bluuebunny/crossref_metadata_2025 huggingface dataset:
Model-Based Analysis of the Start-Up Improvement of a CCPP due to Steam Turbine Warm-Keeping With Air
Authors: Toebben Dennis , Burgard Tobias , Berg Sebastian , Wirsum Manfred , Pei Liu , Zheng Li , Mohr Wolfgang F. D. , Helbig Klaus
Published: November 2019

Combined cycle power plants (CCPP) have many advantages compared to other fossil power plants: high efficiency, flexible operation, compact design, high potential for combined heat and power (CHP) applications and fewer emissions. However, fuel costs are relatively high compared to coal. Nevertheless, major qualities such as high operation flexibility and low emissions distinctly increase in relevance in the future, due to rising power generation from renewable energy sources.

An accelerated start-up procedure of CCPPs increases the flexibility and reduces the NOx-emissions, which are relatively high in gas turbine low load operation. Such low load operation is required during a cold start of a CCPP in order to heat up the steam turbine. Thus, a warm-keeping of the thermal-limiting steam turbine results in an accelerated start-up times as well as reduced NOx-emissions and lifetime consumption.

This paper presents a theoretical analysis of the potential of steam turbine warm-keeping by means of hot air for a typical CCPP, located in China. In this method, the hot air passes through the steam turbine while the power plant is shut off which enables hot start conditions at any time. In order to investigate an improved start-up procedure, a physical based simplified model of the water-steam cycle is developed on the basis of an operation data set. This model is used to simulate an improved power plant start-up, in which the steam turbine remains hot after at least 120 hours outage. The results show a start-up time reduction of approximately two-thirds in comparison to a conventional cold start. Furthermore, the potential of steam turbine warm-keeping is discussed with regards to the power output, NOx-emissions, start-up costs and lifetime consumption.
Effect of Turbulence Model on the Prediction of Performance and Span-Wise Mixing in High-Speed Highly-Loaded Multi-Stage Axial-Flow Compressor
Authors: Goto Takashi , Oshio Tetsuya , Tani Naoki , Aotsuka Mizuho , Pallot Guillaume , Kato Dai
Published: November 2019

Despite significant advancements in computational power and various numerical modeling in past decades, flow simulation of a multi-stage axial-flow compressor is still one of the most active areas of research, for it is the critical component in engine performance and operability, and there are so many elements that need to be looked into to predicting correct matching of the stages and accurate flow distribution inside the machine. Modeling unsteadiness, both deterministic and random types, and real geometries are among the most important features to be considered in such prediction.

The authors have conducted in their previous studies a series of unsteady RANS (URANS) simulations of a 6.5-stage high-speed highly-loaded axial-flow compressor, and explored many unsteady effects as well as effects of real geometries such as Variable Stator Vane (VSV) clearance and inter-stage seal leakage flow on the compressor performance. However, all the analyses failed to predict correct stage matching, total pressure and temperature radial profiles, or mass-flow with adequate accuracies.

In the present study, an Improved Delayed Detached Eddy Simulation (IDDES) with SST k-omega model is applied to the simulation of the same compressor configuration at aerodynamic design point. Fifth-order WENO scheme is employed for improved spatial accuracy to suppress significant increase in mesh size. Total number of mesh points are over 400 million for 1/10th sector model. Computations are ensemble averaged for 20 sector passage. Computed overall performance and flow field are compared with the compressor rig test data. The predictions of inter-stage total temperature radial profiles are noticeably improved over the URANS with the same mesh, discretization scheme and eddy turbulence model. Good comparison with the rig data indicates the current simulation is properly capturing the span-wise mixing phenomena. Unsteady flow field are compared between IDDES and URANS to locate the cause for the enhanced mixing. It is shown that components of Reynolds stress responsible for radial diffusion and anisotropic features are intensified in the tip leakage vortex at the rotor exit for the IDDES.
Effect of Wet Gas Behavior on Centrifugal Compressor Shaft Power
Authors: Kawaguchi Daisuke , Kobayashi Katsutoshi
Published: November 2019

The focus of this work is the influence of atomizing flow on a centrifugal compressor. First, the authors clarify that the performance of the centrifugal compressor under wet gas conditions decreases with the increase of LMF as a result of an increase to the impeller shaft power, as suggested in their previous report. A new method for predicting the compressor shaft power based on the liquid behavior in the impeller is then proposed. The authors hypothesize that the increment of the impeller shaft power under wet gas conditions is different when liquid film is dominant in the impeller than when liquid droplets are. In the previous report, the predicted shaft power under the condition that the liquid film was assumed to be dominant in the impeller was experimentally verified. This paper experimentally verifies the predicted shaft power under the condition that the liquid droplets are assumed to be dominant.
Scale-Resolving Simulations of a Fundamental Trailing-Edge Cooling Slot Using a Discontinuous-Galerkin Spectral-Element Method
Authors: Garai Anirban , Murman Scott M. , Madavan Nateri K.
Published: November 2019

