bluuebunny/crossref_metadata_2025_split huggingface dataset:
Blade Health Monitoring System for Gas Turbines Subjected to Contaminated Air
Authors: Tayebi Kamel , Khalidi Abdurrahman , Dawood Alaaeldin 
Published: October 2022

Abstract
Air contamination continues to cause corrosion sometimes leading to catastrophic failures costing tens of millions of dollars in repair/replacement and revenue losses. In the case of heavy-duty gas turbines in the power industry, the problem starts with pitting due to corrosion and progresses to crack initiation, then crack extension due to cyclic load then to unstable crack propagation leading ultimately to blade liberation which in turn creates an extended trail of damage through the various stages of the compressor and the casing. This type of failure usually requires total rotor replacement. It is important to identify the early stages of crack formation and relate it to the level of air contamination and operational parameters of the turbine.
This paper addresses improved methods of commissioning and integrated monitoring of a blade health monitoring (BHM) system installed on a turbine that witnessed a previous compressor failure. We particularly show how BHM can be combined with engine operation information for a better understanding of the impact of operational changes on blade behavior. Such an understanding is necessary to detect potential changes in amplitude or frequency characteristics due to damage initiation and progression. It also enables the development and continuous update of site-specific and engine-specific knowledge bases that can be used in predictive analysis and effective decision making for optimal operational performance.
Secondary Air System: A Current Review and Future Investigations
Authors: Fuchs Fabian , Cordes Laura 
Published: October 2022

Abstract
Since every new scientific work starts with a comprehensive literature study about the state of the art, this paper should give an overview about previous, but still useful, and more recent publications to describe a secondary air system (SAS) for gas turbines. Nevertheless, in current times it is impossible to present a complete research, but the well-disposed reader will get a meaningful insight and may use the references as a start for their own detailed search. The first part will give a description of a typical set up of a SAS and the common flow elements that can be found along the flow path. It also includes an explanation of the elements operating behavior, especially regarding the pressure and temperature changes as well as the resulting air mass flow. In the second part the authors describe the plans at the German Aerospace Centers (DLR) Institute of Test and Simulation for Gas Turbines in the SAS’ field of research.
Heat Transfer Coefficient and Adiabatic Wall Temperature Measurements on a High-Pressure Turbine Nozzle Guide Vanes With Representative Inlet Swirl and Temperature Distortions
Authors: Bacci T. , Picchi A. , Babazzi G. , Facchini B. , Cubeda S. 
Published: October 2022

Abstract
Combustor-exit conditions in modern gas turbines are generally characterized by significant temperature distortions and swirl degree, which in turn is responsible for very high turbulence intensities. These distortions have become particularly important with the introduction of lean combustion, as a mean to control NOx pollutant emissions. For this reasons combustorturbine interaction studies have recently gained a lot of importance. Past studies have focused on the description of the effects of turbulence, swirl degree and temperature distortions on the behavior of the high pressure stages of the turbine, both considering them as separated aspects, and accounting for their combined impact. Aspects like pressure losses, hot streaks migration and film-cooling behavior have been widely investigated. Even if some studies have focused on the characterization of the heat transfer coefficient (HTC) on the nozzle guide vane external surface, none of them have addressed this aspect from a purely experimental point of view. Indeed, when inlet conditions are characterized by both swirl and temperature distortions they represent a severe challenge for the commonly adopted measurement techniques. The work presented in this paper was carried out on a non-reactive, annular, three-sector test rig made by a non-reactive combustor simulator and a nozzle guide vane cascade; it is able to create a representative combustor outflow, characterized by all the flow characteristics described before. A novel experimental approach, that was developed in a previous work, was exploited to experimentally retrieve the heat transfer coefficient and the adiabatic wall temperature distributions on a non-cooled nozzle guide vane. Temperature measurements on the cascade inlet and outlet planes were also used to provide boundary conditions and achieve a better understanding of the investigated phenomena. The results allowed to evidence the effect of the inlet swirl on the heat transfer coefficient distribution, as well as the evolution of the temperature distribution on the vane surface moving through the cascade, constituting the first attempt to evaluate these aspects from a purely experimental point of view.
Experimental Investigation of Local Heat Transfer in a Rotating Two-Pass Cooling Channel Using the Transient Thermochromic Liquid Crystal (TLC) Technique
Authors: Waidmann Christian , Poser Rico , Gutiérrez de Arcos David , Göhring Michael , von Wolfersdorf Jens , Semmler Klaus , Jäppelt Bernhard 
Published: October 2022

