bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synchronization During Multi-Mode Thermoacoustic Oscillations in a Liquid-Fueled Gas Turbine Combustor at Elevated Pressure
Authors: Passarelli Mitchell L. , Cirtwill J. D. Maxim , Wabel Timothy , Steinberg Adam M. , Wickersham A. J. 
Published: November 2019

Abstract
This paper analyzes intermittent self-excited thermoacoustic oscillations in which the pressure (P′) and heat release rate (q̇′) fluctuations are harmonically coupled. That is to say, P′ and q̇′ do not oscillate at the same frequencies, but rather at frequencies in integer ratios. Thus, this system represents a case dominated by nonlinear cross-mode coupling. The measurements were obtained in an optically-accessible combustor equipped with an industrial gas turbine fuel injector operating with liquid fuel under partially-premixed conditions at elevated pressure. High-speed chemiluminescence (CL) imaging of OH* was used as an indicator of the heat release rate. The data was processed using spectral proper orthogonal decomposition (SPOD) to isolate the dominant heat release and pressure modes. Synchronization theory was used to determine when the modes are coupled and how their interaction manifests in the measurements, particularly how it relates to the observed intermittency. The results show three distinct intervals of synchronized oscillation shared by all the mode pairs analyzed. The first interval exhibits the same characteristics as a pair of noisy, phase-locked self-oscillators, with phase-slipping and frequency-pulling. While the behaviour of the second interval differs among mode pairs, strong frequency-pulling is observed during the third interval for all pairs.
A New Approach to Performance Mapping of Radial Inflow Turbines
Authors: Biliotti Davide , Scotti Del Greco Alberto , Cangioli Francesco , Iurisci Giuseppe 
Published: November 2019

Abstract
The performance of radial inflow turbines, and specifically of turboexpanders for oil & gas applications, has been traditionally described in terms of efficiency versus velocity speed ratio (U/C) and discharge flow coefficient (Q/N). Especially in the testing phase, this latter parameter has been often preferred to the angle setting of moveable inlet guide vanes (IGV), which are standard equipment for most turboexpanders. In practice, the expander U/C has been often considered to give the performance backbone, while the Q/N ratio has been used for secondary corrections. Moreover, although the role of pressure ratio (PR) is recognized, its impact has been experimentally unexplored in those cases where testing facilities had capacity limitations. Eventually, in case of variable nozzles, the inlet flow capacity curve has been rarely included among the output performance variables, being the attention mainly focused on efficiency.
In the present paper, beside an overview and an explanation of the physical meaning of traditional performance parameters, an alternative approach based on torque mapping versus U/C is introduced and discussed in detail. As a matter of fact, numerical and experimental data show smooth and regular trends when torque coefficient is used instead of adiabatic efficiency. Moreover, performance based on torque coefficient can be more conveniently extrapolated at extreme off-design conditions such as start-up (locked rotor condition) or full speed no load. The ease of extrapolation is particularly important for machine operability, which often requires accurate modeling of transient missions at very partial loads (as for instance during start-up or shut-down). Examples will be offered to show the advantages of torque coefficient representation and how sensitive this is to IGV setting and pressure.
Dynamic Characterization of a Two Degree of Freedom Planetary Gearbox During Varying Load Conditions
Authors: González-Cruz Claudia , Jauregui Juan , Ceccarelli Marco 
Published: November 2019

