Turbine Casing Research Articles

Experimental Demonstration of Inverse Heat Transfer Methodologies for Turbine Applications

Abstract Gas turbines operate at extreme temperatures and pressures, constraining the use of both optical measurement techniques as well as probes. A strategy to overcome this challenge consists of instrumenting the external part of the engine, with sensors located in a gentler environment, and use numerical inverse methodologies to retrieve the relevant quantities in the flowpath. An inverse heat transfer approach is a procedure that is used to retrieve the temperature, pressure, or mass flow through the engine based on the external casing temperature data. This manuscript proposes an improved digital filter inverse heat transfer method, which consists of a linearization of the heat conduction equation using sensitivity coefficients. The sensitivity coefficient characterizes the change of temperature due to a change in the heat flux. The heat conduction equation contains a non-linearity due to the temperature-dependent thermal properties of the materials. In previous literature, this problem is solved via iterative procedures that however increase the computational effort. The novelty of the proposed strategy consists of the inclusion of a non-iterative procedure to solve the non-linearity features. This procedure consists of the computation of the sensitivity coefficients in the function of temperature, together with an interpolation where the measured temperature is used to retrieve the sensitivity coefficients in each timestep. These temperature-dependent sensitivity coefficients are then used to compute the heat flux by solving the linear system of equations of the digital filter method. This methodology was validated in the Purdue Experimental Turbine Aerothermal Laboratory (PETAL) annular wind tunnel, a two-minute transient experiment with flow temperatures up to 450 K. Infrared thermography is used to measure the temperature in the outer surface of the inlet casing of a high-pressure turbine. Surface thermocouples measure the endwall metal temperature. The metal temperature maps from the IR thermography were used to retrieve the heat flux with the inverse method. The inverse heat transfer method results were validated against a direct computation of the heat flux obtained from temperature readings of surface thermocouples. The experimental validation was complemented with an uncertainty analysis of the inverse methodology: the Karhunen–Loeve expansion. This technique allows the propagation of uncertainty through stochastic systems of differential equations. In this case, the uncertainty of the inner casing heat flux has been evaluated through the simulation of different samples of the uncertain temperature field of the outer casing.

Uncertainty Quantification for Extreme Quantile Estimation With Stochastic Computer Models

Extreme quantiles are important measures in reliability analysis. At the system design stage, quantiles are often estimated via stochastic simulations. This article aims to quantify quantile estimation uncertainties by constructing confidence intervals using importance sampling when quantiles are estimated via stochastic computer models. We validate the asymptotic normality for the importance sampling quantile estimator and construct a theoretically valid confidence interval in a closed form. A drawback of the theoretical confidence interval is that it needs to consistently estimate a variance parameter. To resolve the limitation of the theoretical confidence interval, we present batching-based approaches that are also built upon the asymptotic normality of the quantile estimator. We compare the estimation performance of studied methods and other alternative methods using numerical examples and wind turbine case study.

RANS turbulence model development using CFD-driven machine learning

This paper presents a novel CFD-driven machine learning framework to develop Reynolds-averaged Navier-Stokes (RANS) models. The CFD-driven training is an extension of the gene expression programming method Weatheritt and Sandberg (2016) [8], but crucially the fitness of candidate models is now evaluated by running RANS calculations in an integrated way, rather than using an algebraic function. Unlike other data-driven methods that fit the Reynolds stresses of trained models to high-fidelity data, the cost function for the CFD-driven training can be defined based on any flow feature from the CFD results. This extends the applicability of the method especially when the training data is limited. Furthermore, the resulting model, which is the one providing the most accurate CFD results at the end of the training, inherently shows good performance in RANS calculations. To demonstrate the potential of this new method, the CFD-driven machine learning approach is applied to model development for wake mixing in turbomachines. A new model is trained based on a high-pressure turbine case and then tested for three additional cases, all representative of modern turbine nozzles. Despite the geometric configurations and operating conditions being different among the cases, the predicted wake mixing profiles are significantly improved in all of these a posteriori tests. Moreover, the model equation is explicitly given and available for analysis, thus it could be deduced that the enhanced wake prediction is predominantly due to the extra diffusion introduced by the CFD-driven model.

