Industrial Steam Turbine Research Articles

Vibration Prediction of Bladed Disks Coupled by Friction Joints

The present review article addresses the vibration behavior of bladed disks encountered e.g. in aircraft engines as well as industrial gas and steam turbines. The utilization of the dissipative effects of dry friction in mechanical joints is a common means of the passive mitigation of structural vibrations caused by aeroelastic excitation mechanisms. The prediction of the vibration behavior is a scientific challenge due to (a) the strongly nonlinear contact interactions involving local sticking, sliding and liftoff, (b) the model order required to accurately describe the dynamic behavior of the assembly, and (c) the multi-disciplinary character of the problem associated with the need to account for structural mechanical as well as fluid dynamical effects. The purpose of this article is the overview and discussion the current state of the art of vibration prediction approaches. The modeling approaches in this work embrace the description of the rotating bladed disk, the contact modeling, the consideration of aeroelastic effects, appropriate model order reduction techniques and the exploitation of the rotationally periodic nature of the problem. The simulation approaches cover the direct computation of periodic, steady-state externally forced and self-excited vibrations using the high-order harmonic balance method, the formulation of the contact problem in the frequency domain, methods for the solution of the governing algebraic equations and advanced simulation approaches, including the concept of nonlinear modes.

Improving stability and operation of turbine rotors using adjustable journal bearings

A theoretical study on the application of parametric excitation through fluid film journal bearings in order to extend the stability margins is presented in this paper. The proposed 2-arc and 3-arc journal bearing configurations are able to provide periodical stiffness and damping variation in certain frequency and amplitude introducing parametric anti-resonances or resonances in the system, leading to stable or unstable operation respectively. Furthermore, the use of the proposed bearings as a mean for real time adjustment of the journal center and the shaft-line is highlighted for further investigation. The theoretical application of the proposed bearings to a medium size industrial steam turbine of higher speed demonstrates the extension of stability margins at rotating speeds even five times supercritical.

Numerical and experimental analysis of low-pressure steam turbine blades coupled with lacing wire

Many industrial steam turbine applications require the capability for variable speed operation in combination with high mass flow rates and high back pressure levels. Especially the low-pressure blading has to be designed carefully with respect to the mechanical integrity. An effective way to reduce blade vibration is the introduction of a simple lacing wire to couple the moving blades. In this paper, the structural behavior of blades coupled by a wire is verified by means of linear and nonlinear finite element method. Different modeling techniques for the coupling effects are presented and discussed. Special focus is put on the nonlinear effects of the contact between blade and wire to investigate the frictional damping performance of the system. The obtained numerical results are validated by strain gauge measurements on a full-scale test turbine under real steam conditions in an industrial steam turbine test rig. The experimental data show low blade vibration amplitudes in the whole operational range indicating a high damping performance of the investigated wire design. The calculation results from the forced response analysis including the frictional effects are in good agreement with the experimental data.

Experimental and Numerical Investigation of the Flow in a Low-Pressure Industrial Steam Turbine With Part-Span Connectors

An experimental and numerical study on the flow in a three-stage low-pressure (LP) industrial steam turbine is presented and analyzed. The investigated LP section features conical friction bolts in the last and a lacing wire in the penultimate rotor blade row. These part-span connectors (PSC) allow safe turbine operation over an extremely wide range and even in blade resonance condition. However, additional losses are generated which affect the performance of the turbine. In order to capture the impact of PSCs on the flow field, extensive measurements with pneumatic multihole probes in an industrial steam turbine test rig have been carried out. State-of-the-art three-dimensional computational fluid dynamics (CFD) applying a nonequilibrium steam (NES) model is used to examine the aerothermodynamic effects of PSCs on the wet steam flow. The vortex system in coupled LP steam turbine rotor blading is discussed in this paper. In order to validate the CFD model, a detailed comparison between measurement data and steady-state CFD results is performed for several operating conditions. The investigation shows that the applied one-passage CFD model is able to capture the three-dimensional flow field in LP steam turbine blading with PSC and the total pressure reduction due to the PSC with a generally good agreement to measured values and is therefore sufficient for engineering practice.

