bluuebunny/crossref_metadata_2025 huggingface dataset:
Further Development of Modified Theta Project Creep Models With Life Fraction Hardening
Authors: Day W. David , Gordon Ali P.
Published: August 2017

In order to optimally design a hot section component for creep, the designer and turbine durability specialist must have confidence in their predictive tools and be able to gain design insight from these analytical tools. The modified theta projection (MTP) creep model was previously presented as an accurate means of describing creep behavior as a function of stress, temperature and time. The MTP was then implemented in an analytical model using a life fraction hardening (LFH) rule to calculate creep in the presence of time-varying stresses, and the results presented in a second paper. This paper presents improvements to the technique through the use of state variables in addition to the previously shown strain life fraction (ELF) and temperature margin (TMar). The need for performing multiple creep analyses is avoided by adding state variables to that track estimates of the effect of temperature changes on stress relaxation and life fraction, as well as an allowance for material variability and an inexact fit of material behavior.

The results of creep tests, on a nickel blade alloy, with incrementally increasing or decreasing loads are presented to provide validation of the accuracy of the life fraction hardening rule. The use of MTP and LFH has now been expanded to steels. Incremental testing results are examined for a NiCrMoV rotor steel to further validate the technique. The effect of true stress on model accuracy is also presented. Now that an accurate creep model and hardening rule have been implemented, expansion of the techniques to provides more useable design information and allows us to improve the structural integrity of turbine blades, vanes and rotors.
Oil Film Thickness Measurements on Surfaces Close to an Aero-Engine Ball Bearing Using Optical Techniques
Authors: Hee Jee Loong , Santhosh R. , Simmons Kathy , Johnson Graham , Hann David , Walsh Michael
Published: August 2017

In a civil aero-engine transmission system a number of bearings are used for shaft location and load support. A bespoke experimental test facility in the University of Nottingham’s Gas Turbine and Transmissions Research Centre (G2TRC) was created to investigate oil shedding from a location bearing. An engine representative ball bearing was installed in the rig and under-race lubrication was supplied via under-race feed to three locations under the inner race and cage. The oil was supplied in an engine representative manner but the delivery system was modified to provide circumferentially even flow. An electromagnetic load system was designed and implemented to allow engine representative axial loads between 5 and 35 kN to be applied to the bearing. In this phase of testing the rig was operated at shaft speeds between 1,000 rpm and 7,000 rpm for a range of oil flow rates and low and high load conditions. The rig was designed with good visual access and high speed imaging was used to investigate film formation and movement on surfaces close to the bearing.

This paper presents images and qualitative observations of thin film formed on the static surfaces forming the outer-periphery of the bearing compartment as well as the gap between orbiting cage and static outer race. Quantitative film thickness was obtained at two circumferential locations (90° and 270° from top dead centre) and three axial locations, through sophisticated analysis of the high speed images. The effect on film thickness of the varied parameters rotational speed, axial load and oil feed input flow rate are presented in this paper.

It was observed that for all axial planes of measurement in both co-current and counter-current regions film thickness decreases with increase in shaft rotational speed. At 5,000 and 7,000 rpm film thicknesses are around 0.75 mm – 1 mm and are similar at 90° and 270°; at 3,000 rpm films tend to be somewhat thicker at around 1.5 mm – 2 mm and are thicker in the counter current region, particularly closer to the bearing. It is suggested that at higher shaft speeds interfacial shear dominates whereas at lower speed the effect of gravity in slowing the film in the counter-current region causes a measureable difference.

It was further observed that increasing the input oil flow rate from 5.2 litres per minute to 7.3 litres per minute did not produce significant effect on film thickness. However, the increase of axial bearing load from 10 kN to 30 kN yielded thicker films at the location above the cage.

In all cases there was waviness on the film surface at the bearing outer periphery; imaging was not sufficient to see if the film surface close to the bearing is wavy.
Effect of Flow Acceleration on Mainstream-to-Coolant Flow Interaction for Round and Shaped Film Cooling Holes
Authors: Vinton Kyle R. , Wright Lesley M.
Published: August 2017

Film cooling flow fields under a favorable, mainstream pressure gradient have been experimentally investigated at various blowing and density ratios. Three dimensional velocity and vorticity distributions have been obtained above a flat plate with cylindrical holes (θ = 30°) and laidback, fanshaped holes (θ = 30°, β = γ = 10°) using the stereoscopic particle image velocimetry (S-PIV) technique. In a low speed wind tunnel, accelerating flows were studied with density ratios of 1 and 3. The effect of blowing ratio was also studied by varying the ratio from 0.5 to 1.5. With a flow acceleration parameter comparable to previous investigations, the effect of flow acceleration on these film cooling flows is presented. The flow field measurements were performed at two planes near the film cooling holes (x/d = 0 and the downstream edge) for both the round and shaped holes. These flow field measurements provide a foundation for understanding the flow interactions that produce various film cooling effectiveness and heat transfer coefficient distributions on the surface of the airfoil. The S-PIV measurements show that a favorable pressure gradient reduces jet separation and increases the width of the jet and counter rotating vortex pair. The effects are caused by the thinning of the boundary layer that occurs in favorable pressure gradient flows.
An Experimental Investigation of the Effects of Grooved Tip Geometry on the Flow Field in a Turbine Cascade Passage Using Stereoscopic PIV
Authors: Tian Yangtao , Ma Hongwei , Wang Lixiang
Published: August 2017

