bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability Analysis for Unsymmetrical Shaft With Flexible Bladed-Disk
Authors: Masoud Samer , Khader Naim
Published: December 2014

The governing equations of motion for a rotating flexible blade-rigid disk-flexible shaft system are derived. The bladed disk is attached at one end of an asymmetric shaft with uniformly distributed mass, mass moment of inertia, and stiffness. The shaft is held by two isotropic supports; one at the far end from the bladed disk, modeled by two translational and two rotational springs, and an intermediate support, modeled by two translational springs only. The effect of shaft asymmetry on the dynamics behavior of the rotating bladed disk shaft system is examined over a wide range of rotational speed, and for different combinations of springs’ stiffness, which determines the type of shaft supports. The cantilever, and the simply supported shaft with an over hang can be looked upon as special cases of the described above shaft configuration, since the former is obtained by assigning large stiffness for both translational and rotational springs at the end support, and zero spring stiffness at the intermediate one, whereas the latter is obtained by assigning large stiffness for the translational springs at both supports and zero stiffness for the rotational springs. Stability boundaries are calculated, and presented in terms of shaft asymmetry and rotor speed for given bearing stiffness.
Investigation of Tip Leakage Effects in Transonic Flow Using a Parallel Unstructured Navier-Stokes Code
Authors: Hustad C-W. , Bölcs A. , Wehner M.
Published: December 2014

Calculated results for tip flow around two different blade configurations are presented and compared with experimental data. The first configuration (case number 1) is a flat-plate profile tested in a linear transonic tunnel — the profile is an idealized representation of the aft-section of some highly curved turbine blades. The second configuration (case number 2) originates from the outer profile on the last-stage-blade of a steam turbine, however it is also reminiscient of a section from a turbine blade with supersonic exit flow. This configuration was tested in an annular cascade at Mach numbers representative of engine operating conditions.

The computed results were obtained using a parallel 3D unstructured Navier-Stokes code. The code runs on a work-station cluster, as well as being optimized for the 256 processor Cray T3D at EPFL: the code is capable of gigaflop performance using more than 3 million cells — adaptive mesh refinement thus allows enhanced resolution within the tip gap region.

For each configuration we have calculated two Runs. In both cases, Run-1 is similar to the experimental conditions, so that direct comparison between measured and calculated results is possible. With case number 1/Run-2 we re-calculated the flow without imposing a prescribed inflow boundary-layer along the sidewall. Comparison between the two runs helped reveal how free-stream total pressure can establish itself within the tip gap region. For the second configuration — in the annular cascade — we were interested in observing the influence of relative movement between the blade tip and adjacent sidewall. Hence for case number 2/Run-2 we imposed a circumferential velocity on the adjacent sidewall. This modified the effective sidewall boundary-layer and had a noticeable influence on the development of the tip-leakage flow.
Measurement and Prediction of Tip Leakage Losses in an Axial-Flow Transonic Turbine
Authors: Wehner M. , Bütikofer J. , Hustad C-W. , Bölcs A.
Published: December 2014

This paper presents a simple method for predicting tip leakage losses in transonic axial-flow turbines. The method is based upon experimental work conducted on a flat plate at 5° incidence and with isentropic exit Mach number of 1.26. The tip gap height was varied from zero up to 15% of chord. Measurements were made (using Laser-2-Focus) of velocity vectors around the tip gap region. These revealed a strong shear layer emerging from the gap onto the suction side of the plate. The relative angle between the leakage flow and the freestream was identified as a key parameter determining the subsequent mixing and overall loss generation. The proposed model applies two-dimensional potential flow analysis to estimate the flow angle as a function of tip gap height and the angle of incidence.

Subsequently, comparisons were made with experimental results obtained in an annular cascade on the outer profile of the last-stage blade of a steam turbine. The predicted tip leakage losses compare favourably with the measured values.
A Prediction Method for the Frictional Torque of a Rotating Disk in a Stationary Housing With Superimposed Radial Outflow
Authors: Gärtner W.
Published: December 2014

Experimental data from various sources for the frictional torque of a rotating disk in a stationary housing under the influence of a superimposed radial outflow were correlated.

Existing correlations were found to overpredict the frictional torque when the superimposed flow exceeds the pumped flow of the rotating disk. Therefore a new correlation is established for this case to improve the agreement with experimental results. Since the governing equation is an integral which can only be solved numerically the method is installed in a PC-based spread sheet programme for convenient use in the engineering practice.

For throughflow rates less or equal than the pumped flow of the rotating disk an existing correlation is modified to take account of the effect on the frictional torque of the axial distance between the disk and the stationary housing.
Effect of Main Flow Pressure Asymmetry on Seal Characteristics of a Gas Turbine Rotor-Stator System
Authors: Ishida K. , Hamabe K.
Published: December 2014

The effect of circumferential pressure asymmetry of the main flow on sealing characteristics of a shrouded rotor-stator system has been studied.

