bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Characterization of the Flow-Field Downstream of an Innovative Ultra Low NOx Injection System
Authors: Berrino Marco , Satta Francesca , Ubaldi Marina , Zunino Pietro , Colantuoni Salvatore , Di Martino Pasquale
Published: September 2014

The present paper is focused on the characterization of the aerodynamics of the nonreacting flow downstream of an innovative Ultra Low NOx (ULN) injection system. The system is aimed at reducing NOx emissions and combustor axial length, to obtain a more compact and lighter low-emission combustor. The flow path downstream of the injection system has been investigated by means of Particle Image Velocimetry (PIV) and Hot Wire Anemometry (HWA). Particle Image Velocimetry measurements have been carried out in the meridional plane and in three frontal planes, in order to measure mean velocity components and their fluctuations, as well as to identify the coherent structures that characterize the time-varying flow. Hot Wire Anemometry has been used to investigate the unsteady behavior of the flow and to detect the presence of velocity fluctuation frequencies at different radial and axial positions downstream of the injection system. The HWA technique allowed the identification of the frequencies associated with the precession motion due to the vortex breakdown and with the coherent structures at the interface between the inverse flow region and the jets. The experimental results show a large reverse flow region at the exit, without any back-flow within the injection system, hence offering the evidence that the injection system may be able to stabilize the flame, without inducing risks of flash-back or auto-ignition phenomena. Moreover, the mean velocity distributions show the injection system ability of keeping separated the two jets coming out from the internal and external swirlers, with the consequent possibility of applying fuel-staging.

Furthermore, the experimental results have been compared to CFD RANS calculations and used for the validation of the numerical procedure.
A Method for Forecasting the Condition of HPT NGVs by Using Bayesian Belief Networks and a Statistical Approach
Authors: Giesecke Daniel , Friedrichs Jens , Kenull Thomas , Binner Matthias , Siegert Martin
Published: September 2014

Jet engine maintenance is a very competitive field in terms of time and costs. To increase planning security and reduce turnaround time (TAT) of the maintenance process it is important to get as much engine data as possible before disassembly. Aero engines are especially subjected to environmental and operational influences. For the high pressure turbine (HPT), the following parameters have been identified to describe the deterioration of its nozzle guide vane (NGV): On-wing cycles, NGV material, airport region, engine wing position, thrust rating, vane repair history and customer business segment.

The combined influences of the parameters are non-trivial and it is not possible to acquire them analytically. There are no known mathematical laws connecting the above-mentioned parameters. The linear regression method set limits for processing data in an adequate manner. This is confirmed by the analysis of the arithmetic means and standard deviations. Especially the standard deviation values fit in a broad spectrum due to various reasons. Thus, it is not feasible to make an appropriate forecast with a simple statistical method due to the multidimensional character of the parameters influencing the accuracy. For this reason, advanced methods need to be developed to derive a feasible forecast method.

By applying a statistical hypothesis test, a bayesian belief network (BBN) has been designed. It allows the use of imprecise data without suffering a significant loss in forecast accuracy and additionally, the implementation of expert knowledge. The objective of this study is to develop an effective BBN in order to adequately predict the next repair of the first stage HPT NGV of the General Electric CF6-80C2 engine. The reason for selecting the NGV is due to its high susceptibility to different influences, combined with the significant costs and TAT during the maintenance process.

Having poor forecasting quality by using a simple statistical method, the evaluation of the BBN provides very satisfactory accuracy of above 80 percent which is equivalent to 19 out of 23 vane segments. Furthermore, the developed BBN emphasises robustness when detecting the expected tendencies while having only a limited amount of input parameters. Further work includes application of this method on other engine components as well as establishing the business value of the developed method. In conclusion, BBN have tremendous potential for forecasting the repair of the entire jet engine.
Unsteady 360 CFD Validation of a Turbine Stage Mainstream/Disc Cavity Interaction
Authors: Mirzamoghadam A. V. , Kanjiyani S. , Riahi A. , Vishnumolakala Reddaiah , Gundeti Lavan
Published: September 2014

