bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization and Control of Lean Blowout Using Periodically Generated Flame Balls
Authors: Albrecht Peter , Bauermeister Frank , Bothien Mirko , Lacarelle Arnaud , Moeck Jonas , Paschereit Christian Oliver , Gutmark Ephraim
Published: September 2008

Combustion near LBO involves the complex physical processes including turbulence, air/fuel mixing, and chemical kinetics. The goal of this paper was to identify the typical combustion behaviour near LBO of the burner and to develop an effective actuator that will have the necessary control authority without having adverse effects such as increased emissions. Early detection and effective extension of lean blowout (LBO) are the keys to ensure flight safety and low emissions for aero engines, and are of importance to industrial gas turbines for operation below regulated NOx limits. In addition, efficient actuation are crucial for effective active LBO control. An experimental investigation of LBO was carried out using a swirl-stabilized atmospheric combustor with separate pilot and premix gaseous fuel (natural gas) injection systems. Systematic tests were performed including measurements of pressure, OH chemiluminescence and emissions for different combustor lengths, fuel split ratios, preheat temperatures and air flow rates. Operation near LBO may involve excitation of undesired thermoacoustic instabilities that have to be mitigated. LBO was approached by reducing the fuel flow rate while keeping the air flow rate, the preheat temperature and the other parameters constant. Control of the LBO and thermoacoustic instabilities was achieved by generating periodic flame balls. The LBO could be extended by 13 % relative to the natural lean blowout limit at nearly 50% reduced NO emission in comparison to common pilot fuel modulation. A spark discharge system was installed at the pilot fuel injection location. The periodic spark discharge was synchronized with the pulsed fuel injection at a phase shift of 165° and an operating frequency of 22 Hz to produce flame balls that affected the main combustion region. The flame balls excitation provided an effective tool for controlling the premix combustion characteristics at the LBO.
A Numerical Model for Predicting Biomass Particle Depositions in a PF Furnace
Authors: Ma L. , Pourkashanian M. , Williams A. , Jones J. M.
Published: September 2008

Using biomass as a fuel stock in pf furnaces has been recognized as an important measure that is taken in order to reduce emissions in the power generation industry. However, firing biomass presents a number of technical problems, that substantially limit its use in existing coal-fired plants and the formation of deposits in the system is one of the key issues. This paper presents a computational fluid dynamics model that predicts biomass particle depositions in an industrial pf combustion test furnace where the release of potassium in the biomass has been modeled and the residual ash composition determines the stickiness of the particle. The direct impact of the particles on the deposition surface has been considered as the dominant pathway of the particle deposition in the furnace and the overall deposition rate is determined by the chemical and kinetic states of the particles when they come in contact with the deposition surface. When the combustion products leave the furnace then undergo cooling in the boiler section. The processes that take place are discussed, and the information is given on the deposition of the potassium species. A number of simulations have been performed and the model predictions have been compared with the limited available experimental data. The effects of the various model constants on the formation of the deposition have been discussed.
A Virtual Laboratory for Education on Gas Turbine Principles and Operation
Authors: Mathioudakis K. , Aretakis N. , Kotsiopoulos P. , Yfantis E. A.
Published: September 2008

A software package created for educating engineering students on the principles of gas turbines is presented. It starts from the presentation of basic material on the principles of gas turbine components operation (turbomachinery, combustion chambers, inlets, exhausts). The usual textbook material is supported by audiovisual material that enhances the student’s ability to assimilate the principles taught. Computational tools are included, allowing the execution of design studies as well as performance simulations, for a wide range of gas turbine types. Both aircraft and land based gas turbines are covered. A user friendly interface allows the execution of calculations, whose results can be presented in a variety of formats, with the help of a flexible graphical user interface. A number of specific engines have been chosen to be represented, one of the reasons for this choice being that the package in its current form is primarily intended for use by air force and naval academy students, expected to come in contact with the specific engines employed by the corresponding organizations. Finally, a number of laboratory exercises are included. The exercises are performed in a way that is a reproduction of actual laboratory tests. The software employs audio-visual effects, including videos and other animations, to support the instruction of gas turbine principles, and is implemented in a classroom specifically designed for this purpose. The audiovisual effects are employed to transfer the actual physical reality into the classroom, creating thus the virtual environment.
Gas Turbine Fault Diagnosis From Fast Response Data Using Probabilistic Methods and Information Fusion
Authors: Kyriazis A. , Aretakis N. , Mathioudakis K.
Published: September 2008

