bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and Commissioning of a Blowdown Facility for Dense Gas Vapours
Authors: Robertson Miles C. , Newton Peter J. , Chen Tao , Martinez-Botas Ricardo F.
Published: November 2019

The Organic Rankine Cycle is a candidate technology for low grade heat recovery, from sources as diverse as geothermal, solar and industrial/vehicle waste heat. The organic working fluids used within these systems often display significant real-gas effects, especially in proximity of the thermodynamic critical point. Significant research has therefore been performed on the design of real-gas expansion devices, including both positive displacement and rotordynamic machinery. 3D Computational Fluid Dynamics (CFD) is commonly used for performance prediction and flow field analysis within expanders, and experimental validation of these simulations within a real-gas environment are scarce within the literature. This paper therefore presents a dense-gas blowdown facility constructed at Imperial College London, for the purpose of experimentally validating numerical simulations of these fluids.

The system-level design process for the blowdown rig is detailed within this paper, including the sizing and specification of major components. A hemispherically-ended 3.785 L cylinder was selected as the main blowdown vessel, allowing a designpoint pressure and temperature of 3751 kPa and 477 K, respectively. Regulating valves were placed either side of the test section, allowing a Pressure Ratio to be fixed across the measurement section.

The primary design focus of this paper is that of the test section — a converging-diverging nozzle producing an expansion of Mach 2 at the nozzle exit plane. The nozzle profile is generated by Method of Characteristics (MoC) modified to account for real-gas effects. Both mechanical and fluid dynamic design are discussed, along with location and thermal management of the nine pressure transducers, located along the nozzle centreline.

A series of blowdown tests are conducted, firstly for a fluid conforming closely to the ideal gas Equation of State - Nitrogen (N2) at room temperature. A comparison between the experimental measurements and a CFD analysis of these results is taken as a benchmarking example. A second set of tests with refrigerant R1233zd(E) are run, across multiple inlet pressures - CFD simulations are subsequently performed, with the refrigerant modeled by Ideal Gas, Peng-Robinson, and Helmholtz energy (via REF-PROP) Equations of State. An error analysis is conducted for each, identifying that an increase in fluid model fidelity leads to reduced deviation between simulation and experiment. An average discrepancy of 11.1% in nozzle Pressure Ratio with the Helmholtz energy EoS indicates an over-prediction of expander power output within the CFD simulation.
Analysis of Operational Effects on Cooled H-Class Gas Turbines
Authors: Uysal Selcuk Can , Black James B.
Published: November 2019

During the operation of an industrial gas turbine, the engine deviates from its new condition performance because of several effects including dirt build-up, compressor fouling, material erosion, oxidation, corrosion, turbine blade burning or warping, thermal barrier coating (TBC) degradation, and turbine blade cooling channel clogging. Once these problems cause a significant impact on engine performance, maintenance actions are taken by the operators to restore the engine to new performance levels.

It is important to quantify the impacts of these operational effects on the key engine performance parameters such as power output, heat rate and thermal efficiency for industrial gas turbines during the design phase. This information can be used to determine an engine maintenance schedule, which is directly related to maintenance costs during the anticipated operational time. A cooled gas turbine performance analysis model is used in this study to determine the impacts of the TBC degradation and compressor fouling on the engine performance by using three different H-Class gas turbine scenarios. The analytical tool that is used in this analysis is the Cooled Gas Turbine Model (CGTM) that was previously developed in MATLAB Simulink®. The CGTM evaluates the engine performance using operating conditions, polytropic efficiencies, material properties and cooling system information.