Creepage of the Inner Shell of the High-Pressure Cylinder of the Steam Turbine К-325-23.5

The body parts are the most critical elements of steam turbines that operate being exposed to the action of the complicated thermal power loads. These parts are not subject to their replacement during the entire period of their operation. The defects are accumulated in them due to the low-cycle fatigue and creepage. For the reliable determination of the thermostressed state of turbine casings we need to solve thermomechanical problems with variable boundary conditions and temperature-dependent material properties. Special FEM (finite element method) – based computation technique and software package were developed to carry out the 3D simulation of the kinetics of thermostressed state peculiar for power equipment elements. The calculation studies were carried out for the thermostressed state of the inner shell of the high-pressure cylinder used by the steam turbine К-325-23.5. To take into account its structural properties the available software was improved through the introduction of the new types of finite elements. The temperature field distribution was derived from the solution of the heat conductivity problems using the boundary heat exchange conditions of a third kind on appropriate surfaces. The creepage was defined by the theory of aging using isochoric steel curves for 200 thousand hours. The obtained data showed that a significant redistribution of equivalent stresses was observed in the high-temperature zone of the casing due to the metal creepage. Maximum equivalent tensile and compressive creepage strains have actually the same level and do not exceed 0.31 % for the given time. It means that the inner shell has a considerable in-service life reserve.

The Effect of the Brake Location and Gear Defects on the Dynamic Behavior of a Wind Turbine

Wind turbines have been used for decades in order to produce electricity. Its main advantage is that its energy is clean, does not harm the nature and maintains its balance. For this reason, researchers and engineers have been focused on improving its design, performance and reliability. In addition, its condition monitoring has been studied for many years by processing its vibration signature. The latter is performed either by collecting it from the real mechanical system using sensors or by modeling its vibration signature. In this paper, a wind turbine drivetrain dynamic behavior is developed under different excitation conditions considering the influence of two-disk brake position. Main key factors involved in the dynamic behavior, such as wind turbine dimensions, gear mesh stiffness fluctuation, driving torque, braking torque and bearing stiffness, are taken into account in the model. To investigate a complex damage case, a typical gear fault, profile error and assembly defect are introduced. The dynamic response of the wind turbine, for healthy and damaged cases, is studied based on time series and spectra of acceleration signals. To diagnose gear faults, three indicators (RMS, STD and kurtosis) are used. Based on signal observations, it can be concluded that the disk brake location, wind turbine characteristics and gearbox defects have a direct influence on the dynamic behavior of the system.

Flow analysis of the vertical axis Savonius current turbine (VASCT) performance for Myring blade n = 1 using CFD aproach

The flow visualization of vertical axis Savonius current turbine has been investigated numerically by using Myring formula n of 1. Computational Fluid Dynamics or CFD approach has been carried out by using Gambit for geometry and ANSYS 17.0 running to solve the incompressible U-RANS. This work has been done by comparing the performance between Myring and conventional Savonius. The y+ in the first layer of blade surface has been made between 30 and 100 with y+ in about 52. The turbulence model will be chosen the Realizable k-epsilon (RKE) for this turbine case. The numerical obtain the torque and power coefficient and the power coefficient called the turbine performance. The numerical simulation has been validated by experimental results towards torque coefficient. The results have indicated that the Myring formula n = 1 have the best performance compared this one by decreasing the pressure in attached flow area.

Effect of additional holes on crack propagation and arrest in gas turbine casing

Gas turbines casings are susceptible to cracking at the edge of eccentric pin hole, which is the most likely position for crack initiation and propagation. This paper describes the improvement of transient thermal fatigue crack propagation life of gas turbines casings through the application of additional holes. A series of finite element patterns were developed and tested in ASTM-A395 elastic perfectly-plastic ductile cast iron. The effect of arrangement of additional holes on transient thermal fatigue behavior of gas turbines casings containing hole edge cracks was investigated. ABAQUS finite element package and Zencrack fracture mechanics code were used for modeling. Thermal fatigue test was performed. The result shows that the fractured surfaces of the failed specimen are in good agreement with the stress concentration areas and cracked areas of the casing. The effect of the reduction of transient thermal stress distribution around the eccentric pin hole on the transient thermal fatigue crack propagation life of the gas turbines casings was discussed. The result shows that transient thermal fatigue crack propagation life could be extended by applying additional holes of larger diameter and decreased by increasing the vertical distance, angle, and distance between the eccentric pin hole and the additional holes. The results from the numerical predictions were compared with experimental data.