The paper covers firstly the use of probabilistic neural networks for the classification of spectral fault signatures obtained from fast response data (sound, vibration, unsteady pressure). The method is compared to other alternatives, such as geometrical and statistical pattern recognition. The effectiveness of the method is demonstrated by presenting the results from application to data from a radial compressor and an industrial gas turbine. Further, probabilistic methods are used to perform information fusion. The outcomes of different diagnostic methods are used as a first level of diagnostic inference, and are fed to two different fusion processes which are based on i) Probabilistic Neural Networks and ii) Bayesian Belief Networks. It is demonstrated that these fusion processes provide powerful tools for effective fault classification.
Application of the Turbulent Potential Model to Heat Transfer Predictions on a Turbine Guide Vane
Authors: Pecnik Rene , Sanz Wolfgang
Published: September 2008

The accurate numerical simulation of the flow through turbomachinery depends on the reliable prediction of laminar to turbulent boundary layer transition phenomena. The aim of this paper is to study the ability of the turbulent potential model to predict those non-equilibrium turbulent flows for several test cases. Within this model turbulent quantities are described by the turbulent scalar and turbulent vector potentials of the turbulent body force — the divergence of the Reynolds stress tensor. For model validation firstly flat plate test cases with different inlet turbulence intensities, zero pressure gradient and non-uniform pressure gradient distributions along the plate were calculated and compared by means of skin friction values measured in the experiments. Finally the model was validated by heat transfer measurement data obtained from a highly loaded transonic turbine guide vane cascade for different operating conditions.
Numerical Evaluation of Mode I Stress Intensity Factor as a Function of Material Orientation for BX-265 Foam Insulation Material
Authors: Knudsen Erik , Arakere Nagaraj K.
Published: September 2008

Foam, a cellular material, is found all around us. Bone and cork are examples of biological cell materials. Many forms of man-made foam have found practical applications as insulating materials. NASA uses the BX-265 foam insulation material on the external tank (ET) for the Space Shuttle. This is a type of Spray-on Foam Insulation (SOFI), similar to the material used to insulate attics in residential construction. This foam material is a good insulator and is very lightweight, making it suitable for space applications. Breakup of segments of this foam insulation on the shuttle ET impacting the shuttle thermal protection tiles during liftoff is believed to have caused the space shuttle Columbia failure during re-entry. NASA engineers are very interested in understanding the processes that govern the breakup/fracture of this complex material from the shuttle ET. The foam is anisotropic in nature and the required stress and fracture mechanics analysis must include the effects of the direction dependence on material properties. Material testing at NASA MSFC has indicated that the foam can be modeled as a transversely isotropic material. As a first step toward understanding the fracture mechanics of this material, we present a general theoretical and numerical framework for computing stress intensity factors (SIFs), under mixed-mode loading conditions, taking into account the material anisotropy. We present mode I SIFs for middle tension — M(T) — test specimens, using 3D finite element stress analysis (ANSYS) and FRANC3D fracture analysis software, developed by the Cornell Fracture Group. Mode I SIF values are presented for a range of foam material orientations. Also, NASA has recorded the failure load for various M(T) specimens. For a linear analysis, the mode I SIF will scale with the far-field load. This allows us to numerically estimate the mode I fracture toughness for this material. The results represent a quantitative basis for evaluating the strength and fracture properties of anisotropic foam insulation material.
Heat Transfer at High Rotation Numbers in a Two-Pass 4:1 Aspect Ratio Rectangular Channel With 45-Degree Skewed Ribs
Authors: Zhou Fuguo , Acharya Sumanta
Published: September 2008