Abstract
This paper presents the dynamic characterization of a two degree of freedom planetary gearbox prototype during the variation of the load condition. Tests with varying load are developed at three different operating speeds of the input shaft: 190, 380 and 590 rpm. The dynamic torques and vibrations on the input and output shafts are acquired during the experiments, such as the angular velocity of the output shaft. The experimental data are analyzed to evaluate the dynamics of the system during the exchange of operation between the first and second DOF operation. Then, the radial vibrations are analyzed during the operation of the second DOF by means of a methodology using different signal processing tools: first, the continuous wavelet transform is used to identify the nonlinear behavior and the main frequency content of the system; then, the vibrations are filtered by means of passband filters in order to keep the main frequencies of the system and delete any other; finally, the filtered signals are analyzed with both, the Kuramoto’s order parameter to quantify the dynamic synchronization of the gearbox and the phase diagram to characterize its stability. The results demonstrates the utility of the second DOF in the design of the planetary gearbox in order to avoid excessive torques in the components of the system. Furthermore, it is found that the synchronization of the system increases at higher operating speed, however, the system becomes unstable as the operating speed is increased.
Challenges Associated With Replicating Rotor Blade Deposition in a Non-Rotating Annular Cascade
Authors: Bowen Christopher P. , Ameri Ali , Bons Jeffrey P. 
Published: November 2019

Abstract
A computational analysis is performed to determine if particulate impact events on the external surfaces of gas turbine engine rotor blades can be faithfully replicated in an experimental rotor cascade. The General Electric (GE) Energy Efficient Engine (E3) first-stage turbine flow-field at cruise conditions is first solved using a steady state explicit mixing plane approach with non-reflecting treatment. To model flow in the cascade, a single E3 rotor periodic domain is then constructed with an inlet section matching the relative flow incidence angle from the mixing plane calculation. The mass-averaged relative flow conditions at the inlet and outlet of the mixing plane rotor section are imposed on the cascade boundaries and a steady solution is found. Particles with diameters ranging from 1 to 25 μm are tracked through each fluid domain using a Lagrangian approach, and the OSU Deposition Model is implemented to dictate the sticking and rebounding action when particles interact with solid surfaces. The impact locations on the blade are compared between the rotating (mixing plane) and stationary (cascade) cases. It is discovered that both the locations and parameters of the particle impacts in the cascade vary significantly from the engine environment. For smaller particles, this deviation is credited to a stronger upstream influence of the blade on the cascade flow-field. As particle size increases, this effect tapers off, and the differences in deposition are instead driven by the interaction of the full-stage vane with the particles. The lack of a vane in the cascade causes drastically different particle inlet vectors over the rotor than are seen in the engine setting. The radial differences of particle impact locations are explored, and the role that absolute pressure plays is considered.
Study on the Effect and Fuzzy Compensation of Nonlinear Characteristics on SOFC-GT Fuel Supply System
Authors: Chen Jinwei , Sun Shengnan , Li Jingxuan , Zhang Huisheng 
Published: November 2019

Abstract
Fuel supply system, the regulation system for fuel delivery to fuel cell, is one of the most important auxiliary systems in a solid oxide fuel cell-gas turbine hybrid system. It plays a significant role in the dynamic performance and safety. Commonly, the fuel supply system is always simplified as a linear system which means that the relationship between valve opening and fuel flow rate is linear. However, the servo actuator and metering valve have some nonlinear characteristics such as hysteresis, dead zone, relay, and saturation. These nonlinear characteristics can directly affect the dynamic performance of the hybrid system. In this paper, a 328kW SOFC-GT hybrid system was taken as a research object. Firstly, a fuel supply system model considering the nonlinear characteristic was combined with the hybrid system. Then, the effect of dead zone-relay characteristic of servo amplifier was analyzed. The results show that the dead zone width has a great effect on the dynamic performance of the hybrid system. When the dead zone width is too small, the fuel flow rate will be oscillating causing unstable of the electrical characteristics in SOFC. The hybrid system will be stable with the increase of dead zone width. However, the larger dead zone width causes the hysteresis and the increase of the dynamic response time. At an improvement method with a two-dimensional fuzzy compensation was proposed. The results show that the fuzzy compensation can solve the oscillation problem caused by the dead zone-delay effectively. Finally, a servo actuator experiment system is developed based on an electro-hydraulic servo actuator facility and a software component of fuzzy compensator. The test rig was conducted an experiment to validate the simulation result. The results show that the experiment results match well with the simulation results.
Meanline Modeling of Asymmetrical Twin-Scroll Turbine: Loss Coefficient Transferability Between Turbines of Different Sizes
Authors: Chiong Meng Soon , Rajoo Srithar , Martinez-Botas Ricardo F. , Palenschat Torsten , Weitzman Peter , Anderson Mark , Ebel Thiago 
Published: November 2019

