Effect of Scaling of Blade Row Sectors on the Prediction of Aerodynamic Forcing in a Highly-Loaded Transonic Turbine Stage

2011 ◽  
Author(s):  
Seyed Mohammad Hosseini ◽  
Florian Fruth ◽  
Damian M. Vogt ◽  
Torsten H. Fransson
Keyword(s):  
Structural Characteristics ◽  
High Sensitivity ◽  
Element Model ◽  
General Purpose ◽  
Forced Response ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Turbine Stage ◽  
Reference Case ◽  
Scaling Technique

The viability of a scaling technique in prediction of forced response of the stator and rotor blades in a turbine stage has been examined. Accordingly the so called parameter, generalized force, is defined which describes the excitation of a modeshape due to the unsteady flow forces at a certain frequency. The capability of this method to accurately predict the generalized forces serves as the viability criterion. The scaling technique modifies the geometry to obtain an integer stator, rotor blade count ratio in an annulus section while maintaining steady aerodynamic similarity. A non-scaled configuration is set up to serve as the reference case. Further configurations with different scaling ratios are also generated for accuracy comparison. Unsteady forces are calculated through 3D Navier-Stokes simulations by VolSol, which is based on an explicit, time-marching. A general purpose finite element model of blades is also provided to enable modal analysis with the harmonic forces. The generalized forces of stator and rotor blades revealed high sensitivity towards modification of stator blades while acceptable accuracy was obtained by moderate modifications of the rotor blades for first harmonic forces. Moreover the influence of variable blade’s structural characteristics proved to be remarkable.

Numerical Modelling of Fluid-Structure Interaction in a Turbine Stage for 3D Viscous Flow in Nominal and Off- Design Regimes

2010 ◽  
Author(s):  
Romuald Rzadkowski ◽  
Vitaly Gnesin ◽  
Lubov Kolodyazhnaya
Keyword(s):  
Boundary Layer ◽  
Viscous Flow ◽  
Gas Turbines ◽  
Element Model ◽  
Boundary Layer Separation ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Turbine Stage ◽  
Flow Distortion ◽  
Boundary Layer Interaction

In recent years there have been major developments in turbomachinery aeroelasticity methods. There are now greater possibilities to predict blade vibrations arising from self-excitation or inlet flow distortion. This is not only important with regard to aircraft compressor and fan blade rows, but also in the case of the last stages of steam and gas turbines working in highly loaded off-design conditions. In order to predict the unsteady pressure loads and aeroelastic behaviour of blades (including the computation of shock waves, shock/boundary layer interaction and boundary layer separation), complete Reynolds-averaged Navier-Stokes (RANS) equations are used in modelling complex and off-design cases of turbomachinery flows. In this paper the 3D RANS solver, including a modified Baldwin and Lomax algebraic eddy viscous turbulence model, is presented to calculate unsteady viscous flow through the turbine stage, while taking into account the blade oscillations but without the separating of outer excitation and unsteady effects caused by blade motion. The numerical method uses the second order by time and coordinates an explicit finite-volume Godunov’s type difference scheme and a moving H-O structured grid. The structure analysis uses the modal approach and a 3D finite element model of blade. To validate the numerical viscous code, the numerical calculation results were compared with the 11th Standard Configuration measurements. Presented here are the numerical analysis results for the aeroelastic behaviour of a steam turbine last stage with 760 mm rotor blades in a nominal and an off-design regime.

Forced Response Assessment Using Modal Force Based Indicator Functions

2008 ◽  
Author(s):  
M. Vahdati ◽  
C. Breard ◽  
G. Simpson ◽  
M. Imregun
Keyword(s):  
Finite Element ◽  
Structural Model ◽  
Stokes Equations ◽  
Linear Time ◽  
Response Assessment ◽  
Element Model ◽  
Forced Response ◽  
Navier Stokes ◽  
Modal Force ◽  
Indicator Functions

This paper will focus on core-compressor forced response with the aim to develop two design criteria, the so-called chordwise cumulative modal force and heightwise cumulative force, to assess the potential severity of the vibration levels from the correlation between the unsteady pressure distribution on the blade’s surface and the structural modeshape. It is also possible to rank various blade designs since the proposed criterion is sensitive to changes in both unsteady aerodynamic loads and the vibration modeshapes. The proposed methodology was applied to a typical core-compressor forced response case for which measured data were available. The Reynolds-averaged Navier-Stokes equations were used to represent the flow in a non-linear time-accurate fashion on unstructured meshes of mixed elements. The structural model was based on a standard finite element representation from which the vibration modes were extracted. The blade flexibility was included in the model by coupling the finite element model to the unsteady flow model in a time-accurate fashion. A series of numerical experiments were conducted by altering the stator wake and using the proposed indicator functions to minimize the rotor response levels. It was shown that a fourfold response reduction was possible for a certain mode with only a minor modification of the blade.

