Our recent progress on studying wave interaction with a lift-type rotor is discussed in this paper. The particular focus is on characterization of the rotor’s unidirectional responsiveness in waves. The rotor consists of six hydrofoil blades in two sets. One blade set has three blades laid out as a vertical-axis wind turbine of the Darrieus type. The other blade set has three blades configured like a Wells turbine. In combination, the formed rotor can be driven by flows in any direction to perform unidirectional rotation about its vertically mounted shaft. This unidirectional responsiveness of the rotor also holds in waves, making the rotor a valuable device for wave energy conversion. For parametric study of the rotor, hydrofoil blades using different cross sectional profiles and chord lengths have been employed to configure the rotor. The rotor was then tested in a wave flume under various wave conditions in a freewheeling mode. Experimental results were analyzed and discussed. The yielded research findings will greatly enhance the fundamental understanding on the rotor performance in waves, and effectively guide the prototype rotor development for practical applications.

In previous references, no study has been done on the optimization of rotary regenerative air preheaters (RAPHs) used in coal-fired power plants yet. The key structure parameters of RAPH include rotor radius, fluid section angles and matrix layer heights. In this study, work on the multi-objective design optimization of an RAPH was conducted by combing the thermal hydraulic calculation program which is developed to calculate the temperature and the pressure drop and the non-dominated sorting genetic algorithm (NSGA-II). The maximum heat transfer rate and the minimum friction, namely minimum outlet gas temperature and pressure drop, are considered as the conflicting objectives in the multi-optimization. The layer heights, rotor radius, angles of fluid sections and heights of matrix layers are involved in the design variables in the optimization. The optimization includes three cases in which the rotor radius upper limits are 7 m, 8 m and 9 m respectively. Sets of the Pareto-optimal front points were obtained for the different cases. The obtained optimal air-preheaters with larger upper limit of rotor radius would have better Pareto results. The optimum rotor radius is the upper limit value for different design range of rotor radius. The air-preheaters with larger upper design limit of rotor radius would have better Pareto results. In other words, if the upper design limit of rotor radius is too small, all the Pareto points in this case could not satisfy the performance requirements of heat transfer and friction, and the only way is to increase the upper design limit of rotor radius. The ratio of each optimum fluid section angle is determined by the fluid flow rate of each section.

In recent years, there has been a growing demand for high-power-density direct-drive generators in the wind industry owing to their high reliability, torque per unit volume, and conversion efficiencies. However, direct-drive wind turbine generators are very large, low-speed electric machines, which pose remarkable design and manufacturing issues that challenge their upscaling potential and cost of implementation. With air-gap tolerance as the main design driver, the need for high stiffness shifts the focus toward support-structure design that forms a significant portion of the generator’s total mass. Existing manufacturing processes allow the use of segmented-steel-weldment disk or spoke-arm assemblies that yield stiffer structures per unit mass but tend to be heavier and more expensive to build. As a result, there is a need for a transformative approach to realize lightweight designs that can also facilitate series production at competitive costs. Inspired by recent developments in metal additive manufacturing (AM), we explore a new freedom in the structural design space with a high potential for weight savings in direct-drive generators. This includes the feasibility of using nonconventional complex geometries, such as lattice-based structures as structurally efficient options. Powder-binder jetting of a sand-cast mold was identified as the most feasible AM technology to produce large-scale generator rotor structures with complex geometry. A parametric optimization study was performed and optimized results within deformation and mass constraints were found for each design. The response to the maximum Maxwell stress due to unbalanced magnetic pull was also explored for each design. Further, a topology optimization was applied for each parameter-optimized design to validate results and provide insights into further mass reduction. These novel designs catered for AM are compared in both deflection and mass to conventional rotor designs using NREL’s systems engineering design tool, GeneratorSE. The optimized lattice design with a U-beam truss resulted in a 24% reduction in structural mass of the rotor and 60% reduction in radial deflection. It is demonstrated that additive manufacturing shifts the focus from manufacturability constraints toward lower mass.