Improving site assessment tools in emerging technologies: The case of highway vertical-axis wind turbines in the United States

Despite the benefits of renewable energy—including mitigation of climate change, emission-free electricity generation, and public health benefits—technology siting is plagued by social, political, and cultural challenges. These non-technical challenges often remain outside the scope and responsibility of engineers’ assessments. This study uses early-stage stakeholder engagement to examine the non-technical barriers to siting of vertical axis wind turbines (VAWTs) along traffic corridors throughout the United States. Stakeholder feedback is analyzed in terms of Niklas Luhmann's social system theory via the Socio-Political Evaluation of Energy Deployment (SPEED) framework to assess broader, system-wide feasibility. By identifying points of resonance—situations in which the logics of different systems overlap, allowing interaction—the knowledge and capacities of different stakeholder groups can support development of new technologies. This method of stakeholder engagement occurs at earlier stages of project development and includes larger socio-political scales than typical site-level analysis. Stakeholder feedback—from a variety of fields, including engineering, transportation, project management, and law—is incorporated into a multi-criteria and analytic hierarchy tool to aid in turbine siting. This paper argues that early stakeholder engagement beyond a strictly technical focus creates a more robust account of project feasibility, shown through the potential for right-of-way VAWT arrays.

Pengaruh rasio diameter terhadap parameter-parameter energi turbin arus laut horizontal

The ducted tidal turbine models have been developed to utilize convertion of the kinetic energy on ocean currents. The research on refining the turbine characteristics has been carried out by modifying the turbine’s shape and size. The study of the duct diameter ratio effect on the energy characteristics of the turbine was done in this work. This study was conducted by modifying the duct diameter ratio ( ) with the constant inlet diameter D 0 and outlet D 2 . The flow conditions are analyzed for five cases of turbines with different shapes and diameters to determine the optimum conditions. The optimum value of the diameter ratio could be obtained at the maximum value of power coefficient C P . Flow velocity in the ducted turbine was measured at three turbine sections, namely; the inlet section, the impeller housing section, and the outlet section. The measurement of flow in turbines was carried out at the free stream velocity U 0 = 1,5 m/s. The power coefficient C P and thrust coefficient C T were calculated based on flow velocity data on the turbine cVennell sections for each case. The power coefficient C P reaches the maximum value (Betz limit) at the resistance coefficient K = 2 and the value of axial induction factor a = 0,37. These values were founded at diameter ratio d=0,66. The value of thrust coefficient C T reaches the maximum value at K = 3,9, a = 0,53 and . The optimum value of the diameter ratio was founded at d=0,69.

Health-aware LPV Model Predictive Control of Wind Turbines

Wind turbine components are subject to considerable stress and fatigue due to extreme environmental conditions to which they are exposed to, especially when located offshore. Interest in the integration of control with system health monitoring has increased in recent years. The integration of a health management module with model predictive control (MPC) provides the wind turbine a mechanism to operate safely and optimize the trade-off between components’ life and energy production. In this paper, a health-aware LPV model predictive control approach for wind turbines is proposed. The proposed controller establishes a trade-off between the economic objective based on maximizing the energy production but at the same time taking into account the minimization of accumulated stress on the wind turbine blades. The controller uses an LPV model for dealing with the non-linearity of the wind turbine model and the inclusion of the stress model. The proposed approach is tested on a well-known wind turbine case.

Estimating the Energy Loss in Pelton Turbine Casings by Transient CFD and Experimental Analysis

