Steam Turbine Stage Research Articles

Effect of the water erosion on the non-equilibrium condensation in steam turbine cascade

In the final stage of steam turbines, droplets formed by non-equilibrium condensation continuously impact and erode the blades, leading to changes in surface roughness and leading edge erosion. This study investigates the effects of roughness changes and leading edge erosion, induced by water erosion, on non-equilibrium condensation in steam turbine cascades using numerical simulation methods. In a Moses-Stein nozzle, the mechanism of roughness influencing non-equilibrium condensation is analyzed. Subsequently, entropy generation theory is applied to assess the loss distribution caused by roughness variations in a Dykas cascade. Furthermore, flow field analysis and entropy generation theory are utilized to examine the loss distribution pattern resulting from leading edge erosion. Results show that increased roughness delays non-equilibrium condensation, reducing average outlet humidity (from 0.05351 to 0.04361 as roughness rises from 0 to 500 µm). The effect of roughness on thermodynamic entropy generation exhibits a non-linear relationship, balancing steam flow losses with mitigated phase-change-related losses at a roughness of 896 µm. Significant blade erosion (>3 mm) alters leading edge geometry, causing local flow separation and a substantial increase in airfoil losses.

Numerical Analysis of A Two-Phase Turbine: A Comparative Study Between Barotropic and Mixture Models

Abstract Two-phase turbines offer the potential to significantly enhance the performance of power generation and refrigeration systems. However, their development has been hindered by comparatively lower efficiencies resulting from additional loss mechanisms absent in single-phase turbines. To date, most multiphase CFD studies on turbomachinery have focused on condensation in the final stages of steam turbines, and on cavitation in hydraulic pumps and turbines. These applications, however, are not representative of the conditions in two-phase turbines, where a liquid-dominated mixture undergoes a large expansion ratio, leading to a significant increase in the gas phase volume fraction throughout the entire flow. This paper aims to identify a suitable modeling methodology for two-phase turbines. Our evaluation is centered around two models: the mixture model and the barotropic model. The validity and accuracy of these two modeling approaches is assessed using existing experimental data from a single-stage impulse turbine operating with several mixtures of water and nitrogen as working fluid. The results indicate that both the mixture and barotropic models are consistent and accurately predict the nozzle mass flow rate, yet, both models systematically overpredict the nozzle exit velocity and rotor torque. Adding correction terms for windage and unsteady pumping losses significantly improves the torque predictions, bringing them within the uncertainty range of the experimental data. In addition, refining the models to account for the effect of slip presents a promising avenue to enhance the prediction of nozzle exit velocity and overall performance of two-phase turbines.

Effect of Blade Material of Steam Turbine Rotor on Aeroelastic Characteristics

Elements of powerful steam turbines are subjected to significant unsteady loads, in particular the rotor blades of the last stages. These loads, in some cases, can cause self-excited oscillations, which are extremely dangerous and have a negative impact on the efficiency and service life of the blade cascade. Therefore, when designing new or modernizing existing steam turbine stages, it is recommended to study the aeroelastic characteristics of the blades. The conditions for the occurrence of self-excited oscillations are influenced by both the geometric characteristics and the alloy from which the blade is made. To determine the effect of the blade material on the aeroelastic behaviour, a numerical analysis of the aeroelastic characteristics of the last stage blades made of steel and titanium alloy was performed. For the analysis, the method of simultaneous modeling of unsteady gas flow through the blade cascades and elastic vibrations of the blades (coupled problem) was used, which allows obtaining the amplitude-frequency spectrum of the interaction of unsteady loads and blade vibrations. The paper presents the results of numerical analysis for harmonic oscillations with a given amplitude and a given inter-blade phase angle, as well as for the regime of coupled vibration of blades under the action of unsteady aerodynamic forces. The dependences of the aerodamping coefficient on the inter-blade phase angle and the distribution of the coefficient along the blade are presented. The results of modeling the coupled vibration of the blades for the first six natural forms are presented in the form of a time-evolving displacement of the blade peripheral section, as well as forces and moments acting on the peripheral section. The corresponding amplitude-frequency spectra of displacements and loads in the peripheral section are also presented. The analysis of the results showed an insignificant difference in the characteristics of the proposed blade materials. For the first natural form of blade oscillations, the possibility of self-excited oscillations was found, and for the second form, there are conditions for the appearance of stable self-oscillations.

