bluuebunny/crossref_metadata_2025 huggingface dataset:
Review on Grinding Tool Wear With Regard to Sustainability
Authors: Linke Barbara S.
Published: December 2014

Manufacturing processes have to become more sustainable. For grinding processes, this means that tool wear and performance need to be critically evaluated in their economic, environmental, and social impact. Tool wear affects several stakeholders. Different wear mechanisms on the grit and bond level lead to a change in tool profile and sharpness. For the user, wear changes tool costs, process stability, and maybe worker safety. Tool manufacturers need tool wear to sell replacements, whereas tool users might not like the higher waste and costs from tool wear but need tool self-sharpening.
Hybrid Deposition Manufacturing: Design Strategies for Multimaterial Mechanisms Via Three-Dimensional Printing and Material Deposition
Authors: Ma Raymond R. , Belter Joseph T. , Dollar Aaron M.
Published: December 2014

This paper describes a novel fabrication technique called hybrid deposition manufacturing (HDM), which combines additive manufacturing (AM) processes such as fused deposition manufacturing (FDM) with material deposition and embedded components to produce multimaterial parts and systems for robotics, mechatronics, and articulated mechanism applications. AM techniques are used to print both permanent components and sacrificial molds for deposited resins and inserted parts. Design strategies and practical techniques for developing these structures and molds are described, taking into account considerations such as printer resolution, build direction, and printed material strength. The strengths of interfaces between printed and deposited materials commonly used in the authors' implementation of the process are measured to characterize the robustness of the resulting parts. The process is compared to previously documented layered manufacturing methodologies, and the authors present examples of systems produced with the process, including robot fingers, a multimaterial airless tire, and an articulated camera probe. This effort works toward simplifying fabrication and assembly complexity over comparable techniques, leveraging the benefits of AM, and expanding the range of design options for robotic mechanisms.
Steady-State Response of a Piping System Under Harmonic Excitations Considering Pipe-Support Friction With Variable Normal Loads
Authors: Argüelles José , Casanova Euro
Published: December 2014

Dynamic loads in piping systems are mainly caused by transient phenomena generated by operating conditions or installed equipment. In most cases, these dynamic loads may be modeled as harmonic excitations, e.g., pulsating flow. On the other hand, when designing piping systems under dynamic loads, it is a common practice to neglect strong nonlinearities such as shocks and friction between pipe and support surfaces, mainly because of the excessive cost in terms of computational time and the complexity associated with the integration of the nonlinear equations of motion. However, disregarding these nonlinearities for some systems may result in overestimated dynamic amplitudes leading to incorrect analysis and designs. This paper presents a numerical approach to calculate the steady-state response amplitudes of a piping system subjected to harmonic excitations and considering dry friction between the pipe and the support surfaces, without performing a numerical integration. The proposed approach permits the analysis of three dimensional piping systems, where the normal forces may vary in time and is based in the hybrid frequency–time domain method (HFT). Results of the proposed approach are compared and discussed with those of a full integration scheme, confirming that HFT is a valid and computationally feasible option.
Experimental Evaluation of a Metal Mesh Bearing Damper
Authors: Zarzour Mark , Vance John
Published: December 2014

Metal mesh is a commercially available material used in many applications including seals, heat shields, filters, gaskets, aircraft engine mounts, and vibration absorbers. This material has been tested by the authors as a bearing damper in a rotordynamic test rig. The test facility was originally used to support the design of a turboprop engine, developing squirrel cages and squeeze film dampers for both the gas generator and power turbine rotors. To design the metal mesh damper, static stiffness and dynamic rap test measurements were first made on metal mesh samples in a specially designed nonrotating test fixture. These property tests were performed on samples of various densities and press fits. One sample was also tested in an Instron machine as an ancillary and redundant way to determine the stiffness. Using the stiffness test results and equations derived by a previous investigator, a spreadsheet program was written and used to size metal mesh donuts that have the radial stiffness value required to replace the squirrel cage in the power turbine. The squirrel cage and squeeze film bearing damper developed for the power turbine rotor was then replaced by a metal mesh donut sized by the computer code.

Coast down tests were conducted through the first critical speed of the power turbine. The results of the metal mesh tests are compared with those obtained from previous testing with the squeeze film damper and Show that the metal mesh damper has the same damping as the squeeze film at room temperature but does not lose its damping at elevated temperatures up to 103 °C. Experiments were run under several different conditions, including balanced rotor, unbalanced rotor, heated metal mesh, and wet (with oil) metal mesh. The creep, or sag, of the metal mesh supporting the rotor weight was also measured over a period of several weeks and found to be very small. Based on these tests, metal mesh dampers appear to be a viable and attractive substitute for squeeze film dampers in gas turbine engines. The advantages shown by these tests include less variation of damping with temperature, ability to handle large rotor unbalance, and the ability (if required) to operate effectively in an oil free environment. Additional testing is required to determine the endurance properties, the effect of high impact or maneuver loads, and the ability to sustain blade loss loads (which squeeze films cannot handle).
Prediction of Turbulent Spot Growth Rates
Authors: Johnson Mark W.
Published: December 2014