Heat transfer measurements are reported for a rotating 4:1 aspect ratio (AR) coolant passage with ribs skewed 45 degree to the flow. The study covers Reynolds number (Re) in the range of 10,000–70,000, rotation number (Ro) in the range of 0–0.6, and density ratios (DR) between 0.1–0.2. These measurements are done in a rotating heat transfer rig utilizing segmented copper pieces that are individually heated, and thermocouples with slip rings providing the interface between the stationary and rotating frames. The results are compared with the published data obtained in a square channel with similar dimensionless rib-geometry parameters, and with the results obtained for a 4:1 AR smooth channel. As in a 1:1 AR channel, rotation enhances the heat transfer on the destabilized walls (inlet-trailing wall and outlet-leading wall), and decreases the heat transfer ratio on the stabilized walls (inlet-leading wall and outlet-trailing wall). However, the rotation-induced enhancement/degradation for the 4:1 rectangular channel is much weaker than that in the square ribbed channel, especially in the inlet (the first passage). The results on the inlet-leading wall are in contrast to that in the smooth channel with the same AR, where rotation causes heat transfer to increase along the inlet-leading wall at lower Reynolds number (Re = 10,000 and 20,000). Higher DR is observed to enhance the heat transfer on both ribbed walls in the inlet (the first passage) and the outlet (the second passage), but the DR effects are considerably weaker than those in a ribbed square channel. Measurements have also been parameterized with respect to the buoyancy parameter and results show the same general trends as those with respect to the rotation number. In addition, pressure drop measurements have been made and the thermal performance factor results are presented.
Flow Characteristics Within and Downstream of a Double-Row Array of Shallow Spherical and Cylindrical Dimples
Authors: Khalatov Artem , Byerley Aaron
Published: September 2008

The experimental program was performed in the U.S. Air Force Academy water tunnel to visualize details of the unsteady flow structure in front of, within and downstream of a double-row array of shallow (h/D = 0.1) spherical and cylindrical dimples placed on a flat plate. The dimple projected diameter was 50.8 mm. The center of the first array was located at 88,0 mm downstream of the elliptically-shaped leading edge of the plate, the spanwise dimple pitch is 76.2 mm (Sz/D = 1.50). The second array was arranged in a staggered mode with the same spanwise pitch and the axial pitch between rows of 88.0 mm (Sx/D = 1.73). The diameter-based Reynolds number ReD ranged from 3,260 to 23,450, while the length-based Reynolds number Rex in front of the first array varied from 4,010 to 28,840. The laminar flow existed upstream of the first array for all flow conditions studied. In front of the second array the flow structure appeared to have either laminar or turbulent depending on the Reynolds number and streamline location. Flow visualizations were performed at 13 different flow speeds using the dye visualization technique. All recordings were made with a SONY-DCR VX2000 video camera. Adobe Premiere 6.5 software was used to analyze the flow characteristics using the slow motion feature. The results presented include details of the unsteady flow structure, bulk flow fluctuations and laminar-turbulent flow transition. The upstream vortex structures reduce bulk flow fluctuations beyond the second array making them smaller than those after the first array. At ReD > 13,000 the spherical dimples in the second array produce more significant bulk flow fluctuations than cylindrical dimples.
Fault Detection and Identification by Gas Path Analysis Approach in Heavy Duty Gas Turbine
Authors: Della Gatta Stefania , Adami Paolo
Published: September 2008