Local distribution of seal efficiency was measured using a tracer gas method. Blocks of various height were placed in the main flow path to generate circumferential pressure asymmetry. The range of main flow static pressure asymmetry (the ratio of difference between maximum and minimum pressure to main flow dynamic pressure) was 2% to 38%.

The test results showed that pressure asymmetry of main flow has a dominant effect on seal efficiency, and local distribution of seal efficiency is strongly correlated with pressure asymmetry. An experimental correlation of mean seal efficiency and pressure asymmetry was obtained.
Effects of Unmixedness in Piloted–Lean Premixed Gas Turbine Combustors
Authors: Barnes J. C. , Mellor A. M.
Published: December 2014

The characteristic time model (CTM) represents the dominant physical subprocesses related to combustor performance in terms of characteristic times. Properly formulated, these characteristic times account for variations in combustor geometry, fuel characteristics, and operating conditions. Here, a CTM for piloted–lean premixed combustor NOx emissions is used to investigate the sensitivity of NO formation in such combustors to fuel/air unmixedness and suggests an experimental method of evaluating premixed performance under fired conditions that is discussed in the companion paper.
On the Inverse Design of Inter-Stage Ducts, Diffuser Walls and Meridional Geometry of Turbomachines
Authors: Zangeneh M.
Published: December 2014

In this paper a method is presented for the design of diffuser walls, interstage ducts and meridional geometry of turbomachines. In this method the wall geometry is designed subject to a specified meridional velocity distribution. The effect of variations in inlet velocity (or inlet shear flow) to the duct is modelled by using a vorticity term related to spanwise variations in stagnation enthalpy and the drift function. The flow field is then solved by using a streamfunction and a kinematic condition based on the vorticity in the flow. A simple transpiration model is used to update the wall geometry. To design the meridional geometry of turbomachines a vorticity related to bound circulation is introduced. This vortex term together with the inviscid slip condition can be used to find the swirl distribution when blade shape is specified (blade analysis mode) or the blade shape when the swirl distribution is specified (blade design mode). The results of the application of the method to a converging duct, an S-shaped duct with non-uniform inlet flow and the meridional geometry of a centrifugal compressor impeller confirm the validity of this approach.
A 3D Rotating Stall Stability Model for Axial Flow Compressor
Authors: Cao Ren-Jing , Zhou Sheng
Published: December 2014

Rotating stall phenomenon is usually characterized by 3D aerodynamic stability behavior. The earlier models mainly considered the flow effects in terms of 1D and 2D spatial variables. In order to involve the characteristics of the 3D flow of the compressor, it is necessary to improve the existing rotating stall stability models and further develop the models to consider the effects of the 3D disturbance. In this paper, a new aerodynamic stability model concerning the effects of a radial disturbance produced by the compressor, and explaining more mechanisms about the aerodynamic stability of compressor is presented. Using the developed rotating stall stability model, the stall margins are calculated and compared to experimental data for two axial flow compressors. The calculated results show that the developed 3D rotating stall stability model gives better stall margin prediction than that by the 2D model.
Effects of Temperature on Formation of Insolubles in Aviation Fuels
Authors: Balster Walter J. , Jones E. Grant
Published: December 2014

Ten aviation turbine fuels (five Jet-A fuels, three JP-5, one JP-8, and one JPTS) were stressed at 185 and 225°C in a single-pass heat exchanger. On the basis of several criteria applied at 185°C, these fuels cover a broad thermal-stability range from lesser-quality fuels to the most stable JPTS fuel. Three of these fuels contain significant concentrations of dissolved metal (copper, > 30 ppb). The surface and bulk insolubles formed from each fuel have been quantified using surface-carbon burnoff of tubing sections and of in-line filters. The total insolubles measured at 185 and 225°C fall in the range 0.3–7.5 μg/mL and 0.1–2 μg/mL, respectively. In general, the greater the quantity of insolubles formed at 185°C, the greater its reduction at 225°C. Possible explanations for this effect are offered, and implications relative to understanding surface fouling are discussed.
Model Based Fuzzy Logic Sensor Fault Accommodation
Authors: Healy Timothy A. , Kerr Laura J. , Larkin Louis J.
Published: December 2014

Sensor in-range fault accommodation is a fundamental challenge of dual channel control systems in modem aircraft gas turbine engines. An on-board real-time engine model can be used to provide an analytical third sensor channel which may be used to detect and isolate sensor faults. A fuzzy logic based accommodation approach is proposed which enhances the effectiveness of the analytical third channel in the control system’s fault isolation and accommodation scheme. Simulation studies show the fuzzy accommodation scheme to be superior to current accommodation techniques.
The Meaning of Activation Energy and Reaction Order in Autoaccelerating Systems
Authors: Ervin J. S. , Heneghan S. P.
Published: December 2014