Abstract
The meanline modeling of asymmetrical twin-scroll turbocharger turbine performance has been in continuous development since its first introduction in 2008 by Daimler AG. Asymmetric turbine features scrolls of different sizes to enable high-pressure exhaust gas recirculation (EGR), which has been proven to be effective. However, the asymmetric feature of the scrolls has been identified as the major difficulty in the meanline modeling. This is particularly true at unequal-admission operating conditions, where the two volute scrolls are subjected to different magnitude of pressure and mass flow rate. Tuning a mean-line model for one particular turbine unit is usually possible, depending on the amount of flexibility in its loss sub-models. However the transferability of loss coefficients for the use of different turbine sizes has not been studied in the case of asymmetrical twin-scroll turbine. The feasibility in doing so, and the consequences, difficulties and outcomes, will be presented in this paper. The modeling work in this study will be carried out using commercial meanline tool — RITAL™ from Concepts NREC. The loss model is first tuned for the largest asymmetrical twin-scroll turbine in Daimler AG’s product line, at different admission conditions. After the model prediction has been validated with coldflow experimental data, the same loss coefficient settings are then used for performance prediction of a smaller asymmetrical twin-scroll turbine. The finding of this paper suggests that the fraction of the volute flow exit area varies with turbine admission state. The variation trend exhibits a unique function of the turbine geometry, and found to be consistent across the turbine sizes. On the other hand, the rotor loss coefficient may remain constant regardless of the turbine operation. The goal of this study is to establish the confidence level for blind performance prediction in the future.
Improvement of Rotordynamic Performance of Integrally Geared Centrifugal Compressors Through a Systematic Design Modification Approach
Authors: Luo Zhusan , Schwarz Carl 
Published: November 2019

Abstract
Integrally geared centrifugal compressors have found wide applications in air separation plants and the petrochemical industry because they can be readily designed to run at a higher efficiency than in-line compressors. Many of these compressors with multiple stages are designed to meet the demands for high power and high speed applications with high efficiency and high reliability. These requirements are challenges for their rotordynamic designs. Some compressors may experience excessive synchronous or subsynchronous vibrations during commissioning or in a short period of service. This study starts with discussing the vibration characteristics of a compressor pinion-bearing system, including undamped critical speeds, unbalance responses, and rotordynamic stability. To improve the rotordynamic performance, a systematic and feasible approach for modifying a rotordynamic design has been proposed. It has been showed that damped modes at an operating speed are key indicators of the rotordynamic performance. The sensitivities of damped modes to main design variables, i.e. bearing geometry, shaft geometry and impeller mass properties, are thoroughly examined. A procedure for design modification is proposed for general guidance. The feasibility and effectiveness of this method have been demonstrated in the modification of a pinion-bearing system. In addition, this paper also proposes a method to evaluate the torsional natural frequencies of an equivalent pinion model and briefly discusses the application of optimal design methodology to the rotordynamic design modification.
Numerical Investigation on Cooling Air Flow and Resistance Characteristics Inner Laminated Cooling Structures
Authors: Song Wei , Xu Huazhao , Cheng Xiaofang , Wang Jianhua 
Published: November 2019