The possibility to get information about gas turbine “health” state is largely based on availability and reliability of operational data and on-line acquisition systems. However, further instruments are needed in order to deduce useful information in maintenance scheduling from actually measured data. In Gas Path Analysis approaches, a model to simulate the engine behavior is required. Furthermore, in order to individuate, locate and evaluate faulty conditions, a diagnostic approach needs to be developed and introduced. This paper presents a critical discussion of the problem to highlight the main requirements of a diagnostic approach. Furthermore, some procedures to verify the ability of a diagnostic tool can be obtained directly from the theoretical background of GPA. To demonstrate how these procedures work, an application case has been examined. An engine model has been specifically developed for the monitored heavy-duty gas turbine. It allows to calculate thermodynamics data and to identify performance parameters through a mathematical modeling process. The suitability of this model to be introduced in a diagnostic system has been investigated. An exhaustive description of the procedures and discussion of results are reported.
Calculations of Cooled Turbine Efficiency
Authors: Horlock J. H. , Torbidoni Leonardo
Published: September 2008

The efficiency of a cooled turbine stage has been discussed in the literature. All proposed definitions compare the actual power output with an ideal output, which has to be determined; but usually one of two definitions has been used by turbine designers. In the first, the so-called Hartsel efficiency, the mainstream gas flow and the various coolant flows to rotor and stator are assumed to expand separately and isentropically to the back pressure. In the second it is assumed that these flows mix at constant (mainstream) gas pressure before expanding isentropically (sometimes the rotor coolant flow is ignored in this definition). More recently it has been suggested that a thermodynamically sounder definition is one in which the gas and coolant flows mix reversibly and adiabatically before isentropic expansion to the back pressure. In the current paper these three efficiencies are compared, for a typical stage — the first cooled stage of a multistage industrial gas turbine. It is shown that all the efficiencies fall more or less linearly with increase of the fractional (total) coolant flow. It is also shown that the new definition of efficiency gives values considerably lower than the other two efficiencies, which are more widely used at present. Finally, the various irreversibilities associated with the flow through a cooled turbine are calculated. Although all these irreversibilities increase with the fractional coolant flow, it is shown that the “thermal” irreversibility associated with film cooling is higher than the other irreversibilities at large fractional coolant flow.
Water Injection Effects on Compressor Stage Operation
Authors: Roumeliotis I. , Mathioudakis K.
Published: September 2008

In the present paper, experimental work concerning the effect of water injection on a compressor stage is presented. The effect on compressor stage performance and stability is examined for water injection up to 2%. The behaviour of the air flow in the blade rows is examined through aerodynamic measurements. The results indicate that although the water injection appears to not have any significant effect on the flow pattern and to stage pressure rise and stall margin, there is a measurable effect on compression efficiency which seems to result mainly from losses of mechanical nature and water acceleration. The efficiency degradation is proportional to the water ratio entering the engine.
The Application of CFD to Underpin the Design of Gas Turbine Pre-Swirl Systems
Authors: Snowsill G. D. , Young C.
Published: September 2008

The technique of pre-swirling cooling air to reduce its relative total temperature, as felt by rotating components, is well established. It is important to optimise the design of such systems in order to achieve maximum cooling effectiveness and to minimise the impact on cycle efficiency. Traditionally, these cooling systems have been developed by a combination of experimental investigation and careful evolution. However, more recently it has become practical to apply CFD to such problems. The nature of gas turbine cooling systems generally mandates the presence of discrete features on both static and rotating components, so that a fully rigorous analysis would need to be both 3D and unsteady, with the sub-domains adjacent to static and rotating surfaces solved in an appropriate frame of reference, together with a suitable interfacing procedure to communicate the evolving solution between each sub-domain. Such analyses are challenging for current CFD codes, both in terms of computation time and numerical stability. The present work explores the various options that are available to make such computations more practical and hence more accessible to the secondary systems modelling community. Significant reductions in set-up time can be achieved by adopting unstructured calculational meshes, although this may be at the expense of some loss of accuracy and increase in computational time relative to structured meshes. In the present work, an attempt has been made to quantify the effect of these choices. Depending on the configuration of the system under investigation, it may be permissible to ignore the unsteady interactions and to model the system using the more computationally efficient multiple reference frame (MRF) approach. Guidelines are proposed for assessing the likely impact of these simplifications on the results obtained.
Flow Analysis in Gas Turbine Pre-Swirl Cooling Air Systems: Variation of Geometric Parameters
Authors: Jarzombek K. , Dohmen H. J. , Benra F.-K. , Schneider O.
Published: September 2008

