Free Vibration in a Mistuned Steam Turbine Last Stage Bladed Disk

2015 ◽  
Author(s):  
Marcin Drewczynski ◽  
Romuald Rzadkowski ◽  
Artur Maurin ◽  
Piotr Marszalek
Keyword(s):  
Steam Turbine ◽  
Natural Frequencies ◽  
Numerical Study ◽  
Mode Shapes ◽  
Fem Model ◽  
Bladed Disk ◽  
Turbine Efficiency ◽  
Pressure Steam ◽  
Fourth Series ◽  
Last Stage

The design of blades in the last stage of a steam turbine is one of the most demanding engineering tasks in the turbomachinery field. Increasing turbine efficiency has led to the designing of higher tip-to-hub ratios. Slender blading conforms to reliability requirements, such as high blade stiffness and a high first mode natural frequency. Several high vibration amplitude problems were reported regarding a slender last stage blading of a commercial low-pressure steam turbine. During maintenance it was decided that the blades would be geometrically mistuned to prevent self-excitation. This paper presents a numerical study of LP steam turbine last stage bladed disk mistuning. Two different approaches to mistuning were applied and numerically compared: geometrical and material. The mode shapes and natural frequencies of the steam turbine bladed disk were calculated on the basis of an FEM model. The smallest range of mistuning (0,5Hz) in a bladed disk contaminates nodal diameters up to the fourth series. This should be taken into account when tip-timing method is adapted for steam turbine operation monitoring.

Forced Vibration of Mistuned Bladed Discs in Last Stage LP Steam Turbine

2016 ◽  
Author(s):  
Romuald Rzadkowski ◽  
Artur Maurin ◽  
Leszek Kubitz ◽  
Ryszard Szczepanik
Keyword(s):  
Steam Turbine ◽  
Forced Vibration ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Lower Stress ◽  
Free And Forced Vibrations ◽  
Specific Order ◽  
Last Stage ◽  
Forced Vibration Analysis ◽  
Blade Geometry

During the exploitation of a commercial LP steam turbine, self-excitation occurred in the last stage of slender blades, inducing high vibration amplitudes. These problems were solved by changing the geometry of certain blades (feathering) and arranging them in a specific order (alternating mistuning). This paper presents free and forced vibrations of various mistuned steam turbine bladed discs. The natural frequencies and mode shapes of the steam turbine bladed discs were calculated using FEM models. Two different approaches to mistuning were applied: either the blade geometry or the Young’s Modulus were changed. Next, the results were compared. This showed that blade geometry mistuning gave the best results for long blades in the case of higher mistuning. The forced vibration analysis showed that the maximal blade stress location differed, depending on the kind of mistuning. The application feathering and alternating mistuning showed lower stress levels than the tip-timing measured standard mistuning pattern.

Optimal Stiffness Parameters of the Turbine Bladed Disk Computational Model

2013 ◽  
Author(s):  
Pavel Polach
Keyword(s):  
Computational Model ◽  
Steam Turbine ◽  
Topical Application ◽  
Natural Vibration ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Centrifugal Forces ◽  
Bladed Disk ◽  
Real Contact ◽  
Optimal Stiffness

Motivation for introducing this paper is the topical application of the method using the rotational periodicity of the structure at calculating natural vibration characteristics of the steam turbine bladed disk with continuous binding, in this case in the form of integral shrouding and in the middle of the blade with the tie-boss connection. Part of the shroud and the part of the tie-boss are the integral parts of the blade. Blades are free at non-rotating bladed disk. Blades of the advanced design are continuously coupled in the zone of the shroud and in the tie-boss zone by the blades untwist caused by the centrifugal forces acting at turbine rotation. The method used for the calculation of natural frequencies and mode shapes of the bladed disk with the continuous binding does not enable to model the real contact properties. The contact must be modeled by the flexible connection. The stiffness of the connection in the zones of adjoining blades contact is “tuned” at turbine operational speed (i.e. at 3000 rpm) in such a way that the values of calculated natural frequencies may come as near as possible to the values of the measured natural frequencies.

