This paper presents the verification of the mathematical model utilized to calculate the damping capacity of a dry friction damper. The mathematical model is based on determining natural frequencies and mode shapes, as well as relative characteristics of the friction energy losses. To estimate the applicability of the mathematical model to full-scale assemblies of a gas-turbine engine, the model was verified by the results of the experiment. The experiment was carried out in a laboratory where the damping capacity of the gas-turbine engine blade with a model under-platform damper was examined at constrained and damped oscillations. During the experiment multiple materials of contact pair were examined to determine how microslip affects the damping capacity. Based on the results of comparing calculations with the experiment, by selecting the dry friction coefficient, a good convergence on the oscillation decrement and natural frequency was achieved. The conducted research has shown that the mathematical model provides reliable results with Coulomb friction and can consider microslip effects on the damper capacity.
При тензометрировании количество каналов для измерения вибронапряжений элементов газотурбинного двига-теля всегда ограничено. На начальном этапе экспериментальных исследований, когда еще не определено динамиче-ское поведение детали, какие из резонансных режимов опасны, а какие нет, желательно с помощью небольшого коли-чества тензорезисторов «перекрыть» все расчетные собственные формы колебаний. В данной работе представлен расчетный метод определения оптимального размещения тензорезисторов и определения коэффициентов чувстви-тельности форм колебаний тензорезисторов. Расчетный метод разработки схемы препарирования основан на расчете собственных форм колебаний детали. Для оценки качества размещения тензорезистора введено понятие коэффициен-та чувствительности тензорезистора к форме колебаний и выделено три диапазона значений чувствительности по его применимости. Введено понятие «покрытия» формы колебаний, показывающее, что такая схема препарирования по-зволяет достоверно измерить динамические напряжения по данной форме. Для количественной оценки качества схемы препарирования определяется количество покрываемых данной схемой форм. Проведена отработка метода определе-ния оптимального положения тензорезисторов на рабочих лопатках компрессора высокого давления. Было рассмотре-но три варианта схем препарирования и для каждого определены коэффициенты чувствительности форм колебаний. Два варианта схем препарирования разработаны на базе опыта экспериментальных исследований лопаток и предвари-тельного анализа результатов расчета вибрационных характеристик лопаток. Третий вариант схемы препарирования разработан с применением метода определения оптимального размещения тензорезисторов. Третья схема разработа-на для лопатки, концентраторы напряжений по формам колебаний которой расположены в труднодоступных для раз-мещения тензорезисторов местах. Для нее же определены коэффициенты чувствительности форм колебаний по отно-шению к максимальному значению интенсивности напряжений в профиле лопатки. Для всех схем препарирования оп-ределено среднее значение «покрытия» форм.Ключевые слова: схема препарирования, коэффициент чувствительности тензорезистора к форме колебаний, «покрытие» формы колебаний, вибронапряжения, оптимальное положение тензорезистора. M.V. Pivovarova DEVELOPMENT OF EVALUATION METHOD FOR DETERMINING THE STRAIN GAUGES OPTIMAL PLACEMENT AND DETERMINING THE STRAIN GAUGES MODE SHAPE SENSITIVITY FACTORThe number of measurement channels of dynamic stresses is always limited. At the initial stage of the study when it is not determined which of the resonant modes are dangerous and which are not, it is desirable to cover the greatest possible number of natural forms with a small amount of strain gauges. The estimated method of determining the optimal position of the strain gauge and determining the strain gauge mode shape sensitivity factor is persecuted in the study. This method is based on estimated the free modes. To analyze the quality of the preparation designs, the concept of the strain gauge mode shape sensitivity fact...
At present, the process of designing a GTE involves a large amount of computational modeling. With the help of computational modeling, it is possible to predict a behavior of an engine part during engine operations before conducting experimental studies. For example, the numerical dynamic behavior analysis of compressor blades and prediction of dynamic stress levels during fluctuations in free modes are urgent problems. A high level of dynamic stress in the compressor blades in resonant modes can break a blade and stop an engine. In this paper, we propose a simple vibration stress estimation method for the compressor blades based on the calculation of natural frequencies and vibration forms. The method is based on a comparative analysis and scaling of stresses by the value of the total potential or kinetic energy. This estimation method is valid for local changes in the blade geometry, which do not lead to changes in the natural frequencies and vibration forms of the blades, assuming that the geometry change does not change the level of the aerodynamic excitation of the blade or its damping. At the stage of development or revision of the blade, a large number of variants of the blade geometry needs to be analyzed in order to reduce dynamic stresses. The proposed vibration stress estimation method has shown its high efficiency in developing and refining the geometry of the compressor blade. The vibration stress estimation method was tested using the rotor blade of a high-pressure compressor. As a result of the experimental study of the rotor blade, a high level of vibration stresses exceeding the permissible level was found for natural frequencies and vibration forms. To reduce the vibration stresses, measures were proposed to modify the geometry of the blade. For the modified blade geometry, the vibration stress estimation was performed with a prediction of the vibration stress values based on the manifested vibration forms. In order to verify the estimated vibration stress change, an experimental study of the modified blade was conducted. The vibration stress estimation method for the compressor blades was successfully verified.
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