The accurate prediction of turbulent mixing in high-pressure turbines that incorporate various airfoil surface-cooling strategies is becoming increasing critical to the design of modern gas turbine engines where the quest for improved efficiency is driving compressor overall pressure ratios and turbine inlet temperatures to much higher levels than ever before. In the present paper, a recently developed computational capability for accurate and efficient scale–resolving simulations of turbomachinery is extended to study the turbulent mixing mechanism of a simplified abstraction of an airfoil trailing-edge cooling slot — a plane wall jet with finite lip thickness discharging into an ambient flow. The computational capability is based on an entropy–stable, discontinuous–Galerkin approach that extends to arbitrarily high orders of spatial and temporal accuracy. The numerical results show that the present simulations capture the trends observed in the experiments. Discrepancies between the simulations and experiments are believed to be due to differences in the inflow profiles and tunnel side–wall effects. The thick lip configuration leads to a thicker wake and higher unsteadiness in the wall jet compared to the thin lip. A detailed comparison of the turbulent flowfields is presented to highlight differences arising due to lip thickness variations.
Effect of Curvilinear Element Blade for Open-Type Centrifugal Impeller on Stator Performance
Authors: Tsukamoto Kazuhiro , Sakamoto Kiyohide , Hiradate Kiyotaka , Shinkawa Yasushi
Published: November 2019

The effect of a curvilinear element blade for an open-type centrifugal impeller on stator performance was investigated by experiment using an actual single stage compressor. This investigation focused on the stator part performance located at the downstream of the impeller for both a vane-less diffuser and a vaned diffuser.

Centrifugal compressors are widely used in various industrial plants, and some customers require higher stage performance. The curvilinear element blade technique, which is one of the key techniques for increasing the efficiency of closed-type centrifugal impellers, was investigated, and it effected an increase in stator efficiency. For this reason, the effect of the curvilinear element blade for the open-type centrifugal impeller was investigated. Our previous study reported that the curvilinear element blade with the open-type impeller increased the impeller efficiency by decreasing the loss derived from the impeller tip leakage flow with the parameter study of the curvilinear element blade geometries using numerical simulations. This paper reports the results of the experimental verifications using the geometries from the previous report.

Experimental results indicated that the compressor stage efficiency increased by 0.7% compared with that of the conventional impeller, which has a linear element blade by using the vane-less diffuser. However, a rotating stall occurred at a higher flow rate than that of the conventional case in the vane-less diffuser. This is due to the decrease of the impeller outlet flow angle derived from the effect of the curvilinear element blade, which makes the velocity distribution equal and reduces the blockage regions near the shroud side.

On the other hand, the curvilinear element blade impeller could increase the stage efficiency by 1.2% over the conventional impeller by using the vaned diffuser. This is due to not only the impeller performance increase but also the diffuser performance increase derived from the equality of the flow distributions by the curvilinear element blade. In addition, there was no diffuser rotating stall.
Probabilistic Response of a Bladed Disk With Uncertain Geometry
Authors: Carassale Luigi , Cavicchi Andrea , Bruzzone Silvia , Brunenghi Michela Marrè
Published: November 2019

Geometric uncertainties in the blade manufacturing process have important consequences in terms of dynamical properties of bladed disks. In this paper we address the problem of modeling a full bladed disk composed by blades having uncertain geometry. The geometric imperfection of the blades is represented and analyzed according to a procedure previously presented by the authors, based on the principal component analysis and the mesh morphing. The dynamical model of the full disk is constructed following the component mode synthesis approach. The blade geometry is represented using a probabilistic model constructed from an experimental dataset. The effect of the geometric uncertainties is assessed using a linear propagation approach, leading to a procedure that is fast enough to be embedded into a Monte Carlo simulation loop.
Implementing Environmental Impact Assessment on the Life Cycle for Industrial Gas Turbines Development
Authors: Musacchio Alessandro , Vicarelli Mattia , Colantoni Simone , Bartocci Pietro , Fantozzi Francesco
Published: November 2019

Nowadays a preliminary evaluation of environmental impact of a new product becomes more and more important, especially when the case study refers to an industrial gas turbine both for power generation and mechanical drive applications. The environmental impact evaluation, as well as the preliminary lifecycle cost analysis, will represent a critical driver to develop a competitive product during the conceptual design phase where the engine architecture is an outcome of different alternatives trade-offs.

Scope of the following paper is the presentation of a set of Design-for-Environment considerations obtained through gas turbine functional decomposition in modules, identification of the most critical, assessment of their contribution compared to the whole engine in terms of environmental impact as well as the effect on the engine use depending on ambient and operating conditions.