To investigate the negative impacts on engine performance due to structural changes in TBC material, compressor fouling, and their combined effect, CGTM is used in this study for three different H-Class engine scenarios that have various compressor pressure ratios, turbine inlet temperatures, and power and thermal efficiency outputs; each determined to represent different classes of recent H-Class gas turbines. Experimental data on the changes in TBC performance are used as an input to the CGTM as a change in the TBC Biot number to observe the impacts on engine performance. The effect of compressor fouling is studied by changing the compressor discharge pressures and polytropic compressor efficiencies within the expected reduction ranges. The individual and combined effects of compressor fouling and TBC degradation are presented for the shaft power output, thermal efficiency and heat rate performance parameters. Possible improvements for the designers to reduce these impacts, and comparison of the reductions in engine performance parameters of the studied H-Class engine scenarios are also provided.
Point Cloud to Parameter: An Inverse Geometric Approach to Probabilistic Design
Authors: Meckstroth Christopher , Brown Jeffrey
Published: November 2019

A method is presented to enable probabilistic design based on manufacturing blade variation. The goal of Point Cloud to Parameter (P2P) process is to autonomously extract design parameters from measured, three-dimensional scans of turbine engine blade profiles. Rather than simply determining statistical field variation in the blade surface, these extracted design parameters relate back to the creation of the original blade geometry, such that they could be utilized to recreate the blade in a CAD program. Designers can then use these results to compare and quantify design intent dimensions with manufacturing dimensions, and similarly, the intended performance of the blade. Results are presented of initial tests performed on a measured point cloud of blisk geometry with 18 blades. The parameters extracted using the P2P algorithm are compared to the results of a mesh deformation effort performed on the same geometry and it is shown that the P2P parameters correlate well with FEA computed frequencies.
Modelling Droplet Heat and Mass Transfer in Aero-Engine Bearing Chambers
Authors: Arcila Dafne Gaviria , Morvan Hervé , Simmons Kathy , Ambrose Stephen , Walsh Michael , Kakimpa Bruce
Published: November 2019

The oil inside aeroengine bearing chambers can be found in many forms, including droplets which interact with the core airflow. The ability to model such bearing chambers computationally is desirable and thus a better understanding of the evaporation process of oil droplets is of great interest. Previous studies have analyzed the flow of isothermal droplets in bearing chambers. However, further investigation is needed into the heating of droplets in the highly rotating core region. This will enable designers to evaluate the behavior of droplets in a chamber and the likelihood that they will evaporate.

The aim of this research is to analyze the oil droplet evaporation process under aeroengine bearing chamber representative conditions. An ultimate goal is the ability to predict the oil-air heat and mass transfer in the core flow region, as well as to develop an understanding of the flow inside a droplet, and how this affects evaporation. This latter is important as it has not been studied before.

This paper presents the results of a numerical study of the evaporation process of a single droplet under bearing chamber temperature and air flow conditions. The two-phase flow is simulated using ANSYS Fluent with the volume of fluid approach and the evaporation process with the “D−square law”. First, the modelling approach is validated against previous experimental and numerical analysis of fuel droplets in an air flow with heat transfer. The simulation results were in excellent agreement with a benchmarking data set. The validated approach is then applied for investigation to smaller, bearing chamber representative droplets of an oil base stock used in jet engines.

The oil evaporation rate was quantified as well as the evolution of droplet diameter, which revealed the effect of different air velocities and temperatures on the droplet. The extent to which evaporation rate increased with air velocity and temperature is quantified. It is concluded that droplets of initial diameters less than 200μm that remain in the chamber core region for more than 0.3s are likely to evaporate completely.

This study allows us to estimate droplet heat and mass transfer and the associated phase change in a bearing chamber. It also provides best practice to predict the performance of small droplets under the effects of high temperature and velocity convective air flows. In future work this methodology will be applied in simulations in a representative bearing chamber to predict how the cooling process is affected by oil evaporation.
Emulation of As-Manufactured Transonic Rotor Airfoil Modal Behavior and the Significance of Frequency Veering
Authors: Brown Jeffrey M. , Carper Emily B. , Beck Joseph A. , Kaszynski Alexander A.
Published: November 2019