A method for the speed matching of the second rotor (R2) with equal power for two rotors was proposed to avoid the overload of the second motor under low flow rate and the rapid decrease in pressure-rise and efficiency of R2 under high flow rate. The speed matching of two-stage rotors is proposed and analyzed to improve the stability margin of the counter-rotating fan (CRF). The fan performances during constant speed operating and during the speed matching operating are presented and discussed using experimental research. The results show that, the speed matching of R2 operating decreases the load of R2 under low flow rate and increases the pressure-rise and efficiency of R2 under high flow rate. Thus, the efficient working range and the blocking condition margin are increased. Reducing n 1 and increasing n 2 under low flow rate can regulate the position of unstable working line leftward without reducing the pressure-rise of the fan. Thus, the stability margin of the CRF is expanded.

The tip clearance of the compressor has always been a key part in both the design and operation of gas turbine. Surge margin and aerodynamic performance of the compressor will be affected if the tip clearance is too large, while risk of rubbing between the blades and casing will arise if the tip clearance is too small. Generally speaking, the calculation and analysis of tip clearance under stable design condition is relatively easy, because the metal temperature field of both rotor and stator components that significantly affect the tip clearance is in stable condition at that time. However, the transient tip clearance under start-up and shut-down condition is difficult to be calculated and analyzed, due to the fact that both the aerodynamic parameters and metal temperature field are instable, and complicated heat-exchange occurs between the metal components and gas. In this paper, the transient deformation of both rotor and stator components of compressor of a certain gas turbine is analyzed in detail by using thermo-solid coupling analysis technology, finally obtained real-time tip clearance. The non-contact measurement technology is used to measure the tip clearance during operation of the unit. The experimental result indicates that the real-time tip clearance value obtained by the calculation method in the paper is in a very good agreement with the measured value. In addition, both the analysis and experimental results show that the moment of smallest tip clearance usually happens at shut-down progress and the influence of tip clearance must be considered when designing unit’s running curve.

A method for speed matching of the second rotor (R2) with equal power for two rotors was proposed to improve the performance of the counter-rotating fan under off-design conditions. In this method, the speed of R2 is adjusted until the power of R2 is equal to the power of the first rotor (R1). The fan performance during constant speed operation and during R2 speed matching operation is presented and discussed using theoretical analysis, numerical simulation, and experimental research. The results show that R2 speed matching improves the power and efficiency characteristics of R2. Thus, the pressure rise and power characteristics of the fan were improved. The load of R2 under low flow rates condition was decreased, and the pressure rise and efficiency of R2 under high flow rates condition were increased. The blocking condition margin increased from 37.2% to 48.0%, and the high-efficiency working range of the fan increased from 33.2% to 37.9%.

The aerodynamic and mechanical performance of the last stage was numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solution and Finite Element Analysis (FEA) coupled with the one-way and two-way fluid-structure interaction models in this work. The part-span damping snubber and tip damping shroud of the rotor blade and aerodynamic pressure on rotor blade mechanical performance was considered in the one-way model. The two-way fluid-structure interaction model coupled with the mesh deformation technology was conducted to analyze the aerodynamic and mechanical performance of the last stage rotor blade. One-way fluid-structure interaction model numerical results show that the location of nodal maximum displacement moves from leading edge of 85% blade span to the trailing edge of 85% blade span. The position of nodal maximum Von Mises stress is still located at the first tooth upper surface near the leading edge at the blade root of pressure side. The two-way fluid-structure interaction model results show that the variation of static pressure distribution on long blade surface is mostly concentrated at upper region, absolute outflow angle of long blade between the 40% span and 95% span reduces, the location of nodal maximum displacement appears at the trailing edge of 85% blade span. Furthermore, the position of nodal maximum Von Mises stress remains the same and the value decreases compared to the oneway fluid-structure model results.

