Numerical analysis of the turbomachine blade row aeroelastic oscillations with taking into account the disc deformation

Нестационарные явления, вызванные колебаниями лопаток под действием возмущающих сил, характеризуются обменом энергией между потоком газа и колеблющимися лопатками и составляют основу физического механизма самовозбуждающихся колебаний, которые могут или затухать (аэродемпфирование), или проявляться в устойчивой форме автоколебаний, или в неустойчивой форме флаттера, который может привести к разрушению конструкции. Поэтому аэроупругое поведение лопаток представляет важную проблему надежности и безопасности газо- и паротурбинных двигателей с высокими аэродинамическими показателями и соответственно высоко нагруженными лопатками. Одним из подходов к повышению устойчивости колебаний лопаток является расстройка собственных форм, связанная с деформацией диска. Представлен численный анализ влияния деформации диска на аэроупругие колебания лопаток рабочего колеса турбомашины. Деформация диска характеризуется количеством узловых диаметров, что определяет межлопаточный угол сдвига по фазе колебаний соседних лопаток (МЛФУ), который влияет на нестационарные аэродинамические нагрузки и амплитуды колебаний лопаток. В работе показано, что уменьшение межлопаточного угла сдвига по фазе колебаний лопаток приводит к повышению аэроупругой устойчивости, т. е. к снижению амплитуд колебаний лопаток. Предложенный численный метод решения связанной аэроупругой задачи в трехмерном транзвуковом потоке идеального газа позволяет прогнозировать аэроупругое поведение лопаток, включая вынужденные, самовозбуждающиеся колебания и автоколебания с целью повышения экономичности и надежности лопаточных аппаратов турбомашин.The unsteady phenomena caused by blades oscillations by action of forced forces are characterized with energy change between gas flow and oscillating blades and formulate the base of physical mechanism of self-excited oscillations that can or to attenuate (aerodamping), or to be displayed in stable form of autooscillations, or in unstable form of flutter, which can activate to the structure destruction. Therefore aeroelastic blades behaviour represents the important problem of reliability and safety of gas and steam turbines with high aerodynamic indicators and high loaded blades. One of approaches to increase the stable blades oscillations is detuning of natural forms bound to disc deformation. There presented the numerical analysis of effect of disc deformation on aeroelastic blades oscillations of turbomachine blade row. The disc deformation is characterized by disc nodal diameters number that defines the interblade phase angle of blades oscillations shift (IBPA), and impacts on unsteady aerodynamic loads and blades oscillations amplitudes. In paper there shown that decrease of IBPA causes to increase of aeroelastic stability that is to reduction of blades oscillations amplitudes.The proposed numerical method of coupled aeroelastic problem solution for threedimensional transonic ideal gas flow allows to predict aeroelastic behaviour of blades including the forced, self-excitation oscillations and autooscillations with purpose to increase the efficiency and reliability of turbomachines blades devices

Computational fluid dynamics analysis of 1 MW steam turbine inlet geometries

This paper analyses the influence of three different ring-type inlet duct geometries on the performance of a small 1 MW backpressure steam turbine. It examines the efficiency and pressure drop of seven turbine variants, including four spiral inlet geometries and three stages with a mass flow rate around 30 t/h. A one-pipe and two-pipe inlets are analysed from aerodynamical point of view, taking into account stator and rotor blades in three stages without the outlet. An outlet is added to the best variant. Also analysed is the occurrence of vortices in the inlets of the studied variants 1–7 as well as the efficiency, drop pressure, turbine power and mass flow. Finally, the best inlet for a 1 MW steam turbine is suggested