This effort investigates the ability to efficiently emulate the modal characteristics of a transonic compressor rotor as a function of measured geometric variations. The transonic rotor is measured with a structured blue light scanner that provides a dense geometric representation of the as-manufactured part. Principal component analysis (PCA) is applied to create a reduced order, orthogonal basis of parameters used as independent emulator parameters. Ordinary least squares (OLS) and Gaussian stochastic process (GSP) regression models are employed as emulators for airfoil frequency and mode shape across the first twenty resonant modes. While many modes are emulated with high accuracy, some challenge conventional emulation. It is shown that geometric variations cause significant variation in modal behavior for closely spaced frequencies. This work identifies that as-manufactured geometry deviations can lead to frequency veering and associated chaotic modal behavior. Effective emulation of frequncy and mode shape is demonstrated, but the physics-based understanding of as-manufactured geometry frequeny veering defines the way for future improvements in emulation accuracy and computational requirements.
Experimental Investigation of Sweeping Jet Film Cooling in a Transonic Turbine Cascade
Authors: Hossain Mohammad A. , Asar Munevver E. , Gregory James W. , Bons Jeffrey P.
Published: November 2019

The sweeping jet (SJ) film cooling hole has shown promising cooling performance compared to the standard shaped hole in low-speed conditions. The present work demonstrates the first attempt of sweeping jet film cooling at an engine relevant Mach number. An experimental investigation was conducted to study the sweeping jet film cooling on a nozzle guide vane suction surface. A well-established additive manufacturing technique commonly known as Stereolithography (SLA) was unitized to design a transonic, engine representative vane geometry in which a row of SJ holes was used on the vane suction surface. Experiments were performed in a linear transonic cascade at an exit Mach number of 0.8 and blowing ratios of BR = 0.25–2.23. The measurement of heat transfer was conducted with the transient IR method and the convective heat transfer coefficient (HTC) and adiabatic film cooling effectiveness were estimated using a dual linear regression technique (DLRT). Aerodynamic loss measurements were also performed with a total pressure Kiel probe at 0.25Cax downstream of the exit plane of the vane cascade. Experiments were also conducted for a baseline shaped hole (777-hole) for a direct comparison. Results showed that the SJ hole has a wider coolant spreading in the lateral direction near the hole exit due to its sweeping action that improves the overall cooling performance particularly at high blowing ratios (BR>1). Aerodynamic loss measurement suggested that the SJ hole has a comparable total pressure loss to the 777-shaped hole.
Characterisation of Waves and Ligaments in Films Close to an Aeroengine Ball Bearing
Authors: Hee Jee Loong , Simmons Kathy , Hann David , Walsh Michael
Published: November 2019

Surface waves are observed in many situations including natural and engineering applications. Experiments conducted at the Gas Turbine and Transmissions Research Centre (G2TRC) used high speed imaging to observe multiscale wave structures close to an aeroengine ball bearing in a test rig. The dynamic behavior and scale of the waves indicate that these are shear-driven although highly influenced by gravity at low shaft speed.

To understand the interactions between gas and liquid phases including momentum and mass transfers, characterization of the observed waves and ligaments was undertaken. Waves were studied at surfaces close to the ball bearing and ligaments were assessed near the cage. Characterization was in terms of frequency and wavelength as functions of speed, flow-rate, bearing axial load and gravity. The assessments confirmed the existence of gravity-capillary waves and capillary waves.

Gravity-capillary waves were measured to have a longer mean wavelength on the co-current side of the bearing (gravity and shear acting together) compared to the counter-current side (gravity and shear opposing). Using a published definition of critical wavelength (λcrit), measured wavelengths at 3,000 rpm were 2.56λcrit on the co-current side compared to 1.86λcrit at the countercurrent location. As shaft speed increases, wavelength reduces with transition to capillary waves occurring at around 0.83λcrit. At shaft speeds beyond 5000 rpm, capillary waves were fully visible and the wavelength was obtained as 0.435λcrit. Flow-rate and load did not significantly influence wavelength.

Wave frequency was found to be proportional to shaft speed. The gravity-capillary waves had frequencies within the range 13–25 Hz while capillary waves exhibited a frequency well beyond 100 Hz. The frequencies are highly fluctuating with no effect of load and flow rate observed.

