bluuebunny/crossref_metadata_2025_split huggingface dataset:
Performance Assessment of an Integrated Gasification Combined Cycle Under Flexible Operation
Authors: Ravelli S. , Perdichizzi A. 
Published: August 2018

In this paper a simulation tool (Thermoflex®) has been setup to model an entire Integrated Gasification Combined Cycle (IGCC) on the basis of the report entitled “Cost and Performance of PC and IGCC Plants for a Range of Carbon dioxide Capture” by DOE/NETL [1]. The investigated layout has no water-gas-shift (WGS) reactor and does not allow for any CO2 capture. Two gasification islands are included, each of which consists of Air Separation Unit (ASU), GEE radiant-only gasifier, quench and syngas scrubber as well as syngas cleanup. Two advanced GE’s F-class gas turbines (2 × 232 MW), coupled with two heat recovery steam generators and one steam turbine (276 MW) constitute the power block.
In the IGCC simulation, the base model of the GE 7F.05 gas turbine has been adapted to burn syngas. Mass and energy balances were carefully computed on design condition to validate the proposed modelling procedure against the IGCC performance data contained in the above mentioned report: the net power output of 622 MW was underestimated by about 5% whereas the net electric efficiency was slightly overpredicted. The off-design behavior of the syngas turbine was then simulated as dependent on ambient temperature and partial load, in preparation for modelling flexible operation of the whole power plant. The variation in IGCC net efficiency and power output was assessed in a load following operational strategy, thus reducing the load factor and varying the number and slope of ramps in a typical day. The IGCC net efficiency goes down from 42.5% to 32.8% when the load is reduced from 100% to 40% of the design rate.
Steady-State Characteristics of a Dual-Rotor System With Intershaft Bearing Subjected to Mass Unbalance and Base Motions
Authors: Chen Xi , Liao Mingfu 
Published: August 2018

A dual-rotor system with an intershaft bearing subjected to mass unbalance and base motions is established. Using Lagrange’s principle, equations of motion for dual-rotor system relative to moving base are derived. Rotary inertia, gyroscopic inertia, transverse shear deformation, mass unbalance, and six components of deterministic base motions are taken into account. Using state-space vector, steady-state characteristics of dual-rotor system are analyzed through dual-rotor critical speed map, mode shapes, unbalance responses considering base rotations, frequency responses due to base motions, and shaft orbits.
The results show that base translations just add external force vectors, while base rotations bring on parametric system matrices and additional force vectors. Base rotations not only change natural frequencies of dual-rotor system, but also break the symmetry of dynamic characteristics in the case of base lateral rotation. Excited by base harmonic translation, resonant frequencies correspond to whirl frequencies. The orbit remains circular under base axial rotation, while it becomes elliptical with a static offset under lateral rotation and then a complicated curve due to harmonic translation. When harmonic frequency of base translation gets close to dual-rotor excitation frequencies, obvious beat vibration appears. Overrall, this flexible approach can ensure calculation accuracy with high efficiency and good expandability.
Fretting Fatigue and Wear of Ti-6Al-4V With HVOF Sprayed Stellite Coating on Contact Surfaces of Shrouds and Stubs of Turbine Blades
Authors: Asai Kunio , Ishizawa Shuichi , Isobe Nobuhiro 
Published: August 2018