This paper reports experimental and numerical results of the flow in a high radius pre-swirl system. Numerical results have been compared with measurement data for the investigated test rig and are in good agreement with the experimental results. To get a better understanding of the flow structure and the influence of geometric parameters in pre-swirl systems, variations were performed by 3D-CFD simulations on a derived and simplified model. Variations of radius ratio of pre-swirler to receiver, the pre-swirl cavity height and the pre-swirl cavity width are shown. The influencing effects of the varied parameters are shown by looking at pre-swirl effectiveness and total pressure losses.
Multipoint Non-Linear Method for Enhanced Component and Sensor Malfunction Diagnosis
Authors: Kamboukos Philippos , Mathioudakis Kostas
Published: September 2008

Operating gas turbine engines are usually equipped with a limited number of sensors. This situation is the common issue of gas turbine diagnostics where the absence of sufficient measurements from the engine gas path reduces the effectiveness of the applied methods. In addition the installed sensors of the engine deteriorate with time or present abrupt malfunctions which are not always detectable. One way to overcome this problem is the exploitation of information from a number of different operating points by constructing a multipoint diagnostic procedure. Information from different operating points is combined in order to increase the number of measurements and thus to form a well determined diagnostic system for the estimation of engine component health parameters. The paper presents the extension of the method in order to be able to assess both engine and sensors state. Initially the ability of the method to estimate the condition of a high bypass turbofan engine, exploiting information from different instances of its flight envelop is depicted. The problem of selecting the appropriate operating points is analyzed on the basis of the numerical condition of the formed diagnostic system. The method is also applied to a single shaft turbojet, for estimation of engine component health parameters and sensors state. Finally a number of aspects related to the formulation of the method are examined. These are the comparison between full method and its linear approximation, the effect of measurement noise on the derived estimation and the computational cost.
Influence of an Axial and Radial Rim Seal Geometry on Hot Gas Ingestion Into the Upstream Cavity of a 1.5-Stage Turbine
Authors: Bohn Dieter E. , Decker Achim , Ohlendorf Nils , Jakoby Ralf
Published: September 2008

In gas turbines hot gas ingestion into the cavities between rotor and stator disks has to be avoided almost completely in order to ensure that the guaranteed lifetime of the turbine rotor disk will be reached. The influence of an axial and radial rim seal configuration geometry on the phenomenon of hot gas ingestion into the rim seal section and inside the front cavity of a 1.5-stage axial turbine is experimentally investigated. The results obtained for the reference axial configuration are compared to those for the radial configuration in the upstream cavity of the turbine. The hot gas ingestion phenomenon is examined for different flow parameters such as non-dimensional seal flow rate, Reynolds number in the main annulus and rotational speed. The sealing efficiency is determined by measurements of the carbon dioxide gas concentration in the cavity. Static pressure distributions are measured using pressure taps at the stator disk and rim seal lip. It will be shown for the axial rim seal geometry that the guide vanes mainly influence the flow field in the rim seal gap and inside the cavity whereas for the radial rim seal geometry such an influence is limited almost exclusively to the rim seal gap. For the radial rim seal a higher sealing efficiency was detected, mainly due to the different type of the rim seal.
Predicting Transition on Concave Surfaces
Authors: Johnson Mark W.
Published: September 2008