Ligaments were characterized using Weber number and Stability number. The number of ligaments increased with shaft speed. A correlation for ligament number based on operating conditions is proposed.
A Low Reynolds Number Experimental Evaluation of Tubercles on a Low-Pressure Turbine Cascade
Authors: Pym Stephen A. , Asghar Asad , Allan William D. E. , Clark John P.
Published: November 2019

Aircraft are operating at increasingly high-altitudes, where decreased air density and engine power settings have led to increasingly low Reynolds numbers in the low-pressure turbine portion of modern-day aeroengines. These operating conditions, in parallel with highly-loaded blade profiles, result in non-reattaching laminar boundary layer separation along the blade suction surface, increasing loss and decreasing engine performance. This work presents an experimental investigation into the potential for integrated leading-edge tubercles to improve blade performance in this operating regime. A turn-table cascade test-section was constructed and commissioned to test a purpose-designed, forward-loaded, low-pressure turbine blade profile at various incidences and Reynolds numbers. Baseline and tubercled blades were tested at axial chord Reynolds numbers at and between 15 000 and 60 000, and angles of incidence ranging from −5° to +10°. Experimental data collection included blade surface pressure measurements, total pressure loss in the blade wakes, hot-wire anemometry, surface hot-film measurements, and surface flow visualization using tufts. Test results showed that the implementation of tubercles did not lead to a performance enhancement. However, useful conclusions were drawn regarding the ability of tubercles to generate stream-wise vortices at ultra-low Reynolds numbers. Additional observations helped to characterize the suction surface boundary layer over the highly-loaded, low-pressure turbine blade profile when at off-design conditions. Recommendations were made for future work.
An Analytical Shock-Loss Model Fully Integrated to a Streamline Curvature Method for Axial-Flow Compressors
Authors: Aguirre Hasani Azamar , Pachidis Vassilios , Templalexis Ioannis
Published: November 2019

The constant and increasing demand to obtain more accurate turbomachinery performance prediction in the design and analysis process has led to the development of higher fidelity flow field models. Despite extensive flow field information can be collected from 3-D RANS numerical simulations, the computational cost is expensive in terms of time and resources, especially if they are used as solvers within a design-optimisation framework. In contrast, 2-D throughflow methods, such as streamline curvature (SLC), provide an acceptable flow solution in minutes.

The use of modern and advanced-design transonic axial-flow compressors and fans has been expanding due to their high shock-induced single-stage pressure ratios while being light, compact and robust. Transonic-flow analysis in blading is complex due to the shock structures involved and associated phenomena. Previous 2-D SLC tools have failed to replicate the real compressible-flow physics, assuming and oversimplifying the shock-system shape and location. The situation aggravates, when the assumed overall shock configuration applies only for design point at unstarted operations, requiring of empirical correlations to estimate the shock-loss coefficient for off-design operations. The overall compressor performance prediction is thence highly-dependent on the shock modelling quality.

For this reason, a physics-based shock -structure and -loss model was developed and implemented into an existing in-house 2-D SLC compressor performance simulator to enhance the aerodynamic prediction in transonic axial-flow compressors. The novel shock-loss model is fully coupled to the 2-D SLC software, for which a blade-element-layout method was adapted to obtain the profile geometry definition. The analytical shock-loss model possesses the capability to operate at started and unstarted passages utilizing an iterative-solution method to position the choke-induced passage-shock. A significant contribution of the new shock-loss model is the solution of the relative total-pressure loss for the entire blade span, comprising the inlet relative subsonic supercritical and supersonic regions.

In this manner, shock losses were determined throughout the blade span and for various off-design operating conditions, including those at choking. 2-D SLC simulations were conducted for the NASA Rotor 67 Fan to validate the models accordingly against test-rig data and verify against previous model estimations and 3-D CFD results. The analytical shock - structure and -loss model improved the shock-loss prediction between 40–50% with respect of the state-of-the-art models and showed satisfactory agreement against measured data within 0.6% at the blade tip and 0.3% at mid-span sections.
Evaluation of Spray Performance of Pyrolysis Oil
Authors: Yun Sangsig , Choi Minji , Kumar Ashwani
Published: November 2019

