bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Modelling of an Intermediate Pressure Steam Turbine by Means of Conjugate Heat Transfer: Simulation and Validation
Authors: Born Dominik , Stein Peter , Marinescu Gabriel , Koch Stefan , Schumacher Daniel
Published: September 2016

Today’s power market asks for highly efficient turbines which can operate at a maximum flexibility, achieving a high lifetime and all of this on competitive product costs. In order to increase the plant cycle efficiency, during the past years, nominal steam temperatures and pressures have been continuously increased. To fulfill the lifetime requirements and still achieve the product cost requirements, accurate mechanical integrity based assessments on cyclic lifetime became more and more important. For this reason, precise boundary conditions in terms of local temperatures as well as heat transfer coefficients are essential. In order to gain such information and understand the flow physics behind them, more and more complex thermal modelling approaches are necessary, like Computational Fluid Dynamics (CFD) or even Conjugate Heat Transfer (CHT). A proper application of calculation rules and methods is crucial regarding the determination of thermal stresses, thermal expansion, lifetime or creep. The aim is to exploit during turbine developments the limits of the designs with the selected materials. A huge effort especially in validation and understanding of those methodologies was done with detailed numerical investigations associated to extensive measurement studies at onsite turbines in operation. This paper focuses on the validation of numerical models based on CHT calculations against experimental data of a large intermediate pressure steam turbine module regarding the temperature distribution at the inner and outer casing for nominal load as well as transient shut-down.
Modal Identification of Dynamically Coupled Bladed Disks in Run-Up Tests
Authors: Carassale Luigi , Marrè-Brunenghi Michela , Patrone Stefano
Published: September 2016

The spin test is a standard industrial practice employed for the qualification of rotor blades and disks. The expected results are the modal properties of blades and assemblages at different rotation velocities. If a significant dynamic coupling among the blades exists, global vibration modes appear, reflecting into a set of closely spaced natural frequencies for each mode family. In case of perfectly-tuned bladed disks, the circumferential structure of the mode shapes is known and can be exploited during the identification process so that traditional single-dof models may be applied. On the contrary, the mode irregularities produced by mistuning prevents the use of single-dof models requiring the development of more sophisticated approaches. In this work, we propose a multi-dof identification technique organized as follow: 1) the FRF of the bladed disk in the neighborhood of a resonance crossing is identified by the wavelet transform of the measured response; 2) the modal parameters of the system are estimated using a mixed stochastic-deterministic subspace algorithm formulated in the frequency domain. The procedure is validated using a realistic numerical simulation.
Multi-Disciplinary Optimization of a Centrifugal Compressor for Micro-Turbine Applications
Authors: Perrone Andrea , Ratto Luca , Ricci Gianluca , Satta Francesca , Zunino Pietro
Published: September 2016

The present paper presents the multi-disciplinary optimization of a centrifugal compressor for a 100kW micro gas turbine. The high rotational speed fixed by the cycle optimization (75,000 rpm) required a simultaneous analysis of flow aerodynamics and mechanical behavior to account for the high centrifugal stresses the blades are subjected to, while maximizing the aerodynamic performance. A commercial 3D (three dimensional) computational fluid dynamics (CFD) solver adopted for the aerodynamic computations and an open source finite element FEM code for the mechanical integrity calculations have been coupled with metamodels to speed up the optimization process. Home-made scripting modules, which manage multidisciplinary optimization, mesh generation, geometry parameterization and result post-processing have been written and utilized. A sample data-base has been generated on the basis of the parameters selected to describe aerodynamic and mechanical constraints, and an optimization procedure based on a genetic algorithm has been performed. A RANS (Reynold Averaged Navier Stokes) steady approach with a two-equation SST (Shear Stress Transport) model has been adopted for the aerodynamic computations during the optimization procedure. The optimized compressor so achieved showed an important boost in aerodynamic performance, without any penalty in the mechanical behavior, as compared with the preliminary design. The optimized configuration has been tested also by means of URANS (Unsteady Reynolds Averaged Navier Stokes) phase-lag investigations, which confirmed the aerodynamic performance increase predicted by steady RANS calculations.
Statistical Sensitivity Study of Frequency Mistuning on the Prediction of the Flutter Boundary in a Transonic Fan
Authors: Tateishi Atsushi , Watanabe Toshinori , Himeno Takehiro , Aotsuka Mizuho , Murooka Takeshi
Published: September 2016