ЧИСЕЛЬНИЙ АНАЛІЗ АЕРОПРУЖНИХ КОЛИВАНЬ ЛОПАТКОВОГО ВІНЦЯ ТУРБОМАШИНИ З УРАХУВАННЯМ ДЕФОРМАЦІЇ ДИСКУ

The unsteady phenomena caused by blades oscillations by action of forced forces are characterized with energy change between gas flow and oscillating blades and formulate the base of physical mechanism of self-excited oscillations that can or to attenuate (aerodamping), or to be displayed in stable form of autooscillations, or in unstable form of flutter, which can activate to the structure destruction. Therefore aeroelastic blades behaviour represents the important problem of reliability and safety of gas and steam turbines with high aerodynamic indicators and high loaded blades. One of approaches to increase the stable blades oscillations is detuning of natural forms bound to disc deformation. There presented the numerical analysis of effect of disc deformation on aeroelastic blades oscillations of turbomachine blade row. The disc deformation is characterized by disc nodal diameters number that defines the interblade phase angle of blades oscillations shift (IBPA), and impacts on unsteady aerodynamic loads and blades oscillations amplitudes. In paper there shown that decrease of IBPA causes to increase of aeroelastic stability that is to reduction of blades oscillations amplitudes. The proposed numerical method of coupled aeroelastic problem solution for threedimensional transonic ideal gas flow allows to predict aeroelastic behaviour of blades including the forced, self-excitation oscillations and autooscillations with purpose to increase the efficiency and reliability of turbomachines blades devices.Нестаціонарні явища, викликані коливаннями лопаток під дією сил, що обурюють, характеризуються обміном енергією між потоком газу і коливними лопатками і складають основу фізичного механізму самозбудних коливань, які можуть або затухати (аеродемпфування), або проявлятися в стійкій формі автоколивань, або в нестійкій формі флатера, який може привести до руйнування конструкції. Тому аеропружна поведінка лопаток являє важливу проблему надійності і безпеки газо- і паротурбінних двигунів з високими аеродинамічними показниками і відповідно високо навантаженими лопатками. Одним з підходів до підвищення стійкості коливань лопаток є розлад власних форм, пов'язаний з деформацією диска. Представлено чисельний аналіз впливу деформації диска на аеропружні коливання лопаток робочого колеса турбомашини. Деформація диска характеризується кількістю вузлових діаметрів, що визначає міжлопатковий кут зсуву по фазі коливань сусідніх лопаток (МЛФК), який впливає на нестаціонарні аеродинамічні навантаження і амплітуди коливань лопаток. В роботі показано, що зменшення міжлопаткового кута зсуву по фазі коливань лопаток призводить до підвищення аеропружної стійкості, тобто до зниження амплітуд коливань лопаток. Запропонований чисельний метод розв'язання зв'язаної аеропружної задачі в тривимірному транзвуковому потоці ідеального газу дозволяє прогнозувати аеропружну поведінку лопаток, включаючи вимушені, самозбудні коливання і автоколивання з метою підвищення економічності і надійності лопаток апаратів турбомашин

Steam turbine stress control using NARX neural network

Considered here is concept of steam turbine stress control, which is based on Nonlinear AutoRegressive neural networks with eXogenous inputs. Using NARX neural networks,whichwere trained based on experimentally validated FE model allows to control stresses in protected thickwalled steam turbine element with FE model quality. Additionally NARX neural network, which were trained base on FE model, includes: nonlinearity of steam expansion in turbine steam path during transients, nonlinearity of heat exchange inside the turbine during transients and nonlinearity of material properties during transients. In this article NARX neural networks stress controls is shown as an example of HP rotor of 18K390 turbine. HP part thermodynamic model as well as heat exchange model in vicinity of HP rotor,whichwere used in FE model of the HP rotor and the HP rotor FE model itself were validated based on experimental data for real turbine transient events. In such a way it is ensured that NARX neural network behave as real HP rotor during steam turbine transient events

ЧИСЛЕННЫЙ АНАЛИЗ ТРЁХМЕРНОГО НЕСТАЦИОНАРНОГО ПОТОКА ИДЕАЛЬНОГО ГАЗА В ПОСЛЕДНЕЙ СТУПЕНИ ТУРБОМАШИНЫ С УЧЁТОМ НЕОСЕСИММЕТРИЧНОГО ВЫХЛОПНОГО ПАТРУБКА

A problem related to the forecast of the aeroelastic behavior and aeroelastic instability of blades (in particular self-oscillations, flutter, and resonance vibrations) becomes of great importance for the development of high-loaded compressor and vent rows and the last turbine stages whose long and flexible blades can be exposed to such phenomena. The solution of this problem requires the development of new models for the nonstationary three-dimensional flow, the use of contemporary numeric methods and the comparison of theoretical and experimental data. This scientific paper gives the data of numerical simulation of the 3-D flow of ideal gas passing through the last stage of turbine machine taking into account the flow nonuniformity caused by guide blades and nonuniform pressure distribution in the exhaust pipe branch and also nonstationary effects caused by blade vibrations. The numerical method is based on the solution of combined aeroelastic problem for the 3-D flow of ideal gas passing through the turbine stage and the nonaxisymmetric exhaust pipe branch including the annular diffuser. To solve the combined problem a partially integral method was used that includes integral equations of gas dynamics (Euler equations) and vibrating blade dynamics (modular approach) at each time step with the information exchange. The given method of the solution of combined aeroelastic problem allows us to predict the amplitude-frequency spectrum of blade vibrations in the three-dimensional flow of ideal gas including forced self-excited vibrations and self-vibrations to increase efficiency and reliability of the blade units of turbine machines.Представлены результаты численного моделирования трехмерного потока идеального газа через последнюю ступень турбомашины с учетом неравномерности потока, вызванной направляющими лопатками, неосесимметричным патрубком, и нестационарных эффектов, вызванных колебаниями лопаток. Представленный метод решения связанной аэроупругой задачи позволяет прогнозировать амплитудно-частотный спектр колебаний лопаток, включая вынужденные, самовозбуждающиеся колебания и автоколебания с целью повышения экономичности и надежности лопаточных аппаратов турбомашин