On setting boundary conditions for calculations of turbomachines in 3-d computer packages

Unfortunately, in a growing number of publications of the results of the study of turbomachines in ANSYS and other packages, insufficient attention is paid to the choice of the flow model (absolute or relative) and the setting of boundary conditions in the areas adjacent to the rotating impeller: shroud seal, diaphragm (end) seals, gap over shroudless blades, steam balance holes, etc.As a rule, these areas contain such elements of geometry as a “ledge”, “projection”, “crest”, the flow around which, and, consequently, their resistance depends on the angle of incoming flow relative to the barrier. In the stages of turbomachines in sections behind fixed blade units, angle α1 between the flow velocity vector (in absolute motion) and the circumferential velocity is 10°÷25° (for steam turbine stages), 20°÷35° (for gas turbine stages) and 40°÷75° ((for axial compressor stages). It is shown (using the example of viscous flow around the “ledge + projection” system) that a change in the angle in the range of 15°÷90° changes the resistance by almost 2 times.The choice of a particular type of flow model (absolute or relative) for the domain primarily determines the value of the angle of interaction of the flow lines with an obstacle: it remains close to α1, or close to β1 = α1 + 20°÷70°, which significantly changes the qualitative picture of the viscous flow around the characteristic elements of geometry (“ledge”, “projection”, “crest”), and the values of integral parameters (flow rate, power, efficiency). The lack of recommendations on the correct choice of boundary conditions will inevitably lead not only to the inability to compare the results of various published studies, but also to their objective value. Therefore, the need to substantiate proposals for the choice of flow models in the areas of labyrinth seals, steam balance holes, gaps over shroudless blades, etc. is very relevant.

Determining the Idle Mode of the Last Stages of Powerful Steam Turbines for Wet Steam Area

Determining the Idle Mode of the Last Stages of Powerful Steam Turbines for Wet Steam Area

Numerical study of the impact of hot steam injection in the condensation flow through the low-pressure stage of steam turbine

Nowadays, steam turbines are the devices vastly used for energy generation in power plants. Accordingly, their performance and efficiency are crucially significant. In the last stages of the steam turbine, the presence of liquid phase decreases the efficiency and causes thermodynamic and dynamic losses. Various parameters can affect the steam flow and change the liquid droplets generated as well as the wetness fraction. In the present study, the hot steam injection parameter which affects the wetness decrease for the low-pressure stage of a steam turbine (LPST) has been investigated. First, the impact of hot steam injection (HSI) was studied on the wet steam flow parameters. Hot steam is injected on the suction surface of the stator with various slot angles and slot widths to select the optimal case. The goal of this study is to achieve the optimal value of injection variables to use this method further. To apply this, the LKHCE (Liquid mass, Kinetic energy, Hot steam, Condensation loss, Efficiency) criterion is used for all modes. Also, by examining the results of this method and using the TOPSIS, the optimal case can be selected. The condensing flow of wet steam through the stator-rotor blades is modeled using an Eulerian-Eulerian model and the SST k-turbulence model. Case 6 (angle 40°, slot width 0.1(cm)) for HSI is predicted as the optimal case, in which RL and RC decrease by 35.5 % and 34.6%, respectively, and RE is increased by 1.3%. The HSI caused a slight decrease in RK by 0.3% at the steam turbine stage’s outflow.

Optimization of operating conditions in the stage of steam turbine by black-box method

From the point of view of performance and economical in power plants, it is necessary to pay attention to the measurement of wet steam. The objective of this research is to employ the multi-objective black-box technique to minimize thermodynamic losses related to wet losses and improve the efficiency of the steam turbine, disregarding the process of film water deposition on the blade surface. For this purpose, a complete model of the steam turbine stage consisting of a stator-rotor is used to study wet steam. The simultaneous effects of two design variables on the performance of the steam turbine stage have been analyzed. The numerical model of wet steam flow has been used for calculating the values of the optimization criteria, including integral of wetness fraction (IWF), integral of mean droplet radius (IDR), turbine stage efficiency (TSE), condensation loss rate (Lr), and mass flow rate (Mr). According to the results, the temperature and pressure ratio were suggested to be 339.44 (K) and 0.51 (−), respectively, which improved the IWF by 30% and the IDR by about 7.3%. Also, the optimal mode increased TSE by about 1.3% and led to the reduction of Lr and Mr, by about 29%, and 1.3%, respectively.