This paper aims at quantifying the stabilization effect of mistuning in transonic fan flutter. The results are used to support the evaluation of flutter boundary and to clarify the reason for the mismatch observed in the numerical predictions reported in our previous study. Mistuning is modeled by the deviation of blade-mode frequency, and the stability analysis of vibrating blades is formulated as an eigenproblem of the equation of motion including self-excited aerodynamic force obtained by fluid-structure interaction simulations. Statistics about the modal properties are obtained by Monte Carlo simulation. The change in the averaged damping rate and flutter boundary is evaluated in a wide range of mistuning levels and operating conditions. Nominal levels of mistuning due to manufacturing tolerance have little effect to the flutter boundary because the decline in aerodynamic damping is very steep. Therefore, the accuracy associated with the computational fluid dynamics is likely to have caused the mismatch in the flutter boundary. Histograms of modal properties show that the inter-blade phase angle and blade amplitudes in flutter mode can be highly scattered, even if the level of mistuning is nominal. For largely mistuned cases, new crests which do not exist in nominal cases appear in the eigenvalue histogram. They were found to be highly-localized, single-blade dominant mode.
Design for Additive Manufacturing: Internal Channel Optimization
Authors: Pietropaoli M. , Ahlfeld R. , Montomoli F. , Ciani A. , D’Ercole M.
Published: September 2016

The new possibilities offered by Additive Manufacturing (AM) can be exploited in gas turbines to produce a new generation of complex and efficient internal coolant systems. The flexibility offered by this new manufacturing method needs a paradigm shift in the design approach and a possible solution is offered by Topology Optimization.

The overall goal of this work is to propose an innovative method to design internal channels in gas turbines that that fully exploit AM capabilities. The present work contains a new application of a Fluid Topology sedimentation method to optimize the internal coolant geometries with minimal pressure losses while maximizing the heat exchange. The domain is considered as a porous medium with variable porosity: the solution is represented by the final solid distribution that constitutes the optimised structure. In this work the governing equations for an incompressible flow in a porous medium are considered together with a conjugate heat transfer equation that includes porosity dependent thermal diffusivity. An adjoint optimisation approach with steepest descent method is used to build the optimisation algorithm.

The simulations are carried out on two different geometries: a U-Bend and a straight duct. For the U-Bend a series of splitter is automatically generated by the code, minimizing the stagnation pressure losses. In the straight duct the impact of different porosity dependant thermal diffusivity is analysed to achieve high thermal exchange. The results show “rib like” structures that enhance the heat transfer.
Application of Film Cooling to an Unshrouded HP Turbine Casing
Authors: Collins Matthew , Chana Kamaljit , Povey Thomas
Published: September 2016

In this paper we describe the design, modelling and experimental testing of a film cooling scheme employed on an unshrouded HP rotor casing.

The casing region has high thermal loads at both low and high frequency, with the flow being dominated by the potential field of the rotor and over-tip leakage flows. Increasingly high turbine entry temperatures necessitate internal and film cooling of the casing to ensure satisfactory service life and performance. There are, however, very few published studies presenting CFD and experimental data for cooled rotor casings.

Experimental testing was performed on a film cooled rotor casing in the Oxford Turbine Research Facility (OTRF) — a rotating transonic facility of engine scale. Unsteady CFD of a HP rotor blade row with a film cooled casing was performed with a domain utilizing a sliding interface in the tip gap.

Specific advances in validation data and understanding include:

1. A discussion of the challenges faced in the design of a casing film cooling scheme. We show that the seemingly hostile film cooling environment can be managed with the use of holes shaped to utilize acoustic pressure wave reflections.

2. Time resolved and time averaged predictions of adiabatic film effectiveness on the rotor casing are presented. Mechanisms for interaction of the coolant with the rotor tip are proposed and discussed.

3. Acoustic effects due to the passing of the rotor are demonstrated on a 3D CFD geometry, supporting conclusions drawn by Collins and Povey [1] on the importance of this effect in a casing film cooling system.

4. Time-resolved and time-mean measurements of TAW and η’ taken using a high density array of thin film heat flux gauges are presented and compared to CFD predictions for the casing region (−30 % to +125 % CAX).
Development of the Supercritical Carbon Dioxide Power Cycle Experimental Loop in KIER
Authors: Cho Junhyun , Shin Hyungki , Ra Ho-Sang , Lee Gilbong , Roh Chulwoo , Lee Beomjoon , Baik Young-Jin
Published: September 2016

Three supercritical carbon dioxide (CO2) power cycle experimental loops have been developed in Korea Institute of Energy Research (KIER) from 2013. As the first step, a 10 kWe-class simple un-recuperated Brayton power cycle experimental loop was designed and manufactured to test its feasibility. A 12.6 kWe hermetic turbine-alternator-compressor (TAC) unit which is composed of a centrifugal compressor, a radial turbine and the gas foil bearings was manufactured. The turbine inlet design temperature and pressure were 180 °C and 130 bar, respectively. Preliminary operation was successful at 30,000 RPM which all states of the cycle existed in the supercritical region. Second, a multi-purpose 1 kW-class test loop which operates as a transcritical cycle at a temperature of 200 °C was developed to concentrate on the characteristics of the cycle, control and stability issues of the cycle. A high-speed turbo-generator was developed which is composed of a radial turbine with a partial admission nozzle and the commercial oil-lubricated angular contact ball bearings. Finally, a 60 kWe-class Brayton cycle is being developed which is composed of two turbines and one compressor to utilize flue-gas waste heat. As the first phase of development, a turbo-generator which is composed of an axial turbine, a mechanical seal and the oil-lubricated tilting-pad bearings was designed and manufactured.
Transient Performance Analysis of an Industrial Gas Turbine Operating on Low-Calorific Fuels
Authors: Singh Vrishika , Axelsson Lars-Uno , Visser W. P. J.
Published: September 2016