A computational technique is presented for determining the fully 3-d viscid unsteady perturbation to a non-developing steady boundary layer flow. Streamlines through the perturbed region depict a strong hairpin vortex which bounds the calmed region. The nose of the hairpin projects into the rear of the turbulent spot. The streamlines show that the hairpin is responsible for mixing low momentum fluid forward of the hairpin with high momentum fluid from the rear and ejecting this fluid forward into the spot. The movement of the extremities of the spot and the calmed region are used to determine the trailing and leading edge celerities, the spot spreading angle and the propagation rate for Ree = 50 to 1000 and λ = −9 to 12. The spot growth is significantly suppressed at Ree below 200. Strong favourable pressure gradients also lead to a modest suppression in growth rate, but adverse pressure gradients increase growth rates substantially. New correlations for the celerities, spot spreading half angle and propagation parameter are formulated. These improve on previous correlations by including the effect of Reynolds number as well as pressure gradient.
Influence of Coolant Feed Direction and Hole Length on Film Cooling Jet Velocity Profiles
Authors: Brundage A. L. , Plesniak M. W. , Ramadhyani S.
Published: December 2014

Measurements were taken of the exit velocity and turbulence intensity distributions for film cooling holes fed from a narrow plenum above the middle jet in a row of five jets using hot-wire anemometry. Parameters varied in the experiments included the length-to-diameter ratio of the holes, the coolant-to-mainstream blowing ratio, the angle of inclination of the holes, and the plenum flow direction, which was either in the same direction as, or opposite to, the mainstream. Flow visualization within the film cooling holes and in the plenum revealed large secondary flow structures that affected the jet exit velocity distributions. The exit velocity profiles for short holes had “peaky” signatures associated with jetting in the upstream portion of the 35° holes and in the downstream portion of the 90° holes. For the longer holes, the exit velocity profiles were more uniform. Crossflow boundary layer fluid was found to enter into the film cooling holes in some short hole configurations. The coolant feed direction affects the details of the flow separation at the hole entrance and within the hole, and consequently influences the jet exit velocity profile. These effects are most pronounced for higher blowing ratios.
Film Cooling Effectiveness and Heat/Mass Transfer Coefficient Measurement Around a Conical-Shaped Hole With a Compound Angle Injection
Authors: Cho H. H. , Rhee D. H. , Kim B. G.
Published: December 2014

The present study investigates local film cooling effectiveness values and heat/mass transfer coefficients around a conical-shaped film cooling hole with compound angle orientations. Three types of film cooling hole geometry are compared in this study; one is cylindrical hole geometry with constant cross section and the others are shaped hole geometries with conically-enlarged hole exits. The shaped holes have cylindrical passage sections at the hole inlet region to obtain a certain pressure drop through the holes. One shaped hole expands 4° in all directions from the middle of hole to the exit. The other shaped hole has the tilted center-line by 4° between the conical and metering holes and is enlarged by 8° to downstream side. The hole area ratios of the exit to the inlet are 2.55 and 2.48, respectively. The compound-angled film cooling jet is ejected through the single holes, which are inclined at 30° to the surface based on the metering hole and are rotatable in lateral direction from 0° to 90°. The blowing rates are changed from 0.5 to 2.0. The naphthalene sublimation technique is used to determine local heat/mass transfer coefficients and local adiabatic/impermeable wall film cooling effectiveness around the injection hole. The results indicate that the injected jet protects the surface effectively with low blowing rates and spreads more widely with the compound angle injections than the axial injection. For the shaped hole enlarged by 4° in all directions, the penetration of jet is reduced and higher cooling performance is obtained even at relatively high blowing rates because the increased hole exit area reduces hole exit velocity. Furthermore, the film cooling effectiveness is fairly uniform near the hole due to the wide lateral spreading of coolant with the expanded cooling hole exit.
High Resolution Measurements of Local Heat Transfer Coefficients by Discrete Hole Film Cooling
Authors: Baldauf S. , Schulz A. , Wittig S.
Published: December 2014

Local heat transfer coefficients on a flat plate surface downstream a row of cylindrical ejection holes were investigated. The parameters blowing angle, hole pitch, blowing rate, and density ratio were varied in a wide range emphasizing on engine relevant conditions. A high resolution IR-thermography technique was used for measuring surface temperature fields. Local heat transfer coefficients were obtained by a Finite Element analysis. IR-determined surface temperatures and backside temperatures of the cooled testplate measured with thermocouples were applied as boundary conditions in a heat flux computation. The superposition approach was employed to obtain the heat transfer coefficient hr referring to adiabatic wall temperatures in the presence of film cooling. Therefore, heat transfer results with different wall temperature conditions and adiabatic film cooling effectiveness results of identical flow situations (constant density ratios) were combined. Characteristic surface patterns of the locally resolved heat transfer coefficients hf depending on the various parameters were recognized and quantified. The detailed results are used to discuss the specific local heat transfer behavior in the presence of film cooling. They also provide a base of surface data essential for the validation of the heat transfer capabilities of CFD-codes in discrete hole film cooling.
Hydromechanical Control for a Variable Delivery, Positive Displacement Fuel Pump
Authors: Gaudet Timothy J.
Published: December 2014