Comparative assessment of aerodynamic losses in turbine stages with supercritical carbon dioxide and steam

To investigate the aerodynamic loss mechanisms in supercritical carbon dioxide turbine (CT) and steam turbine (ST) stages, entropy generation and entropy generation rate are used to analyze various losses in stage passages. The results reveal that under sealing clearance at 2.5 % blade height, the leakage losses of CT and ST constitute over 7 % of total available energy. Rotor and stator losses of CT and ST decrease as the Mach number of stage outlet increases. The endwall losses of CT and ST rotor are both predominant, constituting over 1.78 % of total available energy, with lower endwall losses of CT rotor. Furthermore, the stator profile loss of CT represents the majority of stator loss and is notably higher than that of ST. The impact loss and separation loss are more pronounced in CT. The conclusions will provide direction, guidance, and data support for the design and optimization of CT and ST.

Evaluation of a New Droplet Growth Model for Small Droplets in Condensing Steam Flows

As the condensation phenomenon occurs in the low-pressure stages of steam turbines, an accurate modelling of the condensing flows is very crucial and has a significant impact on the development of highly efficient steam turbines. In order to accurately simulate condensing steam flows, it is essential to choose the right condensation model. Further research to enhance condensation models is of special importance because the outcomes of numerical studies of condensation models in recent years have not been entirely compatible with the experiments and there are still uncertainties in this area. Therefore, the main aim of this paper is to evaluate a proposed droplet growth model for modelling condensation phenomenon in condensing steam flows. The new model is derived to profit from the advantages of models based on the continuum approach for large droplets and those based on the kinetic theorem for small droplets, which results in the model being robust for a wide range of Knudsen numbers. The model is implemented into a commercial CFD tool, ANSYS Fluent 2022 R1, using UDFs. The results of the CFD simulations are validated against experimental data for linear cascades within the rotor and stator blade geometries of low-pressure steam turbine stages. The findings clearly demonstrate the superiority of the new model in capturing droplet growth, particularly for very small droplets immediately following nucleation. In contrast, widely used alternative droplet growth models tend to either underpredict or overpredict the droplet growth rate. This research significantly contributes to the ongoing efforts to enhance condensation modeling, providing a more accurate tool for optimizing the design and operation of low-pressure steam turbines, ultimately leading to a higher energy efficiency and a reduced environmental impact.

Advanced Noncontact Sensors for Blade Tip-Timing Systems

The conference paper addresses noncontact sensors for measuring vibrations of machine blades using the Blade Tip Timing method. An overview of sensors based on the electromagnetic principle suitable for the harsh environment of low-pressure stages of steam turbines is presented. Special attention is further given to magnetoresistive sensors and possibilities for increasing their sensitivity. Variants of the sensors with controlled, adaptive, and intelligent operating principles are discussed. The properties and advantages of each version of the solution are demonstrated.

Simulation of Active Power Generation During Operation of a Steam Turbine Stage in Low-Steam and Motor Modes

The operation mode of the steam turbine stage in low-steam and motor modes is considered. The features of the operation of the steam turbine stage in the motor mode are given. It is shown that the condition accepted in earlier studies of hydrodynamic processes in the turbine stage during its operation in the motor mode, that the cooling steam flows through the stage without expansion, i.e. without generating active power, is valid if the entire flow part of the turbine is under pressure in the condenser and there is no pressure drop in the stages. The conditions under which the stage operates in the ventilation mode or in the mode of generating active power are determined. The technique developed with this condition in mind allows, with known parameters before the stage and the pressure ratio before and behind the stage, to determine the operating mode of the stage.