The demand for more environmentally friendly and economic power production has led to an increasing interest to utilize alternative fuels. In the past, several investigations focusing on the effect of low-calorific fuels on the combustion process and steady-state performance have been published. However, it is also important to consider the transient behavior of the gas turbine when operating on non-conventional fuels. The alternative fuels contain very often a large amount of dilutants resulting in a low energy density. Therefore a higher fuel flow rate is required, which can impact the dynamic behavior of the gas turbine.

This paper will present an investigation of the transient behavior of the all-radial OP16 gas turbine. The OP16 is an industrial gas turbine rated at 1.9 MW, which has the capability to burn a wide range of fuels including ultra-low-calorific gaseous fuels. The transient behavior is simulated using the commercial software GSP including the recently added thermal network modeling functionality. The steady-state and transient performance model is thoroughly validated using real engine test data.

The developed model is used to simulate and analyze the physical behavior of the gas turbine when performing load sheds. From the simulations it is found that the energy density of the fuel has a noticeable effect of the rotor over-speed and must be considered when designing the fuel control.
Oil Scoop Simulation and Analysis Using CFD and SPH
Authors: Korsukova Evgenia , Kruisbrink Arno , Morvan Hervé , Paleo Cageao Paloma , Simmons Kathy
Published: September 2016

The process of rotating scoops capturing oil coming out of a stationary jet nozzle was simulated with CFD (Computational Fluid Dynamics) and SPH (Smoothed Particles Hydrodynamics). The aim was to determine the efficiency of the oil capture, and the effects of varying parameters such as angular velocity of the scoops, the speed and direction of the oil jet and arrangement of the oil jets (in case of more than one jet). This configuration is found in engine cooling and/or lubricating systems: where oil scoops are used to deliver the oil to the places where direct injection is not possible. In CFD both two- and three-dimensional geometries were used; the models were then run using the Volume of Fluid method with the SST k-ω model. SPH is a meshless Lagrangian method for flow simulation, where the fluid is represented by particles. In addition to the conventional SPH formulation, three main highlights were introduced in the current work: the rotating ghost particles (representing the scoops), the particle collision model (Korzilius et al., 2014) and source and sink particles (representing the oil coming out from the nozzle and captured at the scoops respectively). The simulations allowed for the observation of the free surface of the oil jet (before, during, and after cutting of the jet by the blade), the pressure and velocity fields for the air and oil, and the efficiency of the system, defined as the ratio of oil outflow (via scoops) and inflow. This is a comparative study between CFD and SPH, where SPH is explored for a lubrication of a high-speed rotating component. The results of CFD and SPH, in particular the oil free surface and the efficiency, were then compared and validated with experimental results, demonstrating good agreement. The setup and comparison of the results obtained with the described techniques are presented in this work.
Reducing Solid Particle Erosion on Steam Turbine Stages
Authors: Chen Tie , Singh Gurnam , Millington Peter , Haller Brian
Published: September 2016

Solid Particle Erosion (SPE) damage can be found on steam turbine stages. These solid particles are caused by the exfoliation of iron oxides formed on the inner surfaces of both boiler tubes and steam pipes which are exposed to elevated temperature. They can damage both fixed and Moving Blades, as well as both outer extension ring and tip seals. Severe SPE damages can be expensive for the utility industry due to reduced efficiency and lost power generation, as well as increased costs of repair or replacement of eroded components. Thus it is very important to understand this phenomenon and propose cost effective solutions to reduce the damage.

This study investigates the effects of SPE damage using particle trajectory calculations. This investigation confirms that “Bounce Back” is the dominant cause for the SPE damage on both Fixed Blade trailing edge and Moving Blade leading edge. The particles do not accelerate at same speed as steam, therefore they travel much slower when they hit the Moving Blade leading edge. Then they are thrown back towards the Fixed Blade to hit the trailing edge. Due to strong centrifugal forces, the particles are also thrown radically outwards and damage both outer extension ring and tip seals.