In the unshrouded axial turbine, the tip clearance gap can cause the losses of turbine efficiency and the penalty of turbine performance. Based on previous investigations, changing the blade tip geometry plays an important role in improving the turbine efficiency and performance. In this paper, the Stereoscopic Particle Imaging Velocimetry (SPIV) measurements were conducted to study the effects of grooved tip geometry on the flow field inside a turbine cascade passage. During the measurements, the double-frame CCD cameras were configured at different sides of the laser light sheet. Additionally, the Diisooctyl Sebacate (DEHS) was treated as the tracer particle. The tip clearance gap of both grooved tip and flat tip was set to 1.18% of the blade chord. The groove height was specified as 2.94% of the blade chord. In this study, the flow field results of eight measured planes were presented. Some typical features of the complicated flow structures, such as tip leakage vortex formation, development, breakdown and the dissipation, the variations of turbulence intensity and Reynolds stress, the blockage characteristic, were discussed as well. The experimental results show that the tip leakage flow/vortex is weakened by the grooved tip. The blockage effect and the flow capacity of the turbine passage are also improved. The tip leakage vortex breaks down at about 70% camber line, but the pattern of leakage vortex has changed into an ellipse at 60% camber line, which is an indication of the vortex breakdown. As for the decomposed and reconstructed flow, the first modal flow is the most similar to the original flow field. And it can capture the dominant flow features in flow field. And the flow of mode 2 and mode 3 generates many eddies with small scale.
Combinatorial Optimization of Mistuned Blade Rearrangement Based on Reduced-Order FEA Model
Authors: Liu Tianyuan , Guo Ding , Zhang Di , Xie Yonghui
Published: August 2017

This paper is focused on the optimization of mistuned blades assembling rearrangement under the forced response. First, in order to avoid the greatly increase of the calculation greatly by the whole circle bladed-disk finite element model, a reduced-order model is developed based on the component mode synthesis. CPU+GPU heterogeneous architecture parallel computation is used to accelerate modal analysis of the disk and blade sectors substructures. Second, a modified ant colony algorithm is applied to the combinatorial optimization to find the optimal rearrangement pattern of bladed-disk assembly. Different from classical algorithm, the individual mistuned information is used to construct heuristic function based on intentional mistuning pattern, which can avoid slow convergence of ant colony algorithm and increase the search speed efficiently. At last, a high-fidelity 3D FEM model with 43 mistuned blades is used to demonstrate the capabilities of the techniques in reducing the maximum displacement resonance response of the bladed-disk system. The numerical simulation showed that this program based on the reduced-order model proposed in this article gained 4.3 speedup compared with ANSYS full model under the scale of 500k nodes. The displacement response amplitude of the blades decreased by 32% with 60 steps (1200 times FEM calculation) by the new optimization method. The physical mechanism of reducing the bladed-disk response is explained by comparing the optimized and worst arrangement patterns. The results clearly demonstrate that the optimized rearrangement pattern of mistuned blades is able to reduce the response amplitude of the forced vibration significantly, and the algorithm proposed in this article is practical and effective.
Effect of Cooling on the Aerodynamic Performance in the Intercooled Compressor Vanes
Authors: Liu Long-gang , Li Xue-song , Ren Xiao-dong , Gu Chun-wei
Published: August 2017

An intercooling technique using convective cooling channels in the compressor stator vanes has been proposed in recent years. In this paper, two cooling methods are presented and conjugate heat transfer method is used in the numerical simulation to study the effect of cooling on the laminar boundary layer and turbulent boundary layer in compressors. The overall performance of the compressor is also analyzed.

A flat plate in T3C series experiments under adverse pressure gradient has been simulated to verify the aerodynamic simulation and preliminarily investigate the cooling effect. Subsequently, a two-dimensional compressor vane NACA65-(12A2I8b)10 has been numerically simulated to study the cooling effect on two-dimensional boundary layer of the curve surface. The numerical simulation results of the vane without cooling channel are in good agreement with the experiment data by NASA. By comparing it with the case which has convective cooling channels, it can be found that the cooling decreases the size of laminar separation bubble and delays the turbulent separation, which reduces the loss at both the design and off-design angle of attack.