Global reaction mechanisms and rate constants are commonly used in computational fluid dynamics models which incorporate chemical reactions to study aviation fuel thermal and oxidative thermal stability. Often these models are calibrated using one set of conditions, such as flow rate and temperature. New conditions are then calculated by extrapolation using the global expressions. A close inspection of the origin of global oxidation rate constants reveals that in systems that undergo autocatalysis or auto inhibition, a simple over-all global activation energy and reaction order are not good descriptors of the reaction process. Furthermore, pseudo-detailed chemical kinetic modeling of a fuel which experiences autocatalysis shows that the observed reaction order for oxygen consumption varies with initial oxygen concentration, extent of reaction, and temperature. Thus, a simple global rate expression used to describe oxygen consumption in an autoaccelerating system is insufficient to allow extrapolation to different temperature or time regimes.
Ideal Power Output — An Alternative Aircraft Engine Performance Comparator
Authors: Schmidt Marvin F. , Norden Christopher M. , Stricker Jeffrey M.
Published: December 2014

The gas turbine is applied in four basic configurations; the turbojet, the turbofan, the turboprop and the turboshaft. Comparisons of the performance of these various configurations is difficult since they convert the energy to different forms, i.e. thrust or shaft power. Cycle variables which do not necessarily constitute advancements in the state-of-the-art such as bypass ratio and fan pressure ratio can have a profound effect on thrust and shaft power. Differences in flight speed and altitude capability further confound the comparisons. What is required is a comparison methodology that removes all of these variables and yet puts all the various types of engines on an equitable basis. This paper will provide such a comparison tool. All turbomachinery, regardless of configuration, can be compared with this method.
A Study of Integrally Augmented State Feedback Control for an Active Magnetic Bearing Supported Rotor System
Authors: Flowers George T. , Szasz Gyorgy , Trent Victor S. , Greene Michael E.
Published: December 2014

State feedback controller designs allow for pole-placement in an effective manner, but reduction of static offset is difficult. On the other hand, classical control methodology allows for the increase of system type and the elimination of static offset. An integrally augmented state feedback controller provides the benefits of standard feedback designs while allowing for the elimination of static offsets (through the increase of system type). Static offset is a particular problem with magnetic bearing supported rotor systems, in that gravitational effects, current biasing, and operational loading tend to exacerbate this problem. In order to assess the effectiveness of this technique, an integrally augmented state feedback controller is developed, implemented, and tested for a magnetic bearing supported rotor system. Results for several selected configurations are presented and compared. Some conclusions and recommendations concerning the effectiveness of integrally augmented state feedback controller designs are presented.
Investigation of the Solidity and the Blade Vibration Behaviour of Unshrouded Centrifugal Compressor Impellers With Different Aerodynamic Design
Authors: Hasemann H. , Weser G. , Hagelstein D. , Rautenberg M.
Published: December 2014

The efficiency and the characteristics of unshrouded centrifugal compressors depend on the thermodynamic and aerodynamic design of the stage and especially of the impeller. Both, the efficiency and the characteristics, can strongly be influenced by a variation of the geometry of the blade structure.

The design of the leading edge depends on the given inlet flow angle distribution and the outlet part of the blade is fixed by the desired outlet angle distribution. Due to the manufacturing process, the selected material, the solidity and the blade vibration, the restrictions and limitations have to be taken into consideration during the aerodynamic optimization process of the blade geometry.

By means of Finite Element Code computations of the solidity and the vibration behaviour the possibilities, the restrictions and the limits of a modern aerodynamic design especially in the inlet and outlet part of the impeller blades were investigated.

The results of this work could demonstrate the importance of integrating the Finite Element Code computation in the design process — not only to see the limits, but also to try and realize new ideas of design optimization.
Reducing Lateral Vibrations of a Rotor Passing Through Critical Speeds by Acceleration Scheduling
Authors: Millsaps Knox T. , Reed Gregory L.
Published: December 2014

A method is presented for reducing the lateral response of an imbalanced rotor accelerating or decelerating through its first lateral bending critical speed by using a variable acceleration rate. A lumped parameter model along with a numerical integration scheme is used to simulate the response of a simply supported, single disk rotor during fast acceleration and deceleration through critical speed. The results indicate that the maximum response and/or the total vibrational energy of a rotor passing through the critical speed can be reduced significantly by using a variable acceleration schedule. That is, reducing the acceleration rate after the nominal critical speed is passed. These predictions were verified experimentally for a single disk rotor.
Aspects of Vane Film Cooling With High Turbulence: Part II — Adiabatic Effectiveness
Authors: Ames Forrest E.
Published: December 2014