In order to keep a high efficiency of a gas turbine, it is important to make a suitable maintenance. Gas turbine nozzle guide vanes (NGVs) and turbine rotor blades deteriorate through a long-time operation due to various causes such as a particle attachment, erosion, and a thermal stress. In the present study, a numerical investigation has been carried out to clarify the influence of the NGV and the rotor blade deterioration on aerodynamics in a 3-stage gas turbine. Geometries of the NGV and the rotor blade were measured from a real gas turbine using a 3-D scanner. The first stage NGVs and rotor blades usually deteriorate seriously and are usually replaced at certain intervals. Two kinds of the geometries of the NGV and the rotor blade of the first stage were obtained, which are the new ones before use and the used ones to be replaced. For the second stage and the third stage, the geometries before use were used in the computations. The numerical results show that the isentropic efficiency of the first stage increases and that of the second stage decrease due to the deterioration of the first stage. The efficiency of the third stage is not affected significantly. The mechanisms are discussed from the observation of the flow fields.

Shafting is one of the key units of large steam turbine generator set, its dynamic characteristics directly affect the technical level and operation effect of the new type large capacity Turbine-generator unit. The forces acting on the disc and the shaft are complex in operation. A composite rotor has various dynamic characters for a large capacity nuclear power Turbine-generator comparing with general rotor for its different structure. Numerical simulation was carried out to a composite rotor for a large capacity nuclear power T-G set, so as to analyze the influence of different length to diameter ratio on the vibration characteristics of the low pressure rotor and to study the effect of Interference Amount Between disc and shaft by using the three-dimensional finite element analysis in order to meet the requirements of the good vibration characteristics of the rotor. Firstly, the geometric model of the rotor is set up, and then the element model of the shafting is built, finally natural frequency of the rotor is calculated by using the mechanical module. Vibration characters such as the natural frequency and corresponding mode were obtained by analysis of vibration for the disc and shaft. The effect of the interference fit on critical speeds of the rotors are analyzed preliminarily. The results show that critical speeds of T-G rotor vary sensitively with magnitude of interference. (CSPE).

Marine and hydrokinetic (MHK) turbine development projects use power converters to convert harnessed variable power to grid compatible constant frequency AC. Using power converters in similar projects such as harnessing tidal energy through bi-directional rotor blades, or by using direct-drive technology for harnessing tidal and ocean wave energy, are rapidly expanding all around the world. However, power converters are known to have the lowest mean-time-to-failure among turbines’ components and have significant impact on increasing the cost of energy, especially at larger MHK turbine scales. This work proposes the potential of a novel MHK turbine drivetrain with three main modules. The first module is an “energy harnessing module” to harness variable hydrokinetic power. The waterwheel with a large catchment area is effective in harnessing low head, free flowing hydrokinetic energy. The second module is a novel “speed controlling module” that is a replacement of currently used power converters; it is the focus of this work. It produces a constant speed output from a variable input speed. Finally, the third module is the “power generating module” that generates grid-compatible constant-frequency electricity. The test results showed the superior performance of the proposed speed converter in obtaining constant speed frequency output from a variable input speed range.

This work is focused on developing a technique to assess high cycle fatigue of shrouded HP compressor blades subjected to thermo-mechanical loads like centrifugal stresses, vibratory stresses and thermal stresses in a gas turbine rotor. In practice, the blades are also subjected to resonance condition during steady or transient conditions of operation when passing through critical speeds. Hence, shrouds are added initially at 3/4 length along blade height which helps in reducing vibration amplitude by providing suitable stiffness to the blade and hence better structural integrity. Industrial best practice like Campbell diagram is used for the above purpose. Two approaches employed here for fatigue analysis are linear Finite element analysis (FEA) and Elasto-Plastic FEA. Fictive elastic results are recalculated using Neuber’s Rule. Strain amplitude approach is followed and Coffin-Manson Equation is used to determine the number of start-up and shut-down cycles. Design and analysis is performed using ANSYS 14.5 tool for reliable fatigue life estimation and to predict catastrophic failure due to High Cycle Fatigue.