A three-dimensional highly-loaded five-stage axial compressor whose stator vanes have cooling channels and cooling endwalls has also been numerically simulated. The cooling channels and endwalls decrease the temperature rising of the main stream with a slight increase of the pressure rising, which indicates that this intercooling method can be used in the intercooled and recuperated (ICR) cycle. Cooling channels decrease the temperature of the stator vanes and protect them from the high temperature. Besides, the effect of cooling on the turbulent separation in the corner region has also been investigated. The cooling channels decrease the total pressure loss, which indicates that cooling has a beneficial effect on the aerodynamic performance of the compressor.
Modeling and Analysis of the Inlet Circumferential Fluctuations in Subsonic Rotors
Authors: Tang Mingzhi , Jin Donghai , Gui Xingmin
Published: August 2017

Throughflow method has the limitation inherited from the axisymmetric assumption. With this assumption, the effects induced by three-dimensional blade shaping, such as sweep, cannot be sufficiently described. To conquer these shortcomings, a transport model for the circumferential fluctuation (CF) stresses is developed and integrated into a throughflow model. Three subsonic rotors are selected to validate the transport model and investigate the effect of the CF source terms on the flow fields. The results show that the CF source terms can affect the prediction of mass flow, and redistribute the radial distribution of blade loading. Besides, the radial equilibrium at the inlet of the blade passage is also altered by the CF source terms. Moreover, the CF source terms may have different effects for different swept blades.
Numerical Simulations of Flow Fields and Heat Transfer Characteristics in Tenon Joint Gap Between Turbine Blade and Disk Under Rotating Conditions
Authors: Chen Da-wei , Zhu Hui-ren , Xu Yang , Jia Xiao-meng , Liu Cong , Lu Hai-ying
Published: August 2017

Turbine blades and the disks are connected by tenons. There is a pair of jagged assembly clearance between each tenon and corresponding mortise. In practical engineering applications, flow and heat transfer characteristics in assembly clearance used to be simplified. In order to obtain more accurate temperature fields of the turbine blades and disks, detailed study of the flow and heat transfer mechanism in tenon joint gap is necessary.

In this paper, two typical assembly clearances under the stationary and rotating conditions were investigated numerically, including double S-shaped and double Crescent-shaped. The inlet Reynolds numbers range from 5,500 to 50,000 and the Rotation numbers range from 0 to 0.005. The results show that the fluids in the two branches of the double S-shaped channel have different flow characteristics under rotating conditions. A vortex is formed at the corner of the left branch and the vortex scale can be influenced by Re and Ro. The large vortex decreases the local heat transfer coefficient. In the right branch, the three-dimensional flow from the flat wall to the concave wall increases the local heat transfer coefficient of different regions. For the double Crescent-shaped channel, the region with higher velocity is offset to the right of the channel which leads to higher local heat transfer coefficient under rotating conditions. The simulation results have great significance to the heat transfer analysis of turbine blades and disks.
Development of Porous Injection Technology to Reduce Emissions for Dry Low NOx Combustors: Micromixer and Swirl Injectors
Authors: Bhayaraju Umesh , Hamza Mahmoud , Jeng San-Mou
Published: August 2017

The Combustion and Fire Research Laboratory (CFRL) at the University of Cincinnati (UC) is working on the development of advanced next generation injectors for DLN combustors. Several inputs were received from the project partners during the development phase. In the present paper, developmental work on two novel injectors with Porous Injection Technology (PIT) is presented. The technology has the potential to reduce NOx emissions to single digit PPM level with a stable combustion across wide range of load conditions.

One of the key factors that are essential for lowering NOx levels is the efficient mixing of fuel-air in both spatial and temporal domains. The porous injection technology has the potential to reduce the spatial and temporal gradients to a minimum. In the present paper, two measurement techniques were used to evaluate the fuel-air mixing under atmospheric conditions. The CO2 mixing technique was used to quantify the spatial variations in the fuel mass fraction. Planar Laser Induced Fluorescence (PLIF) was used to obtain both spatial and temporal fuel mass fractions. The CO2 mixing measurements were used to validate the PLIF data for quantification. The RMS fluctuations in spatial and temporal domains were quantified from PLIF data. The combustion experiments were carried out at atmospheric pressure with a preheated temperature of air of 500–650 K and equivalence ratio of 0.5–0.8. The pressure drop across the injector was 4%. Natural gas with 90% methane and 9% ethane was used as fuel. The results show a stable flame for both injectors without combustion instabilities. Both injectors show low NOx levels. For conventional swirl stabilized design with PIT, the NOx levels were of the order of 1.5 ppm at the firing temperature of 1866 K whereas for the novel micromixer design, the NOx levels were of the order of 4 ppm @ ∼1866 K.
Staged Combustion System for Improved Emissions Operability and Flexibility for 7HA Class Heavy Duty Gas Turbine Engine
Authors: Karim Hasan , Natarajan Jayaprakash , Narra Venkat , Cai Jun , Rao Shreekrishna , Kegley Jonathan , Citeno Joseph
Published: August 2017

Driven by global warming, a relentless march towards increased fuel efficiency has resulted in increased firing temperature for HA-class engines without an increase in baseload emissions. Moreover, emissions compliance for CO, NOx, and unburned hydrocarbons are desired over increased range in gas turbine load. In addition, exceptional gas turbine operational flexibility is desired to address potential intermittency due to the penetration of renewables in the electrical grid.