The amount of cooling air assigned to seal high pressure turbine rim cavities is critical for performance as well as component life. Insufficient air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disc or cover plate life. Excessive purge air, on the other hand, adversely affects performance. Experiments on a rotating turbine stage rig which included a rotor-stator forward disc cavity were performed at Arizona State University. The turbine rig has 22 vanes and 28 blades, while the cavity is composed of a single-tooth lab seal and a rim platform overlap seal. Time-averaged static pressures were measured in the gas path and the cavity, while mainstream gas ingestion into the cavity was determined by measuring the concentration distribution of tracer gas (carbon dioxide) under a range of purge flows from 0.435% (Cw = 1540) to 1.74% (Cw = 6161). Additionally, particle image velocimetry (PIV) was used to measure fluid velocity inside the cavity between the lab seal and the rim seal. The data from the experiments were compared to time-dependent CFD simulations using FLUENT CFD software. The CFD simulations brought to light the unsteadiness present in the flow during the experiment which the slower response data did not fully capture. An unsteady RANS, 360-degree CFD model of the complete turbine stage was employed in order to increase the understanding of the swirl physics which dominate cavity flows and better predict rim seal ingestion. Although the rotor-stator cavity is geometrically axisymmetric, it was found that the interaction between swirling flows in the cavity and swirling flows in the gas path create non-periodic/time-dependent unstable flow patterns which at the present are not accurately modeled by a 360 degree full stage unsteady analysis. At low purge flow conditions, the vortices that form inside the cavities are greatly influenced by mainstream ingestion. Conversely at high purge flow conditions the vortices are influenced by the purge flow, therefore ingestion is minimized. The paper also discusses details of meshing, convergence of time-dependent CFD simulations, and recommendations for future simulations in a rotor-stator disc cavity such as assessing the observed unsteadiness in the frequency domain in order to identify any critical frequencies driving the system.
Evaluation of Gaseous Emissions From Hydrogen Combustion Aircraft Engines
Authors: Borm Oliver
Published: September 2014

From an engineering point of view, hydrogen is an interesting aircraft fuel. Compared to hydrocarbon fuels, the number of emission species that may occur is reduced, if pure hydrogen is considered as fuel. All emissions containing carbon atoms might be neglected. Thus, the well known relationships for emission indices, combustion efficiency as well as the dry air–fuel–ratio, especially the presented analytic equations, are no longer applicable. Hence, a new set of equations for hydrogen air combustion is derived in this paper, which has not yet been done according to the author’s knowledge. This derivation is based on the basic definitions and assumptions from ARP1533B. Thus, the analysis strategy is very similar. As modern computational power is large enough to invert a small matrix in real time, the matrix method already described was chosen. This also has the advantage of incorporating interference effects easily. The emission analysis algorithm is validated by means of a generic test case. Furthermore, a statistically non–linear sensitivity analysis of the input parameters was carried out in order to quantify their measurement uncertainty as a propagated error on the output parameters. Additionally, some small mistakes and improvements, which attracted attention in ARP1533B, will also be mentioned within this paper.
Quantitative CFD Analyses of Particle Deposition on a Transonic Axial Compressor Blade: Part II — Impact Kinematics and Particle Sticking Analysis
Authors: Suman Alessio , Morini Mirko , Kurz Rainer , Aldi Nicola , Brun Klaus , Pinelli Michele , Spina Pier Ruggero
Published: September 2014

In heavy-duty gas turbines, the micro-particles not captured by the air filtration system can cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the micro-particle ingestion (0–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic code. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. The NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase model were previously validated by the authors in the first part of this work.

The kinematic characteristics (velocity and angle) of the impact of micrometric and sub-micrometric particles with the blade surface of an axial transonic compressor are shown. The blade zones affected by particle impact were extensively analyzed and reported in the first part of this work, forming the starting point for the analyses shown in this paper.

The kinematic analysis showed a high tendency of particle adhesion on the suction side, especially for the particles with a diameter equal to 0.25 μm. Fluid dynamic phenomena and airfoil shape play a key role regarding particle impact velocity and angle.

This work has the goal of combining, for the first time, the kinematic characteristics of particle impact on the blade with fouling phenomenon by the use of a quantity called sticking probability adopted from literature.

From these analyses, some guidelines for a proper management of the power plant (in terms of filtration and washing strategies) are highlighted.
A Study of the Three-Dimensional Unsteady Real-Gas Flows Within a Transonic ORC Turbine
Authors: Wheeler Andrew P. S. , Ong Jonathan
Published: September 2014

In this paper we investigate the three-dimensional unsteady real-gas flows which occur within Organic Rankine Cycle (ORC) turbines. A radial-inflow turbine stage operating with supersonic vane exit flows (M ≈ 1.4) is simulated using a RANS solver which includes real-gas effects. Steady CFD simulations show that small changes in the inducer shape can have a significant effect on turbine efficiency due to the development of supersonic flows in the rotor. Unsteady predictions show the same trends as the steady CFD, however a strong interaction between the vane trailing-edge shocks and rotor leading-edge leads to a significant drop in efficiency.
Flameholding Tendencies of Natural Gas and Hydrogen Flames at Gas Turbine Premixer Conditions
Authors: Sullivan-Lewis Elliot , McDonell Vincent
Published: September 2014