Abstract
A test rig for the investigation of rotating turbine blade internal cooling channel configurations is presented. Local heat transfer distributions are evaluated using the transient thermochromic liquid crystal (TLC) technique. The rig can be operated at rotational speeds of up to 900 rpm, mass flow rates between 3 g/s and 30 g/s, fluid temperatures between −100 °C and +80°C and fluid pressures of up to 10 bar. This allows for a broad range of possible test conditions.
The investigated cooling channel model is a two-pass leading edge configuration manufactured out of acrylic glass. It consists of a first pass with a trapezoidal cross-section and radially outward flow, a 180° bend, and a second pass with a rectangular cross-section and radially inward flow. The suction side and pressure side surfaces are equipped with angled ribs.
The evaluation method is based on the measurement of TLC indication times. A sudden fluid temperature change is applied to cool down the TLC-coated heat transfer surfaces. This induces a TLC color play which is captured using cameras that are co-rotating with the test model. Assuming 1D heat conduction inside a semi-infinite wall, heat transfer coefficients are then calculated from the TLC indication times and the fluid reference temperature measurements.
The data evaluation procedure and the results of a typical experiment are presented. Heat transfer data are shown in contour plots of the Nusselt number distribution. Furthermore, a method to directly compare the results of a rotating with a corresponding non-rotating experiment using normalized Nusselt number ratios is shown. Finally, data reduction methods are described that provide line-averaged values as well as histograms of normalized Nusselt number ratios.
Numerical Prediction of a Lean Blow-Out Event of a Lab-Scale, Swirl-Stabilized Spray Flame
Authors: Ruoff Stephan , Eckel Georg , Le Clercq Patrick , Aigner Manfred 
Published: October 2022

Abstract
Alternative jet fuels have a high potential to reduce emissions in aviation and to increase the independence from mineral oil. However, as a safe operation must be guaranteed, new fuels have to pass elaborate and expensive tests to be finally certified. To reduce the costs and time of the certification process, numerical simulations can be used to assess the impact of a new fuel on combustion. Further, the detailed simulations provide an insight into the fuel sensitive sub-processes. The lean blowout (LBO), i.e. the lower stability limit of a gas turbine combustor, is of primary concern for safe operation and the approval of alternative jet fuels. The paper at hand focuses on the formulation of a calculation protocol for the numerical representation of a lab-scale LBO experiment. The test case is a swirl-stabilized spray flame, which mimics several key features of aero-engine combustors. The LBO-limits are determined by a stepwise reduction of the fuel mass flow starting from a stable operation point above the measured blowout limit. Towards extinction, the heat release rate in the combustor drops. Furthermore, fuel is still evaporating, but less fuel is burned, leading to an accumulation of fuel in the combustion chamber. The blow-out is defined by a steep drop in heat release combined with a large increase of the gaseous fuel mass fraction in the computational domain. The semi-automated calculation protocol is able to successfully capture a blowout event at an equivalence ratio of ϕ = 0.32 and can thus be applied to evaluate alternative jet fuels in the future. In addition, a reignition event is observed for equivalence ratios slightly above ϕLBO.
An Approximate Time Domain Nonlinear Harmonic Method for Analyzing Unsteady Flows With Multiple Fundamental Modes
Authors: Wang Dingxi , Zhang Sen 
Published: October 2022