Mathematical modeling, validation, and operation optimization of an industrial complex steam turbine network-methodology and application

Complex turbine (i.e., steam turbine with multiple controlled and uncontrolled extractions) is one of the most important components in industrial utility system. The function of complex turbine is to generate power electricity, provide steam for the processes, and heat boiler feedwater using uncontrolled extraction steam. Although many studies have focused on the modeling and optimization of utility systems of different scales, few works have been reported on the modeling and operation optimization for utility system containing multiple complex steam turbines. In this paper, a superstructure of utility network consists of multiple interconnected various types of complex turbines (ICSTUN) is constructed. The superstructure demonstrates not only an external utility network that supplies utility energy for the processes but also an internal utility network that supplies boiler feedwater. A systematic modeling approach is developed for robust simulation, validation and operation optimization of ICSTUN. A mixed-integer nonlinear programming (MINLP) model based on an improved modeling principle of complex turbine is formulated for the operation optimization of ICSTUN. The MINLP model is able to simultaneously optimize the external and internal utility networks. A solving strategy incorporating model decomposition, model relaxation and case initialization is proposed to find a feasible solution. A large utility network in a petrochemical complex is studied to test the accuracy of the complex turbine model and the effectiveness of the proposed operation optimization methodology. The validation results of the complex turbine model show that the mean relative error between field operation data and simulation data is less than 1.18% and is acceptable in engineering application. The optimization of a single utility plant yields a maximum coal reduction rate of 4.59%, and the optimization of the total utility system consisting of two utility plants yields a maximum coal reduction rate of 6.01%. The optimization contribution is discussed in detail, and several conclusions and suggestions are presented.

Numerical and experimental study on aerodynamic optimization of part-span connectors in the last stage of a low-pressure industrial steam turbine

Industrial steam turbines are operated over an extremely wide range of operating conditions. In order to ensure safe turbine operation, even in blade resonance condition, conical friction bolts are mounted between blade reinforcements of adjacent last stage low-pressure blades. These part-span connectors (PSC) provide blade damping and coupling. However, additional losses are generated, which affect the performance of the turbine. In this paper, a numerical and experimental study on aerodynamic optimization of PSCs is presented. State-of-the-art three-dimensional computational fluid dynamics (CFD) applying a nonequilibrium steam model is used to examine the wet steam flow in coupled last stage blading. The one-passage CFD model with parameterized PSC geometry features structured high-resolution hexahedral meshes. Experimental data of measurements with pneumatic multi-hole probes in an industrial steam turbine test rig are used for validation. According to the good agreement between measured and predicted flow field downstream of the last stage rotor blading, the CFD model is valid to capture the loss induced by the PSC. A numerical study on the aerodynamic effects of geometrical variations of PSCs concerning blockage area and shape is presented in this work. Based on this study, a performance assessment of different PSC designs is discussed and numerical results are compared to the loss coefficients predicted by Traupel’s analytical correlation, which is widely used in industry.

The series of siemens SST-200 to SST-900 steam turbines in Russia

The chronology of cooperation between the transnational German concern Siemens and Russia is given. The designs of the SST-200-SST-900 series of industrial steam turbines for electrical capacities ranging from 10 to 180 MW that were installed at thermal power plants and industrial facilities of Russia in the period 2004–2014 are reviewed. The design features of the SST-600 steam turbine used as part of the PGU-200 combined-cycle plant installed at the Southwest cogeneration station are considered.

Analysis of flow-induced instability in a redesigned steam control valve

Industrial steam turbines represent one of the largest fractions of prime movers. Regardless of the steam-turbine application being considered, speed and/or load control will be required. Speed control is the primary control loop for all turbine applications, industrial as well as utility. The inlet of industrial steam turbine is usually controlled by a single valve, or a series of valves (multi-valve assembly) working in concert. These valves are required to operate under wide ranges of valve openings and pressure ratios. As a turbine governing valve, the venturi valve, has been widely used in steam turbines to regulate inlet flow in the last 40 years. But as turbine output power become larger, a number of valve failure incidences started to be reported and improving the valve designs became a high priority. Despite numerous investigations to eliminate valve failure, the attempts were not fully successful due to the complicated nature of the fluid–structure interaction mechanisms, and the basic mechanism causing valve vibration and failure is still far from being fully understood. As a continuation of previous valve studies, a newly designed valve has been investigated experimentally and. This paper presents detailed experimental investigations to clarify the mechanisms of valve instability caused by unsteady flows around the valve. A result of the asymmetric unstable flow, noise and vibration characteristics of the valve together with an overall performance assessment of the valve is presented.

