Flutter of Fan Blades in the Aircraft Engine in the Three-Dimensional Subsonic Gas Flow

Aeroelasticity problems arise in the different fields of technology. The accident-free operation of the airborne machines is one of the most important factors that should be taken into account during their designing and upgrading. The solution of this problem involves the implementation of many measures to provide the system reliability on the whole, including its individual elements, in particular aircraft engine, its fan whose wide-chord blades can be exposed to the wreckage due to different reasons including the aeroelastic effects, i.e. self-excited vibrations. As a result, the origination of the aeroelastic phenomenon (flutter) in design and off-design modes should be eliminated at the stage of the design and operational development of the rotor wheel that would result in a considerable increase of the level of reliability of the aircraft engine. Based on the analysis of the available methods used for the flutter prediction we can draw a conclusion that the most promising approach to the analysis of the aeroelastic behavior of the blade ring of fan is the use of the method based on the three-dimensional model of the aerodynamics and dynamics (the method used for the solution of the coupled aeroelastic problem). By solving the coupled aeroelastic problem of the nonstationary aerodynamics and elastic vibrations of the blades we can get the amplitude –frequency blade vibration spectrum for the three-dimensional gas flow, including forced vibrations and self-excided vibrations in order to increase the reliability of the blade row of turbine machines. The developed numerical method was used for the analysis of the aeroelastic behavior of the blade ring of the fan mounted in the airborne engine for the operation mode of 3520 rmp with appropriate boundary conditions at the inlet and outlet behind the ring. The computation data confirmed the origination of self-vibrations for the given fan operation mode.

Экспериментальное исследование отрывных течений потока в криволинейных каналах постоянного сечения

Целью работы является выявление особенностей течения газа в криволинейных каналах. Приводится анализ влияния различных воздействий на отрывные явления в сильноизогнутых криволинейных каналах. Это связано с тем, что в малорасходных турбинах с большим поворотом потока в ступени применяются активные ступени с сильноизогнутыми межлопаточными каналами рабочего колеса. Отрывные явления, происходящие в таких каналах, существенно снижают к.п.д. турбин. В статье приводятся результаты экспериментального исследования дозвуковых течений газового потока в криволинейных каналах при воздействии на отрыв пограничного слоя пассивных генераторов вихрей в виде песочной шероховатости и треугольных канавок. Исследования проводились на воздухе с моделями криволинейных каналов постоянного поперечного сечения при различной геометрической величине пассивных генераторов вихрей. Высота бугорков песочной шероховатости менялась от 50 мкм до 100 мкм, а количество турбулизаторов в виде треугольных канавок варьировалось от трех до шести. Показано, что наиболее положительный эффект достигается при использовании пассивных генераторов вихрей в виде треугольных канавок. Песочная шероховатость дает меньший эффект, а в некоторых случаях даже ухудшает характеристики потокаGoal of the work is identification of features gas flows in curved channels. The analysis of the influence of various effects on separation phenomena in strongly curved channels is given This is due to the fact that active stages with strongly curved blade channels of the rotor wheel are used in low-consumption turbines with a large flow turn in the stages. Separation phenomena occurring in such channels significantly reduce the efficiency of turbines. The paper presents the results of an experimental research of subsonic gas flow in curved channels when passive vortex generators in the form of sand roughness and triangular grooves act on the separation of the boundary layer. The studies were conducted in air with models of curved channels of constant cross-section for various geometric sizes of passive vortex generators. The height of the sand roughness tubercles varied from 50 cm to 100 cm, and the number of turbulators in the form of triangular grooves varied from three to six. It is shown that the most positive effect is achieved using passive vortex generators in the form of triangular grooves. Sand roughness gives less effect, and in some cases even worsens flow characteristics