Many consider the Pelton turbine a mature technology, nevertheless the advent of Computational Fluid Dynamics (CFD) in recent decades has been a key driver in the continued design development. Impulse turbine casings play a very important role and experience dictates that the efficiency of a Pelton turbine is closely dependent on the success of keeping vagrant spray water away from the turbine runner and the water jet. Despite this overarching purpose, there is no standard design guidelines and casing styles vary from manufacturer to manufacturer, often incorporating a considerable number of shrouds and baffles to direct the flow of water into the tailrace with minimal interference with the aforementioned. The present work incorporates the Reynolds-averaged Navier Stokes (RANS) k-ɛ turbulence model and a two-phase Volume of Fluid (VOF) model, using the ANSYS® FLUENT® code to simulate the casing flow in a 2-jet horizontal axis Pelton turbine. The results of the simulation of two casing configurations are compared against flow visualisations and measurements obtained from a model established at the National Technical University of Athens. Further investigations were carried out in order to compare the absolute difference between the numerical runner efficiency and the experimental efficiency. In doing so, the various losses that occur during operation of the turbine can be appraised and a prediction of casing losses can be made. Firstly, the mechanical losses of the test rig are estimated to determine the experimental hydraulic efficiency. Following this, the numerical efficiency of the runner can then be ascertained by considering the upstream pipework losses and the aforementioned runner simulations, which are combined with previously published results of the 3D velocity profiles obtained from simulating the injectors. The results indicate that out of all of the experimental cases tested, in the best case scenario the casing losses can be approximated to be negligible and in the worst case scenario ≈3%.

Determination of Boiler Startup Curves Due to Stresses in Critical Pressure Elements

The article discusses the possibility of accelerating the startup of a steam boiler with natural circulation. During startup and load changes in thick-walled pressure elements of boilers operating at high temperatures, high thermal stresses are caused. Critical elements that limit the rate of change of working fluid units include drums, fresh steam superheater outlet chamber, injection chamber of steam coolers, tees and valve casings, rotor and turbine casing. Due to the high pressure and large diameters, the walls of these elements are much thicker compared to other elements of the boiler operating at the same pressure. Permissible changes in temperature and pressure during startup can be determined by the European Standard EN 12952-3. The article shows how the starting curves of a steam block can be determined. First, the heating rate of the component at the start of startup is determined using the EN standard. Then the heating speed of the pressure element is interpolated by a straight line between the pressures at the beginning and end of heating. The temperature of steam is determined from the solution of the first order ordinary differential equation. It was assumed that the steam is saturated. Calculation results show that the starting time of the analyzed block can be significantly shortened compared to boiler startup time in power plants. The long startup time of the boiler in power plants results from the very low heating rates of the pressure element adopted by the boiler manufacturers. It should be added that the low permissible heating rates adopted by the boiler manufacturers are too conservative and are not confirmed by three-dimensional stress analyses.

МОДЕЛИРОВАНИЕ И АНАЛИЗ КОЛЕБАНИЙ КОРПУСА ТУРБИНЫ 500 МВт ПРИ СНИЖЕНИИ РАБОЧЕЙ ЧАСТОТЫ

Problem. The problem of increased vibration of bodies of a steam turbine cases with a capacity of steam turbine of 500 М W is considered. The m а in cause of the increased vibration of the steam turbine is the rotor's unbalance and insufficient stiffness of the system elements. The c а se of operating pr а ctice is considered, where the rotational alignment did not significantly change the vibration parameters. Go а l . In this work the purpose was to make simulation of the forced kind of oscillations of the low-pressure cylinders flexible bodies in the turbineunit-foundation-base system with a turbine unit K-500-65/3000 KHTZ, to study the different causes of their increased level of vibration in case of less work frequencies. Methodology . Т he research is made using the method of oscillation, the method of finite elements, as well as the author's methods of constructing models and conducting research on oscillations of the turbineunit-foundation-base system. Res и lts . Т h е results of the research is as follows: a three-dimensional complex finite-element model of the turbine-foundation-base system was obtained, as well as the amplitude-frequency dependences for the points of the cylinder body of low pressure. The conducted study made it possible to draw conclusions about the different causes of increased vibration of the parts of the steam turbine unit flexible bodies. Originality . The type of designed three-dimensional models of the turbine unit-foundation-base system is unique. Due to the features of the developed model, it is possible to make a vibration processes study at a low level that enables to analyze the oscillations of complex system elements. For individual kinds of studies, further unique specification of the individual parts of the considered system is required. This enables to use the features of the finite element method to specify the turbine unit-foundation-base system in accordance with the actual operating conditions. Other researchers did not solve the problem or clarified it. Value to practice. The significance of the work done in practical terms is primarily an illustration of the technique as a tool for developing specific models in the study of oscillations of a turbine-foundation-base system, as well as for solving practical problems of concretizing and localizing the causes of increased vibration of individual elements of a complex system. The results obtained in the work were used to improve the vibration state of the buildings of units with a steam turbine power unit with the capacity of of 500 MW.