Pyrolysis oil has become an important subject of research as it is considered to be a potential environmentally friendly and cheap alternative to conventional fossil fuels. Unfortunately, due to the significant differences of the chemical and physical properties of pyrolysis oil than that of fossil fuels, the deployment of pyrolysis oil in existing power systems such as gas turbines and internal combustion engines has been highly restricted. Thus, major research on pyrolysis oil has been conducted to overcome these challenges related to the unfavorable physical and chemical properties of pyrolysis oil. This paper reports experimental work on the effects of physical properties of the pyrolysis oil on spray performance of nozzles. Effort to evaluate the spray performance by using different types of atomizers has been made as well. Laser based diagnostics was applied to obtain qualitative comparisons spray characteristics of various pyrolysis oils. Experimental data such as the distribution of fuel droplet sizes and overall spray shapes was analyzed, which could provide valuable guidelines to design fuel nozzles. Lastly, the paper will also present NRC’s plans to accelerate the deployment of such pyrolysis oils in industrial gas turbines.
High-Speed Spectrally Resolved Imaging Studies of Spherically Expanding Natural Gas Flames Under Gas Turbine Operating Conditions
Authors: Parajuli Pradeep , Paschal Tyler , Turner Mattias A. , Petersen Eric L. , Kulatilaka Waruna D.
Published: November 2019

Natural gas is a major fuel source for many industrial and power-generation applications. The primary constituent of natural gas is methane (CH4), while smaller quantities of higher order hydrocarbons such as ethane (C2H6) and propane (C3H8) can also be present. Detailed understanding of natural gas combustion is important to obtain the highest possible combustion efficiency with minimal environmental impact in devices such as gas turbines and industrial furnaces. For a better understanding the combustion performance of natural gas, several important parameters to study are the flame temperature, heat release zone, flame front evolution, and laminar flame speed as a function of flame equivalence ratio. Spectrally and temporally resolved, high-speed chemiluminescence imaging can provide direct measurements of some of these parameters under controlled laboratory conditions. A series of experiments were performed on premixed methane/ethane-air flames at different equivalence ratios inside a closed flame speed vessel that allows the direct observation of the spherically expanding flame front. The vessel was filled with the mixtures of CH4 and C2H6 along with respective partial pressures of O2 and N2, to obtain the desired equivalence ratios at 1 atm initial pressure. A high-speed camera coupled with an image intensifier system was used to capture the chemiluminescence emitted by the excited hydroxyl (OH*) and methylidyne (CH*) radicals, which are two of the most important species present in the natural gas flames. The calculated laminar flame speeds for an 80/20 methane/ethane blend based on high-speed chemiluminescence images agreed well with the previously conducted Z-type schlieren imaging-based measurements. A high-pressure test, conducted at 5 atm initial pressure, produced wrinkles in the flame and decreased flame propagation rate. In comparison to the spherically expanding laminar flames, subsequent turbulent flame studies showed the sporadic nature of the flame resulting from multiple flame fronts that were evolved discontinuously and independently with the time. This paper documents some of the first results of quantitative spherical flame speed experiments using high-speed chemiluminescence imaging.
Adiabatic Film Cooling Effectiveness Measurement of High Performance Combustion Liner Slot Jets
Authors: Flores Wilmer , Curbelo Andres , Calderon Luisana , Kapat Jayanta S. , Ahmed Kareem
Published: November 2019

The present study experimentally investigates adiabatic film cooling effectiveness for high performance flow auxetic geometries (S-Slot and Ellipsoid). Both geometries are auxetic structures that were designed around a Negative Poisson Ratio (NPR). Manufactured NPR combustion liners offer higher quality fracture resistance [1] and high energy absorption [2]. Film cooling effectiveness results for test geometries were non-dimensionalized by a baseline case of circular inline orifices. Non-intrusive pressure sensitive paint (PSP) technique was utilized to obtain local surface pressure gradients for each experimental geometry. Adiabatic film cooling effectiveness measurements were tested for multiple blowing ratios (BR) ranging between 0.05–1.15. Three plate configurations were studied with void inclination angles of 0 degrees. Analyses demonstrate that blowing ratios of 0.5 and 0.75 are optimal for S-slot adiabatic effectiveness. Film cooling results for the Ellipse configuration show increasing effectiveness up to an optimal blowing ratio of 0.5, and decreases as BR is increased beyond that. Additional experiments were performed by keeping the differential pressure across the plates constant. Results indicate that the S-slot provides optimum film cooling effectiveness while the differential pressure conserved in comparison to Ellipses and Circles.
Measurements of End Cap Temperatures in a Multistage Barrel-Style Centrifugal Compressor
Authors: Smith Natalie R. , Wilkes Jason C. , Wade Jonathan , Allison Timothy C. , Day Towler Meera , Moore J. Jeffrey , Weinberg Ian , McCune Michael
Published: November 2019