Ground based gas turbines are responsible for generating a significant amount of electric power as well as providing mechanical power for a variety of applications. This is due to their high efficiency, high power density, high reliability, and ability to operate on a wide range of fuels. Due to increasingly stringent air quality requirements, stationary power gas turbines have moved to lean-premixed operation. Lean-premixed operation maintains low combustion temperatures for a given turbine inlet temperature, resulting in low NOx emissions while minimizing emissions of CO and hydrocarbons. In addition, to increase overall cycle efficiency, engines are being operated at higher pressure ratios and/or higher combustor inlet temperatures. Increasing combustor inlet temperatures and pressures in combination with lean-premixed operation leads to increased reactivity of the fuel/air mixture, leading to increased risk of potentially damaging flashback. Curtailing flashback on engines operated on hydrocarbon fuels requires care in design of the premixer. Curtailing flashback becomes more challenging when fuels with reactive components such as hydrogen are considered. Such fuels are gaining interest because they can be generated from both conventional and renewable sources and can be blended with natural gas as a means for storage of renewably generated hydrogen. The two main approaches for coping with flashback are either to design a combustor that is resistant to flashback, or to design one that will not anchor a flame if a flashback occurs. An experiment was constructed to determine the flameholding tendencies of various fuels on typical features found in premixer passage ways (spokes, steps, etc.) at conditions representative of a gas turbine premixer passage way. In the present work tests were conducted for natural gas and hydrogen between 3 and 9 atm, between 530 K and 650K, and free stream velocities from 40 to 100 m/s. Features considered in the present study include a spoke in the center of the channel and a step at the wall. The results are used in conjunction with existing blowoff correlations to evaluate flameholding propensity of these physical features over the range of conditions studied. The results illustrate that correlations that collapse data obtained at atmospheric pressure do not capture trends observed for spoke and wall step features at elevated pressure conditions. Also, a notable fuel compositional effect is observed.
The Experimental Studies of Improving the Aerodynamic Performance of a Turbine Exhaust System
Authors: Guillot Stephen , Ng Wing F. , Hamm Hans D. , Stang Ulrich E. , Lowe Kevin T.
Published: September 2014

Analysis and testing was conducted to optimize an axial diffuser-collector gas turbine exhaust. Two subsonic wind tunnel facilities were designed and built to support this program. A 1/12th scale test rig enabled rapid and efficient evaluation of multiple geometries. This test facility was designed to run continuously at an inlet Mach number of 0.41 and an inlet hydraulic diameter-based Reynolds number of 3.4 × 105. A 1/4th geometric scale test rig was designed and built to validate the data in the 1/12th scale rig. This blow-down rig facilitated testing at a nominally equivalent inlet Mach number, while the Reynolds number was matched to realistic engine conditions via back pressure. Multi-hole pneumatic pressure probes, particle image velocimetry and surface oil flow visualization was deployed in conjunction with computational tools to explore physics-based alterations to the exhaust geometry. The design modifications resulted in a substantial increase in the overall pressure recovery coefficient of +0.07 (experimental result) above the baseline geometry. The optimized performance, first measured at 1/12th scale and obtained using CFD was validated at the full scale Reynolds number.
Endwall Vortex Effects on Turbulent Dispersion of Film Coolant in a Turbine Vane Cascade
Authors: Yapa Sayuri D. , Elkins Christopher J. , Eaton John K.
Published: September 2014

Turbine vane cascades produce strong secondary flows due to flow turning. The dominant flow feature is the passage vortex, located in the corner between the endwall and the suction surface of the airfoil. Full-field, 3D velocity and concentration measurements were made using magnetic resonance imaging to study turbulent mixing in a realistic film-cooled nozzle vane cascade. The passage vortex has large effects on the flow features in the vane wake and consequently, on coolant mixing. Cross-flow vorticity on the vane’s suction side rolls up and forms the suction-side leg of the horseshoe vortex, which then interacts with the cross-flow boundary layer and rolls up into the passage vortex. The passage vortex does not measurably increase the turbulent diffusivity, although it does strongly distort streamlines near the endwall.
Unsteady Wake and Vortex Interactions in 3-D Steam Turbine Low Pressure Final Three Stages
Authors: Miyake Satoshi , Koda Itsuro , Yamamoto Satoru , Sasao Yasuhiro , Momma Kazuhiro , Miyawaki Toshihiro , Ooyama Hiroharu
Published: September 2014

A practical unsteady 3-D wet-steam flow through stator-rotor blade rows in a low-pressure steam turbine final three stages is numerically investigated. In ASME Turbo Expo 2013, we presented numerical results of unsteady 3-D wet-steam flows through three-stage stator-rotor low-aspect blade rows in a low-pressure steam turbine model designed by Mitsubishi Heavy Industry (MHI) assuming nonequilibrium condensation. The last study is extended to the final three stages with large aspect blade rows. The discussion in this paper is mainly focused on the effect of unsteady wake and vortex interactions on nonequilibrium condensation computed by our in-house code “Numerical Turbine System (NTS)”. In addition, the NTS and the future perspective are also briefly introduced.
Identification of Contact Area From Full Field Displacement Surface Measurements
Authors: Chatelet Eric , Nouri Baranger Thouraya , Jacquet-Richardet Georges , Saulot Aurélien
Published: September 2014