Fuel pumps for gas turbine engines have traditionally been fixed delivery, positive displacement type pumps. The critical pump sizing criteria are typically the fuel flow and pressure needed for engine lightoff at cranking speeds (approximately 10% of full speed). However, these pump sizing criteria result in excess fuel delivery at higher engine speeds and altitudes. This excess fuel is typically bypassed back to the pump inlet, resulting in significant fuel heating. In contrast, a variable delivery, positive displacement fuel pump has the ability to vary delivery flow, to thereby match engine demands for a wide range of engine speeds and altitudes. This eliminates the excessive fuel delivery and resulting heat generation inherent in fixed delivery pumps. An approach to controlling fuel flow delivered to the engine is presented in which the differential pressure across a fuel metering valve is regulated by simultaneously-varying the pump displacement and a small amount of bypass flow. This approach results in improved transient response and steady state accuracy at all operating conditions, as compared with alternate methods.
A Perspective on Future Directions in Intelligent Health Control of Gasturbines and Auxiliaries
Authors: Eftekhari Shahroudi K.
Published: December 2014

Despite their seemingly impressive claims, current products for Condition Monitoring, Diagnostic and Decision Support Systems (CMD&D) do not provide the reliable bottom line information that end users and operators need. Instead they confuse the issue with gigabytes of logged trends, complex cause-effect matrices, fault signatures etc. The term “Intelligent Health Control” here refers to the next generation of such systems which provide usable information on:

• the existence and severity of faults;

• how their severity will progress with utilization;

• how this progress can be influenced or controlled.

In this paper the fundamental shortcomings of current approaches are discussed prior to introducing the basics of Intelligent Health Control in terms of fault models and how they can be used to close the diagnostic, prognostic and intelligent control triangle.

The industry will unavoidably shift towards an “information centric” view from the currently predominant “data centric” view. Gigabytes of performance trends will no longer be relevant. Instead, reliable bottom line information will be required on how to minimize or control the costs associated with machinery health degradation or faults. In order to keep the discussion real, the current state of the art of enabling technologies are discussed, including:

• Open Information Buses;

• Adding real time data server functionality to the control system;

• Computational Steering, Human-in-the-Loop Optimization (or semi-automatic problem solving);

• Fault Models;

• Faster than real time simulation;

• Neural Nets.
Thermodynamic and Techno-Economic Analyses of a Combined Cycle Power Plant With a Simple Cycle Gas Turbine, the Bottoming Air Turbine Cycle and the Reverse Brayton Cycle
Authors: Shnaid Isaac
Published: December 2014

The modem combined cycle power plants achieved thermal efficiency of 50–55% by applying bottoming multistage Rankine steam cycle. At the same time, the Brayton cycle is an attractive option for a bottoming cycle engine. In the author’s US Patent No. 5,442,904 is described a combined cycle system with a simple cycle gas turbine, the bottoming air turbine Brayton cycle, and the reverse Brayton cycle.

In this system, air turbine Brayton cycle produces mechanic power using exergy of gas turbine exhaust gases, while the reverse Brayton cycle refrigerates gas turbine inlet air. Using this system, supercharging of gas turbine compressor becomes possible.

In the paper, thermodynamic optimization of the system is done, and the system techno-economic characteristics are evaluated.
The Three-Dimensional Aerodynamic Design and Test of a Three-Stage Transonic Compressor
Authors: Li Y. S. , Wells R. G.
Published: December 2014

This paper presents the aerodynamic design and initial test results from a three-stage transonic compressor developed by ALSTOM Gas Turbines Ltd. The Advanced Transonic Compressor (ATC) was designed using a design system based on three-dimensional (3D) Navier-Stokes CFD codes in contrast to the more conventional design approach centred around the use of throughflow and blade to blade solvers. The customised 3D multiple-circular-arc (MCA) and controlled-diffusion (CD) airfoils have replaced the double-circular-arc (DCA) profiles used previously. The use of both single row and multistage 3D CFD codes has enabled the potential performance improvements from the application of new blade designs to be predicted and comparisons between conventional and new blades to be made. Rig test results have confirmed that the target design mass flow rate and pressure ratio have been successfully achieved in the first build with a design point efficiency higher than that possible from the conventional design. Tests have demonstrated that the compressor has the required surge margin at design and off design speeds to ensure satisfactory operation when transferred to the multistage compressor environment.
The Virtual Energy Laboratory (VEL): A Didactic Graphical Simulator for Thermal System Design
Authors: Perez-Blanco Horacio , Hinojosa Luis
Published: December 2014