Boundary layers on concave surfaces differ from those on flat plates due to the presence of Taylor Goertler (T-G) vortices. These vortices cause momentum transfer normal to the blade’s surface and hence result in a more rapid development of the laminar boundary layer and a fuller profile than is typical of a flat plate. Transition of boundary layers on concave surfaces also occurs at a lower Rex than on a flat plate. Concave surface transition correlations have been formulated previously from experimental data, but they are not comprehensive and are based on relatively sparse data. The purpose of the current work was to attempt to model the physics of both the laminar boundary layer development and transition process in order to produce a transition model suitable for concave surface boundary layers. The development of the laminar boundary layer on a concave surface was modeled by considering the profiles at the upwash and downwash locations separately. The profiles of the boundary layers at these two locations were then combined to successfully approximate the spanwise averaged profile. The ratio of the boundary layer thicknesses at the two locations was found to be as great as 50 and this leads to laminar boundary layer shape factors as low as 1.3 and skin friction coefficients up to 12 times the value for a flat plate laminar boundary layer. Boundary layers therefore grow much more rapidly on concave surfaces than on flat plates. The transition model assumed that transition commenced in the upwash location boundary layer at the same transition inception Reθ observed on a flat plate. Transition at the downwash location then results from the growth of turbulent spots from the upwash location rather than through the initiation of spots. The model showed that initially curvature promotes transition because of the thickened upwash boundary layer, but for strong curvature the T-G vortices effectively stabilise the boundary layer and transition then occurs at a higher Reθ than on a flat plate. Results from the transition model were in broad agreement with experimental observations. The current work therefore provides a basis for the modeling of transition on concave surfaces.
Modelling Sub-Grid Scale Features in Congested Engine Ventilation Zones
Authors: Alizadeh Sohail , Moss Barrie
Published: September 2008

In the increasingly congested accessory zones of gas turbine engine casings, it is important that the several temperature-sensitive components, like the electronic engine control unit (EEC), are bathed in an appropriate ventilation environment. Additionally it must be ensured that heat sources, like the geometrically complex gear box components, furthest from the inflows do not sit in stagnant zones. In this paper CFD methods have been used to study in detail the ventilation and heat transfer environment of one particular zone — that of the fan casing in the engine nacelle of a high by-pass turbofan. A particular challenge was the appropriate modelling of the extensive pipe systems that existed in this environment, ensuring that their impact on the flow field and heat transfer was suitably taken into account. Whilst in past practice large components and ducts have been modelled in CFD studies, the small scale pipe systems and electrical harnesses do not lend themselves easily to explicit modelling strategies. In this work a methodology is presented whereby the effects of all small scale pipe systems within the zone are represented using a sub-grid modelling approach. The momentum drag and heat release associated with all small scale pipes have been modelled and their impact on the ventilation and heat transfer characteristics of the accessory zone environment assessed. Comparisons made with the explicit methodology, not employing sub-grid models, have revealed that the small scale pipe systems have a significant impact on the flow and heat distribution, particularly around the EEC. Finally, limited comparisons with similar test rig flow visualisation data have been made, confirming the overall flow pattern within the zone. The work also suggests approaches in which the sub-grid methodology may be extended and verified for engine design purposes.
Design of a Carbon-Carbon Finned Surface Heat Exchanger for a High-Bypass Ratio, High Speed Gas Turbine Engine
Authors: Filburn Tom , Kloter Amanda , Cloud Dave
Published: September 2008