The outcome of this study is an approach to preliminarily evaluate the engine life-cycle impact as well as a set of indications to drive machine architecture, material selection and production processes towards the sustainability during manufacturing and operational phases.
Large Eddy Simulation of Combustor and Complete Single-Stage High-Pressure Turbine of the FACTOR Test Rig
Authors: Thomas Martin , Dombard Jerome , Duchaine Florent , Gicquel Laurent , Koupper Charlie
Published: November 2019

Development goals for next generation aircraft engines are mainly determined by the need to reduce fuel consumption and environmental impact. To reduce NOx emissions lean combustion technologies will be applied in future development projects. The more compact design and the absence of dilution holes in this type of engines shortens residence times in the combustion chamber and reduces mixing which results in higher levels of swirl, turbulence and temperature distortions at the exit of the combustion chamber. For these engines interactions between components are more important, so that the traditional engine design approach of component-wise optimization will have to be adapted. To study new lean burn architectures the European FACTOR project investigates the transport of hot streaks produced by a non-reactive combustor simulator through a single stage high-pressure turbine. In this work high-fidelity Large Eddy Simulation (LES) of combustor and complete high-pressure turbine are discussed and validated against experimental data. Measurement data is available on P40 (exit of the combustion chamber), P41 (exit of the stator) and P42 (exit of the rotor) and generally shows a good agreement to LES data.
Assessment of a Machine-Learnt Adaptive Wall-Function in a Compressor Cascade With Sinusoidal Leading Edge
Authors: Tieghi Lorenzo , Corsini Alessandro , Delibra Giovanni , Angelini Gino
Published: November 2019

Near-wall modelling is one of the most challenging aspects of CFD computations. In fact, integration-to-the-wall with low-Reynolds approach strongly affects accuracy of results, but strongly increases the computational resources required by the simulation. A compromise between accuracy and speed to solution is usually obtained through the use of wall functions, especially in RANS computations, which normally require that the first cell of the grid to fall inside the log-layer (50 < y+ < 200) [1]. This approach can be generally considered as robust, however the derivation of wall functions from attached flow boundary layers can mislead to non-physical results in presence of specific flow topologies, e.g. recirculation, or whenever a detailed boundary layer representation is required (e.g. aeroacoustics studies) [2].

In this work, a preliminary attempt to create an alternative data-driven wall function is performed, exploiting artificial neural networks (ANNs). Whenever enough training examples are provided, ANNs have proven to be extremely powerful in solving complex non-linear problems [3]. The learner that is derived from the multi-layer perceptron ANN, is here used to obtain two-dimensional, turbulent production and dissipation values near the walls. Training examples of the dataset have been initially collected either from LES simulations of significant 2D test cases or have been found in open databases. Assessments on the morphology and the ANN training can be found in the paper. The ANN has been implemented in a Python environment, using scikit-learn and tensorflow libraries [4][5]. The derived wall function is implemented in OpenFOAM v-17.12 [6], embedding the forwarding algorithm in run-time computations exploiting Python3.6m C_Api library. The data-driven wall function is here applied to k-epsilon simulations of a 2D periodic hill with different computational grids and to a modified compressor cascade NACA aerofoil with sinusoidal leading edge. A comparison between ANN enhanced simulations, available data and standard modelization is here performed and reported.
Parametric Study on Ported Shroud Locations and Geometries for a Turbocharger Compressor
Authors: Thamizullah Suheab , Nassar Abdul , Davis Antonio , Giri Gaurav , Moroz Leonid
Published: November 2019

Turbochargers are commonly used in automotive engines to increase the internal combustion engine performance during off-design operating conditions. When used, the widest operating range for the turbocharger is desired, which is limited on the compressor side by the choke condition and the surge phenomenon. The ported shroud technology is used to extend the operable working range of the compressor, by permitting flow disturbances that block the blade passage to escape and stream back through the shroud cavity to the compressor inlet. The impact of this technology, on a speed-line, at near optimal operating condition, near choke operating condition and near surge operating condition is investigated.

The ported shroud (PS) self-recirculating casing treatment is widely used to delay the onset of surge by enhancing the aerodynamic stability of the turbocharger compressor. While the ported shroud design delays surge, it usually comes with a small penalty in efficiency.

This research involves designing a single-stage centrifugal compressor for the given specifications, considering the application of an automotive turbocharger. The ported shroud was then introduced in the centrifugal compressor. The performance characteristics were obtained, both at the design and at off-design conditions, both with and without the ported shroud. The performance was compared at various off-design operating speed lines. The entire study, from designing the compressor to optimizing the ported shroud configuration, was performed using the commercial AxSTREAM® software platform. Parametric studies were performed to study the effect of ported shroud axial location along the blade axial length on the operating range and performance. The baseline design, without the ported shroud (P0), and the final geometry with it for all PS inlet axial locations (P1 to P5) were analysed using a commercial CFD package and the results were compared with those from the streamline solver.
Experimental Investigation of Heat Transfer on the Internal Tip Wall in a Rotating Two-Pass Rectangular Channel
Authors: Chia Kai-Chieh , Huang Szu-Chi , Liu Yao-Hsien
Published: November 2019