A teaching tool for thermal system design has been developed for use in standard personal computers. This tool, called the Virtual Energy Lab (VEL), is designed to facilitate the integration of energy conversion and transfer devices into systems that meet specified heating, cooling and power loads. The VEL has a modular configuration, allowing the designer to choose from a number of components to meet given design objectives. The output of some components can be used as inputs to others, and the user can exercise creativity in combining them. As the thermal system is assembled on the graphical interface, the relevant equations are selected automatically and solved as required by the particular design. The models for each VEL component are either based on basic performance equations for generic equipment or on performance charts of actual devices. The thermodynamic irreversibility is the figure of merit used for assessing each design.
The Combination of SOFC and Microturbine for Civil and Industrial Cogeneration
Authors: Campanari Stefano , Macchi Ennio
Published: December 2014

Recent studies have shown the possibility of obtaining extremely high electric efficiencies in distributed electric power generation with small capacity advanced plants based upon the combined technologies of solid oxide fuel cells and microturbines. This paper investigates the potential energy savings achievable by the application of this novel technology to cogeneration.

Due to the high electrical efficiency of these systems (approaching 65% LHV), their heat/electricity ratio is unusually low. The addition of a heat pump can dramatically increase the heat/electricity ratio as well as add flexibility to the system. The application of these systems to distributed electricity generation connected to residential heating is discussed. Detailed results are presented, in terms of annual energy balances; they indicate high primary energy savings and reduction in emissions of carbon dioxide.
The Dry Low Emissions Industrial Avon
Authors: Moran John , Corbett Nicholas C. , Todman Michael T.
Published: December 2014

The Rolls-Royce Avon aeroderivative gas generator has amassed over 45 million hours of operation in industrial applications since its introduction in 1964. However, its reputation for reliability and long life has kept it in the forefront in many markets. With the increasing world-wide requirements for lower emissions, the decision was taken to incorporate a Dry Low Emissions (DLE) combustion system to provide operators with increased options. It was also decided that the retrofit market would be fully addressed, thus driving the need to minimise changes to the basic engine. How this project has been approached, with a low risk solution both to the mechanical and operational integrity, is the basis for this paper.
Effects of Periodic Wake Passing Upon Aerodynamic Loss of a Turbine Cascade: Part II — Time-Resolved Flow Field and Wake Decay Process Through the Cascade
Authors: Funazaki Ken-ichi , Tetsuka Nobuaki , Tanuma Tadashi
Published: December 2014

This paper, Part II of the study on wake-passing effect upon the aerodynamic performance of the turbine cascade, demonstrates the detailed measurements of the time-varying flow field downstream of the turbine cascade as well as of the moving bars. The experiment employs a single hot-wire probe to measure pitchwise distributions of the ensemble-averaged velocity at the blade midspan. The resultant data consequently provide clear images of the incident bar wakes that are bowed and directed to the suction side of the blade wake. A custom-made total pressure probe, instrumented with a miniature fast-response pressure transducer, are also adopted to understand time-resolved feature of the wake-affected stagnation pressure fields downstream of the cascade. Furthermore, a decay process of the bar wake through the test cascade is examined in detail, which serves for the discussion related to wake recovery and its impact on the stage loss.
Effects of Stator Pressure Field on Upstream Rotor Performance
Authors: Graf M. B. , Greitzer E. M. , Marble F. E. , Sharma O. P.
Published: December 2014

Effects of stator pressure field on upstream rotor performance in a high pressure compressor stage have been assessed using three-dimensional steady and time-accurate Reynolds-averaged Navier-Stokes computations. Emphasis was placed on: (1) determining the dominant features of the flow arising from interaction of the rotor with the stator pressure field, and (2) quantifying the overall effects on time averaged loss, blockage, and pressure rise. The time averaged results showed a 20 to 40% increase in overall rotor loss and a 10 to 50% decrease in tip clearance loss compared to an isolated rotor. The differences were dependent on the operating point and increased as the stage pressure rise, and amplitude of the unsteady back pressure variations, was increased.

Motions of the tip leakage vortex on the order of the blade pitch were observed at the rotor exit in all the unsteady flow simulations; these were associated with enhanced mixing in the region. The period of the motion scaled with rotor flow-through time rather than stator passing.

Three steady flow approximations for the rotor-stator interaction were assessed with reference to the unsteady computations: an axisymmetric representation of the stator pressure field, an inter-blade row averaging plane method, and a technique incorporating deterministic stresses and bodyforces associated with stator flow field. Differences between steady and unsteady predictions of overall rotor loss, tip region loss, and endwall blockage ranged from 5 to 50% of the time average, but the steady flow models gave overall rotor pressure rise and flow capacity within 5% of the time averaged values.
Combustion Instabilities in Industrial Gas Turbines — Measurements on Operating Plant and Thermoacoustic Modelling
Authors: Hobson David E. , Fackrell John E. , Hewitt G.
Published: December 2014

Measurements of vibration and combustion chamber dynamic pressures have been taken on a number of 150MW industrial gas turbines operating on pre-mixed natural gas, both during long periods of base-load operation and during short duration load-swings. The data has been analysed in terms of the frequency and bandwidth of the principle peak in the vibration and pressure spectra as a function of load and other operating parameters. It is observed that bandwidth, which is a measure of the damping of the resonant mode of the combustion chamber’s acoustic resonance, decreases towards zero as the machines approach their combustion stability limits.