Based on these enhanced understandings, a practical solution is proposed to reduce SPE damage. It is predicted to have negligible impact on the stage performance. Evidence from the latest inspection demonstrates that this solution is very effective in reducing SPE damage to the Fixed Blade trailing edge.
Experimental and Numerical Investigation of Annular Casing Impingement Arrays for Faster Casing Response
Authors: Dann Andrew , Dhopade Priyanka , Bacic Marko , Ireland Peter , Lewis Leo
Published: September 2016

The Transient Heat Transfer Facility (THTF) was developed at the University of Oxford to test full-scale high pressure compressor and turbine casing air systems using gas turbine engine representative secondary air system mass flow rates, total temperatures and total pressures. Transient casing response together with blade and disc responses governs achievable tip clearances in both compressors and turbines. Traditionally, casing thermal response is faster than disc response and so requires cooling. However, future engine designs may have thermal responses of the discs that are faster than the casings. In this paper we investigate the use of air impingement as a means to speed up the casing response to match such future designs. Two different impingement configurations were selected from a total of eight designs based on steady Reynolds-averaged Navier-Stokes (RANS) predictions of maximum heat transfer coefficient (HTC). The 3D thermal growth of the casing was characterised by the surface temperature rise over a given period of time to assess achievable dynamic response. The configurations were tested in the THTF as a rainbow set. The resulting casing metal temperatures were used in conjunction with an explicit solution of the conduction in the casing wall to calculate HTC due to impingement. The experimental set-up resembles a typical aircraft engine and therefore includes measurement uncertainties arising from features such as fixtures, seals, geometries and large surface areas that are then subjected to varying thermal inertias. These can lead to circumferential temperature non-uniformities, as evident from the experimental results. An uncertainty analysis was performed to quantify these effects on the overall casing thermal response. The experimental data was then compared against numerical predictions from an axisymmetric, 90° sector, conjugate heat transfer model of the facility using the two impingement plate designs. Overall, the values of HTC agreed well across the experimental and numerical results. Both approaches predicted differences in which of the two designs was more effective; however, advantages and limitations were identified in both approaches. The combined experimental and numerical study shows the significance of analysing the full annulus, at engine representative conditions and the benefit of an impingement array to potentially speed up casing response for future engines.
Effect of Gaseous Admixtures on Cycles With Supercritical Carbon Dioxide
Authors: Vesely Ladislav , Dostal Vaclav , Stepanek Jan
Published: September 2016

Supercritical carbon dioxide cycles are recently very perspective and they are researched all around the world. CO2 is an interesting medium for applications in many technologies, from nuclear energy through geothermal, solar and waste heat recovery systems. However, S-CO2 cycles have several issues which have to be researched, one of them being the presence of the so called pinch point in the heat exchangers design. Therefore, the Czech Technical University (CTU) conducts research on supercritical carbon dioxide cycles, which are focused on the effect of the gaseous admixtures in S-CO2 on different cycle components. The research is primarily focused on the pinch point shift within heat exchangers caused by gaseous admixtures. Previous work has shown that the pinch point can be removed with the addition of small amounts of another gases. However, it is also important to describe the effect on the performance of the cycles. This is the main topic of this paper. One of the reasons for this research is the positive effects on components are possible. The first part of the study is focused on the development of computational code for calculation of the basic S-CO2 cycles with mixtures. The second part of the study is focused on the calculation of basic cycles for binary mixtures. The calculation will be performed for pure CO2 and some binary mixture. He, CO, O2, N2, Ar will be used for the calculation as the most common admixtures, furthermore H2, CH4 and H2S will be used as well. The last part of the study will be focused on the optimization of individual cycles for different amount of admixtures in CO2. The result of this study will define the optimum ratio of admixtures and description of their effect on cycle efficiency.
Influence of the Blade-Spoke Connection Point on the Aerodynamic Performance of Darrieus Wind Turbines
Authors: Bianchini Alessandro , Balduzzi Francesco , Ferrara Giovanni , Ferrari Lorenzo
Published: September 2016

The assessment of robust CFD techniques is casting new light on the aerodynamics of airfoils rotating around an axis orthogonal to flow direction, with particular reference to flow curvature effects and stall mechanisms. In particular, Darrieus wind turbines’ designers are taking profit from these new discovers to improve the aerodynamic design of the rotors, in view of an increase of the overall efficiency and a reduction of the structural stresses on the blades.

A controversial design parameter for Darrieus turbines, especially in case of small-size rotors, is represented by the location of the blade-spoke connection along the chord.

The most common solution is indeed to place the connection at approximately airfoil’s quarter chord, i.e. where the pressure center is commonly located for low incidence angles. In some cases, however, the blade is connected at middle chord due to symmetry or aesthetic reasons. In some small turbines, innovative designs have even disregarded this parameter. Even if one can argue that the blade connection point is about to have some aerodynamic effects on the turbine’s performance, the real impact of this important design parameter is often not fully understood.