The current study experimentally studied heat transfer characteristics of the blade tip wall in a rotating internal cooling channel. The aspect ratio of this rectangular channel was 1:4, and the hydraulic diameter was 25.6 mm. Due to the impact of the 180° turn, complex three dimensional flow significantly affected heat transfer on the internal tip surface. The liquid crystal method is used to capture the heat transfer contour on the internal tip surface. In this study, the leading and trailing surfaces of the channel wall were either smooth or roughened with 45° angled ribs. The Reynolds number inside the pressurize two-pass cooling channel ranged from 10,000 to 30,000 at both stationary and rotating conditions. Furthermore, two channel orientations (90° and 135°) were tested. The effect of Coriolis force on heat transfer is studied with the rotation number up to 0.53. The tip heat transfer from the smooth channel wall was more sensitive to rotation and the largest heat transfer enhancement as a result of rotation was 68%.
Loss Analysis of Unsteady Turbomachinery Flows Based on the Mechanical Work Potential
Authors: Leggett John , Richardson Edward , Priebe Stephan , Shabbir Aamir , Michelassi Vittorio , Sandberg Richard
Published: November 2019

Loss analysis is a valuable technique for improving the thermodynamic performance of turbomachines. Analysing loss in terms of the ‘mechanical work potential’ (Miller, R.J., ASME Turbo Expo 2013, GT2013-95488) provides an instantaneous and local account of the thermal and aerodynamic mechanisms contributing to the loss of thermodynamic performance. This study develops the practical application of mechanical work potential loss analysis, providing the mathematical formulations necessary to perform loss analysis using practical Reynolds-Averaged Navier-Stokes (RANS) or Large Eddy Simulations (LES). The analysis approach is demonstrated using RANS and LES of a linear compressor cascade, both with and without incoming wakes. Spatial segmentation is used to attribute loss contributions to specific regions of the flow, and phase-averaging is performed in order to associate the variation of different loss contributions with the periodic passage of wakes through the cascade. For this un-cooled linear cascade, viscous dissipation is the dominant source of loss. The analysis shows that the contribution of the viscous reheat effect depends on the operating pressure of the compressor stage relative to the ambient ‘dead state’ pressure — implying that the optimal blade profile for a low-pressure compressor stage may be different from the optimal profile for a high-pressure compressor stage in the same engine, even if the operating conditions for both stages are dynamically-similar.
Mandrel-Free Hot-Spinning of 17-4 PH Truncated Cone
Authors: Ikawa Ken , Imamura Yoshihide , Motoyama Kojiro , Iwasaki Hayato , Hirakawa Takeo
Published: November 2019

Forming experiments were carried out using 17-4 PH plates with 490 mm dia. × 5 mm thick and 7 mm thick. A truncated cone with 30 degrees wall angle was formed at 600 °C and 850 °C by using mandrel-free hot-spinning. The material properties and shape accuracy of the formed product were investigated with as-formed products and products subjected to a solution and aging treatment.

It was found that the mandrel-free hot-spinning is able to form 17-4 PH plate into truncated cone. From the viewpoint of the forming accuracy and material properties of formed product, mandrel-free hot-spinning can be applied to 17-4 PH plate by forming at a temperature above 850 °C followed by an appropriate solution and aging treatment. In addition, it was confirmed that the deformation behavior of the formed product shows the same tendency as the deformation behavior of the Ti-6Al-4V alloy plate.
CFD Simulation of Air Ingestion in a Squeeze Film Damper
Authors: Yan Wang , Xuesong Li , Yuhong Li
Published: November 2019

Squeeze film damper (SFD) is widely adopted in the high performance rotor-bearing systems to eliminate rotor vibration and improve stability. Experiments show that the air ingestion from the open end would have notable impact on the SFD performance. Multiphase Computational Fluid Dynamics (CFD) calculation on the air ingestion in the SFD is conducted in this work. Results are validated with the experimental data to prove the capability of the multiphase CFD on predicting the air ingestion. Air and oil flow in the SFD are analyzed in details. By comparing the CFD results with and without air ingestion, the effect of air ingestion is revealed. Results show that CFD is capable of predicting the air-oil flow in the SFD. The maximum air region is located in the vicinity of the largest bearing clearance region rather than the low pressure zone. And air ingestion in the largest bearing clearance region counteracts the hydrodynamic pressure effect in the vicinity.
TURBODYNA: Centrifugal/Centripetal Turbomachinery Dynamic Simulator and its Application on a Mixed Flow Turbine
Authors: Yang Bijie , Martinez-Botas Ricardo
Published: November 2019