A theoretical model of the thermoacoustic behaviour of the combustion system has been developed to see to what extent the observed behaviour on the operational machines can be explained in terms of an acoustic model of the ductwork and a flame characterised simply by a time-delay. This time delay is obtained from the frequency response function of the flame in response to unsteady perturbations in inlet velocity and is calculated using computational fluid dynamics.

The model has also been used to illustrate the importance of fuel supply system design in controlling combustion stability. It is shown that stability can be a strong function of the acoustic impedance of the fuel supply and that this can lead to enhanced or reduced stability depending on the flame characteristics.
Investigation of Ignition Probability in a Gas Turbine Combustor Using Laser Ignition
Authors: Hicks R. A. , Wilson C. W. , Sheppard C. G. W. , Woolley R. , Wyatt J.
Published: December 2014

For an aircraft gas turbine engine, the ignition performance is usually expressed in terms of the range of flight conditions over which stable combustion can be established. At present, the size of an aircraft’s gas turbine combustor is governed predominately by its altitude relight performance and is principally derived from existing empirical design rules. These indicate the volume required to give adequate primary zone airodynamic loading to achieve the desired relight performance. A possible means of improving altitude relight performance is to relocate the point of ignition away from the combustor wall to a more favourable location within the combustion chamber. One way of achieving this is through the use of laser ignition. Reported in the paper is an initial programme of work in which the possibility of using laser ignition has been investigated in a gas turbine research combustor operating at several inlet conditions. Comparative results show that, when sited at the same location, laser ignition gave no noticeable improvement in ignition performance when compared to a standard surface discharge igniter (SDI). However, by using laser ignition to locate the ignition site away from the combustor wall, the range of combustor mass flow and AFR at which ≥75% ignition probability could be achieved was increased by approximately 33%.

In conjunction with the experimental study, an ignition probability model, based on the local magnitude of a Karlovitz stretch factor, has been developed to identify suitable regions within the combustor in which to apply laser ignition. The Karlovitz parameter gives an indication as to whether or not a flame kernel will propagate successfully and has been used in conjunction with flow field and scalar distributions generated by Computational Fluid Dynamics (CFD) to yield a 2D map of ignition probability. However, the sensitivity shown by the model to the accuracy of the CFD predictions meant that reliable estimates of optimum ignition sites could only be obtained using experimental fuel and turbulence intensity distributions.
Robust Optimal Design of a Gas Turbine Cogeneration Plant Based on Minimax Regret Criterion
Authors: Yokoyama Ryohei , Ito Koichi
Published: December 2014

A robust optimal design method based on the minimax regret criterion is proposed for unit sizing of energy supply plants so that they are robust economically against the uncertainty in energy demands. Equipment capacities and utility contract demands as well as energy flow rates are determined to minimize the maximum regret in the annual total cost and to satisfy all the possible energy demands. This optimization problem is formulated as a kind of multilevel linear programming one, and its solution is derived by repeatedly evaluating lower and upper bounds for the optimal value of the maximum regret in the annual total cost. Through a case study on a gas turbine cogeneration plant for district energy supply, it is shown that determining equipment capacities appropriately is more important under uncertain energy demands rather than certain ones. It is also shown that the ratio of power generating capacity to total power supply capacity decreases with an increase of the uncertainty in energy demands.
Energy Comparison Among Load Following, Hydro Storage and Two-Shift Operation Strategies for Intermediate Fossil Fuel Power Units
Authors: Bianchi M. , Gadda E. , Peretto A.
Published: December 2014

During the night hours, to match the lowest load demand by a power generation system, many different strategies can be employed: unit load following, unit shutdown and hydro storage. Obviously, the utilized strategy influences the power production (gas turbines, hydro turbines, etc.) during the peak load demand.

In this paper, the energy comparison among the above different strategies is carried out as a function of the load demand, the heat rate of the peaking units, the hydro storage total efficiency and the hydro stored energy.

In particular, two sets of intermediate load fossil fuel power units (conventional and advanced) are considered.