A four vane subsonic cascade was used to investigate the influence of turbulence on vane film cooling distributions. The influence of film injection on vane heat transfer distributions in the presence of high turbulence was examined in part I of this paper. Vane effectiveness distributions were documented in the presence of a low level of turbulence (1%) and were used to contrast results taken at a high level (12%) of large scale turbulence. All data were taken at a density ratio of about 1. The three geometries chosen to study included one row and two staggered rows of downstream film cooling on both the suction and pressure surfaces as well as a showerhead array. Turbulence was found to have a moderate influence on one and two rows of suction surface film cooling but had a dramatic influence on pressure surface film cooling, particularly at the lower velocity ratios. The strong pressure gradients on the pressure surface of the vane were also found to alter film cooling distributions substantially. At lower velocity ratios, effectiveness distributions for two staggered rows of holes could be predicted well using data from one row superposed. At higher velocity ratios the two staggered rows produced significantly higher levels of effectiveness than values estimated from single row data superposed. Turbulence was also found to substantially reduce effectiveness levels produced by showerhead film cooling.
Flow in a “Cover-Plate” Pre-Swirl Rotor-Stator System
Authors: Karabay Hasan , Chen Jian-Xin , Pilbrow Robert , Wilson Michael , Owen J. Michael
Published: December 2014

This paper describes a combined theoretical, computational and experimental study of the flow in an adiabatic pre-swirl rotor-stator system. Pre-swirl cooling air, supplied through nozzles in the stator, flows radially outward, in the rotating cavity between the rotating disc and a cover-plate attached to it, leaving the system through blade-cooling holes in the disc. An axisymmetric elliptic solver, incorporating the Launder-Sharma low-Reynolds-number k-ε turbulence model, is used to compute the flow. An LDA system is used to measure the tangential component of velocity, Vϕ, in the rotating cavity of a purpose-built rotating-disc rig. For rotational Reynolds numbers up to 1.2 × 106 and pre-swirl ratios up to 2.5, agreement between the computed and measured values of Vϕ is mainly very good, and the results confirm that free-vortex flow occurs throughout most of the rotating cavity. Computed values of the pre-swirl effectiveness (or the nondimensional temperature difference between the pre-swirl and blade-cooling air) agree closely with theoretical values obtained from a thermodynamic analysis of an adiabatic system.
Influence of a Mixing-Jet on Film Cooling
Authors: Martiny M. , Schulz A. , Wittig S. , Dilzer M.
Published: December 2014

An experimental analysis of the slot film cooling performance downstream of a mixing jet has been performed. The mixing jet was blown into the main flow at a position five jet diameters downstream of the slot exit. Flow visualizations of the jet and of the cooling film are presented for blowing rates of 1 and 2 with jet momentum rates of 7 and 10. LDV-measurements in the symmetry plane show the strong perturbation acting on the cooling film downstream of the mixing jet injection. Heat transfer coefficients and adiabatic wall effectiveness were determined using electrical heater foils in combination with infrared-thermography. The results clearly show the decrease in film cooling performance in the region downstream of the mixing jet.
The Effects of Fatigue Cracks on Free Torsional Vibration of Shafts
Authors: Yen H.-Y. , Shen M.-H. Herman
Published: December 2014

The effect of a single-edge fatigue crack on the torsional vibration of shafts is investigated. A generalized variational principle is used to formulate the equation of motion and associated boundary conditions for the free vibration of a nonrotating shaft with a fatigue crack of arbitrary size and location. The fatigue crack is introduced in the form of a single-edge crack. The stress and strain of the cracked shaft are determined by introducing a crack function and a displacement function into the shaft’s compatibility relations. The crack function is designed to have the maximum value at the cracked section and decay exponentially away from the crack along the shaft’s longitudinal direction. A displacement function is constructed to modify the in-plane displacement and its slope near the single-edge crack. The natural response of the free-free shaft is calculated through a Galerkin procedure. The results indicated a clear change in the natural frequencies of the cracked nonrotating shaft.
Prediction of Turbine Blade Vibratory Response due to Upstream Vane Distress
Authors: Panovsky Josef , Carson Scott M.
Published: December 2014

Turbine blades and vanes operate in a hostile environment which leads to deterioration of these components overtime. This paper describes detailed calculations to predict the vibratory response of a high-pressure turbine blade due to the excitation produced by a single distressed upstream vane in a modern turbofan engine. The approach includes detailed computational fluid dynamics (CFD) analysis of the steady flow field produced by the distressed vane, Fourier decomposition of the flow variables to determine the harmonic content, unsteady CFD analysis to determine the resulting vibratory response of the blade, and crack propagation analysis to determine blade life. Predictions of vibratory stress and threshold crack size are summarized as functions of vane distress level. The results, which indicate that this type of vane distress can indeed be a significant excitation source for the blades, are shown to be in good agreement with engine experience. The method provides, for the first time, a quantitative approach to setting limits for acceptable levels of vane distress in the field.
Alternative Starting Methods for Shipboard Gas Turbine Generators
Authors: Masincup William E. , Jackson Scott
Published: December 2014

The U.S. Navy has long been searching for ways to remove the piping, valves and machinery associated with High Pressure air systems on its ships. This paper discusses alternative methods of starting Ship Service Gas Turbine Generators in order to eliminate these engines as users of HP air.
Turbine Engine Installed Performance Optimisation With a Multi-Axis Thrust Vectoring Nozzle
Authors: Ulizar Iñaki
Published: December 2014

Advanced fighter aircraft engine performance improvements associated with the nozzle can represent important thrust gains as well as reductions in fuel consumption, with the consequent mission range extension and superior acceleration capability.