Nonlinear Dynamics and Combination Resonance of a Flexible Turbine Blade with Contact and Friction of Shrouds

Flexible shrouded blades are commonly adopted in the last stages of steam turbines where complicated dynamical behavior can be induced by dry friction force generated on contacting interfaces between adjacent shrouds and the geometric nonlinearity due to the structural flexibility of the blades. In this paper, combination resonance caused by contact and friction forces generated on shroud interfaces is investigated, which is a concurrence of 1:3 internal resonance involving the first and second modes in the flapwise direction and the primary resonance of the first flapwise mode. The stiffness and damping at the contact interface are obtained by linearizing the contact and friction forces between shrouds through the harmonic balance method. The vibrating blade is modeled as a beam with a concentrated mass of which the responses under the combination resonance are solved through the multiple-scale method. Sensitivities of response with respect to the angle of shrouds, contact stiffness and rotation speed are illustrated, and the influences of these parameters on the periodicity and amplitudes of steady responses are demonstrated. The parametric regions where the combination resonance occurs are pointed out. Finally, parametric analyses are presented to show how the amplitude–frequency relation of the multiple-scale solutions under the combination resonance vary with detuning and design parameters. The present research provides a designing basis for improving the dynamic performance of flexible shrouded blades and suppressing vibrations of blades by adjusting structural parameters in practical engineering.

An investigation comparing various numerical approaches for simulating the behaviour of condensing flows in steam nozzles and turbine cascades

The process of condensation takes place within the low-pressure stages of the steam turbine when undergoing rapid expansion. The dry supercooled steam turns into very tiny liquid droplets, and the resulting wet steam mixture causes additional losses and maintenance problems. Accurate simulation of steam condensing flows helps to obtain accurate information about the thermodynamics of such flows and use this information in the design of highly efficient steam turbine stages. In this study, by using the available numerical models in commercial CFD codes, seven cases are considered for simulating steam condensing flows. The important difference between these cases is the use of different condensation models and different equations of state to calculate the thermodynamic properties of wet steam. The objective of this research is to identify an appropriate model that can be used to simulate the flow of steam condensation effectively. In recent studies, it is still necessary for further improvement of the modelling methods because the numerical results did not fully match the experimental findings, underscoring the persisting uncertainties within this domain. The current study explores various condensation models and equations of state for calculating the thermodynamic properties of wet steam. This diversity of approaches is novel and allows for the comparison of different models to determine the most suitable one for effective flow simulation. The geometries of the IWSEP nozzle (International Wet Steam Experimental Project) and linear cascade of the last-stage rotor blades were considered. To identify the most appropriate model for the simulation of steam condensing flows, the numerical results are validated against in-house experiments. The results indicate that combining the Young droplet growth model with the Vukalovich and Young equations in cases 1 and 2 is not a suitable method for modelling steam condensing flows. However, cases 3 & 4, which are the combination of Gyarmathy and Fuchs-Sutugin droplet growth models with NIST real gas models, are the most appropriate ones. The findings of this research confirm the high sensitivity of the modelling of such flows, and emphasize that the necessary care should be taken in choosing the appropriate numerical model.

Enhancing low-pressure stage steam turbine using the TDLD criterion and the TOPSIS analysis

The liquid phase in the wet steam flow causes thermodynamics losses and affects steam turbine blade durability. The main objective of the present research is the design of the rotor stagger angle and different operating conditions in the low-pressure stage of the steam turbine. A two-phase Eulerian-Eulerian model and the SST k − ω model are used to simulate the viscous wet steam flow inside the steam turbine stage. Frozen rotor methodology is employed for modeling the stator-rotor interaction. The effects of different rotor stagger angles and different outlet pressure levels on the wet steam flow parameters are studied to introduce an improved case. The turbine stage efficiency, droplet average radius, liquid mass fraction, and degree of reaction (TDLD) are considered as design criteria. The search for the improved value of pressure ratio and rotor stagger angle is performed using the TDLD criterion by TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution). The improved case is selected with a rotor stagger angle of 64 degrees and outlet pressure of 6.5 kPa, at which the turbine stage efficiency (TSE) is increased by 21.3% compared to [Formula: see text]. Also, the liquid mass fraction (LMF) and the degree of reaction (DOR) reduced by 39.53 and 26% relative to [Formula: see text], and [Formula: see text], respectively. In addition, droplet average radius (DAR) increases by 26.14% compared to [Formula: see text].