For the sets considered and relatively to the variable costs, the two-shift operation proved to be the most convenient strategy.
Measurement of Transfer Matrices and Source Terms of Premixed Flames
Authors: Paschereit Christian Oliver , Schuermans Bruno , Polifke Wolfgang , Mattson Oscar
Published: December 2014

An experimental method to determine the thermoacoustic properties of a gas turbine combustor using a lean-premixed low emission swirl stabilized burner is presented. To model thermoacoustic oscillations, a combustion system can be described as a network of acoustic elements, representing for example fuel and air supply, burner and flame, combustor, cooling channels, suitable terminations, etc. For most of these elements, simple analytical models provide an adequate description of their thermoacoustic properties. However, the complex response of burner and flame (involving a three-dimensional flow field, recirculation zones, flow instabilities and heat release) to acoustic perturbations has — at least in a first step — to be determined by experiment. In our approach, we describe the burner as an active acoustical two-port, where the state variables pressure and velocity at the inlet and the outlet of the two port are coupled via a four element transfer matrix. This approach is similar to the “black box” theory in communication engineering. To determine all four transfer matrix coefficients, two test states, which are independent in the state vectors, have to be created. This is achieved by using acoustic excitation by loudspeakers upstream and downstream of the burner, respectively. In addition, the burner might act as an acoustic source, emitting acoustic waves due to an unsteady combustion process. The source characteristics were determined by using a third test state, which again must be independent from the two other state vectors. In application to a full size gas turbine burner, the method’s accuracy was tested in a first step without combustion and the results were compared to an analytical model for the burner’s acoustic properties. Then the method was used to determine the burner transfer matrix with combustion. An experimental swirl stabilized premixed gas-turbine burner was used for this purpose. The treatment of burners as acoustic two-ports with feedback including a source term and the experimental determination of the burner transfer matrix is novel.
Optimization of the Mixing Quality of a Real Size Gas Turbine Burner With Instantaneous Planar Laser-Induced Fluorescence Imaging
Authors: Krämer Hanno , Dinkelacker Friedrich , Leipertz Alfred , Poeschl Gerwig , Huth Michael , Lenze Martin
Published: December 2014

For lean premixed combustion the NOx emission can be reduced by optimizing the degree of fuel-air mixedness. Since both temporal and spatial mixture variations are of importance, the time resolved planar laser technique of acetone tracer-LIF (laser-induced fluorescence) is used to characterize the mixing quality in an one-to-one scale segment of a Siemens ring shaped gas turbine combustor. Variations of the combustor geometry and of additional mixing devices have been tested, showing the potential to increase the mixing quality. Subsequent tests in a fired atmospheric test rig confirm the influence of the mixing quality, leading to up to 30% further reduction of the NOx emissions.
Minimization of Coolant Mass Flow Rate in Internally Cooled Gas Turbine Blades
Authors: Martin Thomas J. , Dulikravich George S. , Han Zhen-Xue , Dennis Brian H.
Published: December 2014

This paper presents a coupled aerodynamic and thermal study of computer-automated design and optimization of internally cooled turbine blades. The turbine blade, thermal barrier coating, coolant passages and struts were developed from a set of design variables, including β-splines for the coolant wall thickness distribution. The turbine inlet temperature, mass flow rate, and coolant wall roughness were also incorporated into the design variable set. The maximum temperature in the metal blade was enforced with equality or inequality constraint functions. Because the coolant flow rate was a design variable, this function could not be explicitly minimized. Instead, three different thermal objective functions were studied: uniform temperature, heat flux extremum, and minimum coolant ejection temperature. Results have shown that it is possible to increase or maintain high turbine inlet temperatures while decreasing the turbine blade coolant requirements. A new constrained hybrid optimization algorithm was developed and used to modify the turbine blade designs until an optimum design was found. This evolutionary optimization package incorporated four popular algorithms (steepest descent, genetic, simplex, and simulated annealing) with automatic switching among them. A computational heat conduction analysis, using the boundary element method (BEM), was iteratively coupled to an unstructured finite volume Reynolds-averaged Navier-Stokes CFD analysis for turbulent hot gas flow. A quasi-one-dimensional system with heat addition and friction was iteratively coupled to the BEM heat conduction via heat flux for the simulation of the airflow in the serpentine coolant passages. This quasi-one-dimensional system yielded correlations for the heat convection coefficients on the coolant passage walls. The coolant passage pressure loss was one of the quantities arising from the quasi-one-dimensional analysis.
Reliable Rotor Dynamic Design of High-Pressure Compressors Based on Test Rig Data
Authors: Wagner Norbert G.
Published: December 2014

The overall design of high-pressure centrifugal compressors is largely influenced by rotordynamic aspects. Rotor instability may restrict operating speed and/or maximum discharge pressure if the destabilizing effects have not been considered accurately during the design phase.

A test rig for high pressures has been designed and operated successfully in order to achieve dynamic labyrinth seal coefficients through simulation of original conditions in every aspect. Details are given of the full-scale test rig, which uses active magnetic bearings as a key feature, as well as results from the comprehensive test program.