Abstract
In this paper, a new hybrid time and frequency domain method called the approximate time domain nonlinear harmonic method is proposed for a robust and efficient analysis of turbo-machinery unsteady flow with more than one fundamental modes. The proposed method combines the features of the nonlinear harmonic method and the time domain harmonic balance method. Unsteady flow components are grouped according to their fundamental frequencies and inter blade phase angles and separate unsteady flow governing equations are constructed for each mode group. These mode groups are connected using the least squares method based Fourier transform. The proposed method is expected to be exact for a linear problem, but approximate for a nonlinear problem. Three sets of analyses with increasing level of difficulties are presented to demonstrate the validity and effectiveness of the proposed method by comparing it with the time domain harmonic balance method based upon the almost periodic Fourier transform.
Effects of the Ribbed-Squealer Tip on the Blade Tip Aerothermal Performance in a High Pressure Gas Turbine Cascade
Authors: Du Kun , Li Huarong , Hui Na , Gao Yuanyuan , Liu Cunliang 
Published: October 2022

Abstract
In modern gas turbines, High-temperature gas gives rise to the heat load dramatically to the tip region, inducing the leakage flow through the blade tip gap by the lateral pressure difference. Squealer tip, as an efficient technique, has been widely utilized to reduce the tip leakage flow and the heat load. In order to enhance efficiency of squealer tip, the present research proposed kinds of ribbed-squealer tip. Ribs along the axial direction and the circumferential direction are inserted inside the conventional squealer tip. The effects of different squealer tips on the blade tip leakage flow and heat transfer characteristic were numerically investigated. Three-dimensional (3D) Reynolds-Averaged Navier-Stokes (RANS) equations and standard k-ω turbulence model were solved to conduct the simulations. The numerical results indicated that the ribs significantly alter the full development of various vortices inside the tip cavity, thus improving the aerothermal performance in the ribbed-squealer tip. In all simulated cases, the case with the staggered rib within 0–40% chord region obtains the smallest heat transfer coefficient, and achieve the best performance in minimizing the tip leakage mass flux within the 0–10% stream-wise region.
The Effect of Nitrogen Impurities on Oxy-Fuel Combustion Under Supercritical-CO2 Conditions
Authors: Gokulakrishnan Ponnuthurai , Shao Jiankun , Klassen Michael , Davidson David , Hanson Ronald 
Published: October 2022

Abstract
The direct-fired supercritical-CO2 (sCO2) cycle has demonstrated the ability to produce clean energy by burning hydrocarbon feed stocks under oxy-fuel conditions. High-pressure operation of the direct-fired cycle allows for more economic extraction of CO2 for carbon capture and storage. However, the presence of nitrogen impurities in the oxidizer (i.e., N2) and in fuel feed stocks (e.g., NH3) can generate NOx in the exhaust. The presence of NOx in the recycled-CO2 stream can impact the combustion process as well as the structural integrity of the system. Also, even trace amounts of nitrogen oxides (considered acid gases) can be detrimental for CO2 capture, transportation and storage at supercritical conditions.
Therefore, it is critical to understand and accurately model the effects of nitrogen impurities on NOx formation and the impact of NOx in the recycled CO2 on combustion kinetics under oxy-fuel sCO2 conditions. It is also important to understand the effects of pressure with a sCO2 medium as the direct-fired sCO2 cycle operates up to 300 atm pressure. In this work, experimental and modeling work were performed to study the effect of nitrogen species on emissions as well as effect of NOx on ignition of CH4 and syngas fuels at sCO2 conditions. A chemical reactor network simulation was used to investigate the effects of nitrogen impurities in fuel and oxidizer stream on emissions from a direct-fired combustor condition. Monte Carlo simulations were also carried out to study the impact of model input variables on the emission profile.
High-pressure shock tube ignition delay time experiments were performed to investigate the effect of NOx on ignition at conditions relevant to direct-fired oxy-fuel sCO2 combustion. The ignition delay time measurements were made for syngas and CH4 fuels with and without NO addition using CO2 as bulk diluent at nominal pressures around 100 atm. Experimental data showed that the presence of NO promotes the ignition at the oxyfuel sCO2 combustion conditions. Reaction sensitivity analyses and model uncertainty analyses were conducted to identify important reactions and their rate uncertainty on the model predictions, respectively.
Investigation of the Performance of Hydrogen-Fueled Wankel Rotary Engine Using 0-D Model
Authors: Du Yang , Yang Zhenghao , Geng Qi , Wang Rui , He Guangyu 
Published: October 2022