The influence of stator-rotor interspace overlap of meridional contours on the efficiency of high-pressure steam turbine stages

The influence of stator-rotor interspace overlap of meridional contours on the efficiency of high-pressure steam turbine stages

Techno-economic assessment of an autothermal poly-generation process involving pyrolysis, gasification and SOFC for olive kernel valorization

The present work elaborates on the simulation and techno-economic analysis of a proposed MW-scale hybrid scheme that enables the production of different marketable products (i.e., electric energy and bio-oil) from the thermochemical exploitation of olive kernel residual biomass. In this regard, detailed calculations for mass and energy balances, process simulation in Aspen Plus and economic analysis with complementary sensitivity scenarios were conducted, with the aim to model and assses the feasibility of an integrated process for electricity and crude bio-oil co-generation via subsequent stages of biomass pyrolysis, bio-char gasification, syngas-fed SOFC and steam turbine. Notably, it was demonstrated that the provision of 20 tn/day of raw olive kernel resulted in a net electricity generation of 1685 kWel as well as production of 3.4 tn/day of bio-oil, without the need for external heating. Equally importantly, the overall electric efficiency and the combined bio-oil/power co-generation efficiency of the integrated process were equal to 46.8% and 77.0%, respectively, being amongst the highest values reported in relevant works. Moreover, economic analysis revealed that syngas clean-up and SOFC units account for 75% of the total fixed capital investment as well as for 62% of the annual operation costs. Nonetheless, increased unit cost is largely counterbalanced by the fact that electricity generation accounts for ∼85% of total profits. Also, it was found that the proposed venture is not profitable considering current market values for electricity and bio-oil. However, sensitivity analysis revealed that a main equipment cost reduction of 70% is a prerequisite for the break-even electricity price to attain the current market values. Moreover, profitability can be marginally improved further by accounting for a state subsidization of more than half of the initial investment and by the increase of the crude bio-oil price at 700 €/tn.

Optimum operation of an ejector-assisted combined flash-binary geothermal cycle using R245fa-isopentane mixture-based secondary working fluids

Combined flash binary geothermal cycle (CFBGC) is a traditional geothermal energy conversion technology. However, in a CFBGC, substantial exergy destruction occurs during the steam flashing. To address this issue, in the present study, the steam flashing device of the conventional CFBGC is replaced by an ejector. The ejector enhances steam cycle power output by ensuring a higher steam flow rate through the high-pressure steam turbine stage. The modified cycle is designated as the ejector assisted combined flash binary geothermal cycle (EACFBGC). To take advantage of temperature glide, various compositions of R245fa-isopentane mixture are considered as secondary working fluid. Optimum operating parameters corresponding to the maximum second law efficiencies of the proposed and conventional cycles are explored by applying an iterative method. Both considered cycles yield the highest second law efficiencies with the 0.7 mol fraction of isopentane in the working fluid mixture. For geo-fluid available at 170 °C, the second law efficiency of the optimized EACFBGC is about 8.08% higher than that of the optimized conventional CFBGC. The corresponding levelized cost of electricity (LCOE) is also 5.7% lower. In a word, the proposed EACFBGC can be considered as the upgraded CFBGC with higher energy conversion efficiency and a lower LCOE.

On the issue of creating the optimal last stage of powerful steam turbines of nuclear power plants

THE PURPOSE. To estimate the most effective length of the working blade of the last stage of a powerful wet-steam turbine in terms of obtaining its maximum efficiency and to optimize the parameters of this stage in the design mode. For this stage, perform multi-mode optimization to select the main characteristics of the stage operating with maximum efficiency according to a given model daily load schedule.METHODS. When solving this problem, the method of calculating the axisymmetric flow of steam in the flow part of the turbine stage as an inviscid single-phase working fluid relative to a stationary guide device and rotating with an angular velocity ω of the impeller used, and the losses energy calculated according to the axisymmetric method of the MPEI.RESULTS. The article describes the relevance of the topic, discusses the features of the use of the author's software in solving the tasks. The characteristics of the stages with different lengths of the working blades presented and the results of their calculation in the nominal mode are given. A model daily schedule selected for a nuclear power plant turbine operating in the central region of Russia. The results of calculations of variable modes of the last stage of the turbine operating according to this daily schedule presented.CONCLUSION. The choice of the maximum length of the working blade is limited not only by its strength characteristics, but also by the increase in wave losses in the gratings due to an increase in the optimal available heat drop, or rather the associated increase in supersonic speeds near the meridional contours. So for a high-speed turbine To-1200-6,8/50 the maximum efficiency of the last stage is achieved at a length of 1400 mm, both when the turbine is configured with both three two-flow LPC and four. Selection of the main characteristics of these stages, such as the available heat drop, the degree of reactivity, etc. it should be made taking into account the variable operating modes of the turbine on the basis of the forecast of daily schedules of loads of turbine units. When using a typical daily load schedule, the average internal relative efficiency in the range of operating modes according to this schedule is higher by 0.6 % when choosing a 10% increased available heat drop compared to the optimal one in the design mode.