ICOPE-15-C150 Numerical Investigation on the Performances of the Last Three Stages in an Industrial Steam Turbine under Different Operation Conditions

ICOPE-15-C150 Numerical Investigation on the Performances of the Last Three Stages in an Industrial Steam Turbine under Different Operation Conditions

ICOPE-15-C143 Unsteady Study on the Performance in a Low-pressure Turbine Stages with Tip Clearance under Design and Off-design Load Conditions

Previous research has shown that tip clearance in a low-pressure turbine stage is of practical significance in evaluating the overall loss and off-design condition always occur due to the complex operating conditions. Both of the vortices and operation under low load condition generate strong unsteadiness and oscillating, which may give rise to unreliability of steam turbine. This research mainly focus on investigating the unsteady performance of last two stages with tip clearance in a 100MW industrial steam turbine under design and off-design load conditions. An unsteady numerical simulation was conducted to predict the transient flow properties in the flow field, in which the K-w SST turbulence model has been used. This paper gives the characteristics curve, then the design point and low volume flow conditions were respectively focused on. The scrolled tip leakage vortex and its interaction with the mainstream were analyzed. Correspondingly, the aerodynamic losses caused by the flow near the wall were also shown. Comparison of the transient results under different volume flow conditions was made. The results show that the variation of the leakage vortex varies with time and different volume flow conditions. The structure, intensity and trajectory of the leakage vortexes and other vortexes were captured. The extending of tip leakage vortex stretches and shrinks with a regular periodic process for the leakage flow at tip clearance. Under design condition, the interaction of tip leakage flow with the mainstream was strong. And under low volume flow condition, a reverse flow region was shown and the unsteadiness was stronger because of the presence of many vortexes. The vortexes influence the flow patterns in stages, and the flow patterns give rise to the corresponding aerodynamic characteristics, since the blade load may show the influence of the tip clearance. The conclusions drawn by this paper may provide a reference for the further low-pressure stage blade design of 100MW industrial steam turbine. By numerical study in this paper, the mechanism and consequence of flow with leakage flows were understood more deeply under design and off-design load conditions.

Numerical Investigation on the Flow in Tip Clearance of the Last Three Stages of Industrial Steam Turbine

Numerical investigation was conducted on the full-three-dimensional flow in the last three stages of steam turbine using by the commercial computational flow dynamics software CFX. And the equilibrium condensation model was adopted to describe the wet steam two phase flows. This article analyzes the internal flow of the turbine with tip clearance and the structure of the leakage flow.

Concept development for the experimental investigation of forced convection heat transfer in circumferential cavities with variable geometry

Cavities of various geometries occur in several technical applications and the knowledge about the heat transfer inside them is limited. For industrial steam turbines, this becomes critical since thermal casing distortion needs to be predicted reliably in the development process. A test rig concept is presented in this paper to investigate the forced convection heat transfer in cavities with various geometries where the enclosed fluid is driven indirectly by an external turbulent air flow. The dimensions are chosen to achieve similarity with side spaces in steam turbines. For estimating the flow conditions in the side spaces, a computational fluid dynamics analysis and experiments at a shallow water duct were conducted. Two different methods will be used to determine the heat transfer coefficient along the outer cavity wall of the compressed air test rig: the overtemperature method and the steady-state inverse method. In order to eliminate flow disturbances due to natural convection in the cavity and interference among the measurement systems, a parametrical finite element analysis was performed to determine an appropriate concept for the sensor arrangement.