ITP is currently developing a multi-axis Thrust Vectoring Nozzle concept with the necessary exit area independent control capability to allow the engine to operate close enough to its optimum condition over the complete flight envelope and at different power settings. This variation is achieved with an innovative system, instead of using the conventional double actuation system already developed.

In this paper both installed and uninstalled thrust losses have been evaluated for a conventional mono-parametric axi-symmetric nozzle fitted on a low bypass ratio turbofan. The optimum exit to throat area ratio schedules are determined for the complete operating range at Max-Dry and Max-Reheat conditions. Several geometric and Fluid-Dynamic constraints have been considered during the optimisation.

Two axi-symmetric schedules have been identified for the multi-axis Thrust Vectoring Nozzle, resulting in two different exits to throat area ratio independent control ranges. The performance improvements in terms of thrust are presented for both cases, showing that at almost every condition the optimum schedule is achievable.

The computer code developed for nozzle performance has been validated with conventional axi-symmetric Con-Di nozzles showing an excellent agreement between measured and calculated thrust.
A Study of Acoustic Resonance in a Low-Speed Multistage Compressor
Authors: Camp T. R.
Published: December 2014

Measurements are presented of a resonant acoustic phenomenon occurring in a low-speed multi-stage compressor. The results show that this phenomenon shares many characteristics with acoustic resonance as measured in high-speed compressors. These similarities include a rotating pressure field, several acoustics frequencies corresponding to different circumferential modes, step changes in frequency as the flow rate is increased, and acoustic frequencies which are independent of flow coefficient, shaft speed and the axial length of the compression system. The paper includes measurements of the helical structure of the rotating pressure field and of the variation in amplitude of the acoustic signal over a stator exit plane.
Local and Mean Heat Transfer Coefficients Along the Internal Housing Walls of Aero Engine Bearing Chambers
Authors: Glahn A. , Busam S. , Wittig S.
Published: December 2014

A proper matching of the heat transfer to the lubrication oil in bearing chambers and subsequent vent and scavenge pipes is one of the major tasks in the design process of secondary air/lubrication oil systems of modern jet engines. For a calculation of lubrication oil flow rates, which should be kept as small as possible in order to reduce parasitic losses due to larger pumps, filters and coolers, a sufficient knowledge of all heat transfer phenomena involved in bearing chamber flows is required. Beside heat sources such as the bearing friction, the heated sealing air flow and the churning and ventilation of two-phase mixtures, the heat transfer at the housing walls has to be considered. The present paper deals with an experimental investigation of the latter effect based on engine relevant pressure and temperature levels bearing chamber operating conditions. Air/oil flow heat transfer measurements at the internal bearing chamber walls are described utilizing the temperature gradient method. It is a stationary technique based on a two-dimensional finite element calculation procedure.

Influences of sealing air flow rate, lubrication oil flow rate and rotational speed on local heat transfer coefficients are discussed. Mean heat transfer coefficients that have been calculated from local data are presented in terms of operational parameters.
Effects of Ambient Conditions and Fuel Composition on Combustion Stability
Authors: Janus Michael C. , Richards George A. , Yip M. Joseph , Robey Edward H.
Published: December 2014

Recent regulations on NOx emissions are promoting the use of lean premix (LPM) combustion for industrial gas turbines. LPM combustors avoid locally stoichiometric combustion by premixing fuel and air upstream of the reaction region, thereby eliminating the high temperatures that produce thermal NOx. Unfortunately, this style of combustor is prone to combustion oscillation. Significant pressure fluctuations can occur when variations in heat release periodically couple to acoustic modes in the combustion chamber. These oscillations must be controlled because resulting vibration can shorten the life of engine hardware.

