Fluid film bearings are widely used in supports of gas turbines, pumps and compressors. They also present in test benches designed for overspeed tests of aircraft engine’s discs. Stiffness and damping of these supporting elements are nonlinear. Moreover fluid film bearing reactions include circulation forces that can bring to well-known types of self-excited vibrations – whirl and whip. Magnitudes of those oscillations are almost not influenced by unbalances and are determined by the system’s properties, in particular – properties of damping and circulation forces. If this type of vibrations does not arise and only forced oscillations present, the corresponding resonance frequencies will depend on unbalances because of fluid film bearing nonlinear stiffness and damping. The listed considerations bring to the necessity of account of nonlinear non-conservative support’s properties in modeling of rotor dynamics. The paper describes the appropriate approach that includes joint use of finite element model of rotor and nonlinear models of supports. The vibrations of rotor with rolling and fluid film bearings in supports are considered as example. Rolling bearings were modeled by nonlinear exponential dependencies of forces on displacements. Those dependencies were computed from the Hertz contact theory. Fluid film bearing was modeled with analytical solution of the Reynolds equation. The problem was solved in nonlinear nonstationary formulation considering mutual influence of rotor displacements and bearing reactions. Results of multiple simulations performed for different values of rotor speed are presented as a frequency response function and a waterfall plot. The results were verified with experimental data.
This article presents an experimental and computational study of bird collision with a flexible plate at different impact speeds. Tests were carried out with the aid of a pneumatic gun. The bird mass in the study was about 300 g, and the speed range was 49-75 m/s. The actual mechanical properties of the plate were determined with tensile tests of flat specimen-witness. A video recording and strain gauging were performed during the strike. Some frames of high speed video recording for the highest bird’s velocity c = 75 m/s are presented in the article to demonstrate the process of bird rupturing. Different models of the bird material were examined to compare computational and measured strains.
Prevention of high cycle fatigue failures of blades caused by increased level of vibrational stresses is important problem in engine design and development. Different types of dampers are usually installed under the blade platforms in the region between the shanks of adjacent blades are usually used to reduce the vibrational stresses in the turbine blades. The action of these dampers is based on the vibrational energy dissipation by the dry friction forces arising due to the relative displacement of the contacting surfaces of the damper and the blade. Adoption of a reliable choice of damper design mass and stiffness at the design stage of the aircraft engines requires an experimentally validated estimation of its damping efficiency and its influence on the blade frequency characteristics. The dampers need to be tested under conditions that are maximally close to the operational conditions. This paper presents an analysis of the stress gauging results of a turbine wheel with box-type dampers of various mass. The tests were carried out on a dynamic bench where resonance oscillations of a stage for a given mode were excited by one of the harmonics to a given rotational speed under the corresponding forces pressing the dampers onto the blade platform. An estimation of the damper efficiency in a wider range of pressing forces was also obtained by conducting the laboratory tests using on a specially designed vibration unit that simulates the dampers effect on a set of three blades. Numerical analysis of the damper mass and stiffness influence on the frequency and damping characteristics of a real turbine wheel was performed. Obtained experimental data and the GAP model of contact interaction of the insert with blades were used in the MSC. Nastran software package. Analysis showed a satisfactory correlation between the calculated and experimental estimates of the decrease in resonant stresses and resonance frequency changes when the dampers are inserted. The results presented here confirm the possibility of increasing the reliability of the choice of mass and stiffness of turbine blade dampers at the design stage.
Центральный институт авиационного моторостроения имени П.И. Баранова, г. Москва Рассмотрены требования к обеспечению эффективности и безопасности стендовых испытаний на птицестойкость вентиляторов путём стрельбы птицами по невращающимся рабочим лопаткам, в том числе требования по обеспечению скорости удара птицы по испытываемой лопатке, установке лопаток под требуемым углом атаки к птице, прочности деталей установки и её ремонтопригодности. Изложены конструктивные особенности разработанной в ЦИАМ установки, включающей в себя две основные де-тали: модельный сектор диска для установки блока лопаток и жёсткую станину, относительно которой сектор диска может быть повёрнут на заданный угол и закреплён в этом положении. Модельный сектор диска представляет собой массивную деталь, имитирующую часть обода диска с профилированными пазами для установки хвостовиков блока исследуемых лопаток. Станина выполняется в виде набора опорных плит с расположенными по периферии отверстиями для их сборки и возможного дополнитель-ного подкрепления с использованием прокатного профиля. Анализ прочности элементов установки в условиях действия больших кратковременных ударных нагрузок выполнен по результатам конечно-элементных 3D расчётов. На установке были успешно проведены стендовые испытания по забросу круп-ной птицы на блок из трёх лопаток вентилятора.Лопатка вентилятора, заброс птиц, стендовые испытания.
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