Compact heat exchanger designs are commonly used in many gas turbine engine applications. Though effective in their heat transfer function, they are often heavy, costly, and poor aerodynamic performers causing a reduction in engine efficiency. In addition, they are complex to manufacture and often prone to leakage. Finned surface heat exchangers are an attractive alternative to traditional compact designs. They can perform efficiently both aerodynamically and thermally. Such units could be mounted in the bypass fan stream of a gas turbine engine where large amounts of heat must be rejected from vital engine fluids such as oil and fuel. This research project investigated the efficiency of various fin designs applied to an oil cooler. Highly conductive materials, such as carbon composites were explored, and then compared to aerospace-quality aluminum alloys. Thermal, aerodynamic, economic, and weight performance comparisons between the carbon and aluminum fin structures were quantified. A three-dimensional numerical estimation of the final design concept was conducted using ANSYS. This research project specifically investigated the design of a finned surface air-oil heat exchanger. Design parameters included a total heat rejection of 2000 Btu/min and an oil temperature change of 100 degrees Fahrenheit with an inlet oil temperature of 300 degrees. The first design phase was conducted using an aerospace quality aluminum alloy. Internal and external flow convection theory was studied closely as well as basic heat exchanger and fin design concepts. A heat exchanger program was developed in Excel, automating the heat transfer based on basic geometric inputs. The program allowed easy iterations of fin/oil passage designs to meet the performance requirements and optimize the heat exchanger’s weight. The final iteration was then numerically modeled in ANSYS. The predicted heat transfer rate was then compared to the numerical estimation in ANSYS. The Excel program was validated by producing results within 2% of the ANSYS predicted solutions. Upon completion of the aluminum design. highly conductive materials, such as carbon composites were explored and implemented. The final designs of this project (both Aluminum and Carbon-Carbon) identified a new method of heat rejection at a significantly lower weight impact to the engine. The aluminum design had a total core weight of 25.4 lb while the carbon-carbon final design had a total core weight of 12.8 lb. In addition, both units have the potential to be incorporated within an existing engine case exposed to the bypass air stream, which may result in an additional weight savings.
Systems-Level Performance Estimation of a Pulse Detonation Based Hybrid Engine
Authors: Goldmeer Jeffrey , Tangirala Venkat , Dean Anthony
Published: September 2008

A key application for a Pulse Detonation Engine concept is envisioned as a hybrid engine, which replaces the combustor in a conventional gas turbine with a Pulse Detonation Combustor (PDC). A limit cycle model, based on quasi 1-D, unsteady Computational Fluid Dynamics (CFD) simulations, was developed to estimate the performance of a pressure-rise PDC in a hybrid engine to power a subsonic engine core. The parametric space considered for simulations of the PDC operation includes the mechanical compression or the flight conditions that determine the inlet pressure and the inlet temperature conditions, fill fraction and purge fraction. The PDC cycle process time scales including overall operating frequency were determined via limit-cycle simulations. The methodology for estimation of performance of the PDC considers the unsteady effects of PDC operation. These metrics include a ratio of time-averaged exit total pressure to inlet total pressure and a ratio of mass-averaged exit total enthalpy to inlet total enthalpy. This information can be presented as a performance map for the PDC, which was then integrated into a systems-level cycle analysis model, using Gate-Cycle, to estimate the propulsive performance of the hybrid engine. Three different analyses were performed. The first was a validation of the model against published data for specific impulse. The second examined the performance of a PDC versus a traditional Brayton cycle for a fixed combustor exit temperature; the results show an increased efficiency of the PDC relative to the Brayton cycle. The third analysis performed was a detailed parametric study varying engine conditions to examine the performance of the hybrid engine. The analysis has shown that increasing the purge fraction, which can reduce the overall PDC exit temperature, can simultaneously provide small increases in overall system efficiency.
Ignition of Lean CO/H2/Air Mixtures at Elevated Pressures
Authors: Kalitan Danielle M. , Petersen Eric L. , Mertens John D. , Crofton Mark W.
Published: September 2008

Shock-tube ignition delay time experiments and chemical kinetics model calculations were performed for several fuel blends of carbon monoxide and hydrogen in air at elevated pressures. Due to the interest in coal-derived fuels, namely syngas, these data are important for characterizing the ignition and oxidation of possible fuel blends used in gas turbines and for the validation of chemical kinetics models. Three lean, CO/H2 (80/20%, 90/10%, and 95/5% by volume) fuel blends in air were studied behind reflected shock waves at temperatures between 929 and 1304 K and pressures ranging from 1.7 to 15 atm. Ignition delay times were monitored using chemiluminescence emission from excited hydroxyl radicals. Results exhibit the second-explosion limit behavior from hydrogen oxidation kinetics at low temperatures and high pressures for all mixtures. In addition, comparisons of modeling results and experimental data show good agreement for the entire temperature range at high pressure and poor agreement with the data at low temperatures in the intermediate pressure regimes. Ignition and reaction sensitivity analyses indicate that the H + O2 + M = HO2 + M termination reaction is important at all conditions herein, and the early formation of HO2 suppresses the growth of the ignition-enhancing radicals H and OH.
The Flowfields in a Model Combustor With Primary Holes After Different Swirl Cups
Authors: Lang Hongjian , Huang Yong , Guo Zhihui
Published: September 2008