Laboratory and engine field testing have shown that instability regimes can vary with environmental conditions. These observations prompted this study of the effects of ambient conditions and fuel composition on combustion stability. Tests are conducted on a subscale combustor burning natural gas, propane, and some hydrogen/hydrocarbon mixtures. A premix, swirl-stabilized fuel nozzle typical of industrial gas turbines is used. Experimental and numerical results describe how stability regions may shift as inlet air temperature, humidity, and fuel composition are altered. Results appear to indicate that shifting instability regimes are primarily caused by changes in reaction rate.
A Detailed Analysis of Film–Cooling Physics: Part I — Streamwise Injection With Cylindrical Holes
Authors: Walters Dibbon K. , Leylek James H.
Published: December 2014

A previously documented systematic computational methodology is implemented and applied to a jet–in–crossflow problem in order to document all of the pertinent flow physics associated with a film–cooling flowfield. Numerical results are compared to experimental data for the case of a row of three–dimensional, inclined jets with length–to–diameter ratios similar to a realistic film–cooling application. A novel vorticity based approach is included in the analysis of the flow physics. Particular attention has been paid to the downstream coolant structures and to the source and influence of counter–rotating vortices in the crossflow region. It is shown that the vorticity in the boundary layers within the film hole is primarily responsible for this secondary motion. Important aspects of the study include: (1) a systematic treatment of the key numerical issues, including accurate computational modeling of the physical problem, exact geometry and high quality grid generation techniques, higher–order numerical discretization, and accurate evaluation of turbulence model performance; (2) vorticity–based analysis and documentation of the physical mechanisms of jet–crossflow interaction and their influence on film–cooling performance; (3) a comparison of computational results to experimental data; and (4) comparison of results using a two–layer model near–wall treatment versus generalized wall functions. Solution of the steady, time–averaged Navier–Stokes equations were obtained for all cases using an unstructured/adaptive grid, fully explicit, time–marching code with multi–grid, local time stepping, and residual smoothing acceleration techniques. For the case using the two–layer model, the solution was obtained with an implicit, pressure–correction solver with multi–grid. The three–dimensional test case was examined for two different film–hole length–to–diameter ratios of 1.75 and 3.5, and three different blowing ratios, from 0.5 to 2.0. All of the simulations had a density ratio of 2.0, and an injection angle of 35°. An improved understanding of the flow physics has provided insight into future advances to film–cooling configuration design. In addition, the advantages and disadvantages of the two–layer turbulence model are highlighted for this class of problems.
Black Liquor-Gasifier/Gas Turbine Cogeneration
Authors: Consonni Stefano , Larson Eric D. , Berglin Niklas
Published: December 2014

The kraft process dominates pulp and paper production worldwide. Black liquor, a mixture of lignin and inorganic chemicals, is generated in this process as fiber is extracted from wood. At most kraft mills today, black liquor is burned in Tomlinson boilers to produce steam for on-site heat and power and to recover the inorganic chemicals for reuse in the process. Globally, the black liquor generation rate is about 85,000 MWfuel (or 0.5 million tonnes of dry solids per day), with nearly 50% of this in North America. The majority of presently-installed Tomlinson boilers will reach the end of their useful lives during the next 15 to 20 years. As a replacement for Tomlinson-based cogeneration, black liquor-gasifier/gas turbine cogeneration promises higher electrical efficiency, with prospective environmental, safety, and capital cost benefits for kraft mills. Several companies are pursuing commercialization of black liquor gasification for gas turbine applications. This paper presents results of detailed performance modeling of gasifier/gas turbine cogeneration systems using different black liquor gasifiers modeled on proposed commercial designs.
The Turbulence That Matters
Authors: Mayle R. E. , Dullenkopf K. , Schulz A.
Published: December 2014

A unified expression for the spectrum of turbulence is developed by asymptotically matching known expressions for small and large wave numbers, and a formula for the one-dimensional spectral function which depends on the turbulence Reynolds number Reλ is provided. In addition, formulas relating all the length scales of turbulence are provided. These relations also depend on Reynolds number.

The effects of free-stream turbulence on laminar heat transfer and pre-transitional flow in gas turbines are re-examined in light of these new expressions using our recent thoughts on an ‘effective’ frequency of turbulence and an ‘effective’ turbulence level. The results of this are that the frequency most effective for laminar heat transfer is about 1.3U/Le, where U is the free-stream velocity and Le is the length scale of the eddies containing the most turbulent energy, and the most effective frequency for producing pre-transitional boundary layer fluctuations is about 0.3U/η where η is Kolmogorov’s length scale. In addition, the role of turbulence Reynolds number on stagnation heat transfer and transition is discussed, and new expressions to account for its effect are provided.
Active Stabilization of Axial Compressors With Circumferential Inlet Distortion
Authors: van Schalkwyk C. M. , Paduano J. D. , Greitzer E. M. , Epstein A. H.
Published: December 2014

This paper describes the first experimental validation of transfer function modeling and active stabilization for axial compressors with circumferential inlet distortion. The inlet distortion experiments were carried out in a three stage low-speed compressor. Theory-experiment comparisons of steady performance, unsteady stall precursor, and forced response (transfer function) data were all used to assess a control-theoretic version of the Hynes-Greitzer distorted flow model. The tests showed good agreement between theory and data and demonstrated that a priori predictions, based on geometry and steady-state performance data, can be used to design control laws which stabilize rotating stall with inlet distortion.