1D modelling is crucial for turbomachinery unsteady performance prediction and system response assessment. The purpose of the paper is to describe a newly developed 1D modelling (TURBODYNA) for turbomachinery. Different from classic 1D modelling, in TURBODYNA, rotor has been meshed and its unsteadiness due to flow field time scale is considered. Instead of direct using of performances maps, source terms are added in Euler equation set to simulate the rotor. By comparing 1D modelling with 3D CFD results, It shows that rotor unsteadiness is indispensable for a better prediction. In addition, different variables response to pulse differently. In the rotor, mass flow is close to quasi-steady while entropy is significantly unsteady. TURBODYNA can capture these features correctly and provide an accurate prediction on pressure wave transportation.
Load Independent Losses of an Aeroengine Epicyclic Power Gear Train: Numerical Investigation
Authors: Bianchini Cosimo , Da Soghe Riccardo , Giannini Lorenzo , Fondelli Tommaso , Massini Daniele , Facchini Bruno , D’Errico Jacopo
Published: November 2019

The development of Ultra-High Bypass Ratio (up to 20) engines with the aim of improving the propulsive efficiency, introduces new challenges for the transmission system in terms of heat management and power losses, since the amount of power transferred through the gearbox is greatly increased. In this respect the accurate estimate of losses at the various flow regimes realized during a typical aeroengine mission within a Power Gear Box (PGB) is essential for the correct design and operation of the engine itself.

This paper proposes a computational methodology to estimate all fluid-dynamic (load-independent) losses, which become a major source of dissipation at the high rotational speeds typical of aeroengines, developing within an epicyclic PGB. The overall procedure is based on the superposition principle and approaches the three fluid-dynamic losses, namely injection, windage and meshing losses, with different numerical techniques.

The simulations of windage effects, which consider the actual PGB geometry including the carrier disk, the lubricant spray-bar and the external casing, are based on steady-state computations. In order to introduce such simplification, a scaling procedure that avoids interference of the stationary and rotating interfaces was implemented following the outcomes of a previous analysis.

The computation of meshing losses employs a fully unsteady dynamic mesh approach and considers a portion of the meshing gears only. Both the sun-planet and planet-ring meshing were considered showing that the latter introduces a much lower level of losses.

Finally the injection losses are calculated considering the oil jet momentum variation with simplified methods based on 0D modelling.

The proposed procedure, based on the superposition principle and applied to a planetary power gear train, is tested against experimental results described in a previous paper focused on a meshing gear pair.
Prediction of Reynolds Number Effects on Low-Pressure Turbines Using a High-Order ILES Method
Authors: Bolinches-Gisbert Marc , Robles David Cadrecha , Corral Roque , Gisbert Fernando
Published: November 2019

A comprehensive comparison between Implicit Large Eddy Simulations (ILES) and experimental results of a modern highlift low-pressure turbine airfoil has been carried out for an array of Reynolds numbers (Re). Experimental data were obtained in a low-speed linear cascade at the Polithecnic University of Madrid using hot-wire anemometry and LDV. The numerical code is fourth order accurate, both in time and space. The spatial discretization of the compressible Navier-Stokes equations is based on a high-order Flux Reconstruction approach while a fourth order Runge-Kutta method is used to march in time the simulations. The losses, pressure coefficient distributions, and boundary layer and wake velocity profiles have been compared for an array of realistic Reynolds numbers. Moreover, boundary layer and wake velocity fluctuations are compared for the first time with experimental results. It is concluded that the accuracy of the numerical results is comparable to that of the experiments, especially for integral quantities such as the losses or exit angle. Turbulent fluctuations in the suction side boundary layer and the wakes are well predicted also. The elapsed time of the is about 140 hours on 40 Graphics Processor Units. The numerical tool is integrated within an industrial design system and reuses pre- and post-processing tools previously developed for another kind of applications. The trend of the losses with the Reynolds number has a sub-critical regime, where the losses scale with Re−1, and a supercrital regime, where the losses scale with Re−1/2. This trend can be seen both, in the simulations and the experiments.
Gas Turbine Combined Cycle Flexibility: A Dynamic Model for Compressor Intake Conditioning Through a Heat-Pump
Authors: Rossi Iacopo , Piantelli Luca , Traverso Alberto
Published: November 2019

The flexibility of power plants is a critical feature in energy production environments nowadays, due to the high share of non-dispatchable renewables. This fact dramatically increases the number of daily startups and load variations of power plants, pushing the current technologies to operate out of their optimal range. Furthermore, ambient conditions significantly influence the actual plant performance, creating deviations against the energy sold during the day-ahead and reducing the profit margins for the operators. A solution to reduce the impact of unpredicted ambient conditions, and to increase the flexibility margins of existing combined cycles, is represented by the possibility of dynamically controlling the temperature at compressor intake. At present, cooling down the compressor intake is a common practice to govern combined cycle performance in hot regions such as the Middle East and Africa, while heating up the compressor intake is commonly adopted to reduce the Minimum Environmental Load (MEL). However, such applications involve relatively slow regulation of air intake, mainly coping with extreme operating conditions. The use of continuously varying, at a relatively quick pace, the air temperature at compressor intake, to mitigate ambient condition fluctuations and to cope with electrical market requirements, involves proper modeling of the combined cycle dynamic behavior, including the short-term and long-term impacts of intake air temperature variations. This work presents a dynamic modeling framework for the whole combined cycle applied to one of IREN Energia’s Combined Cycle Units. The paper encloses the model validation against field data of the target power plant. The validated model is then used to show the potential in flexibility augmentation of properly adjusting the compressor intake temperature during operation.
A Supercritical CO2 Combined Power and Liquefaction Cycle
Authors: Beck Griffin , Ransom David , Hoopes Kevin
Published: November 2019