High velocity oxygen fuel (HVOF) sprayed stellite coating is often adopted on contact surfaces of the shrouds and stubs of titanium turbine blades, in order to increase fretting fatigue strength and reduce fretting wear. To confirm the effectiveness of the sprayed stellite coating, we conducted friction-type fretting tests originally developed to simulate the load condition of shrouds and stubs, vibratory force was carried only by friction force. We also investigated the fretting fatigue mechanism of coated materials by observing non-propagating cracks in the tested specimens and analyzed crack propagation behavior at the interface using fracture mechanics.
The fretting fatigue tests confirmed that the sprayed stellite coating could double the fretting fatigue strength of Ti-6A1-4V. The fretting fatigue mechanism of Ti-6A1-4V with a sprayed stellite coating was revealed as follows: Final fracture was led by a newly initiated micro-crack at the interface as cracks initiated on the coating surface did not continuously propagate into the substrate but mainly propagated along the interface. The micro-crack propagation at the substrate depends on the length of interface crack. The longer interface crack delays micro-crack propagation to the substrate because the lines of force are less concentrated at the crack tip. Hence, the interface crack makes the fretting fatigue strength of coated Ti-6A1-4V higher than that of uncoated specimens. This finding was supported by the cross-sectional observations of non-propagating cracks in the tested specimens, and by FE analysis which revealed that ΔK of the substrate crack initiated at the interface decreases with an increase in delaminated crack length. Ti-6A1-4V with a sprayed stellite coating offers better wear resistance than uncoated Ti-6A1-4V because the coating’s friction coefficient is lower than that of Ti-6Al-4V, although the wear rates of coated and uncoated materials against the consumption energy per cycle were almost the same.
Numerical Investigation of the Compressible Flow Through a Turbine Center Frame Duct
Authors: Chen Li-Wei , Wakelam Christian , Ong Jonathan , Peters Andreas , Milli Andrea , Michelassi Vittorio 
Published: August 2018

Numerical investigation of the compressible flow in the Turbine Center Frame (TCF) duct was carried out using a Reynolds-averaged Navier-Stokes (RANS) method, and a Hybrid RANS/Large Eddy Simulation (HLES) method, i.e. Stress-Blended Eddy Simulation (SBES).
The reference Reynolds number based on the TCF inlet condition is 530,000, and the inlet Mach number is 0.41. It is found that the boundary layer flow behavior is very sensitive to the incoming turbulence characteristics, so the upstream grid used to generate turbulence in the experiment is also included in the computational domain.
Results have been validated carefully against experimental data, in terms of static pressure distribution on hub and casing walls, total pressure and Mach number profiles on the TCF measurement planes, as well as over-all pressure loss coefficient. Further, various fundamental mechanisms dictating the intricate flow phenomena, including concave and convex curvature effects, interactions between inlet turbulent structures and boundary layer, and turbulent kinetic energy budget, have been studied systematically.
The current study is to evaluate the performance of HLES method for TCF flows and develop a further understanding of unsteady flow physics in the TCF duct. The results obtained in this work provide physical insight into the mechanisms relevant to the turbine intercase or TCF duct flows subjected to complex inlet disturbances.
Influence of Scaling Parameters and Gas Properties on Overall Effectiveness on a Leading Edge Showerhead
Authors: Wiese Connor J. , Bryant Carol E. , Rutledge James L. , Polanka Marc D. 
Published: August 2018

Testing new turbine cooling schemes at engine conditions becomes increasingly cost prohibitive as the desired gas-path temperatures increase. As a result, the turbine component is simulated in a laboratory with a large-scale model that is sized and constructed out of a selected material so that the Biot number is matched between the laboratory and engine conditions. Furthermore, the experimental temperatures are lower, so the surface temperature that the metal component would experience in the engine is scaled via the overall cooling effectiveness, ϕ.
Properly measuring ϕ requires that the relevant flow physics must be matched, thus the relevant Reynolds numbers be matched-both those of the freestream and the coolant, as well as the other scaling parameters, such as the mass flux, momentum flux, and velocity ratios. However, if the coolant-to-freestream density ratio does not match that of the engine condition, the mass flux, momentum flux, coolant and freestream Reynolds numbers, and coolant-to-freestream velocity ratios cannot be matched simultaneously to the engine condition. Furthermore, the coolant thermal transfer properties are unaccounted for in these parameters, despite their large influence on the resultant overall effectiveness. While a good deal of research has focused on the effects of the coolant-to-freestream density ratio, this study specifically examines the influence of other thermodynamic properties, in particular the specific heat, which differ substantially between experimental and engine conditions. This study demonstrates the influence of various coolant properties on the overall effectiveness distribution on a leading edge by selectively matching M, I, and ACR with air, argon and carbon dioxide coolants.
Steam Flow and Heat Transfer in the Intermediate Pressure Cylinder of the Ultra-Supercritical Steam Turbine
Authors: Sun Chong , Zhou Daiwei , Zhu Xiaocheng , Du Zhaohui 
Published: August 2018