Staged/sequential combustion is a state of the technology to provide operational flexibility and reduced emissions in power generation gas turbines. GE Power’s 7HA-class gas turbine combustion system combines GE’s proven DLN-2.6+ combustion technology, that has run reliably for over 1.3 million fired hours across more than eighty 9FA.03, 9F.05 & 7FA gas turbine engines, with an axially fuel staged system (AFS). Axially staging combustion to two zones allows for increased firing temperature at baseload (while maintaining the same NOx level) by operating the later/second stage hotter than the first/primary stage. During low load operation as the gas turbine firing temperature is reduced, percentage fuel split in the staged fuel system can either be reduced significantly or turned off and thereby keeping the overall combustion system into emissions compliance over a wider range of firing temperatures.

This paper presents both the development testing of the staged combustion in the FA and HA class gas turbine combustion system rigs at GE Power’s Gas Turbine Technology Laboratory and the validation testing of staged combustion system for the 7HA.01 engine completed during Spring 2016 at GE Power’s engine test facility in Greenville, SC. The paper also discusses the significant simplification of operational principle and flexibility of startup, loading and baseload operation of the 7HA combustion system. Discussion of engine test results will show how axial fuel staging was utilized to demonstrate emissions compliance ( NOx (15% O2) < 25 ppm; CO < 9 ppm), operation from 14% load to 100% load with low combustion dynamics and also to enable wide wobbe capability, which is a normalized measure of fuel flexibility.
Preliminary Design Optimization of an Organic Rankine Cycle Radial Turbine Rotor
Authors: da Silva Edna Raimunda , Kyprianidis Konstantinos G. , Säterskog Michael , Ramirez Camacho Ramiro G. , Sarmiento Angie L. Espinosa
Published: August 2017

The present study describes the application of a preliminary design approach for the optimization of an organic Rankine cycle radial turbine. Losses in the nozzle the rotor have initially been modelled using a mean-line design approach. The work focuses on a typical small-scale application of 50 kW, and two working fluids, R245fa (1,1,1,3,3,-pentafluoropropane) and R236fa (1,1,1,3,3,3-hexafluoropropane) are considered for validation purposes. Real gas formulations have been used based on the NIST REFPROP database. The validation is based on a design from the literature, and the results demonstrate close agreement the reference geometry and thermodynamic parameters. The total-to-total efficiencies of the reference turbine designs were 72% and 79%. Following the validation exercise, an optimization process was performed using a controlled random search algorithm with the turbine efficiency set as the figure of merit. The optimization focuses on the R245fa working fluid since it is more suitable for the operating conditions of the proposed cycle, enables an overpressure in the condenser and allows higher system efficiency levels. The R236fa working fluid was also used for comparison with the literature, and the reason is the positive slope of the saturation curve, somehow is possible to work with lower temperatures. Key preliminary design variables such as flow coefficient, loading coefficient, and length parameter have been considered. While several optimized preliminary designs are available in the literature with efficiency levels of up to 90%, the preliminary design choices made will only hold true for machines operating with ideal gases, i.e. typical exhaust gases from an air-breathing combustion engine. For machines operating with real gases, such as organic working fluids, the design choices need to be rethought and a preliminary design optimization process needs to be introduced. The efficiency achieved in the final radial turbine design operating with R245fa following the optimization process was 82.4%. A three-dimensional analysis of the flow through the blade section using computational fluid dynamics was carried out on the final optimized design to confirm the preliminary design and further analyze its characteristics.
Regression Study on Variables Affecting Vibration Fatigue Behavior of Additive Manufactured Titanium 6Al-4V
Authors: Matissek Kyle , Scott-Emuakpor Onome , George Tommy , Holycross Casey , Crowe Thaddeus , Howard Christopher
Published: August 2017

This discovery type experiment was intended to inspect the vibration fatigue behavior of Laser Powder Bed Fusion (LPBF) Titanium (Ti) 6Al-4V hybrid bending specimens as a function of four parameters: stress amplitude; build type; geometric variation; and surface roughness. These specimens were additively manufactured (AM) with relatively limited disclosure of process parameters but underwent post-fusion treatments of solution heat treatment (SHT), aging, and hot isostatic pressing (HIP), all critical processes to ensure granular uniformity and consistent material strength. Also, specimens were built three distinct ways to assess the effect of build orientation and size. The aerospace industry’s interest in using AM parts to improve performance of small scale gas turbine engines was the motivation of this study. Based on the test results in this investigation, the assumption that the material properties of LPBF parts are the same as conventionally made components presents the risk of unacceptably unpredictable fracture behavior, which can quickly lead to disastrous events in turbine engines. The experiment was intended to improve understanding of the effects of stress amplitude; build type; geometric variation; and surface roughness on vibration fatigue to better predict behavior.
A Centrifugal Compressor Impeller: A Multidisciplinary Optimization to Improve its Mass, Strength, and Gas-Dynamic Characteristics
Authors: Salnikov Anton , Danilov Maxim
Published: August 2017

The high-loaded centrifugal compressor blisk-type impeller, one of the main low-sized gas-turbine engine components, strongly affects engine efficiency. However, its design is a time-consuming and complex task for several reasons, including its high loading, the large number of structural and technological constraints, and the variety of requirements needed for application to a gas-turbine engine centrifugal compressor impeller (e.g., increased efficiency and strength, minimized weight requirements, etc.).