Gas compressor customers desire to operate gas compressors at higher discharge temperatures. In barrel-style centrifugal compressors, dry gas seals are used to limit the leakage along the shaft from the process fluid to atmosphere. The temperature limit of dynamic O-ring seals in the dry gas seal cartridge is one of the primary limiters to operating gas compressors at higher discharge temperatures. While the present discharge temperature limit is conservative compared to the seal limits, without a detailed understanding of the thermal distribution around the discharge-side end cap, operation at compressor discharge temperatures that exceed seal limits has too much risk. Thus, this paper describes the approach taken to characterize the temperatures around the discharge end dry gas seal of a commercial C335EL centrifugal compressor. A phased test matrix with increasing discharge temperatures was conducted so that the temperature distribution throughout the end cap could be assessed. The full-scale, highly-instrumented compressor was operated at discharge pressures and temperatures ranging from 4.7 to 9.4 MPa (680 to 1370 psi) and 113 to 218 degree Celsius (235 to 425 degrees Fahrenheit), respectively. The experimental test set-up and results are presented herein. Results include demonstration of successful compressor operation at discharge temperatures greater than seal limits as well as the end cap temperature sensitivity to lube oil supply and dry gas supply temperatures.
Analysis of Gas Turbine Rim Cavity Ingestion With Axial Purge Flow Injection
Authors: Robak Christopher W. , Faghri Amir , Thole Karen A.
Published: November 2019

Turbine rim cavities require an adequate supply of cooling purge flow to prevent hot gas ingestion from overheating metal components beneath the gas path airfoils. Purge flow is typically introduced into rim cavities through a labyrinth seal at the inner diameter of the cavity, or through conduits in the metal walls of the rim cavity. This numerical study will focus on purge flow introduced through axial holes in the stationary side of a turbine realistic rim cavity. Three dimensional Unsteady Reynolds-average Navier-Stokes (URANS) CFD modeling is utilized to model of cavity sealing effectiveness as a function of axial purge flow rate. CFD modeling is compared with experimental data from the test turbine in the Steady Thermal Aero Research Turbine (START). Results show good agreement with experimental data, especially at lower purge flow rates. Analytical depictions of the flow field setup in the rim cavity are provided, explaining trends observed in experimental data. Differences in sealing effectiveness trends between the upper and lower portions of the rim cavity are predicted by CFD modeling, adding insight to ingestion phenomena in turbine realistic rim cavities with complex geometry and flow leakage paths.
Detailed Experimental Measurement and RANS Simulation of a Low Pressure Turbine With High Lift Blading
Authors: Perez Ethan , Schmitz John T. , Jaffa Nicholas A. , Jemcov Aleksandar , Cameron Joshua D. , Morris Scott C.
Published: November 2019

The aerodynamic characteristics of high–lift airfoil designs is of interest for improved performance and reduced blade count in Low–Pressure Turbine (LPT) design. The present paper presents both experimental measurements as well as numerical simulation results from a single-stage LPT. The airfoils were designed for an embedded stage with a total pressure expansion ratio of 1.75 and a rotor Zweifel coefficient of 1.35. The measurement program was highly unique in that detailed measurements were obtained using a variety of different probe types, including time–resolved total pressure and hot–wires. Agreement between various measurement types was generally good, but differences beyond typically stated uncertainty bounds were noted. The computations were done using RANS and a mixing model via commercially available software. The numerical results were evaluated to determine the efficacy of this type of model for prediction and design of high–lift airfoils. The computations agreed very well with the experimental results in the midspan region, but losses were over–predicted in the lower 40% span near the hub. A basic description and understanding of the flow physics in the LPT stage are presented based on the relative agreement between the experiments and computations.
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

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

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

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

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

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

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

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

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

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.