The cooling protection of the hot end is the key technique for ultra-supercritical steam turbine. Tangential direction cooling chamber has a simple form and stable cooling effectiveness. The influence of inlet Mach number, turbulent Prandtl number, rotational speed, and inlet turbulence intensity on cooling effect of the structure in ideal air model have been made by previous work. The cooling mechanism and the flow characteristic in the ideal air chamber were investigated.
In this paper, the focus of the study is to investigate the flow and heat transfer characteristics of the tangential direction cooling chamber in the real steam model. The cooling chamber coupled with the whole steel shaft are simulated. Different boundary condition are compared. The heat transfer coefficients of the hub are acquired at some different rotational speeds and different hub conditions. The distribution of heat transfer coefficients and wall temperature are mainly affected by the viscous force and the velocity gradient near the hub.
A Sobol' Sequence Parametric Analysis of Rotor Thermal Bow in Gas Turbines
Authors: Smith Evan O. , de Baar Jouke H. S. , Neely Andrew J. 
Published: August 2018

After a jet engine is shut down, hot air rising inside the compressor disc cavities, secondary air systems, and the gas path annulus will result in a vertical temperature gradient. As the compressor rotor cools and contracts in the presence of this thermal gradient, it will bend, in a phenomenon known as thermal rotor bow. Starting an engine under bowed conditions can result in rubbing of the rotor and stator seals, adding heat to the rotor, exacerbating the rotor bow. This causal sequence of rubbing and bending is called the Newkirk Effect.
In this study, 30 simulations of simplified compressor geometries have been run in three-dimensional unsteady conjugate heat transfer computational fluid dynamics coupled with finite element modelling, using a Sobol’ quasi-random sequence coupled with kriging interpolation to study the effects of three important geometric parameters on the thermal bow response of an engine. The three parameters, rotor length, rotor diameter, and compressor case wall thickness, were selected based on a similar screening test analysis performed by authors in a previous study.
The results include response maps of each parameter with respect to rotor bow and clearance reduction onset time, duration, and severity, and show that length and case wall thickness exhibit linear responses due to their effect on stiffness, whereas diameter exhibits a non-linear response, due to the conflicting and competing effects on stiffness and vertical temperature difference.
Optimization of the Straight-Through Labyrinth Seal With a Smooth Land
Authors: Wróblewski Włodzimierz , Frączek Daniel , Szymański Artur , Bochon Krzysztof , Dykas Sławomir , Marugi Krzysztof 
Published: August 2018

The primary goal of this study was to develop and experimentally validate the methodology of labyrinth seals optimization concerning leakage. The problem was investigated using the ANSYS CFX commercial software.
This paper presents the methodology and results of the optimization of a straight-through labyrinth seal with two inclined fins against smooth-land. The optimization was performed using commercial tools implemented in the ANSYS Workbench environment, such as Goal-Driven Optimization (GDO). The response surfaces were created based on Latin hypercube samples found from CFD calculations. The CFD solver — Ansys CFX, using a steady-state scheme with the k-omega Shear Stress Transport turbulence model, was applied. The CFD model was previously validated concerning spatial discretisation and turbulence modelling. A screening algorithm was used to find the best candidates on the response surfaces. The objective function adopted in the labyrinth seal optimization was the minimization of the discharge coefficient value. A wide range of parameters of the fins position and shape, such as the angles, heights and widths, were taken into account, with physically justified degrees of freedom. The leakage reductions being the effect of the optimization were considerable. The cuts in the discharge coefficient significantly exceed the uncertainties of the CFD model and the test rig accuracy. The factors that have the strongest impact on the leakage reduction in are the inclination, thickness of the fin tips, and the distance between fins.
The optimization results were supported with the results of an in-house experiment performed on a stationary, linear test rig. The specimens tested experimentally were on the same scale (1:1) as the optimised ones. The test rig was fed by a high-capacity vacuum air blower, which made it possible to reach critical pressure ratios, with high-precision hot wire anemometry (HWA) mass flow evaluation. The measuring system also enabled assessment of the pressure distribution along the labyrinth structure. The experimental testing results were compared to the CFD calculations and the optimization effects, highlighting some specific tendencies in the labyrinth seal flow behaviour. Good agreement was obtained between the optimization results and the experimental data, which proves that the presented methodology is sufficient for the labyrinth seal optimization. The same methods will also be applied to more sophisticated sealing structures.
Axial Turbine Design for a Twin-Turbine Heavy-Duty Turbocharger Concept
Authors: Anton Nicholas , Genrup Magnus , Fredriksson Carl , Larsson Per-Inge , Christiansen-Erlandsson Anders 
Published: August 2018