One of the most common failure modes for turbomachinery wheels is associated to high-cycle fatigue of blades. A practical way to extend working life is obtained through the introduction of specific devices that allow a reduction in vibrational magnitudes during resonance. Different kinds of components are used such as shrouds and wires for power industries and under platform dampers for aeronautics. The dry friction phenomenon between those devices and the blades induces nonlinear behaviors and flatten associated frequency response functions. This phenomenon is now well known and different modeling techniques of contact are available within numerical simulation softwares. Nevertheless, it is always difficult to estimate or to measure with sufficient precision the actual contact characteristics needed to run those softwares. Due to practical experimental capabilities, measurements are only possible quite far from the contact zone and major quantities such as the transverse loading for example are often unreachable directly.

In this paper, a new inverse methodology is presented. This method uses surface displacement measurements (obtained usually experimentally from conventional accelerometer and fast camera) in order to identify the characteristics of contact zones within elastic body assemblies. The new methodology is validated and illustrated by a numerical approach based on an academic set up.
CFD Investigation of Hydrodynamic and Acoustic Instabilities of Bluff-Body Stabilized Turbulent Premixed Flames
Authors: Lee C. Y. , Cant R. S.
Published: September 2014

Combustion instabilities in propulsion systems are often manifested through high amplitude pressure oscillations that can severely compromise performance and even lead to mechanical failure. Such instability arises from the development of large-scale coherent structures and their breakdown into fine scale turbulence that can alter the flame structure and affect turbulent mixing. When in phase with the pressure, the modulated heat release rate fluctuations can drive the system to the point where it reaches a limit cycle.

Using high fidelity CFD, the present investigation describes the occurrence of combustion-driven instability in bluff-body stabilized turbulent premixed flames, in which there is dynamic coupling between the preferred hydrodynamic modes and the acoustics of the duct. A URANS approach is adopted, using a second moment closure to solve for the anisotropic turbulent Reynolds stresses. This is combined with the Bray-Moss-Libby (BML) combustion model with a modified reaction rate closure that aims to capture the changes in the flame surface density due to external flow perturbations. Two different geometries are used for the investigation: the first is a laboratory-scale planar bluff-body flameholder [1]; and the second is the well-known Volvo afterburner experiment [2]. Four different conditions are presented to illustrate the various self-excited instabilities that can appear depending on the coupling mechanisms between the different fluid-mechanical and acoustic phenomena.

For the planar geometry, a self-sustained hydrodynamic instability induced by large-scale coherent structures occurs under fuel-lean conditions. When the equivalence ratio is increased, the flame becomes strongly wrinkled due to velocity perturbations arising from the Kelvin-Helmholtz (K-H) instability of the shear layer. The combustion heat release becomes modulated such that its phase relationship with the pressure fluctuations is sufficient to trigger thermoacoustic instability. For the Volvo experiment, symmetric shedding takes place and an acoustic mode of the duct is excited when the mixture strength is lean. At higher equivalence ratio, the flame is perturbed by the hydrodynamic instabilities of the most amplified mode. Small scale structures can be seen in the vicinity of the flameholder, and larger fluctuations in the flame occur further downstream. No appreciable feedback from the acoustic modes is present to sustain combustion instabilities.
The Effect of Aircraft Integration Design on Gas Turbine Shaft Thermal Bow and the Newkirk Effect
Authors: Smith Evan Oscar , Neely Andrew J.
Published: September 2014

During the cooling process after shutdown, gas turbines can suffer from differential thermal expansion due to buoyant convection. This process can result in asymmetric cooling of the shaft, which can in turn lead to differential thermal expansion, causing deformation of the shaft, known as thermal bow. Attempts to start a gas turbine in this bowed condition can lead to rotor-to-stator contact, triggering further heating, and subsequently further bow. This phenomenon, known as the Newkirk Effect, can result in severe damage to the engine, representing a risk to both airworthiness and logistics.

This study utilises a technique previously developed by the authors for modelling shaft thermal bow in gas turbines using a combination of 3D conjugate heat transfer (CHT) computational fluid dynamics (CFD) and finite element analysis (FEA). A baseline model comprises a simple hollow shaft supported at each end, enveloped inside a simple case. Body temperatures obtained through 3D CHT CFD at set time intervals are transferred to FEA, where the physical distortion associated with the application of an asymmetric thermal load is measured. The baseline model was allowed to cool down from representative operational temperatures, with the shaft thermal bow measured for 90 minutes of flow time. Simple modifications were then made to the baseline model including the addition of representative helicopter and fast jet inlet and exhaust analogues, and the use of porosity to simulate the presence of blades, to analyse their influence on the onset time, duration, and severity of the shaft deformation.

