no abstract