A closed-loop renewable energy evaluation framework

Abstract Many businesses that have embraced renewable energy projects as part of their corporate sustainability efforts lack direction concerning how the projects are assessed. This study presents a framework that prescribes the necessary stages that allow a robust project evaluation to take place. The framework should assist practitioners in ascertaining if renewable energy projects, such as wind turbines and hydro-electric generators, contribute to energy cost savings and a reduction in CO2 emissions. The conceptual framework was developed using empirical data accessed from an 850-kW wind turbine case study and a 40-kW hydro-electric case study and embraced the action research methodology. Both renewable projects are based in Ireland. The 850-kW wind turbine project was found to display disappointing results. As part of the electrical generator power quality measurement, it was found that there was large dispersion in the wind turbine output signal where the coefficient of variation values of between 128% and 939% were recorded. The simple payback period for the wind turbine investment is 7.34 years. The assessment of the 40-kW hydro-electric project found that positive values could be attributed to the environmental, economic, and social aspects of the project. Coefficient of variation values of between 2.8% and 3.9% were calculated for the hydro-electric plant with a simple payback period of fewer than two years. It was found that the dispersion value affects the actual financial and environmental benefits of the project. This is the first time that the short-term dispersion characteristic of a renewable generator power output signal is considered as part of the power quality analysis. Measurement of the quality of renewable power outputs should include the short-term ramping, dispersion, characteristic of the power signal. An implication for stakeholders is that the short-term ramping variation of renewable energy generators must be measured in each evaluation process.

Rancang Bangun Fixture Perakitan Runner dan Casing Turbin Cross Flow

One of the important turbine components to consider in its manufacture is the runner and turbine casing components. The large number of parts that must be welded and the use of tools that do not meet functional requirements causes some problems during the assembly process, the problem is due to the difficulty of obtaining straightness between the disc and runner shaft where both components occur run-out deviations that exceed the allowable tolerance, as well as casing component assembly where almost all of the joints undergo a simple welding process and use of aids causing a very large dimension deviation from the specified tolerance. The use of very simple tools will cause difficulties in controlling the dimensions or uniformity of the shape during the production process. For this reason, a fixture that is suitable for the runner and turbine casing is needed to get the assembly process that matches the specified geometry tolerance. This research makes the fixture design to be used in runner assembly and turbine casing assembly with the assembly method is carried out in stages. The design is done in five stages, namely the stage of problem statement, the stage of making needs analysis, the stage of gathering information and ideas, the stage of making temporary designs and the stage of making the final draft. Fixture manufacturing is done in two stages, namely ordering materials (purchasing materials) and making fixture components. The final result of making runners and casings using a fixture is able to reduce the aberration in the runner and turbine casing components by producing run-outs at runners of 2.0 mm and the straightness of the casing straightness of 1.6 mm, but have not been able to achieve deviations from the targeted one mm.

Calculation of the Grounding Resistance of Structures Located on Elevated Terrain

We present an analysis of the response of a grounding electrode located on the top of a mountain. Specifically, we derive an analytical solution for the low-frequency response of a hemispheric grounding electrode buried on the top of a cone-shaped mountain characterized by its apex angle. The derived equation is validated using numerical simulations based on the finite element method obtained using COMSOL. Simulation results show that, for the same ground electrical parameters, the grounding resistance of such an electrode for steep mountains can be significantly higher than that obtained if the electrode is on flat ground. Such situations can occur in particular for the case of telecommunication towers or wind turbines located on mountaintops. The study emphasizes the importance of considering the terrain profile in the evaluation of the grounding resistance of structures located in elevated locations.

Design and Analysis of Fixture for Welding Casing Components of Cross-Flow Turbine

The purpose of this research is to improve the quality of the turbine casing product by using the welding fixture. The method used was to design and make welding fixture of turbine casing welding, test the straightness, alignment, straightness, and analyzes the deviation of measurement results. Based on the design result of welding fixture assembling of cross-flow turbine casing component, it had been obtained prototype welding fixture which can facilitate the assembling process of cross-flow turbine casing component. The conclusions of this research are the quality of cross-flow turbine casing products can be increased along with the small geometry deviations in the cross-flow turbine runners by using a fastening tool. The maximum deviation of the straightness of the turbine wall is 1.6 (wall A) and 0.85 (wall B). The process of assembling the components of the turbine runner is shorter by using a faster welding assembly tool with a better level of accuracy.