While the geometries used in this initial study are basic, the results indicate that these aspects of gas turbine design do have an appreciable effect on the onset time, severity, and duration, as well as the axial distribution of the shaft thermal bow. This also indicates the importance of further work in this area using more realistic geometries.
Heat Transfer in a Vane Trailing Edge Passage With Conical Pins and Pin-Turbulator Integrated Configurations
Authors: Kruekels J. , Naik S. , Lerch A. , Sedlov A.
Published: September 2014

The trailing edge sections of gas turbine vanes and blades are generally subjected to extremely high heat loads due to the combined effects of high external accelerating Mach numbers and gas temperatures. In order to maintain the metal temperatures of these trailing edges to a level, which fulfills the mechanical integrity of the parts, highly efficient cooling of the trailing edges is required without increasing the coolant consumption, as the latter has a detrimental effect on the overall gas turbine performance.

In this paper the characteristics of the heat transfer and pressure drop of two novel integrated pin bank configurations were investigated. These include a pin bank with conical pins and a pin bank consisting of cylindrical pins and intersecting broken turbulators. As baseline case, a pin bank with cylindrical pins was studied as well. All investigations were done in a converging channel in order to be consistent with the real part.

The heat transfer and pressure drop of all the pin banks were investigated initially with the use of numerical predictions and subsequently in a scaled experimental wind tunnel. The experimental study was conducted for a range of operational Reynolds numbers. The TLC (thermochromic liquid crystal) method was used to measure the detailed heat transfer coefficients in scaled Perspex models representing the various pin bank configurations. Pressure taps were located at several positions within the test sections. Both local and average heat transfer coefficients and pressure loss coefficients were determined.

The measured and predicted results showed that the local internal heat transfer coefficient increases in the flow direction. This was due to the flow acceleration in the converging channel. Furthermore, both the broken ribs and the conical pin banks resulted in higher heat transfer coefficients compared with the baseline cylindrical pins. The conical pins produced the highest average internal heat transfer coefficients in contrast to the pins with the broken ribs, though this was also associated with a higher pressure drop.
Analysis of the Scatter of the Elastic Properties in Conventionally Cast Nickel Base Superalloys: Quantification, Modeling and Evaluation of the Impact on Gas Turbine Blade Design
Authors: Riva Andrea , Bessone Andrea
Published: September 2014

Cast nickel-base superalloys elastic properties have a very large scatter, mainly because of the coarse grain microstructure and in-grain anisotropy.

This high dispersion must be taken into account in the design of gas turbine blades, in particular when evaluating phenomena directly linked to the elastic behavior, such as blades vibration. This source of elastic properties scatter becomes even more important on specimens for material characterization because of their inferior size, which entails a lesser number of grains (i.e. a larger scatter).

In this paper a model aimed to quantify such scatter is proposed. The performances of the model in predicting the standard deviation of the Young’s modulus (and consequently of the eigenfrequencies) are also shown, both for tested specimens and blades excited on clamps.

Finally, a sensitivity FEM modal analysis is performed in order to evaluate how the elastic property dispersion might affect the blade eigenfrequencies and the relative mode shapes, with particular emphasis on the case of a specific region of a geometrically complex component affected by an anomalous Young’s modulus. Besides, the influence of the blade mass is evaluated through both experimental clamp impact tests and FEM analyses. The effect on blades of such source of scatter is then compared to the effect of the elastic properties dispersion. ANSYS program has been used for the simulations.
Fuel Switchover at High Load, Integration Into an Engine Operation Concept
Authors: Schell Susanne , Singla Ghislain
Published: September 2014

The capability to switch online from a main to a back-up fuel is a necessity for dual fuel gas turbines. The switching procedure is itself challenging; fuel gas, fuel oil and supporting systems need to be operated in parallel, with the safe start-up and shut-down of each system having to be ensured. Additionally, the requirements of gas turbine and combined cycle have to be considered; with the target to provide fast reliable fuel switching, without a major effect on the power output.

Alstom’s GT26/GT24 High Load Fuel Switchover (HLFSW) fulfils these requirements. HLFSW is a concept which allows switching back and forth between fuel gas and fuel oil in the load range of base load down to 60 % relative GT load. A key feature of the HLFSW is the stable load during the complete duration of the fuel switchover process, ensuring nearly constant power output in combined cycle mode from the moment the fuel switchover is triggered until standard operation is achieved on the secondary fuel.