In the process of evaluating a parallel twin-turbine pulse-turbocharged concept, the results considering the turbine operation clearly pointed towards an axial type of turbine. The radial turbine design first analyzed was seen to suffer from sub-optimum values of flow coefficient, stage loading and blade-speed-ratio. Modifying the radial turbine by both assessing the influence of “trim” and inlet tip diameter all concluded that this type of turbine is limited for the concept. Mainly, the turbine stage was experiencing high values of flow coefficient, requiring a more high flowing type of turbine.
Therefore, an axial turbine stage could be feasible as this type of turbine can handle significantly higher flow rates very efficiently. Also, the design spectrum is broader as the shape of the turbine blades is not restricted by a radially fibred geometry as in the radial turbine case.
In this paper, a single stage axial turbine design is presented. As most turbocharger concepts for automotive and heavy-duty applications are dominated by radial turbines, the axial turbine is an interesting option to be evaluated for pulse-charged concepts.
Values of crank-angle-resolved turbine and flow parameters from engine simulations are used as input to the design and subsequent analysis. The data provides a valuable insight into the fluctuating turbine operating conditions and is a necessity for matching a pulse-turbocharged system.
Starting on a 1D-basis, the design process is followed through, resulting in a fully defined 3D-geometry. The 3D-design is evaluated both with respect to FEA and CFD as to confirm high performance and durability.
Turbine maps were used as input to the engine simulation in order to assess this design with respect to “on-engine” conditions and to engine performance.
The axial design shows clear advantages with regards to turbine parameters, efficiency and tip speed levels compared to a reference radial design. Improvement in turbine efficiency enhanced the engine performance significantly.
The study concludes that the proposed single stage axial turbine stage design is viable for a pulse-turbocharged six-cylinder heavy-duty engine. Taking into account both turbine performance and durability aspects, validation in engine simulations, a highly efficient engine with a practical and realizable turbocharger concept resulted.
The Present Challenge of Transonic Compressor Blade Design
Authors: Hergt A. , Klinner J. , Wellner J. , Willert C. , Grund S. , Steinert W. , Beversdorff M. 
Published: August 2018

The flow through a transonic compressor cascade shows a very complex structure due to the occuring shock waves. In addition, the interaction of these shock waves with the blade boundary layer inherently leads to a very unsteady flow behaviour.
The aim of the current investigation is to quantify this behaviour and its influence on the cascade performance as well as to describe the occuring transonic flow phenomena in detail. Therefore, an extensive experimental investigation of the flow in a transonic compressor cascade has been conducted within the transonic cascade wind tunnel of DLR at Cologne. In this process, the flow phenomena were thoroughly examined for an inflow Mach number of 1.21. The experiments investigate both, the laminar as well as the turbulent shock wave boundary layer interaction within the blade passage and the resulting unsteady behaviour. The experiments show a fluctuation range of the passage shock wave of about 10 percent chord for both cases, which is directly linked with a change of the inflow angle and of the operating point of the cascade.
Thereafter, RANS simulations have been performed aiming at the verification of the reproducibility of the experimentally examined flow behavior. Here it is observed that the dominant flow effects are not reproduced by a steady numerical simulation. Therefore, a further unsteady simulation has been carried out in order to capture the unsteady flow behaviour. The results from this simulation show that the fluctuation of the passage shock wave can be reproduced but not in the correct magnitude. This leads to a remaining weak point within the design process of transonic compressor blades, because the working range will be overpredicted.
The resulting conclusion of the study is that the use of scale resolving methods such as LES or the application of DNS is necessary to correctly predict unsteadiness of the transonic cascade flow and its impact on the cascade performance.
Direct Assessment of the Acoustic Scattering Matrix of a Turbulent Swirl Combustor by Combining System Identification, Large Eddy Simulation and Analytical Approaches
Authors: Merk Malte , Silva Camilo , Polifke Wolfgang , Gaudron Renaud , Gatti Marco , Mirat Clément , Schuller Thierry 
Published: August 2018