Experimental and Theoretical Research of a Hot Condition of High Pressure Cylinder of the T-100-130 Steam Turbine

The results of experimental and theoretical studies of the temperature state of the high- pressure cylinder (HPC) of the T-100-130 steam turbine for one of the start modes are presented. Taking into account the dependence of the coefficient of linear expansion on the temperature, the elongations of the individual sections of the casing under different temperatures and its total elongation after the turbine operation starts to correspond to the stationary operation mode have been found. The studies have shown that in the process of actuation the turbine there is a significant difference in temperature along the length of the HPC casing. In this case, the most intense heating occurs in the area from the second to the sixth section. The greatest temperature difference was observed in stationary operation at maximum temperature in the fifth section. Using the orthogonal method of L. V. Kantorovich, an approximate analytical solution of the thermal conductivity problem for a two-layer wall (turbine casing – thermal insulation) under inhomogeneous boundary conditions of the third kind is obtained. With the use of experimental data on the temperature state of the outer surface of the casing of the HPC by solving the inverse problem of thermal conductivity, the average heat transfer coefficients for the actuation period characterizing the intensity of heat transfer from steam to the casing have been found. On the basis of experimental data on the temperature change of any of the controlled parameters of the turbine over time, a theoretical method for predicting its change in a certain time range from the time of the its last measurement has been developed. The use of this method to predict the change in the temperature difference between the top and bottom of the HPC casing during the actuation showed that for a period of time equal to 3–5 minutes the forecast is fulfilled with high reliability.

Investigation of Applicability of Transporting Water Mist for Cooling Turbine Blades

Abstract This paper presents a numerical study to investigate the feasibility of transporting water mist to the rotating blades of a high-pressure turbine. The idea of using mist film cooling to enhance conventional air cooling has been proven to be a feasible technique under laboratory conditions. However, there are challenges in implementing this scheme for real gas turbine systems. The first challenge is how to transport the mist to the rotating blades and the second challenge is delivering the mist to the injection holes and getting the particles to survive within the harsh gas turbine environment. Both a zero-dimensional mist evaporation analytical model and a 3D computational fluid dynamics (CFD) scheme are employed for analysis. In the CFD simulation, the Lagrangian–Eulerian method is used along with the discrete phase model (DPM) to track the evaporation process of each individual water droplet. For transporting the mist to the blades, the high-pressure water mist is injected into the stream of cooling air extracted from the compressor through two different passages. The first passage passes through the rotor cover-plate cavity before entering the blade base. The second passage passes through a diaphragm box on the base of the second vane, then tangentially through a cooling passage in the rotating shaft, and eventually to the blade base. The results show that it is feasible to transport the mist from the turbine casing to the blade through both passages, provided that droplets with sufficient particle diameter and mist loading are used. The shorter passage, through the nozzle diaphragm, alleviates a lot of challenges facing the passage through the blade cavity and seems to be more practical. A side benefit of transporting mist through the internal passages is the additional cooling of the preswirler and rotor cover plates. The results are encouraging for implementing the mist cooling technique under real gas turbine conditions.

Experimental and Numerical Investigation of Wake Interactions of Marine Hydrokinetic Turbines

To study the performance and environmental impacts of marine hydrokinetic (MHK) turbine arrays, we carry out an investigation based on laboratory experiments and numerical models able to resolve the dynamics of turbulent wake interactions and their effects on the river bed. We investigate a scaled Sabella D10 mounted on a mobile bed for a single and two aligned turbines, measuring the flow velocity, the rotor angular velocity, and the scour on the sediment bed. Numerical simulations are performed using a detached-eddy simulation (DES) turbulence model coupled with the blade-element momentum (BEM) approach, which can capture the mean flow and resolve the dynamics of turbulent coherent structures in the wakes. The simulations show a good agreement on the velocity statistics obtained experimentally. Power and thrust coefficients for the downstream turbine show an average decrease and a larger variability due to the turbulent intensity produced by the upstream turbine, as compared to the single turbine case. Results of this investigation also provide a framework to assess the predictive capabilities, scope, and applicability of computational models parameterizing the turbines using BEM, for testing different turbine designs and siting strategies within the MHK array.