scholarly journals Calculation and Correlation of the Unsteady Flowfield in a High Pressure Turbine

2002 ◽  
Author(s):  
Milind A. Bakhle ◽  
Jong S. Liu ◽  
Josef Panovsky ◽  
Theo G. Keith ◽  
Oral Mehmed
Keyword(s):  
High Pressure ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Forced Vibrations ◽  
Forced Response ◽  
Operating Conditions ◽  
Test Facility ◽  
Navier Stokes ◽  
Turbine Stage ◽  
High Pressure Turbine

Forced vibrations in turbomachinery components can cause blades to crack or fail due to high-cycle fatigue. Such forced response problems will become more pronounced in newer engines with higher pressure ratios and smaller axial gap between blade rows. An accurate numerical prediction of the unsteady aerodynamics phenomena that cause resonant forced vibrations is increasingly important to designers. Validation of the computational fluid dynamics (CFD) codes used to model the unsteady aerodynamic excitations is necessary before these codes can be used with confidence. Recently published benchmark data, including unsteady pressures and vibratory strains, for a high-pressure turbine stage makes such code validation possible. In the present work, a three dimensional, unsteady, multi blade-row, Reynolds-Averaged Navier Stokes code is applied to a turbine stage that was recently tested in a short duration test facility. Two configurations with three operating conditions corresponding to modes 2, 3, and 4 crossings on the Campbell diagram are analyzed. Unsteady pressures on the rotor surface are compared with data.

scholarly journals СНИЖЕНИЕ ВИБРОНАПРЯЖЕННОСТИ ПОПАРНО БАНДАЖИРОВАННЫХ РАБОЧИХ ЛОПАТОК ТУРБИНЫ

2020 ◽  
pp. 52-58
Author(s):  
Юрий Петрович Кухтин ◽  
Руслан Юрьевич Шакало
Keyword(s):  
Film Cooling ◽  
Gas Flow ◽  
Stokes Equations ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Turbine Stage ◽  
Turbine Engine ◽  
Exciting Forces ◽  
Working Blades

To reduce the vibration stresses arising in the working blades of turbines during resonant excitations caused by the frequency of passage of the blades of the nozzle apparatus, it is necessary to control the level of aerodynamic exciting forces. One of the ways to reduce dynamic stresses in rotor blades under operating conditions close to resonant, in addition to structural damping, maybe to reduce external exciting forces. To weaken the intensity of the exciting forces, it is possible to use a nozzle apparatus with multi-step gratings, as well as with non-radially mounted blades of the nozzle apparatus.This article presents the results of numerical calculations of exciting aerodynamic forces, as well as the results of experimental measurements of stresses arising in pairwise bandaged working blades with a frequency zCA ⋅ fn, where fn – is the rotor speed, zCA – is the number of nozzle blades. The object of research was the high-pressure turbine stage of a gas turbine engine. Two variants of a turbine stage were investigated: with the initial geometry of the nozzle apparatus having the same geometric neck area in each interscapular channel and with the geometry of the nozzle apparatus obtained by alternating two types of sectors with a reduced and initial throat area.The presented results are obtained on the basis of numerical simulation of a viscous unsteady gas flow in a transonic turbine stage using the SUnFlow home code, which implements a numerical solution of the Reynolds-averaged Navier-Stokes equations. Discontinuity of a torrent running on rotor blades is aggravated with heat drops between an ardent flow core and cold jets from film cooling of a blade and escapes on clock surfaces. Therefore, at simulation have been allowed all blowngs cooling air and drain on junctions of shelves the impeller.As a result of the replacement of the nozzle apparatus with a constant passage area by a nozzle apparatus with a variable area, a decrease in aerodynamic driving force by 12.5 % was obtained. The experimentally measured stresses arising in a pairwise bandaged blade under the action of this force decreased on average by 26 %.