Natural gas production has increased dramatically in recent years due to advances in horizontal drilling and hydraulic fracturing techniques. There are still challenges that must be addressed by industry to better utilize these abundant natural gas resources. For example, due to the cost and complexity with piping installations from remote well sites to processing facilities (should they exist), natural gas is often flared at the site whereas the liquid hydrocarbons are stored in holding tanks.

For the natural gas that is recovered and processed, there are currently economic benefits to exporting the gas to international markets, provided that the gas can be liquefied and shipped. While the number of liquefaction facilities has increased in recent years, additional liquefaction plants are needed.

This paper introduces a novel liquefaction cycle that utilizes a supercritical carbon dioxide (sCO2) power cycle to provide power and initial stages of refrigeration to a natural gas liquefaction cycle. The liquefaction cycle uses a flow of CO2 extracted from the power cycle as well as natural gas to provide several stages of refrigeration capable of liquefying the process stream. The combined sCO2 power and liquefaction cycle is described in detail and initial cycle analyses are presented. The cycle performance is compared to small-scale natural gas liquefaction cycles and is shown to provide comparable performance to the reviewed cycles. Due to the compact nature of the sCO2 power cycle equipment, the sCO2 liquefaction cycle described herein can provide small, modular liquefaction plants that can be employed at individual well sites to liquefy and store the natural gas as opposed to flaring the gas.
High Momentum Jet Flames at Elevated Pressure: Part C — Statistical Distribution of Thermochemical States Obtained From Laser-Raman-Measurements
Authors: Ax Holger , Lammel Oliver , Lückerath Rainer , Severin Michael
Published: November 2019

A detailed investigation on flame structures and stabilization mechanisms of confined high momentum jet flames by 1D-laser Raman measurements is presented. The flames were operated with natural gas (NG) at gas turbine relevant conditions in an optically accessible high pressure test rig. The generic burner represents a full scale single nozzle of a high temperature FLOX® gas turbine combustor including a pilot stage.

1D-laser Raman measurements were performed on both an unpiloted and a piloted flame and evaluated on a single shot basis revealing the thermochemical states from unburned inflow conditions to burned hot gas in terms of average and statistical values of the major species concentrations, the mixture fraction and the temperature. The results are supported by complementary measurement techniques that have been previously conducted and presented in the connected papers part A and B [1,2], such as OH*-chemiluminescence, planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV), that combine to a big picture of the flame structures and help to interpret the results.

The results show a distinct difference in the flame stabilization mechanism between the unpiloted and the piloted case. The former is apparently driven by strong mixing of fresh unburned gas and recirculated hot burned gas that eventually causes autoignition. The piloted flame is stabilized by the pilot stage followed by turbulent flame propagation. The findings help to understand the underlying combustion mechanisms and to further develop gas turbine burners following the FLOX® concept. The combined results of all measurement techniques that have been applied to these two flames thus form a unique and comprehensive data set for the validation of numerical simulation models.
Efficiency Measurement Approach for a Hydrogen Oxyfuel Combustor
Authors: Tanneberger Tom , Schimek Sebastian , Paschereit Christian Oliver , Stathopoulos Panagiotis
Published: November 2019

The increasing generation share of renewable energy sources in the power sector raises the demand for fast and flexible large-scale storage technologies. Steam generation via stoichiometric combustion of H2 and O2 within a steam cycle is a promising way to back convert both gases. These gases can be generated by electrolysis that utilizes excess renewable energy. At the same time, this technology could provide balancing and spinning network reserves. A crucial parameter of this approach is combustion efficiency, since residual H2 or O2 can damage downstream components of the steam cycle. The current paper investigates the combustion efficiency of a H2/O2 burner under steam diluted conditions. The combustion efficiency measurement is very challenging in this case, as the combustor products consist mostly of pure steam and cannot be dried for conventional gas analysis. This is solved by an in-situ measurement method to quantify the combustion efficiency. This approach and relevant challenges are presented along with results regarding the combustion efficiency of a model H2/O2 combustor. Additionally, a design configuration study of the combustor is conducted by varying the swirl intensity and examining jet as well as swirl-stabilized flames. The initial results of the project suggest that steam-diluted H2 oxyfuel combustion with efficiencies close to 100% is possible.
Control Technology Needs for Electrified Aircraft Propulsion Systems
Authors: Simon Donald L. , Connolly Joseph W. , Culley Dennis E.
Published: November 2019