The present study makes use of extensive CFD simulations on a literature case study, using a NACA 0021 airfoil, to assess the influence of the blade-spoke connection point. In particular, the differences in terms of power coefficient curve of the turbine, optimal tip-speed ratio, torque profiles and stresses on the connection are analyzed and discussed. Detailed flow analyses are also shown for azimuthal positions of particular interest. Results on the selected case study showed that the middle-chord blade-spoke connection point seems to guarantee a higher performance of the rotor, even if additional solicitation is applied to the connection itself. It is further shown that the same performance can indeed be obtained with the airfoil attached at quarter chord and properly pitched. By doing so, the stresses are contained and the performance is maximized.
Performance and Life Characteristics of Hybrid Gas Bearing in a 10 MW Supercritical CO2 Turbine
Authors: Thatte Azam , Loghin Adrian , Shin Youngwon , Ananthasayanam Balajee
Published: September 2016

U.S. Department of Energy (DOE) has recently sponsored research programs to develop Megawatt scale supercritical CO2 (sCO2) turbine for use in concentrated solar power (CSP) and fossil based applications. From rotordynamics perspective, the extremely high power densities associated with this sCO2 turbine (similar to those of rocket turbo pump) and the long shaft of the turbine require mid-span support from bearings to achieve the high rotational speeds needed to achieve desired turbine efficiency targets. The mid-span bearings, if oil lubricated, need two sets of seals to isolate the working fluid from lubricating oil and represent a combined parasitic load of as much as 5% of the power plant output. These parasitic loads can be avoided by the use of hybrid gas bearing (HGB) which uses turbine working fluid itself as the lubricant for generating hydrostatic + hydrodynamic pressure and hence can operate in a high temperature, high pressure sCO2 environment. A successful and reliable implementation of HGB is expected to provide significant efficiency improvement in the sCO2 turbine for modular plants in 10MW scale. However, the behavior of hybrid gas bearing with supercritical CO2 as the working fluid has never been studied before. Hence a careful investigation of its hydrodynamic and rotordynamic characteristics with perturbations associated with sCO2 fluid and sCO2 turbine is warranted. In this paper the use of HGB to bring the critical speed ratio of highly power dense 10 MW sCO2 turbine into a manageable regime is investigated. Further, the performance characteristics of HGB in high pressure, high temperature sCO2 are investigated with a coupled fluid-structure interaction model. Differences between load capacity and stiffness characteristics for traditional operation in air versus operation in highly dense and viscous sCO2 are highlighted. Using Bayesian probabilistic models, insights into key design parameters needed to optimize HGB performance are obtained. A 3D fracture mechanics and crack propagation model is also developed to predict life of HGB under typical sCO2 turbine mission cycle for CSP application.
Rigid Mode Vibration Control and Dynamic Behavior of Hybrid Foil-Magnetic Bearing (HFMB) Turbo Blower
Authors: Jeong Sena , Kim Jungwan , Jeon Doyoung , Lee Yong Bok
Published: September 2016

In this study, experimental and analytical analyses of the vibration stability of a 225 kW class turbo blower with a hybrid foil-magnetic bearing (HFMB) were performed. First, critical speed and unbalance vibration responses were examined as part of the rotordynamic research. Then, an experimental double-suction turbo blower with an HFMB was built. The turbo blower consisted of an impeller at each end and a permanent magnet motor in the center. Its shaft diameter was 71.5 mm, its total length was 693 mm, and the weight of the rotor was 17.8 kg. The air foil bearing (AFB) utilized was 50 mm long and had a 0.7 aspect ratio. The results of analyses indicate that rigid mode (conical mode) occurred close to 8,036 rpm, and the results of natural frequency analysis and dynamic behavior prediction of the rotor-bearing system were similar to those obtained experimentally. However, in the experiments conducted, excessive vibration and rotor motion instability occurred in the range 12,000–15,000 rpm, which resulted from insufficient dynamic pressure caused by the length of the foil bearing being too short. Consequently, as the rotor speed increased, excessive rotor motion attributable to aerodynamic and bearing instability became evident.

This study therefore focused on improving rotordynamic performance by rectifying rigid mode unstable vibration at low speed, 20,000 rpm, and asynchronous vibration due to aerodynamic instability by using HFMB with vibration control. Although the normal operating speed is 39,000 rpm, the experiments were conducted at 20,000 rpm. The experimental results obtained were compared for each bearing type (AFB and HFMB) to improve the performance of the vibration in the low speed region.