Based on these results, active feedback control has been used to stabilize the inlet distortion induced instability associated with rotating stall onset. The stabilization allowed stall free operation to be extended below the natural (distorted flow) stall point by up to 3.7% for a 0.8 dynamic head distortion. For a 1.9 dynamic head distortion, 40% of the mass flow range lost due to inlet distortion was regained through active control. The paper elucidates the difficulties associated with active control with distortion, and introduces a new control law that addresses many of these challenges.
Experiments in Active Control of Stall on an Aeroengine Gas Turbine
Authors: Freeman Christopher , Wilson Alexander G. , Day Ivor J. , Swinbanks Malcolm A.
Published: December 2014

This paper describes work carried out between 1989 and 1994 to investigate the application of ‘Active Stall Control’ to a Rolls-Royce Viper turbojet. The results demonstrate that stall control is feasible and can increase the stable operating range by up to 25% of pressure rise. Stall disturbances were detected using rings of high response pressure transducers positioned at different axial planes along the compressor, and processed using a PC-based data acquisition and control system. Actuation was provided by six hydraulically operated sleeve valves positioned to recirculate air over all or part of the compressor.

Stall was artificially induced using combinations of inbleed into the combustor outer casing, fuel spiking, hot gas ingestion and inlet pressure spoiling, thus replicating many of the transient conditions commonly observed to make a compressor prone to stall. Results are compared from a number of stall control strategies including those demonstrated at low speed by Paduano et al [1993] and Day [1993]. Best results were obtained with detection of non-axisymmetric disturbances coupled with axisymmetric control action. A control system of this type is demonstrated to be capable of extending the stable engine operating range at all speeds and with each method of inducing stall.
Experimental Investigation and Mathematical Modelling of Clearance Brush Seals
Authors: Turner Mike T. , Chew John W. , Long Chris A.
Published: December 2014

In this paper an experimental programme and a CFD based mathematical model using a brush seal at two bristle to rotor clearances (0,27 mm. and 0,75 mm.), are presented. The experimental programme examined the radial pressure distributions along the backing ring, the axial pressure distribution along the rotor, and the mass flow through the seal, through a range of pressure ratios while exhausting to atmosphere.

The results from this experimental programme have been used to further calibrate a CFD based model. This model treats the bristle pack as an axisymmetric, anisotropic porous region, and is calibrated by the definition of non-linear resistance coefficients in three orthogonal directions. The CFD analysis calculates the aerodynamic forces on the bristles, which are subsequently used in a separate program to estimate the bristle movements, stresses and bristle and rotor loads.

The analysis shows that a brush seal with a build clearance produces a very different flow field within the bristle pack to one with an interference, and the need to understand the bulk movements of the bristles. These are shown to be affected by the level of friction between the bristles and the backing ring, which has an important effect on the bristles wear and seal leakage characteristics.
Biomass-Fired Atmospheric Gas Turbine Plant-I
Authors: Fesharaki M. , Halozan H. , Jericha H. , Kulhanek G.
Published: December 2014

Considering the expected climate change, biomass is one of the promising energy sources for the future. However, burning and only producing low temperature heat means wasting exergy. To utilise this renewable fuel, highly efficient cogeneration plants are requierd. Existing, small and medium sized power generation systems using gas turbines, have, either complicated flow schemes, or problems with fuel charging of pressurised combustion chambers, which are yet to be solved.

Here is a solution is presented requiring no preparation of the biomass fuel. In several publications (Jericha 1991, Fesharaki 1995, Fesharaki 1996) the inverted gas turbine cycle has been presented. This project deals with the investigation and the development of an atmospheric biomass combustion chamber, combined with an inverted gas turbine cycle. The system consists of a combustor with wood grate firing, working at atmospheric pressure. The exhaust gas from the combustor, with a temperature of 1050 °C, is cooled by water or steam injection, to a temperature of 730 °C. The exhaust gas is purified in a cyclone and expanded in a gas turbine to a pressure of 0.3 to 0.4 bar. The exhaust gas of the turbine can be used for operating a single-pressure steam generator, and for district heating. The exhaust gas is purified again by condensing the moisture in the exhaust gas, which stems from the biomass and the steam, or water injection after the combustion chamber. The purified gas is recompressed to atmospheric pressure, which is used for combustion-air preheating. With such a system a high electrical efficiency can be achieved, dependent upon the turbo machines, and the use of an additional bottoming steam cycle.