Some Remarks on the Dynamic Behaviour of Integrally Shrouded Blade Rows

2011 ◽  
Author(s):  
N. Bachschmid ◽  
S. Bistolfi ◽  
S. Chatterton ◽  
M. Ferrante ◽  
E. Pesatori
Keyword(s):  
Steam Turbine ◽  
Natural Frequencies ◽  
Low Pressure ◽  
Contact Forces ◽  
Mode Shapes ◽  
Torsional Vibrations ◽  
Vibration Modes ◽  
Nodal Diameter ◽  
Blade Row ◽  
Pressure Steam

Actual trend in steam turbine design is to use blades with integral shrouds, for high pressure and intermediate pressure steam turbine sections, as well as also for the long blades of the low pressure sections. The blades are inserted with their root into the seat on the shaft in such a way that the blades are slightly forced against each other in correspondence of the shrouds. In long blades of low pressure stages the forcing can be obtained by the untwisting of twisted blades due to the effect of the huge centrifugal forces. The dynamic behavior of these blade rows is difficult to predict due to the nonlinear effect of the contact forces and due to friction. Different models for the contact are proposed and compared. The resulting natural frequencies of the blade row as a function of the different nodal diameter mode shapes are highly depending on the assumed models. For avoiding resonant conditions with engine order excitations, the natural frequencies must be calculated with good accuracy. Some of the modes of the blade row, typically for the last stage of the low pressure steam turbine, can couple with some vibration modes of the rotor: flexural vibrations of the shaft couple with 1 nodal diameter mode shape of the row in axial direction and torsional vibrations of the shaft couple with the 0 nodal diameter mode in tangential direction. Therefore analyses of lateral and torsional vibrations of low pressure steam turbine shafts require also an accurate analysis of the blade row vibration modes.

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

2018 ◽  
Vol 211 ◽  
pp. 03003
Author(s):  
Romuald Rzadkowski ◽  
Leszek Kubitz ◽  
Michał Maziarz ◽  
Pawel Troka ◽  
Leszek Piechowski ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Natural Frequencies ◽  
Timing Analysis ◽  
Numerical Results ◽  
Mode Shapes ◽  
Fe Model ◽  
Numerical Studies ◽  
Last Stage

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.

scholarly journals Tip-Timing Measurements and Numerical Analysis of Last-Stage Steam Turbine Mistuned Bladed Disc During Run-Down

2019 ◽  
Vol 8 (3) ◽  
pp. 409-415 ◽  
Author(s):  
Romuald Rzadkowski ◽  
Leszek Kubitz ◽  
Michał Maziarz ◽  
Pawel Troka ◽  
Krzysztof Dominiczak ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Natural Frequencies ◽  
Timing Analysis ◽  
Mode Shapes ◽  
Fe Model ◽  
Blade Vibration ◽  
Nodal Diameter ◽  
Mode Localization ◽  
Numerical Studies ◽  
Last Stage

Abstract Background This paper presents the experimental and numerical studies of last-stage low-pressure (LP) mistuned steam turbine bladed discs during run-down. Methods The natural frequencies and mode shapes of the turbine bladed disc were calculated using an FE model. The influence of the shaft on the modal properties, such as natural frequencies and mode shapes, was considered. The tip-timing method was used to find the mistuned bladed disc modes and frequencies. Conclusions The experimental results from the tip-timing analysis show that the mistuning in combination with shaft coupling suppresses pure nodal diameter type blade vibrations associated with the fundamental mode shape of a cantilevered blade. Vibration modes emerge when even a single blade is vibrating due to the well-known mode localization caused by mistuning. The numerical results confirm this.

scholarly journals Failure Analysis in Lacing Wire Of Last Stage Low Pressure Steam Turbine Blade

2021 ◽  
Vol 1096 (1) ◽  
pp. 012097
Author(s):  
A M Kongkong ◽  
H Setiawan ◽  
J Miftahul ◽  
A R Laksana ◽  
I Djunaedi ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Steam Turbine ◽  
Turbine Blade ◽  
Low Pressure ◽  
Pressure Steam ◽  
Steam Turbine Blade ◽  
Last Stage

Detailed Numerical Study of the Main Sources of Loss and Flow Behavior in Low Pressure Steam Turbine Exhaust Hoods

2017 ◽  
Author(s):  
Dickson Munyoki ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Steam Turbine ◽  
Numerical Study ◽  
Flow Behavior ◽  
Low Pressure ◽  
Operating Conditions ◽  
Pressure Recovery ◽  
Exhaust Hood ◽  
Recovery Coefficient ◽  
Pressure Steam ◽  
Underlying Mechanisms