Later on, these results are employed for the design of a compressor for very high pressures, demonstrating the complexity of this design task. Validation of the labyrinth test data and the rotor dynamic analysis is provided by the results from a PTC class I test on a reinjection compressor. During shop testing, this machine has been run with and without swirl brakes and the test results agree very well with the predictions.
An Algebraic Model for High Intensity Large Scale Turbulence
Authors: Ames F. E. , Kwon O. , Moffat R. J.
Published: December 2014

An algebraic turbulence model, which has been developed based on the dynamics of ν′ spectra of external turbulence near a surface, is presented in this paper. The model provides an accurate method of predicting the influence of large-scale high intensity turbulence on heat transfer and boundary layer development in turbomachinery. The model has been developed to predict both laminar and turbulent boundary layer development and heat transfer. The laminar boundary layer model has been tested against boundary layer data taken in a low speed cascade. The model produces accurate velocity and eddy diffusivity distributions. The turbulent boundary layer model is composed of inner and outer layer models combined with an intermittency function. The inner model is written in the form of a conventional mixing length model; while the outer layer model is expressed in terms of the external turbulence characteristics. Predictions of boundary layer profiles and heat transfer distributions are shown for both turbulent and laminar boundary layers.

Vane Stanton number predictions were made for inlet turbulence levels ranging from one to thirteen percent for a chord Reynolds number of 800,000. Predictions agreed with experimentally determined levels within 6 percent on the pressure surface but were underpredicted by up to 15 percent in the stagnation region. Levels of heat transfer predicted in the turbulent region of the suction surface agreed with the data within 10 percent.
Film Cooling Effectiveness Predictions for Short Holes Fed by a Narrow Plenum
Authors: Hale C. A. , Ramadhyani S. , Plesniak M. W.
Published: December 2014

This study evaluates the ability of available turbulence models in the commercial software FLUENT to predict film cooling effectiveness for a single row of short (L / D = 2.91). film cooling holes fed by a narrow plenum (H / D = 1). The results are compared to experimental data obtained by the present investigators. The study concentrates on the near-hole region for the geometry being studied experimentally by the present investigators. The results of the study indicate that the use of wall functions to predict film cooling effectiveness in the near-hole region is inappropriate due to the boundary layer separation in that region. Also, the ability of the Reynolds Stress turbulence model to better predict spanwise spreading of the jet indicates the need for anisotropic turbulnce model capabilities to better predict film cooling effectiveness.
Channel Height Effect on Heat Transfer and Friction in a Dimpled Passage
Authors: Moon H. K. , O’Connell T. , Glezer B.
Published: December 2014

The heat transfer enhancement in cooling passages with dimpled (concavity imprinted) surface can be effective for use in heat exchangers and various hot section components (nozzle, blade, combustor liner, etc.), as it provides comparable heat transfer coefficients with considerably less pressure loss relative to protruding ribs. Heat transfer coefficients and friction factors were experimentally investigated in rectangular channels which had concavities (dimples) on one wall. The heat transfer coefficients were measured using a transient thermochromic liquid crystal technique. Relative channel heights (H/d) of 0.37, 0.74, 1.11 and 1.49 were investigated in a Reynolds number range from 12000 to 60000.

The heat transfer enhancement (NuHD) on the dimpled wall was approximately constant at a value of 2.1 times that (Nusm) of a smooth channel over 0.37≤H/d≤1.49 in the thermally developed region. The heat transfer enhancement ratio Nu¯HD/Nusm was invariant with Reynolds number. The friction factors (f) in the aerodynamically fully developed region were consistently measured to be around 0.0412 (only 1.6 to 2.0 times that of a smooth channel). The aerodynamic entry length was comparable to that of a typical turbulent flow (Xo/Dh = 20), unlike the thermal entry length on dimpled surface which was much shorter (xo /Dh<9.8). The thermal performance Nu¯HD/Nusm/f/fsm1/3≅1.75 of dimpled surface was superior to that 1.16<Nu¯HD/Nusm/f/fsm1/3<1.60 of continuous ribs, demonstrating that the heat transfer enhancement with concavities can be achieved with a relatively low-pressure penalty.

Neither the heat transfer coefficient distribution nor the friction factor exhibited a detectable effect of the channel height within the studied relative height range (0.37≤H/d≤1.49).
The Superposition Approach to Local Heat Transfer Coefficients in High Density Ratio Film Cooling Flows
Authors: Gritsch Michael , Baldauf Stefan , Martiny Moritz , Schulz Achmed , Wittig Sigmar
Published: December 2014

The present paper reports on the use of the superposition approach in high density ratio film cooling flows. It arises from the linearity and homogeneity of the simplified boundary layer differential equations. However, it is widely assumed that the linearity does not hold for variable property flows. Therefore, theoretical considerations and numerical calculations will demonstrate the linearity of the heat transfer coefficient with the dimensionless coolant temperature θ as long as identical flow conditions are applied. This makes it necessary to perform at least two experiments at different θ but with the coolant to main flow temperature ratio kept unchanged.