The experimental results show that the HFMB technology results in superior vibration stability for unbalance vibration and aerodynamic instability in the range 12,000–15,000 rpm (200–250 Hz). The remarkable vibration reduction achieved from vibration control of the hybrid foil-magnetic rotor-bearing system show that oil-free turbomachinery can achieve excellent performance.
Aero-Thermo-Mechanical Modelling and Validation of Transient Effects in a High Pressure Turbine Internal Air System
Authors: Ganine Vlad , Amirante Dario , Hills Nicholas J.
Published: September 2016

Accurate prediction of metal temperatures, blade tip and seal clearances in high pressure compressor and turbine air systems leads to dramatic improvements in overall aero-engine efficiency and component life. Fast transients during an engine flight profile may introduce large changes in geometry between adjacent rotor and stator components. The changing dynamics in a few critical seals and interfaces can change the dynamics of the entire engine, compromising efficiency, integrity and long service life. In this paper we present results of a coupled aero-thermo-mechanical transient simulation of a high pressure turbine assembly throughout an engine flight cycle. The fluid and solid model geometry is approximated as 2D axisymmetric. The problem, formulated as a four field coupled multiphysics system of equations, is simplified using a quasi-steady state assumption: the transient thermal solid problem is coupled to a sequence of steady fluid problems and static structural problems. The predicted results compare well with the experimental measurements over the entire fluid-solid interface. We show improvement in transient predictions isolating the effects of the solid domain deformation. The remaining transient error is linked to temporal uncertainties in the fluid model inlet boundary conditions which were taken as a spatial average of the main annulus flow conditions.
Thermodynamic Analysis of Supercritical and Subcritical Rankine Cycles
Authors: Salazar-Pereyra Martín , Lugo-Leyte Raúl , Bonilla-Blancas Angélica Elizabeth , Lugo-Méndez Helen Denise
Published: September 2016

In this work the thermodynamic analysis of two power cycles operating at ultracritical and supercritical conditions (300 bar, 600°C), and conventional or subcritical (124 bar, 538°C) is made. The supercritical cycle has ten and eight stages of regenerative feed heating. The conventional cycle has seven and six stages of regenerative feed heating. The aim of this analysis is to show the variation of work out, thermal efficiency, the heat rate, specific steam and fuel consumptions and the operating range of the pressure of overheating. For example, supercritical conditions operation of 300 bar and 600°C and a condensation pressure of 0.1107 bar, the maximum pressure reheating is 100 bar, because with a higher pressure, steam quality at the end of the step of expanding the low pressure turbine will be less than 0.88, requiring a second reheating. Additionally, the supercritical Rankine cycles have better thermal efficiency than subcritical cycles, increases in average 6%, and consequently the heat rate and steam and fuel consumption decrease.
Reduced Order Modeling of Bladed Disks With Friction Ring Dampers
Authors: Baek Seunghun , Epureanu Bogdan
Published: September 2016

An efficient methodology to predict the nonlinear response of bladed disks with a dry friction ring damper is proposed. Designing frictional interfaces for bladed disk systems is an important approach to dissipate vibration energy. One emerging technology uses ring dampers, which are ring-like substructures constrained to move inside a groove at the root of the blades. Such rings are in contact with the bladed disk due to centrifugal forces, and they create nonlinear dissipation by relative motion between the ring and the disk. The analysis of the dynamic response of nonlinear structures is commonly done by numerical integration of the equations of motion, which is computationally inefficient, especially for steady-state responses. To address this issue, reduced order models (ROMs) are developed to capture the nonlinear behavior due to contact friction. The approach is based on expressing the nonlinear forces as equivalent nonlinear damping and stiffness parameters. The method requires only sector level calculation, and allows pre-calculation of the response-dependent equivalent terms. These factors contribute to the increase of the computational speed of the iterative solution method. A model of a bladed disk and damper, is used to demonstrate the method. Macro- and micro-slip are used in the friction model to account for realistic behavior of dry friction damping. For validation, responses due to steady-state traveling wave excitations are examined. Results computed by ROMs are compared with results from transient dynamic analysis in ANSYS with the full order model.
Assessment of Porous Type Gas Bearings: Measurements of Bearing Performance and Rotor Vibrations
Authors: San Andrés Luis , Cable Travis A. , Zheng Yong , De Santiago Oscar , Devitt Drew
Published: September 2016

Gas bearings are an attractive means of load support for rotating machinery due to their low mechanical power losses and dispensing of expensive lubrication systems. A subset of gas bearing technology, porous type gas bearings utilize a porous material as a means of feeding externally pressurized gas (typically air) to the bearing clearance region. When compared to typical orifice type hydrostatic bearings, porous bearings distribute pressurized gas more uniformly into the film clearance, thus resulting in a higher load capacity for similar flow rates [1]. The majority of the literature on porous type gas bearings focuses on the numerical evaluation of cylindrical bushings, yet experimental data on their performance is scant. As a follow up to Ref. [2], the paper presents an analysis of measurements of flow, drag torque and rotordynamic response of a large (100 mm OD, ∼275 N) rotor supported on two tilting pad (five-pad) porous journal bearings (specific load∼19 kPa). Measurements of air mass flow into the bearings, with and without the rotor in place, show that the film clearance offers little restriction. The mass flow rate is proportional to the supply pressure and lead to an estimated permeability coefficient. In operation with various levels of supply pressure and with the rotor spinning to 8 krpm (133 Hz, surface speed ∼42 m/s), several rotordynamic response tests (masses up to 6.9 gram) show the rotor amplitude of synchronous response is proportional to the mass imbalance; hence demonstrating the system is linear. Finally, rotor speed coast down tests from 8 krpm show that the bearings offer little drag friction; and increasing the supply pressure gives to lesser drag. The measurements verify the pair of gas bearings support effectively the rigid rotor with little expense in mass flow rate delivered to them. Most importantly, while operating at 10 krpm with a large added imbalance, the system survived a seizure event with little damage to the rotor and bearings, both restored to a near pristine condition after a simple cleaning procedure.
CFD Applied for the Identification of Stiffness and Damping Properties for Smooth Annular Turbomachinery Seals in Multiphase Flow
Authors: Voigt Andreas Jauernik , Iudiciani Piero , Nielsen Kenny Krogh , Santos Ilmar F.
Published: September 2016