The imposition of several constraints for structure modification of the centrifugal wheels can improve one characteristic but can worsen others. The standard solution for this problem is to use an iterative approach, whereby the design process is reduced to a consistent set of impeller element design problem statements and decisions; these are separate for different analysis disciplines.

The main drawbacks to this approach are that it is labor intensive and can cause deterioration of the design quality because this procedure does not consider the design object as a unit. The present work considers a centrifugal compressor wheel design approach based on the use of an integrated multidisciplinary parameterized 3D model. This model includes a number of specialized sub-models that describe the necessary design areas as well as physical process features and phenomena occurring in the designed object. The model also realizes the integration and interaction of sub-models used in an integrated computing space.

The proposed approach allows the optimization of the structure based on several criteria, such as the mass of the wheel, stage efficiency, strength, economic indicators, etc. The result of multi-criteria optimization is not a single product design, but a set of optimal Pareto points, which describes a number of centrifugal wheel models. The optimal configuration is selected from this set, based on what is considered the most important criterion.

Optimization criteria may vary depending on the problem formulation, but the design technology, parameterization scheme, and choice of multidisciplinary integrated mathematical model are retained. Therefore, in the case of a product requirement correction, a new optimal design will require less time. In aggregate, with the nonlinear constrained optimization application, this approach reduces the total time of the design cycle, decreases development costs, and improves quality.
Valve Body Thermal Stress Control While Warming Up
Authors: He Jin
Published: August 2017

Quasi-stationary theory is applied to a simplified one-dimensional solid to work out warm-up thermal stress [1]. This paper verifies the quasi-stationary state exits in the three-dimensional valve body warm-up process, and the relationship of the thermal stress and the temperature difference is similar.

Dynamic analysis of warming-up at constant temperature increasing speed shows that: the ratio of the thermal stresses and the temperature difference gets the max value at the quasi-stationary state. The ratio is not influenced by the surface heat transfer coefficient, the material thermal diffusion coefficient and the temperature raise speed. It is a safety way to estimate the thermal stresses by temperature difference multiplied by this max ratio value. For quasi-stationary, once the temperature measure points be located, the ratio between stresses of any selected point and temperature difference is fixed. Where to set the measure points is unlimited, and the mean metal temperature, which is not easy to get, may not be applied anymore.
Extraction of Linear Growth and Damping Rates of High-Frequency Thermoacoustic Oscillations From Time Domain Data
Authors: Hummel Tobias , Berger Frederik , Stadlmair Nicolai , Schuermans Bruno , Sattelmayer Thomas
Published: August 2017

This paper presents a set of methodologies for the extraction of linear growth and damping rates associated with transversal eigenmodes at screech level frequencies in thermoacoustically non-compact gas turbine combustion systems from time domain data. Knowledge of these quantities is of high technical relevance as an required input for the design of damping devices for high frequency oscillations. In addition, validation of prediction tools and flame models as well as the thermoacoustic characterization of a given unstable/stable operation point in terms of their distance from the Hopf bifurcation point occurs via the system growth/damping rates. The methodologies solely rely on dynamic measurement data (i.e. unsteady heat release and/or pressure recordings) while avoiding the need of any external excitation (e.g. via sirens), and are thus in principle suitable for the employment on operational engine data. Specifically, the following methodologies are presented: 1) The extraction of pure acoustic damping rates (i.e. without any flame contribution) from oscillatory chemiluminescence and pressure recordings. 2) The obtainment of net growth rates of linearly stable operation points from oscillatory pressure signals. 3) The identification of net growth rates of linearly unstable operation points from noisy pressure envelope data. The fundamental basis of these procedures is the derivation of appropriate stochastic differential equations, which admit analytical solutions that depend on the global system parameters. These analytical expressions serve as objective functions against which measured data are fitted to yield the desired growth or damping rates. Bayesian methods are employed to optimize precision and confidence of the fitting results. Numerical test cases given by time domain formulations of the acoustic conservation equations including high-frequency flame models as well as acoustic damping terms are set up and solved. The resulting unsteady pressure and heat release data are then subjected to the proposed identification methodologies to present corresponding proof of principles and grant suitability for employment on real systems.
Predicting the Influence of Damping Devices on the Stability Margin of an Annular Combustor
Authors: Zahn Max , Betz Michael , Schulze Moritz , Hirsch Christoph , Sattelmayer Thomas
Published: August 2017

A numerical modeling approach based on linearized Euler equations is applied to predict the linear stability of an annular combustor with and without dampers. The acoustic properties of all relevant combustor components such as damping devices, swirl burner characteristics, swirl flame dynamics, and combustor exit are individually evaluated via experimental and numerical approaches. All of the components are incorporated subsequently into the combustor model using impedances and acoustic transfer matrices to obtain an efficient procedure.