Study of Autoregressive (AR) Spectrum Estimation Algorithm for Vibration Signals of Industrial Steam Turbines

Spectral analysis of the vibration signals of industrial steam turbines provides efficient reference for the characterization and discrimination of turbine faults. Conventional power spectrum estimation methods often exhibit contradiction between variance performance and resolution, leading to poor estimation results. In this study, we investigated Levision-Durbin recursive algorithm, Burg algorithm and periodogram power spectrum estimation algorithm, and also chose Akalke Information Criterion (AIC) to identify the optimal order p. Based on MATLAB, we wrote a simulation program for Autoregressive (AR) spectrum estimation algorithm and designed a graphic user interface, formulating the AR spectrum estimation algorithm program for vibration signals of industrial steam turbines. After field measurement of a steam turbine with sampling number of 400 and frequency of 256Hz, as well as order of 10 and 80, simulation was performed. It was demonstrated that AIC provides efficient reference for the identification of proper order. With the optimal order, AR spectrum estimation algorithm produces good variance performance and resolution, providing reference for the spectral analysis of vibration signals of industrial steam turbines.

Finite Element Analysis of Four Fracture Mechanism in the Thermal Barrier Coating

With the development of high temperature protective material, thermal barrier coatings are used in the field of aircraft and industrial steam turbine. They have characteristics of complex structure and long-term work in high temperature environment, etc. Because of multilayer material physical properties mismatch, oxidation, interface roughness, creep stress and so on, the coatings system is easy to produce cracks, expand and link near the interface of coating during thermal cycling. By establishing I, II, III, IV four numerical models of crack fracture mechanisms, assuming that the thickness of oxidation layer is constant, considering the influence of interface roughness and material properties mismatch in the process of thermal cycling, it gets the results of residual stress field near the crack and the influence of the interface. Compared to the presence of defects, four kinds of crack failure mechanisms are analyzed. Energy release rate is calculated by the virtual crack closure method, which can conclude the cracks of I, IV tip stress concentration phenomena are obvious, crack II is easy to expand, due to the temperature load, crack III does not appear stress concentration phenomenon at the tip.

Analysis of Flat Plate Honeycomb Seals Aerodynamic Losses: Effects of Clearance

Among the various type of seals used in gas turbine secondary air system to guarantee sufficient confinement of the main gas path, honeycomb seals well perform in terms of enhanced stability and reduced leakage flow. Reliable estimates of the sealing performance of honeycomb packs employed in industrial gas and steam turbines, are however missing in literature, thus, in order to evaluate the complete characteristic curve of the seals in the wide range of working conditions, an experimental campaign was planned. This work reports the findings of an experimental campaign aimed at evaluating aerodynamic losses within honeycomb seals.Due to the generally large amount of honeycomb cells typically present in real seals, it would be convenient to treat the sealing effect of the honeycomb pack as an increased distributed friction factor on the plain top surface that is why the simplest config- uration, the honeycomb facing a flat plate, is employed in this paper. The geometry of the hexagonal cell and the investigated clearances were chosen to well represent actual honeycomb packs employed in industrial compressors. First the pressure distribu- tion within the seal was analysed verifying that downstream the first 5 rows of cells, where entrance effects are predominant, the relative pressure drop is almost constant thus the use of an equivalent friction factor is appropriate to characterize the seal. Subse- quent analysis focused on the characterization of the friction factor as function of the Reynolds number with the aim of establishing the proper geometrical scaling to achieve flow conditions similar to real turbine most critical ones.The different behaviour of the honeycomb sealing depending on the hexagonal cell arrangement and dimensions was evaluated in terms of friction factor.Comparison with results coming from a previous CFD investigation is also presented and discussed in this paper.