Electrified aircraft propulsion (EAP) systems hold potential for the reduction of aircraft fuel burn, emissions, and noise. Currently, NASA and other organizations are actively working to identify and mature technologies necessary to bring EAP designs to reality. This paper specifically focuses on the envisioned control technology challenges associated with EAP designs that include gas turbine technology. Topics discussed include analytical tools for the dynamic modeling and analysis of EAP systems, and control design strategies at the propulsion and component levels. This includes integrated supervisory control facilitating the coordinated operation of turbine and electrical components, control strategies that seek to minimize fuel consumption and lessen the challenges associated with thermal management, and dynamic control to ensure engine operability during system transients. These dynamic control strategies include innovative control approaches that either extract or supply power to engine shafts dependent upon operating phase, which may improve performance and reduced gas turbine engine weight. Finally, a discussion of control architecture design considerations to help alleviate the propulsion/aircraft integration and certification challenges associated with EAP systems is provided.
Experimental Analysis of an Additively Manufactured Cooled Ultra Compact Combustor Vane
Authors: Rathsack Tylor C. , Bohan Brian T. , Polanka Marc D. , Rutledge James L.
Published: November 2019

The Ultra Compact Combustor (UCC) offers a means to reduce overall combustor size. Unlike traditional axial flow combustors, the UCC utilizes an outboard circumferential cavity as the primary combustion zone. This combustor design enables the implementation of a Hybrid Guide Vane (HGV), located radially inboard of the circumferential cavity, to be positioned with the leading edge axially upstream of the hot combustion gases. Previous Computational Fluid Dynamics (CFD) efforts determined the viability of a passive cooling scheme where cooler compressor air was drawn into an opening at the stagnation region of the HGV and used for both internal and film-cooling of the vane. The present study investigates the performance of five cooled HGV configurations each having a unique combination of film-cooling, internal passage area, and internal passage geometry. The effectiveness of film-cooling holes to both protect the hardware and alter the flow path of the hot gases exiting the combustor cavity were evaluated for a range of core flow conditions. Further, the impact of a trailing edge slot to maintain an appropriate coolant flow rate through the HGV was evaluated. Results confirmed the efficacy of HGV with passive air ingestion. A solid structure located inside the cooled vanes affected the internal coolant mass flow and pressure rise and thus the overall cooling effectiveness. Further, optimal blowing ratios were demonstrated to buffer hot streaks in the freestream path resulting in a more uniform radial temperature distribution.
Rig Testing of the Operability of a Transonic Compressor Blade of an Industrial Gas Turbine
Authors: Kang Hyunsu , Ahn Sungjong , Hwang Kyusic , Bock Justin , Kang Jeongseek , Montgomery Matthew
Published: November 2019

This paper describes the flow and vibrations measured in a 1.5-stage transonic research compressor tested at the Notre Dame Turbomachinery Laboratory. The compressor is a sub-scale version of a large-scale industrial gas turbine. The experiment measured the compressor performance and investigated the operability issues of stall and flow-induced blade vibrations due to buffet and flutter. The buffet was investigated at full-speed with fully-closed inlet guide vanes; the full-speed, no-load condition of gas turbines used for power generation. The flutter was investigated at part-speed conditions with partially closed guide vanes; the part-power condition where stall flutter typically occurs for aero-engines. At both of these conditions the blades operate with high incidence and moderate velocity, which can result in flow-induced vibrations.

Aero-elastic simulations were performed to predict the flutter boundary. The flutter analysis predicted positive aerodynamic damping near the operating line, and a decrease in aerodynamic damping as the stall boundary was approached. No flutter was observed in the stable operating range of the compressor.

The experimental campaign used blade tip timing to measure the vibrations and unsteady pressure transducers above the compressor blade. These two types of data were correlated to better understand the drivers of vibration. The paper describes the behavior of the aerodynamic drivers of buffet and flutter and the resulting vibration.
Multipoint Optimization of an Axial Turbine Cascade Using a Hybrid Algorithm
Authors: Châtel Arnaud , Verstraete Tom , Coussement Grégory
Published: November 2019

This paper presents a constrained multipoint optimization of the LS89 turbine cascade. The objective of the optimization consists in minimizing the entropy losses generated inside the cascade over a predefined operating range. The operating range is bounded by two operating points respectively characterized by a downstream isentropic Mach number of 0.9 and 1.01. During the optimization, two aerodynamic constraints are imposed in order to conserve the same performance as the original cascade. The first constraint is established on the outlet flow angle in order to achieve at least the same flow turning as the LS89 turbine. The second constraint limits the mass-flow passing through the optimized cascade. The optimization is performed using a hybrid algorithm which combines efficiently a classical evolutionary algorithm with a gradient-based method. The hybridization process between both methods is based on the Lamarckian approach which consists in incorporating directly the gradient method inside the loop of the evolutionary algorithm. In this methodology, the evolutionary method allows to globally explore the overall design space while the gradient-based method locally improves certain designs located in the most promising regions of the search space. First, the better performance of the proposed hybrid method compared to the performance of a classical evolutionary algorithm is demonstrated on two benchmark problems. Then, the methodology is applied on a turbomachinery application in order to minimize the losses in the linear LS89 cascade.