This study focuses on using this approach to predict an annular combustor’s stability margin and to assess how dampers influence the modal dynamics of the first azimuthal mode. Stability predictions are successfully validated with experimental data. Different combustor components’ contributions to the acoustic damping of the entire system is also determined based on that numerical approach. Damper application in combustors can engender uncertainties in resonance frequency in the case of hot-gas ingestion. The impact of “detuned” resonators on the predicted damping rates with respect to a deviation in the resonance frequency and the eigenfrequency of the attenuated acoustic mode is therefore evaluated. The influence of dampers on the annular combustor’s stability margin is also determined.
Stabilization Mechanisms of Swirling Premixed Flames With an Axial-Plus-Tangential Swirler
Authors: Jourdaine Paul , Mirat Clément , Caudal Jean , Schuller Thierry
Published: August 2017

The stabilization of premixed flames within swirling flows produced by an axial-plus-tangential swirler is investigated in an atmospheric test rig. In this system, flames are stabilized aerodynamically away from the solid elements of the combustor without help of any solid anchoring device. Experiments are reported for lean CH4/air mixtures, eventually also diluted with N2, with injection Reynolds numbers varying from 8 500 to 25 000. Changes of the flame shape are examined with OH* chemiluminescence and OH laser induced fluorescence measurements as a function of the operating conditions. Particle image velocimetry measurements are used to reveal the structure of the velocity field in non-reacting and reacting conditions. It is shown that the axial-plus-tangential swirler allows controlling the flame shape and the position of the flame leading edge with respect to the injector outlet. The ratio of the bulk injection velocity over the laminar burning velocity Ub/SL, the adiabatic flame temperature Tad and the swirl number S0 are shown to control the flame shape and its position. It is then shown that the axial flow field produced by the axial-plus-tangential swirler is different from those produced by axial or radial swirlers. It takes here a W-shape profile with three local maxima and two minima. The mean turbulent flame front also takes this W-shape in an axial plane, with two lower positions located slightly off-axis and corresponding to the positions where the axial flow velocity is minimum. It is finally shown that these positions can be inferred from axial flow velocity profiles under non-reacting conditions.
Influence of Bearing Load on the Performance of Tilting-Pad Journal Bearing Under High Surface Velocity
Authors: Liu Binbin , Wang Weimin , Gao Jinji , Zhang Jian
Published: August 2017

Tilting-pad journal bearings (TPJBs) are dominant as shaft support in high-parameter turbomachinery, particularly in highspeed applications. Bearing test technology and high-precision model simulation are the key technologies for the development of high-end bearings. A bearing test platform which is based on the active magnetic bearing (AMB) loading and excitation is first designed and developed. Two large AMBs are used in the test rig as loader and exciter, and the system has a whole loading capacity up to 20000 N. As the bearing load is not always along the vertical direction, the performance of five-pads TPJBs with inner diameter of 140 mm is tested under the different load directions and load magnitudes in the speed range of 2000 to 12000 r/min. The results indicate that the direction and magnitude of the bearing load have a considerable effect on the experimental characteristics of TPJBs, especially under high-speed and heavy-load operation conditions. The bearing load has less influence on power loss than the rotation speed. By changing the direction of load, the bearing pad in the load direction has much higher temperature than the opposite pad. The change of pad temperature caused by the change of bearing load direction becomes greater under a larger bearing load. By analyzing the influence of the magnitude and direction of the bearing load on the rotor vibration, the mutual relationship among the dynamic stiffness, bearing load and rotor vibration are revealed. The performance test of TPJBs under different load directions with the AMB loading is beneficial to design the tilting pad bearing with high performance, to reduce the power loss of bearing, and to verify the correctness of the numerical model analysis. The results can be used for the performance prediction of the integrally geared centrifugal compressor because of their ever varying bearing load direction and load magnitude.
Numerical Simulation of a Reacting Jet in a Vitiated Cross Flow Using a Novel Progress Variable Approach
Authors: Kulkarni Rohit , Wood John P. , Zuber Mario , Karim Hasan U.
Published: August 2017

Staged/sequential combustion is a state of the art method to provide operational flexibility and reduced emissions in gas turbines. To use Computational Fluid Dynamics (CFD) to study such systems a reliable and computationally inexpensive turbulent combustion model is necessary. A key requisite for such a model is the accurate determination of the flame location in order to predict emissions, flame dynamics, and temperature distribution. Previously a model was developed for reheat combustion, based on a progress-variable method using auto-ignition reactors. However, sequential combustion systems are now being implemented where both auto-ignition and flame propagation are important. Consequently, the reheat model has been extended to consider flame propagation in mixtures that do not auto-ignite. This has been achieved by incorporating a small proportion of combustion products in the reactant mixture considered by the reactor. This approach has broadened the model’s applicability to address the full space between auto-ignition and flame propagation regimes. The revised model has been validated by comparison with reacting jet in vitiated cross-flow experiments demonstrating a significantly better prediction of the position of both attached and lifted flames than the original model.
Experimental Investigation of Periodically Unsteady Wake Impact on the Secondary Flow in a 1.5 Stage Full Annular LPT Cascade With Modified T106 Blading
Authors: Sinkwitz Martin , Engelmann David , Mailach Ronald
Published: August 2017