This study assesses and compares two alternative approaches to determine the acoustic scattering matrix of a pre-mixed turbulent swirl combustor:
1) The acoustic scattering matrix coefficients are obtained directly from a compressible Large Eddy Simulation (LES). Specifically, the incoming and outgoing characteristic waves f and g extracted from the LES are used to determine the respective transmission and reflection coefficients via System Identification techniques.
2) The flame transfer function (FTF) is identified from LES time series data of upstream velocity and heat release rate. The transfer matrix of the reactive combustor is then derived by combining the FTF with the Rankine-Hugoniot relations across a compact heat source and a transfer matrix of the cold combustor, which is deduced from a linear network model. Linear algebraic transformation of the transfer matrix consequently yields the combustor scattering matrix.
A cross-comparison study that includes comprehensive experimental data shows that both approaches successfully predict the scattering matrix of the reactive turbulent swirl combustor.
Prediction of Boundary Layer Flashback Limits of Laminar Premixed Jet Flames
Authors: Hoferichter Vera , Hirsch Christoph , Sattelmayer Thomas 
Published: August 2018

Preventing flame flashback into the premixing section is one of the major challenges in premixed combustion systems. For jet flames, the flame typically propagates upstream inside the low velocity region close to the burner wall, referred to as boundary layer flashback.
The physical mechanism of boundary layer flashback of laminar flames is mainly influenced by flame-wall interaction and flame quenching. Flashback is initiated if the burning velocity at some wall distance is higher than the local flow velocity. Since the burning velocity drops towards the wall due to heat losses, the wall distance of flashback can be defined at the location closest to the wall where the burning velocity still is sufficiently high. The well-established critical gradient concept of Lewis and von Elbe to predict flashback limits of laminar flames represents these assumptions but neglects the important influence of flame stretch on the burning velocity close to the wall. For that reason, a modified prediction model is developed in this work based on similar assumptions as in the critical gradient concept, but including the effect of flame stretch. A validation for hydrogen-air and methane-air flames highlights its advantages compared to the critical gradient concept and shows good prediction accuracy.
A Highly Flexible Approach on the Steady-State Analysis of Innovative Micro Gas Turbine Cycles
Authors: Krummrein Thomas , Henke Martin , Kutne Peter 
Published: August 2018

Steady state simulations are an important method to investigate thermodynamic processes. This is especially true for innovative micro gas turbine (MGT) based cycles as the complexity of such systems grows. Therefore, steady state simulation tools are required which ensure large flexibility and computation robustness. As the increased system complexity result often in more extensive parameter studies also a fast computation speed is required.
While a number of steady state simulation tools for micro gas turbine based systems are described and applied in literature, the solving process of such tools is rarely explained. However, this solving process is crucial to achieve a robust and fast computation within a physically meaningful range. Therefore, a new solver routine for a steady state simulation tool developed at the DLR Institute of Combustion Technology is presented in detail in this paper.
The solver routine is based on Broyden’s method. It considers boundaries during the solving process to maintain a physically and technically meaningful solution process. Supplementary methods are implemented and described which improve the computation robustness and speed.
Furthermore, some features of the resulting steady state simulation tool are presented. Exemplary applications of a hybrid power plant, an inverted Brayton cycle and an aircraft auxiliary power unit show the capabilities of the presented solver routine and the steady state simulation tool. It is shown that the new solver routine is superior to the standard Simulink algebraic solver in terms of system evaluation and robustness for the given applications.