Abstract
Today, laminated cooling structures have been widely used in the designs of advanced gas turbines, because the structures with double walls, pins, impingement holes and film holes can provide much higher overall cooling effectiveness than simple film cooling. Of course, this kind of cooling structures also leads to a higher price due to a larger flow resistance to cooling air injection in comparison with the simple film cooling. The previous investigations concerned with the laminated cooling structures mainly focused on heat transfer performances, the flow resistance characteristics within the complex channel of the structures are relatively less. This paper presents a numerical investigation on the characteristics of the cooling air resistance passing through 6 different laminated structures. The influence factors on the fluid flow and resistance performances of cooling air, such as array, density and shape of film hole, as well as impingement-hole area (diameter), are discussed and compared at the same pressure ratios of the inlet to outlet of the 6 laminated structures. The discussions and comparisons reveal the following interesting phenomena: 1) A larger diameter of impingement hole corresponds to a larger mass flow rate of cooling air at the inlet of the laminated structure, but the inlet velocity is mainly dependent on the density of film hole. At the same total area of film holes, a larger density corresponds to a higher inlet velocity. 2) The flow rate through film hole of laminated structures is influenced more and more obvious by the outlet shape and the inflow angle of film hole as the increasing pressure ratio. 3) The resistance coefficients of the entire laminated structures are dependent on the density and shape of film holes. At the same total area of film holes, a higher density corresponds to a lower resistance coefficient. Although fan-shaped film hole can provide a larger cooling air coverage, the price is a higher resistance coefficient. Therefore, the applications of fan-shaped film holes in the laminated structures should be considered only in the regions with low environment pressures.
New Model to Predict Water Droplets Erosion Based on Erosion Test Curves: Application to On-Line Water Washing of a Compressor
Authors: Borello Domenico , Venturini Paolo , Gabriele Serena , Andreoli Michele 
Published: November 2019

Abstract
Here, a new model for predicting the water droplet erosion (WDE) from online water washing in compressors is developed and its results are discussed in comparisons with a baseline model.
The model development started with the analysis of existing WDE models as well as pertinent experimental campaigns aiming at extracting a comprehensive erosion model able to account for the influence of droplet velocity and diameter, impact angle, surface roughness and hardness on the erosion phenomena.
The new approach is applied to the study of WDE for droplets of 100 μm diameter in a gas turbine compressor and the predictions are compared with those of the Springer model.
Even if the two models (Springer’s and ours) return qualitatively similar results, the erosion prediction is strongly different as in Springer model the erosion rate is four time higher than in the present model. This difference is attributed to the oversimplification of Springer model that does not account for any of the parameters that are relevant for the water erosion such as surface hardness and roughness as well as for a different treatment of the incubation period.
Furthermore, to analyze the effect of all the main quantities affecting WDE process, several simulations were performed. Droplets diameter is found to be the key parameter, in determining the erosion rate. Reducing the diameter one can reduce erosion from online water washing. Surface hardness is also very important, while surface roughness can be relevant depending on the time frame one is interested at.
Experimental Study on the Influence of Casing Treatment on Near-Stall Unsteady Behavior of a Mixed-Flow Compressor
Authors: Du Juan , Kauth Felix , Li Jichao , Zhang Qianfeng , Seume Joerg R. 
Published: November 2019