This paper transfers findings from linear cascade studies to the annular system. Experimental studies have been conducted on the newly designed 1.5 stage full annular rotating axial turbine rig at Chair of Thermal Turbomachinery, Ruhr-Universität Bochum. Therefore, an existing large scale low speed test rig was retrofitted with newly designed T106RUB low pressure turbine (LPT) blading, state-of-the-art measurement technologies and multi-dimensional traversing devices to allow for highly resolved measurements of unsteady wake stator flow interaction in both space and time. Incoming wakes are generated by a variable-speed driven rotor disk equipped with cylindrical bars.

The measuring concept for an in-depth analysis of unsteady flow phenomena is presented and results from highly resolved time-averaged and time-resolved flow field traverses are discussed and compared. In detail the time-dependent interaction of periodically passing bar wakes with the boundary layers and secondary flow structures of the T106RUB stator row is investigated. Special emphasis is put on time-varying dilatation and location of individual components of the vortex system and on potential flow separation along the blade suction surface. It is evaluated how these factors can contribute to a time-dependent homogenization of stator exit flow and a consequent loss reduction in the present configuration.
Computational Study of a Customised Shallow-Sump Aero-Engine Bearing Chamber With Inserts to Improve Oil Residence Volume
Authors: Adeniyi Akinola A. , Chandra Budi , Simmons Kathy
Published: August 2017

An aero-engine bearing chamber is a structure that is used to contain and collect oil used in lubricating and cooling the bearings supporting the high-speed engine shafts. There are various bearings in an aero-engine. Within the bearing chambers, there are typically the bearings, rotating shafts, seals and gears (in some designs). The walls of the bearing chamber are stationary and there are vents and sumps to take out the oil, via an offtake pipe, and the sealing air. The oil collected via the sump and vents is recycled and used again in the loop. To prevent oil degradation and reduce chance of coking in the chamber, it is desired that all of the oil goes through the recycling loop, with no oil staying longer than necessary in the chamber. The sealing air is used to maintain a positive pressure to keep the oil within the chamber. The flow inside a bearing chamber is highly turbulent and consists of a rotating mixture of oil and air.

A smaller amount of the oil, mostly as oil-droplets, exits at the vents and is separated from the air using de-aerators [1]. It is expected that by gravity, most of the oil collects at the sump and can be easily scavenged. This is provided the sump can be large enough. The geometry of a bearing chamber is, however, complex largely because of space limitations. It is very important that oil is not resident longer than necessary to prevent over-heating and therefore deterioration or coking. Experimental observations by Chandra & Simmons [2], have shown that bearing chambers with deep sumps perform better that those with shallow sumps.

Since shallow sumps are inevitable, a number of innovative studies have been done to improve bearing chamber designs. The presence of air in the oil (e.g. as bubbles) reduces the efficiency of the scavenging pump. Other factors such as oil momentum and windage can take oil away from the off-take pipe potentially increasing oil residence volume. Chandra & Simmons [2] placed inserts such as grille cover, perforated plate, etc, on a side of the bearing wall and improvements in the residence volume were seen. In this work, we are looking at a detailed computational fluid dynamics (CFD) simulation of one of the inserts that performed well. This will aid understanding of the flow characteristics of using an insert to improve oil residence in a bearing chamber.
Health Condition Assessment of Gas Turbine Generator on Offshore Platform
Authors: Cao Yunpeng , Wu Minghao , Yang Qingcai , Li Shuying , Yan Dongyang , Chen Lie
Published: August 2017

Based on the function level of a gas turbine generator, this paper presents a method for the quantitative assessment of the health condition of a gas turbine generator by using fuzzy comprehensive assessment (Fuzzy) and an analysis hierarchy process (AHP). First, the failure mode, effects and criticality analysis method (FMECA) is used to construct the assessment framework and obtain the indicator set for the health assessment. The membership degree of each indicator is realized by using triangular and trapezoidal membership functions. Second, the fuzzy comprehensive assessment model with analysis hierarchy process (Fuzzy-AHP) is established to implement the quantitative assessment of the health condition of the gas turbine generator, and the man-made influence on the weight assignment is decreased. Finally, an example of a three-shaft gas turbine generator health assessment is provided to validate and prove that the method is effective and feasible.
The Degradation Simulation of Compressor Salt Fog Fouling for Marine Gas Turbine
Authors: Cao Yunpeng , Chen Lie , Du Jianwei , Yu Fang , Yang Qingcai , Wu Minghao
Published: August 2017