Fluid film bearings provide critical support for the rotors in gas turbines, steam turbines, generators, exciters and other machines through the generation and support of a hydrodynamic film. Industrial bearings are lined with a babbitt material which serves as a sacrificial element during operation and may need to be refurbished depending on the past operating and maintenance history. After inspection, engineering judgment is typically used during a machine overhaul to determine whether a bearing requires refurbishment. This engineering judgment is developed through an understanding of the principals of bearing design, machine operation, machine monitoring and babbitt wear / damage characteristics. This paper describes the criteria to serve as a basis for a decision support tool relative to the refurbishment of a babbitted, fluid-film bearing. Those criteria start with key descriptors of any damage to the bearing and evaluate the remaining load capacity, repairability, bearing support, rotordynamics influence, journal conditions and pivot conditions. The descriptors focus on visual examinations of the condition of the babbitt and seek to be intuitive, yet remaining comprehensive; to this end a graphical interface is used where feasible. Evaluations include specific load capacity calculations, determination of damage factors for the principal modes of babbitt damage and data from lookup tables whose input is based on experience. These evaluations are combined to provide the basis for the refurbishment decision. Scaling efforts are incorporated into the evaluations to allow their combination into a single bearing condition index. Initial experience suggests that discrete ranges of the bearing condition index are preferable to numerical value. One goal of the tool is to allow use by inexperienced engineers as a support to their technical development. Another goal is to better document the decision process for particular bearings. The preliminary tool was applied to a cylindrical, radial bearing in a horizontal orientation and to a bumper thrust bearing. Initial results have confirmed the general strategy employed and have suggested areas requiring refinement.

Prior to choosing a site for a wind farm, its wind resources must be known. On-site measurement of wind speed, using an anemometer or any other appropriate measuring device or the use of historical meteorological data for the site (if they exist) enhance the knowledge of the site’s wind resources. Typically, the use of 50-year historical data is recommended by Wind Energy Engineering Standards. For the offshore site in study, only the 24-year historical data from the National Oceanic and Atmospheric Administration (NOAA) data base is available. Wind speed determined from NOAA’s error bars is used to plot Rayleigh probability distribution curves for each month of the year, based on the operational limit of the 5MW NREL reference wind turbine. The site’s average wind speed and gust are determined based on average wind energy capture. A Gumbel probability distribution curve is plotted based on the operational range of the wind turbine in study, using NOAA’s error bars for the 24year historical hourly wind gust for the site. This study uses the estimated mean wind speed and mean gust, to implement BEMT simulations to investigate the aerodynamic forces caused by the wind or gust on the blades of the HAWT rotor. The wind power captured and the power coefficient are estimated for each scenario. Empirical formulae are developed for the estimation of the rotor blade airfoil’s chord length in terms of blade element radius and the axial induction factor for each scenario, in terms of blade element radius.

Aero-structure interaction during turbomachinery blade design has become an important area of research due to its critical applications in aero engines and land based gas turbines. Studies reveal that a certain mistuning leads to stress build up through mode localization under operating conditions. This paper deals with comparative case studies of aero-structure interaction for free standing and various laced LP blade configurations of a gas turbine. The lacing wire provides better structural integrity as it is more aerodynamic and feasible when compared to cases of free standing blades without lacing wires. Hence calling for the optimum positioning checks at ¼ th , ½, ¾ th and combined positioning at ¼ th and ¾ th along the length of LP compressor blades. The lacing wire of both circular and elliptical cross sections are considered for comparative study for better aerodynamic performance. Assuming 100% fixity at blade root, the study involves critical parametric evaluations involved in achieving mechanical integrity in airfoil design and blade platform design. Mechanical integrity involves stress checks, frequency margins, Campbell Diagram, gross yield stress, Stress Stiffening and Spin Softening of blades and so on, for design and off-design conditions for a given stage efficiency of 93% in an ideal LP compressor of a gas turbine engine.