Design of an active fault tolerant control system for a simulated industrial steam turbine

An active fault tolerant control (FTC) scheme is proposed in this paper to accommodate for an industrial steam turbine faults based on integration of a data-driven fault detection and diagnosis (FDD) module and an adaptive generalized predictive control (GPC) approach. The FDD module uses a fusion-based methodology to incorporate a multi-attribute feature via a support vector machine (SVM) and adaptive neuro-fuzzy inference system (ANFIS) classifiers. In the GPC formulation, an adaptive configuration of its internal model has been devised to capture the faulty model for the set of internal steam turbine faults. To handle the most challenging faults, however, the GPC control configuration is modified via its weighting factors to demand for satisfactory control recovery with less vigorous control actions. The proposed FTC scheme is hence able to systematically maintain early FDD with efficient fault accommodation against faults jeopardizing the steam turbine availability. Extensive simulation tests are conducted to explore the effectiveness of the proposed FTC performances in response to different categories of steam turbine fault scenarios.

A network methodology for structure-oriented modular product platform planning

With the formation of world markets, the competition between enterprises has focused on how to deal with the conflict between scale economy with batch production and customers’ individual requirements in mass customization. An effective method is product family development and design based on product platforms. Considering the characteristics of the complex modular products, two types of network models including parts connection network and generic-modules connection network are built taking parts or generic-modules as nodes. Based on the network model and network properties, generic-modules are divided into basic modules, must-selected module and may-selected module, and the modular main structure of the product family is constructed layer-by-layer via breadth first search. A layer-build model of the modular product platform is proposed and a bottom-up development method is provided for the industrial steam turbine as a case study.

A semi-empirical procedure for the evaluation of multi-stage turbine performances

The available tools for the analysis of fluiddynamic processes inside turbomachines are nowadays extremely powerful and versatile. Despite this, the use of simplified procedures, such as the 2D meridional approach, is still relevant, due to its great running simplicity and good accuracy. The full three-dimensional analysis, in fact, even if it could model thoroughly details the fluid-dynamic phenomena occurring in turbomachines, requires huge computational resources and longer computational times with respect to two-dimensional approaches, and this is justified only after a simplified preliminary study of the machine. Also management simplicity, consistence of the required data and usability of results are aspects that should not be ignored, above all for the possibility of creating tools easily available for turbomachines designers. A through flow method, formulated in terms of pressure rather than velocity, for the analysis of multistage axial turbines is presented. It is designed to provide reliable radial distributions of circumferentially averaged values for the fundamental unknowns. The proposed form of the radial equilibrium equation can represent also sharp velocity gradients in radial direction and deal with very realistic situations as discussed in the applications presented. The code has been used for the analysis of both an experimental multistage gas turbine and an industrial steam turbine. The results obtained have been compared with the circumferentially averaged results of a viscous fully 3D commercial code.

The Modularity and Connectivity of the Master Structure of Complex Product Families

The master structure of product families, as a configuration network, is a collection of a variety of modular components and their configuration relationships. In the forming processes of the master structure of product families, various modularity types reveal complex dynamic behaviors with strong impacts on the connectivity of networks. The connectivity of the directed configuration network of realistic industrial steam turbines is investigated and found to be heterogeneous. The heterogeneity of configuration networks results from the reusability difference of components based on the copy mechanism, and the preferential and random attachment mechanisms of inputs and outputs of directed edges. Finally, an evolving model is established to characterize the growing process of the master structure of product families.

Fault detection and diagnosis of an industrial steam turbine using a distributed configuration of adaptive neuro-fuzzy inference systems

The issue of fault detection and diagnosis (FDD) has gained widespread industrial interest in process condition monitoring applications. An innovative data-driven FDD methodology has been presented in this paper on the basis of a distributed configuration of three adaptive neuro-fuzzy inference system (ANFIS) classifiers for an industrial 440 MW power plant steam turbine with once-through Benson type boiler. Each ANFIS classifier has been developed for a dedicated category of four steam turbine faults. A preliminary set of conceptual and experimental studies has been conducted to realize such fault categorization scheme. A proper selection of four measured variables has been configured to feed each ANFIS classifier with the most influential diagnostic information. This consequently leads to a simple distributed FDD system, facilitating the training and testing phases and yet prevents operational deficiency due to possible cross-correlated measured data effects. A diverse set of test scenarios has been carried out to illustrate the successful diagnostic performances of the proposed FDD system against 12 major faults under challenging noise corrupted measurements and data deformation corresponding to a specific fault time history pattern.