A comprehensive set of experiments is presented to demonstrate the capability of the superposition approach for determining heat transfer coefficients for different film cooling geometries. These comprise coolant injection from two dimensional tangential slots, single holes, and rows of cylindrical holes. Particularly, two dimensional local distributions of the heat transfer coefficient will be addressed.
Heat Transfer and Flow on the First Stage Blade Tip of a Power Generation Gas Turbine: Part 1 — Experimental Results
Authors: Bunker Ronald S. , Bailey Jeremy C. , Ameri Ali A.
Published: December 2014

A combined experimental and computational study has been performed to investigate the detailed distribution of convective heat transfer coefficients on the first stage blade tip surface for a geometry typical of large power generation turbines (>100MW). This paper is concerned with the design and execution of the experimental portion of the study, which represents the first reported investigation to obtain nearly full surface information on heat transfer coefficients within an environment which develops an appropriate pressure distribution about an airfoil blade tip and shroud model. A stationary blade cascade experiment has been run consisting of three airfoils, the center airfoil having a variable tip gap clearance. The airfoil models the aerodynamic tip section of a high pressure turbine blade with inlet Mach number of 0.30, exit Mach number of 0.75, pressure ratio of 1.45, exit Reynolds number based on axial chord of 2.57•106, and total turning of about 110 degrees. A hue detection based liquid crystal method is used to obtain the detailed heal transfer coefficient distribution on the blade tip surface for flat, smooth tip surfaces with both sharp and rounded edges. The cascade inlet turbulence intensity level took on values of either 5% or 9%. The cascade also models the casing recess in the shroud surface ahead of the blade. Experimental results are shown for the pressure distribution measurements on the airfoil near the tip gap, on the blade tip surface, and on the opposite shroud surface. Tip surface heat transfer coefficient distributions are shown for sharp-edge and rounded-edge tip geometries at each of the inlet turbulence intensity levels.
Air Entrainment vs. Lubricant Vaporization in Squeeze Film Dampers: An Experimental Assessment of Their Fundamental Differences
Authors: Diaz Sergio E. , San Andrés Luis A.
Published: December 2014

Squeeze film dampers (SFDs) provide structural isolation and energy dissipation in air breathing engines and process gas compressors. However, SFDs are prone to develop a flow regime where the ingestion of air leads to the formation of a bubbly lubricant. This pervasive phenomenon lacks proper physical understanding and sound analytical modeling, although actual practice demonstrates that it greatly reduces the damper force response. Measurements of film pressures in a test SFD describing circular centered orbits at whirl frequencies varying from 0 to 100 Hz are presented for fully flooded and vented discharge operating conditions. The experiments demonstrate that operation with low levels of external pressurization, moderate to large whirl frequencies, and lubricant discharge to ambient leads to the entrapment of air within the damper film lands. The experiments also elucidate fundamental differences in the generation of film pressures and forces for operation in a flooded condition that evidences vapor cavitation. Damping forces for the vented end with air entrainment are just 15% percent of the forces measured for the flooded damper. Further measurements at constant whirl frequencies demonstrate that increasing the lubricant pressure supply retards the onset of air entainment. Classical fluid film cavitation models predict well the pressures and forces for the lubricant vapor cavitation condition. However, prevailing models fail to reproduce the dynamic forced response of vented (open ended) SFDs where air entrainment makes a foamy lubricant, which limits severely the damper film pressures and forces.
Active Magnetic Bearing With Large Air Gap for Operation With a 3-Phase Power Converter
Authors: Gempp Thomas , Redemann Christian , Schöb Reto
Published: December 2014

In order to reduce the costs, radial active magnetic bearings have been proposed which consist of only three electromagnets. Unfortunately it is not possible to operate the three coils with a 3-phase power converter, since the sum of the coil currents does not equal zero. Three independent amplifier channels are needed for the control of this arrangement. In this paper a radial magnetic bearing is proposed which can be operated by commercial 3-phase power amplifiers. By the use of an arrangement of permanent magnets it is possible to make the sum of the three phase currents become zero. Some problems related to this bearing arrangement as well as solutions are discussed and shown using the example of two prototype bearings.
The Effects of Blade-Row Spacing on the Flow Capacity of a Transonic Rotor
Authors: Chriss Randall M. , Copenhaver William W. , Gorrell Steven E.
Published: December 2014

Results from the ongoing Air Force Stage Matching Investigation are presented. In the present work the effect of upstream blade row wakes on the flow capacity of a downstream stage (where the rotor sets the choking flow) is investigated. An embedded stage was simulated by placing a set of wake generators (similar to inlet guide vanes) in front of a highly loaded single stage transonic core compressor. The wake generator-to-rotor axial spacing was varied in addition to the vane count. A complete parametric test matrix was completed in order to determine which parameters were important to the choking flow capacity.

The results show that for axial spacings above 50% of the upstream axial blade chord, simple wake mixing alone fully accounts for the upstream flow losses and a simple mass flow rate correction based on the rotor face mass averaged total pressure is sufficient. At spacings closer than this, other effects or loss mechanisms may be present. If these loss sources do exist, they are of unknown origin and magnitude and so an embedded overflow condition for these spacings cannot be ruled out. Research is ongoing that will attempt to identify and clarify the relevant details associated with these close blade row spacings.