Abstract
This paper establishes a 0-D model based on the real gas properties and laminar flame propagation speed to predict the performance of a hydrogen-fueled Wankel rotary engine. The performance comparative analysis between hydrogen-fueled and gasoline-fueled Wankel rotary engines is conducted under the same fuel heat value input. Furthermore, the effects of rotational speed, ignition advance angle on the chamber temperature, pressure, heat release rate, engine effective fuel consumption, indicated thermal efficiency and effective power output are investigated. are evaluated. The results show that as the gasoline is replaced by hydrogen with the constant total input heat value, the effective power and indicated thermal efficiency are reduced by 16.93% and 5.97% at design condition, respectively. As the rotational speed increases from 4000rpm to 10000rpm, the effective powers of gasoline and hydrogen are increased by 204% and 238%, respectively. The peak pressure of hydrogenfueled engine appears is 28° ahead of gasoline-fueled engine. With the decreasing ignition advance angle, the effective power output and indicated thermal efficiency of gasoline-fueled engine firstly increase and then drop, while that of hydrogen-fueled increase. Meanwhile, the combustion duration angles of two fuels decrease with decreasing ignition advance angle. The maximum indicated thermal efficiencies of 31.7% and 35.4% for hydrogen-fueled and gasoline-fueled engines are obtained at ignition advance angles of 7°and 27° with nominal rotational speed of 7000rpm, respectively.
Improvement of the Primary Atomization Model for Jet Into Subsonic Crossflow
Authors: Ju Hongyu , Suo Jianqin , Li Yue , Zheng Longxi 
Published: October 2022

Abstract
An improved primary atomization model for the jet-in-crossflow (JICF) atomization has been suggested and incorporated into the solver SprayFoam of OpenFOAM. The assumption of replacing jets with blobs, the maximum growth rate of the Kelvin-Helmholtz (K-H) wave, and its corresponding wavelength in the WAVE model are inherited. The present model assumes that the blobs move uniformly in the jet direction and accelerate uniformly in the crossflow direction to simulate the jet trajectory. It considers the Rayleigh-Taylor (R-T) wave on the liquid surface and assumes that the growth rate determines the R-T wave and K-H wave competition. The frequency, position, and mass of liquid surface breakup, the velocity, and the size of stripping drops are given in detail. Results of the present model have been compared with the experimental data in other literature under varying momentum flux ratios, Mach number, and air Weber number. The agreement between calculated results and the measured value is generally good, and a quantitative assessment of the model performance has been conducted.
Highly Resolved Large-Eddy Simulations of a Transonic Compressor Stage Midspan Section Part I: Effect of Inflow Disturbances
Authors: Bode Christoph , Przytarski Pawel J. , Leggett John , Sandberg Richard D. 
Published: October 2022

Abstract
Flows in modern compressors are highly complex. They are subject to adverse pressure gradients, high levels of unsteadiness and often operate at transonic conditions. Such conditions often render low order methods such as URANS unreliable. This is due to the inherently unsteady nature of shock-boundary layer interaction as well as the interaction between deterministic and stochastic unsteadiness. These issues are further exacerbated by the current design trends towards more compact machines with higher work coefficients. It is therefore desirable to study the flow within a transonic compressor stage using highly-fidelity scale resolving simulation. To enable fully wall resolved stage calculations at a realistic rotor Reynolds number of 1 × 106, a quasi three-dimensional translational setup was carefully generated to feature similar midspan blade loadings to the three-dimensional rotational set up of the Transonic Compressor Darmstadt. Two cases were considered, one with a laminar inflow to the rotor and one with inflow turbulence. It is found that the inflow turbulence suppresses the rotor suction side separation bubble with implications on the shock-boundary layer interaction, mainly in terms of an upstream moved shock location and changes to the shock oscillations, and the shock-related passage losses. The changes to the early development of the rotor suction side boundary layers also affects the boundary layer losses. The stator suction side boundary layer on the other hand appears insensitive to the introduction of inflow disturbances. However, a larger passage loss is found for the laminar inflow case in the stator. Additional URANS calculations of the same setup show overall good comparison with the high-fidelity results for most integral values, but lack in predictive accuracy for some details, such as shock boundary layer interaction as well as wake and passage losses.
Design Optimization of a High-Speed Twin-Stage Compressor for Next-Gen Aircraft Environmental Control System
Authors: Giuffre’ Andrea , Colonna Piero , Pini Matteo 
Published: October 2022