Considering the Austrian situation a feasibility study is being carried out. Special attention has been paid to:

Turbine design,

Exhaust gas purification,

and the cycle control. The feasibility study shows, that this concept is practicable, and that several biomass existing heating systems in Austria could be converted for production of electricity.
Biomass Gasification — Commercialization and Development: The Combined Heat and Power (CHP) Option
Authors: Bain Richard L. , Craig Kevin C. , Overend Ralph P.
Published: December 2014

World-wide, biomass is the most used nonfossil fuel and is expanding from its traditional thermal applications to more usage for liquid fuels and electricity. More than 9 gigawatts of biomass electrical generation capacity have been installed in the United States, primarily by forest products industries, since the Public Utilities Regulatory Policy Act (PURPA) was passed. Combined heat and power (CHP) technologies promise to improve power-to-heat efficiencies to strengthen the economic viability of these electrical generating methods. These technologies, which are now being tested and demonstrated, employ industrial and aeroderivative gas turbines; use a variety of feedstocks including agricultural wastes, residues, and dedicated energy crops; and range in size from 8 MW to 75 MW. Specific demonstrations with the U.S. Department of Energy Biomass Power Program and partners in Vermont and Hawaii are discussed.
Design and Evaluation of a Single-Can Full Scale Catalytic Combustion System for Ultra-Low Emissions Industrial Gas Turbines
Authors: Dutta P. , Cowell L. H. , Yee D. K. , Dalla Betta R. A.
Published: December 2014

The goal of the Advanced Turbine Systems (ATS) program is the design and development of high thermal efficiency gas turbines with pollutant emissions at single digit levels, through the development of advanced recuperated gas turbines. Following successful subscale catalytic reactor testing, a full scale catalytic combustion system was designed to be representative of a single can in a multi-can gas turbine combustor configuration. The full scale catalytic combustion system is modular in design and includes a fuel/air premixer upstream of the catalytic reactor and a post catalyst homogeneous combustion zone downstream of the catalyst bed to complete the homogeneous gas-phase reactions. System start-up is accomplished using a lean-premixed (LP) low emissions fuel injector. The system transitions to catalyst operation using a variable geometry valve that diverts air flow into the catalyst at loads greater than 50% of full load. The variable geometry valve is used to operate the catalyst within the narrow operating window due to limited fuel/air turndown allowed by the catalyst. A catalyst design with preferential catalyst coating on a corrugated metal substrate to limit catalyst substrate temperatures was selected for the system. Mean fuel concentration measurements at the inlet to the catalyst bed using an instrumented catalyst module showed the fuel/air premixing to be within catalyst specifications. Preliminary combustion tests on the system were completed. The catalytic combustion system was tested over the 50-to-100% load range. Using variable geometry control, emissions goals (< 5 ppmv NOx, < 10 ppmv CO and UHC corrected to 15% O2) were achieved for catalyst operation between 50-and-100% load conditions. The system was started and operated under part-load conditions using the LP injector. Efforts are under way to accomplish successful transition from LP mode of operation to catalytic mode of operation using the variable geometry system.
Investigation of Various Parametric Influences on Leading Edge Film Cooling
Authors: Cruse Michael W. , Yuki Ushio M. , Bogard David G.
Published: December 2014

Film cooling adiabatic effectiveness of a simulated turbine airfoil leading edge was studied experimentally. The leading edge had two rows of holes, one at nominally the stagnation line position and the second a few hole diameters downstream. Hole positions at the leading edge, and inclination of the holes with respect to the surface, were different than typically used in previous studies, but were representative of current design practice. Various leading edge film cooling parameters were investigated including stagnation line position, free-stream turbulence level, leading edge geometry, and coolant to mainstream density ratio. Large density ratios were obtained by cooling the injected coolant to very low temperatures. Large scale, high level free-stream turbulence (Tu = 20%) was generated using a specially developed cross-jet turbulence generator. An infrared camera system was used to obtain well resolved surface temperature distributions around the coolant holes and across the leading edge. Results from the experiments showed considerably higher optimum blowing ratios than found in previous studies. The stagnation line position was found to be important in influencing the direction of coolant flow from the first row of holes. High free-stream turbulence levels were found to greatly decrease adiabatic effectiveness at low blowing ratios (M = 1.0), but had little effect at high blowing ratios (M = 2.0 and 2.5). Adiabatic effectiveness distributions were very similar for circular and elliptical leading edges. Experiments conducted at coolant to mainstream density ratios of 1.1 and 1.8 showed distinctly different flow characteristics in the stagnation line region for the different density ratio coolants.
Vibration Analysis of Rotating Cambered Helicoidal Turbomachine Blades
Authors: Rao J. S. , Ramakrishnan C. V. , Gupta K. , Rao K. K.
Published: December 2014

A procedure for the vibration analysis of rotating cambered helicoidal blades using curved shell finite element based on Mindlin theory is given. The strain displacement relations of Gol den’veizer are used in the development of a thick doubly curved helicoidal shell element including initial in-plane stress effect. The method is applied to rotating cambered pretwisted blades.