In this paper the integration of the HLFSW into the engine operation concept is presented. It is shown, how the sequential combustion of the Alstom GT26/GT24 is transferred from primary to secondary fuel by sequential fuel switchover. The focus is on how the high load fuel switchover concept is embedded into the gas turbine’s engine operation concept, allowing a smooth transfer between the fuel gas standard operation concept and the fuel oil standard operation concept and vice-versa, resulting in a fuel switchover concept without any significant disturbances to the heat recovery steam generator (HRSG).
Experimental Analysis of Swirl in Short Annular Diffusers With Negative Wall Angles
Authors: Cerantola D. J. , Birk A. M.
Published: September 2014

Short annular diffuser systems consisting of a conical expansion section with negative wall angles and a solid (full outer diameter) diffusing section were tested experimentally at several inlet swirl angles of 0–40°. Tests analyzed were completed over a range of inlet Reynolds number of Ret = 0.9–2.2 × 105 and considered fully turbulent. Performance — back pressure coefficient, outlet velocity uniformity, and total pressure loss — were appreciably depreciated for inlet swirl number larger than 0.7 and the average 10° curved vane swirler out-performed its straight vaned equivalent. Three centre bodies with length half that of the diffuser and different curvatures were manufactured. Similar performance was achieved but each centre body provided marginal improvements to a particular objective. Most notably, the centre body that gave an initial flow expansion angle of 14° resulted in 1–4% lower back pressure than the other two whose expansion angles were 12° and 16°.
Study of Tabs in a Short Annular Diffuser With a Strong Swirling Flow
Authors: Cerantola D. J. , Birk A. M.
Published: September 2014

Passive augmentation devices are typically added to diffusers to increase pressure recovery; however, applications such as infrared suppression exist where more uniform outlet velocity profiles are also desirable. Square tabs were added to a short annular diffuser system with diffuser effectiveness of 80% in strong swirling subsonic turbulent flow. The number, axial position, width, and height were varied for the tabs with a 135° orientation angle. Results showed that back pressure increased linearly with increasing tab projected area blockage but outlet velocity uniformity was maximum with 7% tab blockage. Tabs placed on the centre body base recovered more dynamic pressure than tabs placed downstream on the centre body with similar tab area blockage.
The Effect of Land Taper Angle on Trailing Edge Slot Film Cooling
Authors: Ling Julia , Elkins Christopher J. , Eaton John K.
Published: September 2014

Trailing edge slot film cooling is a widely used method of protecting the thin trailing edge of turbine blades from hot gas impingement. The structures that separate the slots, known as “lands,” come in a variety of configurations which can be broadly classified as either “tapered” or “straight.” This paper examines the effect of the land taper angle on the mixing of the coolant flow with the main flow by comparing three configurations: a case with straight lands, a previously reported case with slightly tapered lands, and a case with strongly tapered lands. In each case, the slot width and the land width at the plane of the slot exit are kept constant. For each configuration, the mean volumetric coolant concentration distribution and 3-component velocity field were measured using Magnetic Resonance Imaging techniques. It is shown that the land taper angle has a strong effect on the mean flow features and coolant surface effectiveness. Furthermore, the impact of the lands configuration on the flow field and concentration distribution is seen not just in the cutback region, but also in the wake of the blade.
A Method for Conjugate Heat Transfer With Unsteady RANS Simulation
Authors: Yamane Takashi , Tanaka Yuhi
Published: September 2014

The conjugate heat transfer simulation is expected to simulate precise temperature distributions of turbine cooling structures and contribute to the reduction of cooling air usage. This method has mainly been used to predict steady state temperature because of the large difference of time scale between RANS flow simulation and thermal conduction in solid materials, thus the accuracy of temperature estimation depends on the modeling of the turbulence. Despite many efforts to improve turbulence models, an inherent limitation of RANS and turbulence modeling and the necessity of unsteady simulation for better accuracy in heat transfer simulations have been pointed out. The aim of this study is to combine the unsteady RANS simulation with the steady thermal conduction of solid materials. The “Time Smoothing” method was introduced to compensate the large time scale difference between fluid and solid, then the effectiveness of the method was confirmed through conjugate heat transfer simulations around a pipe shape object where strong flow unsteadiness prevails.
Stress Corrosion Cracking and Corrosion Fatigue Analysis of Nuclear Steam Turbine Rotor
Authors: Chen Gang , Jiang Puning , Ye Xingzhu , Zhang Junhui , Hu Yifeng , Hao Zhenzhen
Published: September 2014

Although stress corrosion cracking (SCC) and corrosion fatigue cracking can occur in many locations of nuclear steam turbines, most of them initiate at low pressure disc rim, rotor groove and keyway of the shrunk-on disc. For nuclear steam turbine components, long life endurance and high availability are very important factors in the operation. Usually nuclear power plants operating more than sixty years are susceptible to this failure mechanism. If SCC or corrosion fatigue happens, especially in rotor groove or keyway, it has a major influence on nuclear steam turbine life.