Influence of inlet geometry on the efficiency of 1 MW steam turbine

The process of the design of the 1 MW steam turbine includes designing the stator and rotor blades, the steam turbine inlet and exit, the casing and the rotor. A turbine that operates at rotation speeds other than 3000 rpm requires a gearbox and generator with complex electronic software. This article analyses the efficiency of eight turbine variants, including seven inlet geometries and three stages of stator as well as an eight variant with one of the inlets, all three stages and an outlet. This article analyses the efficiency of 8 turbine variants, including four spiral inlet geometries and tree stages in a 1 MW steam turbine. In the article, inlets and 1st stator blades of various geometries were analysed to obtain maximal turbine efficiency. Changing the inlet spiral from one pipe to two pipes increased the turbine efficiency. The geometry of the blades and turbine inlets and outlet was carried out using Design Modeller. The blade mesh was prepared in TurboGrid and inlet in ANSYS Meshing

An influence of shroud design parameters on the static stresses of blade assemblies

In this study, the structural analysis of the blade assemblies was carried out using the finite element method to determine the influence of design parameters of shroud couplings on the static stresses of turbine rotor blades with zigzag and slant shroud couplings. An angle of inclination of the shroud contact surfaces with respect to the rotor rotation axis was selected as the design parameter. Based on the calculation results, it has been found that irrespective of the type of the shroud coupling, the values of the contact pressure and the stresses in the shroud increase with the angle of inclination of the contact surfaces. Also, for the slant shroud coupling, the stresses increase in the blade airfoil portion with the increase of angle of inclination of the contact surfaces, while for the zigzag shroud coupling the contact stresses decrease with the increase of this angle. It was concluded that the zigzag shroud coupling causes the increase in static stresses when compared to the slant one

Nonsynchronous Rotor Blade Vibrations in Last Stage of 380 MW LP Steam Turbine at Various Condenser Pressures

This paper presents an analysis of nonsynchronous rotor blade vibrations in the last stage of an LP steam turbine at various condenser pressures. The nonlinear least squares Levenberg–Marquardt method is used in a tip-timing analysis to determine nonsynchronous multimode rotor blade vibrations, which is a novelty. This is done with two sensors in the casing and a once-per-revolution sensor. The accuracy of the nonlinear least squares Levenberg–Marquardt multimode method is compared with the one-mode linear method. The algorithm is verified by comparing it with one-mode tip-timing methods for synchronous and nonsynchronous vibrations. The analysis shows that the rotor blades vibrate simultaneously with two modes in non-nominal conditions, which is also a novelty. The rotor frequencies are unchanged, although the blade vibration amplitudes vary, depending on the pressure in the condenser. Flutter does not appear in the last stage for the various condenser pressures and powers that were tested

Nonsynchronous Rotor Blade Vibrations in Last Stage of 380 MW LP Steam Turbine at Various Condenser Pressures

This paper presents an analysis of nonsynchronous rotor blade vibrations in the last stage of an LP steam turbine at various condenser pressures. The nonlinear least squares Levenberg–Marquardt method is used in a tip-timing analysis to determine nonsynchronous multimode rotor blade vibrations, which is a novelty. This is done with two sensors in the casing and a once-per-revolution sensor. The accuracy of the nonlinear least squares Levenberg–Marquardt multimode method is compared with the one-mode linear method. The algorithm is verified by comparing it with one-mode tip-timing methods for synchronous and nonsynchronous vibrations. The analysis shows that the rotor blades vibrate simultaneously with two modes in non-nominal conditions, which is also a novelty. The rotor frequencies are unchanged, although the blade vibration amplitudes vary, depending on the pressure in the condenser. Flutter does not appear in the last stage for the various condenser pressures and powers that were tested

Tip-timing analysis of last stage steam turbine mistuned bladed disc during run-down

This paper presents the experimental and numerical studies of last stage LP mistuned steam turbine bladed discs during run-down. The natural frequencies and mode shapes of the turbine bladed disc were calculated using an FE model. The influence of shaft was considered. The tip-timing method was used to find the mistuned bladed disc modes and frequencies. The numerical results were compared with experimental ones