The optimization process allows to find a new blade profile which reduces the entropy losses over the entire operating range by at least 9.5 %. Finally, the comparison of the flows computed in the baseline and in the optimized cascades demonstrates that the reduction of the losses is due to a decrease of the entropy generated downstream the trailing edges and within the passages between the optimized blades.
Aerodynamic Impact of Manufacturing Variation on a Nonaxisymmetric Multi-Passage Turbine Stage With Adjoint CFD
Authors: Liefke Alexander , Marciniak Vincent , Backhaus Jan , Frey Christian , Gottschalk Hanno , Janoske Uwe
Published: November 2019

Turbomachinery blade design is based on an axisymmetric model assuming identical blades in the circumferential direction. The blade manufacturing process, however, has a finite accuracy leading to surface imperfections and therefore non-identical blades. This leads to a variation in each passage cross area effecting the aerodynamic performance of the turbine.

The simulation of multiple 3D CFD blade passages, nevertheless, is still computational expensive. However, if the effect of nonaxisymmetric blades is small enough to be approximated as linear, the adjoint method is an inexpensive alternative, which can be used in an industrial context. A set of 102 turbine vanes is used to model the manufacturing variations and assess the aerodynamic impact of up to eight nonaxisymmetric blade passages of a transonic high pressure turbine stage.

It is shown that the modeled blade passage results superimpose linearly. Therefore, the aerodynamic impact of surface imperfections can be evaluated by superpositioning the singlepassage results, which are generated by an adjoint computation.
Circumferential Propagation Characteristic of Unsteady Flow in a Subsonic Axial Flow Compressor Rotor at Different Reynolds Numbers
Authors: Chen Zhiyang , Wu Yanhui , Zhang Yanwen , Gan Junwen , An Jinhuaiyuan
Published: November 2019

This paper studies the circumferential propagation characteristic of unsteady flow that occurs close to stall in a subsonic axial compressor rotor at different Reynolds number (Re). Experimental measurements are first conducted at high Re on the ground, and numerical investigations are carried out at two altitudes to explore the mechanism of circumferential propagation characteristic at different Re. The stability operating range of the compressor rotor gets small with the decrease of Re. Rotating instability (RI) is observed in the blade passage near the stall limit of the test rotor at high Re on the ground, which is characterized by a hump frequency band in the spectrum. Characteristic frequencies of numerical pressure signals at fixed frame are limited in the frequency band of RI at high Re. The cross power spectrums of numerical pressure signals detected in the neighboring passages suggest that circumferential disturbances rotates in the flow fields at different Re. Characteristic frequencies of the flow unsteadiness change with the decrease of Re. At high Re, the circumferential propagation of tip leakage flow unsteadiness is controlled by the interaction of the tip leakage flow and incoming flow, which is linked to RI. When the Re is reduced, the tip leakage flow gets weak and the radial flow from the hub to tip induced by the suction surface flow separation is dominant in the tip region. Thereafter, both the tip leakage flow and radial flow are associated with the blade tip loading, which changes the flow mechanism of RI.
A Prognostics and Health Management Framework for Wind
Authors: Sheng Shuangwen , Guo Yi
Published: November 2019

Operation and maintenance costs are a major driver for levelized cost of energy of wind power plants and can be reduced through optimized operation and maintenance practices accomplishable by various prognostics and health management (PHM) technologies. In recent years, the wind industry has become more open to adopting PHM solutions, especially those focusing on diagnostics. However, prognostics activities are, in general, still at the research and development stage. On the other hand, the industry has a request to estimate a component’s remaining useful life (RUL) when it has faulted, and this is a key output of prognostics. Systematically presenting PHM technologies to the wind industry by highlighting the RUL prediction need potentially helps speed up its acceptance and provides more benefits from PHM to the industry. In this paper, we introduce a PHM for wind framework. It highlights specifics unique to wind turbines and features integration of data and physics domain information and models. The output of the framework focuses on RUL prediction. To demonstrate its application, a data domain method for wind turbine gearbox fault diagnostics is presented. It uses supervisory control and data acquisition system time series data, normalizes gearbox temperature measurements with reference to environmental temperature and turbine power, and leverages big data analytics and machine-learning techniques to make the model scalable and the diagnostics process automatic. Another physics-domain modeling method for RUL prediction of wind turbine gearbox high-speed-stage bearings failed by axial cracks is also discussed. Bearing axial cracking has been shown to be the prevalent wind turbine gearbox failure mode experienced in the field and is different from rolling contact fatigue, which is targeted during the bearing design stage. The method uses probability of failure as a component reliability assessment and RUL prediction metric, which can be expanded to other drivetrain components or failure modes. The presented PHM for wind framework is generic and applicable to both land-based and offshore wind turbines.