This paper presents a first venture into quantifying stiffness and damping coefficients for turbomachinery seals in multiphase flow using Computational Fluid Dynamics (CFD). The study focusses on the simplest seal type: the smooth annular seal. The investigation is conducted for both wet-gas and bubbly flow regimes in which the primary phase is gas (air) and liquid (water), respectively. For the wet gas regime three different Liquid Volume Fraction (LVF) conditions are included in the study; 5%, 3% and 0%. Similarly for the bubbly flow regime three Gas Volume Fractions (GVF) conditions are included; 5%, 3% and 0%. An Eulerian-Eulerian modelling approach is taken, applying an inhomogeneous model, where the primary phase is treated as continuous and the secondary phase is included as dispersed. The Instationary Perturbation Method (IPM) is applied to identify the rotordynamic coefficients, in which the rotor is harmonically perturbed, and forces acting on the rotor are quantified through integration of the pressure and shear stresses. The perturbation is repeated for different frequencies to uncover any frequency dependence. The results presented in this paper are intended as an initial comparison basis for the experimental results to be obtained by applying the multiphase seal test facility currently in development, as part of a collaboration between Lloyd’s Register Consulting, the Technical University of Denmark, OneSubsea, TOTAL and Statoil.
Detailed Numerical Study of Flow and Vortex Dynamics in Staggered Pin-Fin Arrays Within a Channel
Authors: Kannan K. , Khoshlessan M. , Herrmann M. , Peet Y.
Published: September 2016

Pin-fin arrays are known to enhance heat transfer from heated surfaces and provide important industrial applications such as increasing internal heat transfer to a turbine blade or solar receiver. Several studies on heat transfer characteristics of various pin-fin arrangements and effects of geometrical parameters on heat transfer have been performed in the past. The present paper aims to address main aspects of fluid flow and heat transfer interactions through a pin-fin array with the help of high-fidelity numerical simulations and focuses on three issues. The first one is to evaluate the effect of three dimensional flow physics such as horseshoe vortices and periodic unsteadiness from vortex shedding on the spatial variation of heat transfer. The second target is to analyze the effect of free end clearance in the case of finite height pin-fin arrays with added flow complexity relative to wall-bounded pin-fin arrays, to provide a comprehensive picture of the flow physics introduced by free ends. The third one is to provide a general guideline for the numerical simulation of flows through pin-fin arrays by comparing simulations on reduced span-wise domains with the full multi-row pin configuration, to elucidate the significance of wall effects. In addition, comparison of the flow characteristics in different stream-wise row locations, is performed to establish the domain length where self-similarity might occur with inflow/outflow conditions. All simulations are conducted for low Mach number incompressible flow with temperature as a passive scalar. The current formulation assumes that variations in temperature have no effect on the fluid motion by choosing appropriate thermal boundary conditions that are still within the realistic parameter range for turbine cooling. In this paper, we perform flow simulations using the Large Eddy Simulation methodology. Two numerical codes, one based on a Finite Volume method and the other based on a Spectral Element approach, are benchmarked with each other and validated versus experiments available in the literature (Ostanek and Thole, 2012).
Influence of Disc Spacing Distance on the Aerodynamic Performance and Flow Field of Tesla Turbines
Authors: Qi Wenjiao , Deng Qinghua , Feng Zhenping , Yuan Qi
Published: September 2016