In this paper, established methods for the SCC and corrosion fatigue-controlled life prediction of steam turbine components were applied to evaluating a new shrunk-on disc that had suffered local keyway surface damage during manufacture and loss of residual compressive stress.
Algebraic Anisotropic Eddy Viscosity Model for Separated Flows of Internal Cooling Channels
Authors: Li Weihong , Yang Li , Ren Jing , Jiang Hongde
Published: September 2014

A new algebraic anisotropic eddy viscosity model (AEVM) is developed to account for the anisotropic characteristics of flow fields for internal cooling channels in a gas turbine. The model consist of two parts: k and ε near wall modeling are improved to obtain precise near wall turbulent characteristics and eddy viscosity; anisotropic ratios are derived to account for anisotropy and further modify the normal Reynolds stresses by combining implicit algebraic stress model and isotropic eddy viscosity model. The new algebraic anisotropic eddy viscosity model is validated in two cases: 1) flow prediction of backward facing step, better results are obtained especially turbulent quantities, 2) flow and heat transfer predictions of internal channels with ribs, numerical reattachment length after each rib is more close to the measured value after anisotropic modification, and heat transfer prediction accuracy is increased by 6–10%. Results indicate the present model can be applied to flow and heat transfer prediction of separated flows in internal cooling channels efficiently.
Evaluation of FEM Based Methods to Predict Temperature Distributions of a Convection Cooled Gas Turbine Blade
Authors: Woerz B. , Mick Y. , Findeisen E. , Jeschke P. , Rabs M.
Published: September 2014

This paper presents different numerical methods to predict the thermal load of a convection cooled gas turbine blade under realistic operating temperature conditions. The subject of the investigation is a gas turbine rotor blade which is equipped with a state-of-the-art convection cooling system.

Firstly, two FEM based methods are introduced. One method, referred to as FEM1D method, uses empirical correlations from the open literature to obtain one dimensional heat transfer coefficients along one flow line inside the cooling channels while in the hot gas path a three dimensional CFD simulation is used. The second method (FEM2D) uses three dimensional CFD simulations to obtain two dimensional heat transfer coefficient distributions for both, the inner cooling channels and the hot gas path. The results from both numerical methods are compared with each other and are validated with experimental data, quantifying also their accuracy limits.

In total this paper gives an evaluation of two different FEM methods to predict temperature distribution in convection cooled gas turbines. Their accuracy, numerical cost and limitations are evaluated. It turns out that the temperature profiles gained by both methods are generally in good agreement with the experiments. However, while causing higher numerical costs the more detailed FEM2D method achieves more accurate results.
NOx Reduction in Gas Turbine Combustors With Compact Non-Premixed Flame Front
Authors: Tsatiashvili V. V. , Avgustinovich V. G.
Published: September 2014

This paper represents results of R&D efforts towards reducing a bypass turbofan engine NOx emission by 45 % compared with CAEP/6 to meet the ICAO NOx emission goal of 2020.

To achieve ICAO NOx technology goal, a new approach is used based on the NOx emission reduction in combustors with non-premixed combustion well proved in operation. The new approach is represented by structured system of low emission combustion principles — a concept of combustor featuring compact non-premixed flame (CNPF). The essence of CNPF concept is in suppression of volume and surface NOx formation sources by flame front blocking in liner primary zone and by increasing of fuel effective burning rate. The paper represents the development of concept up to and including the 4th technology maturity level. It demonstrates CNPF concept independence and interaction with other up-to-date gas turbine low emission concepts. The paper indicates comparison of rig test results between in-service combustor and CNPF adopted combustors carried out on a single liner. A CNPF adopted combustor shows NOx emission index reduction by 35 …47 % at take-off engine conditions. Preliminary estimation shows that it is possible to reach the ICAO goal for NOx emission level of 2020.
Experimental and Numerical Assessment of the Aeroelastic Stability of Blade Pair Packages
Authors: Vega Almudena , Corral Roque , Zanker Achim , Ott Peter
Published: September 2014

The stabilizing effect of grouping rotor blades in pairs has been assessed both, numerically and experimentally. The bending and torsion modes of a low aspect ratio high speed turbine cascade tested in the non-rotating test facility at EPFL (Ecole Polytechnique Fédérale de Lausanne) have been chosen as the case study. The controlled vibration of 20 blades in travelling wave form was performed by means of an electromagnetic excitation system, enabling the adjustement of the vibration amplitude and inter blade phase at a given frequency. Unsteady pressure transducers located along the blade mid-section were used to obtain the modulus and phase of the unsteady pressure caused by the airfoil motion. The stabilizing effect of the torsion mode was clearly observed both in the experiments and the simulations, however the effect of grouping the blades in pairs in the minimum damping at the tested frequency was marginal in the bending mode. A numerical tool was validated using the available experimental data and then used to extend the results at lower and more relevant reduced frequencies. It is shown that the stabilizing effect exists for the bending and torsion modes in the frequency range typical of low-pressure turbines. It is concluded that the stabilizing effect of this configuration is due to the shielding effect of the pressure side of the airfoil that defines the passage of the pair on the suction side of the same passage, since the relative motion between both is null. This effect is observed both in the experiments and simulations.
Design, Validation and Verification of Film Cooling on Gas Turbine Rotor Endwall
Authors: Abba L. , Abram R. , Barigozzi G. , Perdichizzi A.
Published: September 2014

This paper describes the design process carried out to introduce film cooling coverage on the hub platform of a first turbine blade in order to protect from hot gas corrosion the trailing edge platform region.