Abstract
The environmental control system (ECS) is the largest auxiliary power consumer, i.e, around 75% of non-propulsive power, among the aircraft subsystems. The adoption of a novel ECS architecture, based on an electrically-driven vapor compression cycle system, can enable a twofold increase of coefficient of performance (COP), as compared to the conventional air cycle machine (ACM). The core of this technology is a high-speed, miniature centrifugal compressor, consisting of two impellers mounted in back-to-back configuration, and running on gas bearings operating with refrigerant. The fluid dynamic design optimization of the twin-stage compressor, to be installed in the vapor compression cycle test rig under realization at Delft University of Technology, is documented in this paper. First, the scaling analysis for centrifugal compressor is extended to provide guidelines for the design of twin-stage machines. Then, a multi-objective conceptual design optimization is performed by resorting to an in-house reduced-order model (ROM), coupled to a genetic algorithm. The fluid dynamic performance and the structural integrity of the optimal design are assessed by means of a hybrid framework, encompassing CFD and ROMs, and by FEA. The results show that it is possible to design a twin-stage compressor for the target application, featuring an average efficiency higher than 70%, a maximum compression ratio exceeding 9, and an operating range of 0.27 at the design rotational speed, despite the detrimental effects of motor cooling and miniature size.
Modal Identification of Bladed Disks by Time-Frequency Analysis of the Non-Synchronous Response
Authors: Carassale Luigi , Guida Roberto , Marrè-Brunenghi Michela 
Published: October 2022

Abstract
In some circumstances it is impossible to exploit resonance crossings to identify the modal properties of rotor disks. In these cases, the identification process must rely on nonsynchronous vibrations and becomes challenging for two reasons. First, the signals are weak (compared to the levels measured during resonance crossings) and random, thus an averaging procedure is necessary. Second, the dynamical system is time-variant due to the variation of the rotor speed. This paper presents a modal identification procedure formulated in the framework of the time-frequency analysis. A region of the time-frequency plane is stretched to map the system into a fictitious LTI system. Then, the PSD of the response is computed by an averaging procedure. Finally, the modal properties are estimated through an output-only modal identification algorithm. The procedure is applied to simulated and experimental data regarding a bladed disk of a steam turbine.
Performance Investigation of Airfoils for Axial Flow Fans in Low Solidity Cascades Operating at High Inlet Flow Angles
Authors: Cravero Carlo , Milanese Gabriele 
Published: October 2022

Abstract
Axial flow fans are usually characterized by blade sections with low solidity and high inlet flow angles.
Two main approaches are followed in the preliminary design phase, to take into account blade interaction effects: the use of available airfoil cascades data (or related correlations) and that of isolated airfoil data together with interference coefficients.
The working conditions of low solidity airfoil cascades with highly tangential inflow are not widely studied in literature, leaving the designer the possibility to rely on limited cascade data or often on the use of isolated airfoil data, with the assumption of negligible interference effects.
A systematic investigation of the above working conditions for airfoil cascades is performed with RANS simulations. Three different airfoils are used to evaluate the influence of the design lift coefficient and maximum blade thickness. The results provide a better insight into the aerodynamic behaviour of airfoil sections in such operating conditions, showing that interactions cannot be neglected.
The use of metamodeling coupled with CFD simulations is presented as a suitable tool for treating interference effects within the fan design process.
The main findings of the present work can be used as a support for design choices as well as for developing design strategies both for the fan blades and for the airfoil sections.