Simulation of the Erosion-Corrosion Destruction Process of Steam Turbine Low-Pressure Cylinder Blades

This paper is devoted to the important problem of creating a method for predicting the intensity of erosion-corrosion destruction of the working blades material of low-pressure stages of powerful steam turbines, considering the complex physical processes that accompany the emergence, transformation of erosion-hazardous droplets and their interaction with elements of the flow path. The features of the construction of some existing erosion models are considered. The model that is developed at the Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine and based on a deterministic-statistical approach to its creation is analyzed in detail. The calculations performed during the research showed a satisfactory coincidence with the results of experimental tests by various authors, obtained on droplet impact stands, which contributed to the successful use of the model in creating a comprehensive method of predicting the wear of working blades. To do this, it was supplemented by the method of determining the parameters of the erosive environment based on the droplet movement equation, taking into account the size distribution law. Along with that, it is shown that the considered model, although it allows to carry out fairly accurate prediction of the development of erosive wear at the modern level, has difficulties in its construction due to the need to identify it from the data of full-scale experiments, the number of which is limited. It has been established that one of the important reasons for the discrepancies that arise is the failure to include of the electrophysical component of the processes occurring in a two-phase flow. In this regard, the results of comprehensive studies of steam electrization and its influence on the working processes of wet steam turbines are considered. It is shown that the change in the properties of the working medium as a functional erosive medium as a result of electrification causes a significant increase (relative to neutral wet steam) of electrochemical processes. At the same time, the kinetics of the damage accumulation to the metal surface layer changes due to the joint occurrence of several negative processes: droplet impact influence; electrochemical processes caused by mechanical and structural and chemical heterogeneity of the surface; hydrogen absorption; changes in mechanical properties under the electric field influence. It was noted that the contribution of hydrogen absorption to changes in mechanical properties is the greatest. According to a preliminary assessment, the complex negative droplet impact and electrophysical influence on the metal surface reduces the incubation period and intensifies the erosion-corrosion process by approximately 2 times

Aeroelastic Characteristics of Rotor Blades of Last Stage of a Powerful Steam Turbine

Blades of powerful steam turbines are subjected to significant unsteady loads, which, in some cases, can lead to the appearance of self-excited oscillations or auto-oscillations. These fluctuations are extremely dangerous and negatively affect the life time of the blading. When developing new or upgrading existing turbine stages, it is necessary to carry out research on the aeroelastic behavior of the rotor blades. As a result of the modernization of a low-pressure cylinder of a 1000 MW steam turbine, the length of the rotor blades of the last stage increased to 1650 mm. In this regard, a numerical analysis of the aeroelastic characteristics of the last-stage rotor blades in the nominal operation mode was carried out. The analysis used the method of solving the coupled problem of unsteady aerodynamics and elastic blade vibrations, which allows the prediction of the amplitude-frequency spectrum of unsteady loads and blade vibrations in a viscous gas flow. The paper presents the results of numerical analysis of aeroelastic characteristics of the last stage rotor blades both for the mode of controlled harmonic oscillations with a given amplitude and inter-blade phase shift, and for the mode of coupled oscillations of the blades under influence of unsteady aerodynamic forces. The results of the simulation of coupled oscillations of blades for the first five natural forms are presented in the form of the time distribution of displacement of the blade peripheral cross-section, as well as the time distribution of forces and moments acting on the peripheral cross-section. The corresponding amplitude-frequency spectra of displacements and loads in the peripheral section are also given. The results of the calculations showed a positive damping of oscillations, the absence of flutter and auto-oscillations for the first five natural forms of oscillations of the blades in the nominal operation mode of the steam turbine