The different steps described consist in a design phase, a validation by experimental tests, the production follow up and verification feedbacks.

The first stage endwall is a critical region due to secondary flows overheating; critical areas have been identified by 3D thermal analysis and confirmed through damage reports.

A design phase has been carried out to determine the cooling holes configuration in terms of position, number, inclination and diameter.

A CFD analysis allowed to define the hot gas streamlines near the pressure side fillet region in order to identify the best holes arrangement to ensure a proper thermal coverage; the thermal effectiveness and coverage length has been subsequently verified by means of an experimental activity developed by University of Bergamo.

On the basis of the experimental results a 3D thermal analysis of the new holes configuration has highlighted the improvement in terms of local wall temperature reduction.

Finally the new film holes have been introduced in the machining cycle of the blade and realized by electrochemical drilling. During a maintenance inspection after 20000 operating hours an endoscope investigation has confirmed the improvement obtained, showing no substantial signs of overheating.
Rotating Stall Observations in a High Speed Compressor: Part 2 — Numerical Study
Authors: Dodds J. , Vahdati M.
Published: September 2014

In this two part paper the phenomenon of part span rotating stall is studied. The objective is to improve understanding of the physics by which stable and persistent rotating stall occurs within high speed axial flow compressors. This phenomenon is studied both experimentally (part 1) and numerically (part 2).

The experimental observations reported in Part 1 are now explored through the use of 3D unsteady RANS simulation. The objective is to both to validate the computational model and, where possible, explore some physical aspects of the phenomena.

Unsteady simulations are presented, performed at a fixed speed with the three rows of variable stator stagger vanes adjusted to deliberately mismatch the front stages and provoke stall. Two families of rotating stall are identified by the model, consistent with experimental observations from Part 1.

The first family of rotating stall originates from hub corner separations developing on the stage 1 stator vanes. These gradually coalesce into a multi-cell rotating stall pattern confined to the hub region of the stator and its downstream rotor. The second family originates from regions of blockage associated with tip clearance flow over the stage 1 rotor blade. These also coalesce into a multi-cell rotating stall pattern of shorter length scale confined to the leading edge tip region. Some features of each of these two patterns are then explored as the variable stator vanes are mismatched further, pushing each region deeper into stall.

The numerical predictions show a credible match with the experimental findings of Part 1. This suggests that a RANS modelling approach is sufficient to capture some important aspects of part span rotating stall behavior.
Electro-Assist Turbo for Marine Turbocharged Diesel Engines
Authors: Shiraishi Keiichi , Krishnan Venky
Published: September 2014

Turbocharged diesel engines are widely used in the marine industry and have a significant impact on global CO2 and NOx emissions. Turbochargers are an integral component of any diesel engine and they play a critical role in their performance. Mitsubishi Heavy Industries (MHI) and Calnetix Technologies have developed a unique technology called the “Electro-Assist Turbo” (EAT). The EAT unit consists of a specially designed high speed permanent magnet motor directly mounted to the turbocharger rotating assembly. The high speed motor applies torque to the turbocharger rotor enabling it maintain or vary rotor speed at low engine exhaust flow rates in order to supply sufficient charge air to maximize engine performance. Turbocharged diesel engines suffer from inherent deficiencies at low engine speeds; there is not enough energy in the exhaust to produce an optimum and readily available level of boost for the engine intake air system at off-design points. This technology proves even more important as the majority of large marine vessels are now operating in a “slow steaming” part throttle mode. To date the majority of marine diesel engines use auxiliary air blowers (AAB) to supply additional air to the engine intake during off design point operation. These AABs are inefficient and not intended nor designed to be used in constant operation. The EAT unit can provide a higher discharge pressure at the same electrical power consumption as an AAB. This more efficient design with higher discharge pressure further improves fuel efficiency and eliminates the need to run an external piece of machinery during operation, thus lowering maintenance costs.

This paper will provide an overview of the design, integration and initial testing of the 100kW Electro-Assist Turbo into a Mitsubishi Exhaust-gas Turbocharger (MET)-83 marine diesel turbocharger. In addition this paper will go over the custom designed aerodynamic motor housing structure that holds the non-rotating components without penalizing performance of the turbocharger, special software developed for the variable frequency drive system that enables the flexible operation of the high speed motor, and features of the high speed permanent magnet motor that allows for operation without any active cooling. Also, this paper will provide and discuss the initial test results of the EAT integrated into the MET-83 turbocharger along with engine testing results provided by MHI. Low cost designs will be discussed that enable turbochargers currently in operation to be retrofitted and the further improvements taking place to commercialize.