Generator rotor retaining rings are one of the most highly stressed components in the generator rotor. Additionally, some retaining ring materials such as 18Mn5Cr, have been susceptible to Stress Corrosion Cracking (SCC). 18Mn18Cr retaining ring material has been used to replace older 18Mn5Cr material rings with great success. The 18Mn18Cr material has been found to be resistant to SCC in the presence of moisture. Recently, one OEM (Original Equipment Manufacturer) called for inspections of 18Mn18Cr rings, despite its reliable performance in the industry. Although resistant to SCC, some 18Mn18Cr rings have been found with cracks and other damage. The author’s company felt that it would be of value to go back through past job records with rotors that were identified to have 18Mn18Cr retaining rings, and review those records and report on the results of ring inspections due to damage. The author’s company typically rewinds dozens of rotors per year, with many of the rings manufactured from 18Mn18Cr. As part of a rewind, rings are disassembled and inspected. Of course, many rewinds are done because of failures, mostly related to the field winding. An XRF (X-Ray Fluorescence) analyzer is used to determine a ring’s composition. It has excellent accuracy, and can easily distinguish between 18Mn18Cr material and other non-magnetic steels, such as the once common 18Mn5Cr. Magnetic rings are easily distinguishable by a magnet, by manufacturer and rating, and / or by ventilation method. A total of seventeen (17) 18Mn18Cr ring metallurgical investigation reports were reviewed. These metallurgical investigations were conducted between 2008 and 2014. Reports reviewed included only those retaining ring inspections that were done to diagnose some visible damage to one or two retaining rings. In other words, if an 18Mn18Cr retaining had some indication of damage, the detailed inspection report and analysis was included and reviewed as part of this paper. Rings that were inspected and had no issues are not included. Rings that had damage due to some obvious man-made issues were not included. For example, one generator rotor had an 18Mn18Cr ring that had an obvious grinding wheel cut. The owner was aware that this damage had occurred during a prior repair. This metallurgical investigation was not included in this study. Another finding not included in this study was an 18Mn18Cr retaining ring with a high hardness variation, well beyond the tolerance standards and acceptance criteria used by NEC. Since there was no physical damage to the ring surface and no cracking, pitting or other abnormality present, this ring’s inspection report was also excluded. Only rings with some type of visual evidence of pitting, corrosion, fretting or material upset were included and make up the 17 generator rotors.

This paper describes the design and testing of a high-efficiency turbo-generator for use in an Organic Rankine Cycles (ORC) with a power target of 30–100 kWe. The elegant yet simple design consists of a hermetically sealed, single piece rotor, with axial turbine and permanent magnet generator. The design employs compliant foil bearings (CFB), which eliminate the need for any external lubricates or dynamic seals and no contamination risk to the process fluid. A unique partial admission turbine concept is employed which provides better than 80% efficiency across a wide range of seasonal temperature variation, such as those occurring in northern latitudes, where summers can be hot (> 35°C) and humid and winters are extremely cold (< −20°C) and dry. We describe the design and prototype manufacturing as it pertains to micro and meso-scale turbines (< 100 kW) in terms of thermodynamic cycle considerations, turbine design, rotor-bearing dynamics, overall system design and scale-up considerations.

With the increasing demand for clean, renewable energy sources, vertical-axis wind turbine (VAWT) research has gained considerable interest. The technology is primarily used for small-scale power applications in environments with unsteady wind conditions, such as urban locations. For this type of turbine the most important features are self-starting characteristics and energy conversion efficiency. For the Savonius type rotor, performance is increased by reducing drag losses on the advancing blades. The present study addresses the numerical verification of the performance of new designs for drag-driven VAWTs. Two new models were created using SolidWorks along with a standard Savonius model consisting of semicircular blades for benchmarking. All models were designed with the same swept area for comparison. 3D numerical simulation was completed using ANSYS FLUENT. Static conditions were first solved with a moving reference frame (MRF). The results from the MRF simulations were then used to initialize the transient solvers using sliding mesh models (SMM). 3D pressure distributions on the moving blades for each model were analyzed. From inputs of wind and rotational speed, torque values and coefficients of moment were reported. Each model was tested over a range of tip-speed ratios, and power coefficients were calculated. Results were compared to a standard Savonius VAWT, and increased maximum power coefficient was achieved with the new blade geometries.