When a gas turbine operates in a marine environment, gradual performance degradation occurs due to salt fog in the compressor and turbine. Regular water washing of a gas turbine can effectively restore the performance loss caused by compressor salt fog fouling on the flow passage. However, inappropriate washing will increase maintenance costs, cause unnecessary down time and premature erosion of leaf surfaces. In this paper, a coefficient matching method for a three shaft marine gas turbine salt fog fouling degradation factor model is proposed, which can establish a model of salt fog fouling degradation factor according to a change in operating time and exhaust temperature in the washing cycle. The influences of load, environment temperature, inlet pressure loss and salt fog fouling rate on the performance degradation of the gas turbine are simulated and analyzed; then, the degradation regularity of the performance parameters of the gas turbine under different operating conditions and fouling degrees is obtained. Finally, a method of operating cost estimation for marine gas turbines is proposed that can estimate the cost of transient change and cumulative change in the cleaning cycle caused by the salt fog fouling, which can help the operator to determine the cleaning strategy and reduce the operation cost of the gas turbine.
Performance of Adaptive Lubricants in a Hybrid Journal Bearing Operating Under Fully Saturated Conditions
Authors: Chien Ssu-Ying , Cramer Mark , Fu Gen , Untaroiu Alexandrina
Published: August 2017

Adaptive lubricants involve binary mixture of synthetic oil and dissolved carbon dioxide (CO2). Unlike conventional lubricant oils, the lubricant viscosity not only varies with the temperature within the bearing, but also can be directly adjusted through the CO2 concentration in the system. In this study, we investigated the performance of adaptive lubricants in a hybrid journal bearing considering the synthetic oil to be fully saturated by CO2. The adaptive lubricant analyzed for this study was the polyalkylene glycol (PAG) oils with low concentration of CO2 (< 30%). A three-dimensional computational fluid dynamic (CFD) model of the bearing was developed and validated against the experimental data. The mixture composition and the resultant mixture viscosity were calculated as a function of pressure and temperature using empirical equations.

The simulation results revealed that the viscosity distribution within the PAG/CO2-lubricated bearing is determined primarily by the pressure at the low operating speed. When the speed becomes higher, it is the temperature effect that dominates the viscosity distribution within the bearing. Moreover, the PAG/CO2-lubricated bearing can reduce up to 12.8% power loss than the PAG-lubricated bearing due to the low viscosity of PAG/CO2 mixture. Most importantly, we have found the PAG/CO2 can enhance the load capacity up to 19.6% when the bearing is operating at the high speed conditions.
A Novel Test Rig for Assessing Advanced Rotor Blade Cooling Concepts, Measurement Technique and First Results
Authors: Elfner Maximilian , Schulz Achmed , Bauer Hans-Jörg , Lehmann Knut
Published: August 2017

This paper presents a new approach for assessing rotor blade cooling concepts. A new test rig has been designed, built and commissioned, allowing fast comparison of different cooling schemes as well as absolute surface temperature measurements for different cooling concepts. By scaling the test specimen, full aerothermal similarity was achieved at high measurement accuracy and resolution. This similarity however poses high demand on the employed measurement techniques.

Surface temperature (and thus cooling effectiveness) is measured using high resolution, high dynamic range infrared thermography with an improved calibration method for in-situ radiation correction. Furthermore, an improved image evaluation algorithm is presented, allowing angle-of-view dependent emissivity correction and full 3D-evaluation of image data. Those improvements enable the measurement on strongly cooled and strongly curved surfaces, and thus the use of scaled rotor blades with true geometry. First results are presented comparing total cooling effectiveness of a conventionally cooled blade with internal ribs to the effectiveness of an internal swirl design blade. They show the feasibility of the measurements and the importance of the presented correction method.
High Momentum Jet Flames at Elevated Pressure: B — Detailed Investigation of Flame Stabilization With Simultaneous PIV and OH-LIF
Authors: Severin Michael , Lammel Oliver , Ax Holger , Lückerath Rainer , Meier Wolfgang , Aigner Manfred , Heinze Johannes
Published: August 2017

A model FLOX® combustor, featuring a single high momentum premixed jet flame, has been investigated using laser diagnostics in an optically accessible combustion chamber at a pressure of 8 bar. The model combustor was designed as a large single eccentric nozzle main burner (Ø 40 mm) together with an adjoining pilot burner and was operated with natural gas.

To gain insight into the flame stabilization mechanisms with and without piloting, simultaneous Particle Image Velocimetry (PIV) and OH Laser Induced Fluorescence (LIF) measurements have been performed at numerous two-dimensional sections of the flame. Additional OH-LIF measurements without PIV-particles were analyzed quantitatively resulting in absolute OH concentrations and temperature fields.

The flow field looks rather similar for both the unpiloted and the piloted case, featuring a large recirculation zone next to the high momentum jet. However, flame shape and position change drastically. For the unpiloted case, the flame is lifted, widely distributed and isolated flame kernels are found at the flame root in the vicinity of small scale vortices. For the piloted flame, on the other hand, both pilot and main flame are attached to the burner base plate, and flame stabilization seems to take place on much smaller spatial scales with a connected flame front and no isolated flame kernels.

The single shot analysis gives rise to the assumption that for the unpiloted case small scale vortices act like the pilot burner flow in the opposed case and constantly impinge and ignite the high momentum jet at its root.