Experimentally Verified Study of Regeneration-Induced Forced Response in Axial Turbines

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Jens Aschenbruck ◽  
Joerg R. Seume
Keyword(s):  
Vibration Amplitude ◽  
Turbine Blades ◽  
Forced Response ◽  
Rotor Blades ◽  
Response Analysis ◽  
Reference Case ◽  
Angle Variation ◽  
Air Turbine ◽  
Axial Turbines ◽  
Stagger Angle

Geometrical variations occur in highly loaded turbine blades due to operation and regeneration. To determine the influence of such regeneration-induced variances of turbine blades on the aerodynamic excitation, a typical stagger angle variation of overhauled turbine blades is applied to stator vanes of an air turbine. This varied turbine stage is numerically and experimentally investigated. For the aerodynamic investigation of the vane wake, computational fluid dynamics (CFD) simulations are conducted. It is shown that the wake is changed due to the stagger angle variation. These results are confirmed by aerodynamic probe measurements in the air turbine. The vibration amplitude of the downstream rotor blades has been determined by a computational forced response analysis using a unidirectional fluid–structure interaction (FSI) approach and is experimentally verified here by tip-timing measurements. The results of the simulations and the measurements both show significantly higher amplitudes at certain operating points (OPs) due to the additional wake excitation. For typical regeneration-induced variations in stagger angle, the vibration amplitude is up to five times higher than in the reference case of uniform upstream stators. Based upon the present results, the influence of these variations and of the vane patterns on the vibration amplitude of the downstream rotor blade can and should be estimated in the regeneration process to minimize the dynamic stresses of the blades.

3D Unsteady Forces of the Transonic Flow Through a Turbine Stage With Vibrating Blades

2002 ◽  
Author(s):  
Romuald Rza˛dkowski ◽  
Vitaly Gnesin
Keyword(s):  
Transonic Flow ◽  
Gas Flow ◽  
Element Model ◽  
Ideal Gas ◽  
Rotor Blades ◽  
Turbine Stage ◽  
Unsteady Forces ◽  
Outer Flow ◽  
Natural Modes ◽  
Flow Through

Numerical calculations of the 3D transonic flow of an ideal gas through turbomachinery blade rows moving relatively one to another with taking into account the blades oscillations is presented. The approach is based on the solution of the coupled aerodynamic-structure problem for the 3D flow through the turbine stage in which fluid and dynamic equations are integrated simultaneously in time, thus providing the correct formulation of a coupled problem, as the blades oscillations and loads, acting on the blades, are a part of solution. An ideal gas flow through the mutually moving stator and rotor blades with periodicity on the whole annulus is described by the unsteady Euler conservation equations, which are integrated using the explicit monotonous finite-volume difference scheme of Godunov-Kolgan and moving hybrid H-H grid. The structure analysis uses the modal approach and 3D finite element model of a blade. The blade motion is assumed to be constituted as a linear combination of the first natural modes of blade oscillations with the modal coefficients depending on time. The algorithm proposed allows to calculate turbine stages with an arbitrary pitch ratio of stator and rotor blades, taking into account the blade oscillations by action of unsteady loads caused both outer flow nonuniformity and blades motion. There has been performed the calculation for the stage of the turbine with rotor blades of 0.765 m. The numerical results for unsteady aerodynamic forces due to stator-rotor interaction are compared with results obtained with taking into account the blades oscillations.

A Multi Blade-Row Linearised Analysis Method for Flutter and Forced Response Predictions in Turbomachinery

2006 ◽  
Author(s):  
Gabriel Saiz ◽  
Mehmet Imregun ◽  
Abdulnaser I. Sayma
Keyword(s):  
Travelling Waves ◽  
Three Dimensional ◽  
Forced Response ◽  
Navier Stokes ◽  
Test Case ◽  
Test Cases ◽  
Simple Test ◽  
Analysis Method ◽  
Turbine Stage ◽  
Blade Row

A three-dimensional time-linearised unsteady Navier-Stokes solver is presented for the computation of multistage unsteady flow in turbomachinery. The objective is to address multistage aeroelastic effects for both flutter and forced response. Since the method is currently being developed, only forced response applications are studied in this paper. With this approach, travelling waves, known as spinning modes, are propagated across the multistage domain in order to take into account the interaction between the blade-rows. The method is first validated over two simple test cases for which analytical solutions were available. It is then tested on a turbine stage test case and multistage effects are evaluated from the contribution of one spinning mode included in the model. The results are compared with both time-linearised single-row and nonlinear multirow methods. Multi-row effects are shown not to be important in this case. However, the test case serves as a validation for the implementation of the methodology and further work will focus on the implementation of several spinning modes and the computations of forced response and flutter cases with several blade-rows.

scholarly journals Effects of the Rotor Tip Leakage in a Transonic Turbine With Long Blades