Abstract
This paper aims at experimentally demonstrating the effects of axial slot casing treatment and tip gap variation on compressor performance, unsteady tip clearance flow, and stall inception features in a highly-loaded mixed-flow compressor at partspeed. Two tip gaps (0.32% and 0.64% of rotor blade chord at mid-span) were tested at three rotational speeds. A semicircular axial slot casing treatment improves compressor stability. The experimental results show that this casing treatment significantly moves the stability limit at partial speeds towards lower mass flow for both tip gaps, compared to the reference case without casing treatment. In the case of the compressor with casing treatment, efficiency increases for the large tip gap and decreases for the small tip gap. Dynamic pressure transducers installed in the casing upstream and along the rotor tip chord direction are used to detect the unsteady behavior of tip region flow and stall inception signals of the compressor. The characteristic frequency in the tip region decreases, and the oscillating amplitude first decreases and then increases during the throttling process, regardless of tip gap size or casing treatment. For axial compressors, by contrast, the observation in previous work has been an increase of the oscillating amplitude with decreasing flow coefficient. This is a surprising result of our work. Neither experiment nor CFD so far was able to explain why the trend in this mixed-flow compressor is different from the trend expected from axial compressors. The compressor stalls through the spike stall inception both with and without casing treatment. This observation also differs from recent studies on axial compressors, which demonstrated that casing treatments could change the type of stall inception. The unstable disturbance indicating initial stall inception initially appears in the blade tip region from blade mid-chord to trailing edge, and then propagates upstream towards the leading edge. This disturbance might be generated by the reversed flow separation near mid-chord.
Effects of Emulsified Fuel on the Performance and Emission Characteristics of Aeroengine Combustors
Authors: De Giorgi M. G. , Pescini E. , Campilongo S. , Ciccarella G. , Fontanarosa D. , Ficarella A. 
Published: November 2019

Abstract
The aim of the present work is the experimental investigation of the effects of the addition of water and urea into jet fuels, on the reduction of nitrogen oxides (NOx) emissions and eventually improvement of the lean flame stability in aeroengine combustors.
Experiments have been carried out using a 300-kW liquid-fueled swirling combustor. Various urea and/or water concentrations have been tested at the same fuel/air ratio. In order to study the flame behavior, non-invasive optical diagnostic techniques, as charge-coupled device (CCD) cameras in different spectral ranges (Visible and UV ranges, with different optical filters), have been adopted to analyze the shape and the brightness of the flame structure. Measurements of exhaust emissions (NOx, SO2, CO, CO2 and O2) have also been performed in order to evaluate the impact of emulsification on the entire combustion process. Finally, the thermal efficiency losses with respect to the neat jet test case were also analyzed for each emulsified fuel condition.
Active Control of Unsteady Cavitating Flows in Turbomachinery
Authors: De Giorgi Maria Grazia , Ficarella Antonio , Fontanarosa Donato 
Published: November 2019

Abstract
A preliminary 2D numerical investigation of the active control of unsteady cavitation by means of one single synthetic jet actuator (SJA) is presented. The SJA has been applied to hinder the intrinsic instabilities of a cloud cavitating flow of water around a NACA 0015 hydrofoil with an angle of attack of 8° and ambient conditions. It has been placed inside the inception region at a distance of 16% of the chord from the leading edge. Concerning the numerical approach, a Eulerian homogeneous mixture/mass transfer model has been used, in combination with an extended Schnerr-Sauer cavitation model and a Volume of Fluid (VOF) interface tracking method. The synthetic jet has been modeled by means of a user-defined velocity boundary conditions based on a sinusoidal waveform. A sensitivity analysis has been first performed in order to evaluate the influence of the main control parameters, namely the momentum coefficient Cμ, the dimensionless frequency F+ and the jet angle αjet. By combining the cavitating vapor content and the impact on the hydrodynamic performance, the best performing SJA configuration has been retrieved. Then, a deeper analysis of the vapor cavity dynamics and the vorticity field has been conducted in order to understand the modification of the main flow produced by the synthetic jet.
The best SJA configuration was observed at Cμ = 0.0002, F+ = 0.309 and αjet = 90°, which led to a reduction of both the average vapor content and the average torsional load in the measure of 34.6% and 17.8% respectively. A reduction of the average pulsation frequency of the pressure upstream confirmed the beneficial effect of the SJA. The analysis of the coupled dynamics between vapor cavity-vorticity and their POD-based modal structures highlighted that the benefit of the SJA lies on preventing the growth of a thick sheet cavity which tends to cause the development of the highly cavitating cloud dynamics after the cavity breakup. This is mainly due to an additional vorticity close to the hydrofoil surface just downstream the SJA, as well as a local pressure modification close the SJA during the blowing stroke.