This paper provides a detailed analysis of how a rotary regenerative air preheater’s performance parameters such as effectiveness, fluid and metal temperature fields, and ammonium bisulfate (ABS) deposition area vary with rotor rotational speed. A tri-sector rotary regenerative air preheater for a 600MW unit was studied as an example by use of effectiveness–modified number of transfer units ( ε-NTU 0 ) method and a finite difference method. The findings of the research are as follows: (1) There is a nonlinear relationship between matrix temperature distribution and rotational angle, and the degree of nonlinearity, represented by unsteady heat transfer correction factor Π , increases with decreasing rotational speed and varies between sectors; (2) There exist two equilibrium positions around the intersection points of matrix temperature curves for different rotational speeds, one occurring in the heating period and the other in the cooling period; (3) The act of reducing the rotor speed has two effects on ABS deposition. On the one hand, the height range of possible ABS deposition area will expand as the matrix temperature within the first third of gas sector’s angle range further decreases with decreasing rotational speed. On the other hand, after the rotational speed falls below a certain level, the hot-end matrix temperature climbs above the ABS formation temperature during part of the heating period, resulting in gasification and decomposition of the condensed product. The combined effect is yet to be examined through further theoretical and empirical analyses. (4) The trends of average outlet temperatures of primary and secondary air depend on rotor rotation direction and angles of sectors. (5) The effectiveness values calculated by ε-NTU 0 method are greater than those acquired by the finite difference method, especially at low rotor rotational speeds.

This paper presents application of Computational Fluid Dynamics (CFD) in modeling wet gas compression in a multiphase compressor, where liquid is injected inside the compression chamber to enhance cooling and achieve near isothermal compression. CFD is used for detailed flow field and heat transfer analysis. It includes 3D transient simulations of multiphase compressible turbulent flow. During each cycle, compression and suction chambers keep moving and deforming. Computational domains include a gate that separates compression chamber from the suction chamber. Gate moves up and down to always remain in contact with the rotor. A custom program is used to prescribe motion for the moving and deforming domain. Eulerian-Lagrangian method is used to model continuous and discrete (atomized droplets) phases and their interaction. Droplet dynamics under the influence of turbulence, acceleration, diffusion and body forces are studied. Models to capture droplet breakup and coalescence are included. Results from CFD simulations are used to optimize compressor performance. Temperature and pressure variations during the compression cycle are presented. Most of the pressure and temperature rise occurs towards the end of the compression cycle. Atomization details including droplets trajectory, droplet size distribution and droplet velocity variations are presented. Temperature distribution inside the compression chamber is used to optimize location, size, and flow rate of liquid injections.

In this paper a methodology for stage performance analysis of an axial flow compressor is carried out. A 1D/2D simulation based on Aero-thermodynamics is used to study the on and off-design performance of the HP compressor. Performance curves are obtained by changing the performance parameters in terms of design parameters like blade deflection angles, pressure drop, flow and work co-efficient’s, diffusion factor, solidity and Mach number. Results show the effect of diffusion factor on increasing efficiency than that of solidity and also the effect of both diffusion factor and solidity in increasing the amount of compression and compressor efficiency. Highest efficiency was found at the mean line between the root and tip of the blade. Best compressor efficiency is found at outlet metal angle in the range 51° to 55°. It was found that at hot section, HP compressor blades typically fail because of creep. Creep occurred as components are operated under high stresses and temperature over a time period. As per thumb rule (>15°C), i.e 20°C to 25°C increase in blade temperature if observed cuts creep life by 50%. Creep strain is of prime importance, because it leads to progressive reduction of rotor tip clearances causing axial and radial blade tip rubs, calling for fixity of shrouds at the rotor HP blade tip. Creep behavior in rotor HP blades are analyzed effectively by use of Industrial best practice like Larson Miller Parameter diagram.