This paper aims at proposing a feasible method to determine an appropriate disc spacing distance in the design of Tesla turbines. Therefore, a typical Tesla turbine with seven different disc spacing distances was calculated numerically at different rotational speeds to investigate the influence of disc spacing distance on the aerodynamic performance and flow field of Tesla turbines and further to put forward the method. The results show that the isentropic efficiency of Tesla turbines peaks when the disc spacing distance gets its optimal value, and it decreases quickly as the disc spacing distance decreases from its optimal value. What’s more, the dimensionless parameter Ekman number is applied to determine an appropriate disc spacing distance in the design of Tesla turbines. There’s an optimal value of the Ekman number that Tesla turbines obtain its best performance, and it is influenced by the rotational speed. Meanwhile, the optimal value of the dimensionless rotor inlet tangential velocity difference which decides the rotational speed is also affected by the disc spacing distance. Thus, the determination of the optimal values of the dimensionless rotor inlet tangential velocity difference and the Ekman number is a cyclic iterative process to make them at their optimal values or in their optimal ranges respectively.
Effects of Internal and Film Cooling on the Overall Effectiveness of a Fully Cooled Turbine Airfoil With Shaped Holes
Authors: Chavez Kyle , Slavens Thomas N. , Bogard David
Published: September 2016

Adiabatic and overall effectiveness levels were measured in a closed loop linear test section using an inlet Reynolds number of 120,000 for an airfoil model at its designed inlet angle of −30.1°. Two models were used in the study — one made of a low thermal conductivity foam, and one of a higher thermal conductivity material which allowed for the Biot number of the second model to match that of the engine component. Since the ratio of the external to internal heat transfer coefficients were also matched to the engine component, the second model was thermally scaled to the actual engine component, allowing for the measurement of the overall effectiveness of the airfoil. The effects of the internal and film cooling on the overall effectiveness were examined in detail. The cooling configuration consisted of 9 rows of shaped holes, with 5 rows of conical shaped holes at the leading edge, one laidback fan-shaped gill-row, and three laidback fan-shaped holes positioned farther downstream. Furthermore, the model contained three internal coolant passages including an impingement cavity and a serpentine passage. The internal passages were lined with internal rib turbulators to enhance the internal heat transfer coefficient. This study had two main goals. First, assess the performance of a fully-cooled airfoil with shaped holes through measurements of adiabatic, internal, and overall effectiveness levels. Second, examine the effects of shaped holes and the utilization of a conduction correction on the capability to predict overall effectiveness with a simple 1D model. It was found that although the large spacing of the holes in the showerhead region produced low adiabatic effectiveness levels, the through-hole convection and impingement provided adequate levels of cooling, resulting in relatively uniform overall effectiveness levels. It was also found that although the shaped film-cooling holes have a significant effect on the 3D conduction throughout the model, the overall effectiveness is still well predicted between rows of holes, but only when a significant conduction correction to the adiabatic effectiveness data is applied. This study highlights the necessity of applied conduction corrections to adiabatic effectiveness data collected with IR thermography, highlights the use of shaped holes in the showerhead region, and confirms the utility of 1D predictive models for overall effectiveness, even for models utilizing shaped holes.
Integration and Optimization of Coal Gasification Systems With a Near-Zero Emissions Supercritical Carbon Dioxide Power Cycle
Authors: Lu Xijia , Forrest Brock , Martin Scott , Fetvedt Jeremy , McGroddy Michael , Freed David
Published: September 2016

The Allam Cycle is a semi-closed, recuperated, oxy-fuel, supercritical carbon dioxide (sCO2) Brayton power cycle, offering advantages over simple cycle and combined cycle arrangements. The Allam Cycle uniquely combines oxy-combustion with a substantially elevated operating pressure, high sCO2 recirculation flow, high gross turbine efficiency, and inventive low- and high-grade heat recuperation. As a result, the core Allam Cycle meets or exceeds the achievable net efficiencies of existing high efficiency combined cycle plants not equipped for carbon capture, while capturing substantially all CO2 emissions at purities and pressures necessary for downstream CO2 reuse and/or sequestration. Additionally, with minor alterations, the core cycle can operate with a variety of organic fuels. A 50MWt natural gas-fired demonstration of the core cycle is currently under development by 8 Rivers, NET Power, CB&I, Exelon, and Toshiba.

This paper addresses the coal syngas-fired variant of the Allam Cycle system, extending beyond high-level feasibility analyses conducted in previous studies. The paper explores in detail the unique considerations, possible hurdles, and advantages of integrating a commercially-available coal gasifier with the Allam Cycle. In particular, the paper analyzes five (5) primary technical optimizations that drive the Allam Cycle’s advantages in efficiency and cost over conventional baselines. These include: (1) a simpler overall process, requiring fewer critical integration points while still providing for efficient high- and low-grade heat recuperation; (2) high efficiencies regardless of coal rank and type used — further, the efficiency drop when using low-rank coal in an Allam Cycle arrangement is smaller than IGCC arrangements; (3) high efficiencies regardless of syngas composition (such as H2:CO ratio), particularly when compared to gasification in the chemical industry and IGCC with carbon capture and sequestration; (4) the ability to utilize a singular, cost-effective post-combustion SOX/NOX removal mechanism; and (5) considerable water savings versus IGCC and SCPC baselines, with the ability to run substantially water free with only minor impacts to overall efficiency.