1998 ◽  
Author(s):  
Miroslav Št’astný ◽  
Richard Matas ◽  
Pavel Šafařík ◽  
Alexander R. Jung ◽  
Jürgen F. Mayer ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Three Dimensional ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Navier Stokes Equation ◽  
Flow Measurements ◽  
Tip Leakage ◽  
Transonic Turbine

A study of the flow in a transonic turbine stage with long and strongly twisted rotor blades is presented. The focus is on the flow in the near tip region of the blade-to-blade passage of the rotor. The flow has been modelled experimentally in a transonic wind tunnel and numerically by means of 2D and 3D Navier-Stokes equation solvers. The profiles of the rotor cascades are characterized by law turning angles and a high-velocity exit flow. Detailed flow measurements have been carried out and analysed. A comparison has been made between the experimental and numerical results, and is discussed in detail. The design and test data of the flow through the upper sections of the span are presented. The effects of the tip leakage flow are evaluated and the three-dimensional patterns of the main flow are estimated. Other points of interest are the results of 3D Navier-Stokes analysis of the stage flow as compared to 2D simulations and wind tunnel experiments, together with the question of the limitations of the individual methods as they all use approximations to the actual flow in the turbine stage.

Experimentally Verified Study of Regeneration-Induced Forced Response in Axial Turbines

2014 ◽  
Author(s):  
Jens Aschenbruck ◽  
Joerg R. Seume
Keyword(s):  
Vibration Amplitude ◽  
Turbine Blades ◽  
Forced Response ◽  
Rotor Blades ◽  
Response Analysis ◽  
Reference Case ◽  
Angle Variation ◽  
Air Turbine ◽  
Axial Turbines ◽  
Stagger Angle

Geometrical variations occur in highly loaded turbine blades due to operation and regeneration. To determine the influence of such regeneration-induced variances of turbine blades on the aerodynamic excitation, a typical stagger angle variation of overhauled turbine blades is applied to stator vanes of an air turbine. This varied turbine stage is numerically and experimentally investigated. For the aerodynamic investigation of the vane wake, CFD simulations are conducted. It is shown that the wake is changed due to the stagger angle variation. These results are confirmed by aerodynamic probe measurements in the air turbine. The vibration amplitude of the downstream rotor blades has been determined by a computational forced response analysis using a uni-directional fluid-structure interaction approach and is experimentally verified here by tip-timing measurements. The results of the simulations and the measurements both show significantly higher amplitudes at certain operating points due to the additional wake excitation. For typical regeneration-induced variations in stagger angle, the vibration amplitude is up to five times higher than in the reference case of uniform upstream stators. Based upon the present results, the influence of these variations and of the vane patterns on the vibration amplitude of the downstream rotor blade can and should be estimated in the regeneration process to minimize the dynamic stresses of the blades.

scholarly journals Magnetoelastic Coupling and Delta-E Effect in Magnetoelectric Torsion Mode Resonators

Sensors ◽  
2021 ◽  
Vol 21 (6) ◽  
pp. 2022
Author(s):  
Benjamin Spetzler ◽  
Elizaveta V. Golubeva ◽  
Ron-Marco Friedrich ◽  
Sebastian Zabel ◽  
Christine Kirchhof ◽  
...  
Keyword(s):  
Low Frequency ◽  
High Sensitivity ◽  
Element Model ◽  
Mode Number ◽  
Frequency Change ◽  
General Description ◽  
Resonance Modes ◽  
Field Sensor ◽  
Magnetic Sensitivity ◽  
Bending Modes

Magnetoelectric resonators have been studied for the detection of small amplitude and low frequency magnetic fields via the delta-E effect, mainly in fundamental bending or bulk resonance modes. Here, we present an experimental and theoretical investigation of magnetoelectric thin-film cantilevers that can be operated in bending modes (BMs) and torsion modes (TMs) as a magnetic field sensor. A magnetoelastic macrospin model is combined with an electromechanical finite element model and a general description of the delta-E effect of all stiffness tensor components Cij is derived. Simulations confirm quantitatively that the delta-E effect of the C66 component has the promising potential of significantly increasing the magnetic sensitivity and the maximum normalized frequency change ∆fr. However, the electrical excitation of TMs remains challenging and is found to significantly diminish the gain in sensitivity. Experiments reveal the dependency of the sensitivity and ∆fr of TMs on the mode number, which differs fundamentally from BMs and is well explained by our model. Because the contribution of C11 to the TMs increases with the mode number, the first-order TM yields the highest magnetic sensitivity. Overall, general insights are gained for the design of high-sensitivity delta-E effect sensors, as well as for frequency tunable devices based on the delta-E effect.

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