The performance of the axial-radial diffuser downstream of the last low-pressure steam turbine stages and the losses occurring subsequently within the exhaust hood directly influences the overall efficiency of a steam power plant. It is estimated that an improvement of the pressure recovery in the diffuser and exhaust hood by 10% translates into 1% of last stage efficiency [11]. While the design of axial-radial diffusers has been the object of quite many studies, the flow phenomena occurring within the exhaust hood have not received much attention in recent years. However, major losses occur due to dissipation within vortices and inability of the hood to properly diffuse the flow. Flow turning from radial to downward flow towards the condenser, especially at the upper part of the hood is essentially the main cause for this. This paper presents a detailed analysis of the losses within the exhaust hood flow for two operating conditions based on numerical results. In order to identify the underlying mechanisms and the locations where dissipation mainly occurs, an approach was followed, whereby the diffuser inflow is divided into different sectors and pressure recovery, dissipation and finally residual kinetic energy of the flow originating from these sectors is calculated at different locations within the hood. Based on this method, the flow from the topmost sectors at the diffuser inlet is found to cause the highest dissipation for both investigated cases. Upon hitting the exhaust hood walls, the flow on the upper part of the diffuser is deflected, forming complex vortices which are stretching into the condenser and interacting with flow originating from other sectors, thereby causing further swirling and generating additional losses. The detailed study of the flow behavior in the exhaust hood and the associated dissipation presents an opportunity for future investigations of efficient geometrical features to be introduced within the hood to improve the flow and hence the overall pressure recovery coefficient.

scholarly journals High-Fidelity Sensitivity Analysis of Modal Properties of Mistuned Bladed Disks Regarding Material Anisotropy

2018 ◽  
Author(s):  
Adam Koscso ◽  
Guido Dhondt ◽  
E. P. Petrov
Keyword(s):  
Sensitivity Analysis ◽  
Finite Element ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Finite Element Models ◽  
Coordinate Systems ◽  
Bladed Disks ◽  
Bladed Disk ◽  
Material Orientation

A new method has been developed for sensitivity calculations of modal characteristics of bladed disks made of anisotropic materials. The method allows the determination of the sensitivity of the natural frequencies and mode shapes of mistuned bladed disks with respect to anisotropy angles that define the crystal orientation of the monocrystalline blades using full-scale finite element models. An enhanced method is proposed to provide high accuracy for the sensitivity analysis of mode shapes. An approach has also been developed for transforming the modal sensitivities to coordinate systems used in industry for description of the blade anisotropy orientations. The capabilities of the developed methods are demonstrated on examples of a single blade and a mistuned realistic bladed disk finite element models. The modal sensitivity of mistuned bladed disks to anisotropic material orientation is thoroughly studied.

Sequential vs Multidisciplinary Coupled Optimization and Efficient Surrogate Modelling of a Last Stage and the Successive Axial Radial Diffuser in a Low Pressure Steam Turbine

2014 ◽  
Author(s):  
Kevin Cremanns ◽  
Dirk Roos ◽  
Arne Graßmann
Keyword(s):  
Steam Turbine ◽  
Design Process ◽  
Energy Demand ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Low Pressure ◽  
Steam Turbines ◽  
Low Pressure Turbine ◽  
Pressure Steam ◽  
Last Stage

In order to meet the requirements of rising energy demand, one goal in the design process of modern steam turbines is to achieve high efficiencies. A major gain in efficiency is expected from the optimization of the last stage and the subsequent diffuser of a low pressure turbine (LP). The aim of such optimization is to minimize the losses due to separations or inefficient blade or diffuser design. In the usual design process, as is state of the art in the industry, the last stage of the LP and the diffuser is designed and optimized sequentially. The potential physical coupling effects are not considered. Therefore the aim of this paper is to perform both a sequential and coupled optimization of a low pressure steam turbine followed by an axial radial diffuser and subsequently to compare results. In addition to the flow simulation, mechanical and modal analysis is also carried out in order to satisfy the constraints regarding the natural frequencies and stresses. This permits the use of a meta-model, which allows very time efficient three dimensional (3D) calculations to account for all flow field effects.

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