The characteristics of the flow fields in a model combustor’s primary zone, which is confined by different swirl cups and the flame tube with primary holes and cooling air films, is experimentally investigated by a Particle Dynamic Analyzer (PDA). The spray of RP-3 jet fuel from the atomizer is used as the trace particles for laser detection. The inlet air pressure and temperature are 110 KPa and 300 K, respectively. The test sections start from 10 mm and end at 50 mm downstream the swirl cup, ensuring that the primary holes are located within the test range. The results show that the swirl cup with double radial swirlers causes a greater flow expansion than that with double axial swirlers, thus results in a greater recirculation zone. By comparison with the previously reported data for the flow field after a pure swirl cup, it can be concluded that the flow field, especially the recirculation zone, in the primary zone with primary hole jets, is no longer axisymmetrical, as it was after a pure swirl cup. The presence of primary hole air flows remarkably squeezes the recirculation zone, especially for double radial swirlers; thus resulting in a elliptic-like cross section, with the longer axis greater than the shorter one up to 2.3 times, and causing the diminish of the corner recirculation zone. The recirculation zone is always ended at the primary holes, resulting in a much shorter length of the recirculation zone, which is only about 1.3 times of the exit diameter of the swirl cup, instead of 2.5 times for the pure swirl cup structure without the primary holes.
Investigation of the Unstable Flow Structure in a Rotating Cavity
Authors: Bohn Dieter , Ren Jing , Tuemmers Christian
Published: September 2008

Annular cavities are found inside rotor shafts of turbomachines with an axial or radial throughflow of cooling air, which influences the thermal efficiency and system reliability of the gas turbines. The flow and heat transfer phenomena in those cavities should be investigated in order to minimize the thermal load and guarantee system reliability. An experimental rig is set up in the Institute of Steam and Gas Turbines to analyze the flow structure inside the rotating cavity with an axial throughflow of cooling air. The corresponding 3D numerical investigation is carried out with the in-house fluid solver CHTflow, in which the Coriolis force and the buoyancy force are implemented in the time-dependent Navier-Stokes equations. Both the experimental and numerical results show the whole flow structure rotating against the cavity rotating direction. The flow passing the observation windows shows the quite similar trajectories in the experimental and numerical results. The computed sequences and periods of the vortex flow structure correspond closely with those observed in the experiment. Furthermore, the numerical analysis reveals a flow pattern changing between single pair, double pairs and triple pairs vortices. It is suggested that the vortices inside the cavity are created by the gravitational buoyancy force in the investigated case, and the number and strength of the vortices are controlled mainly by the Coriolis force.
Design of Reduced Order State Space Controllers With Adaptive Limiting Functions for Industrial Twin Shaft Gas Turbines
Authors: Beukenberg Markus , Brodmann Michael , Weibel Hans , Mu¨ller Detlef , Schwarzin Alexander
Published: September 2008

The designs of model-based state space controllers for industrial twin shaft gas turbines, presented at last year’s conference [1], were enhanced by a limiting function for selected state variables. In order to avoid the disadvantages of common controller concepts involving abrupt structural changes, the limitation was realised by a parameter-variant state space controller. To reduce the sensitivity of the full state space controller to parameter changes, a reduced order controller was developed, taking into account only the dominant state variables of the system. As in previously presented designs, a PI state space controller was designed for the reduced system using the pole placement method. Subsequently, this reduced controller was adapted to the original nonlinear system. With appropriate pole placements for the reduced order state space controller, a high quality of control, comparable to the behaviour of a full state space controller, can be obtained. The resulting controller also shows a reduced sensitivity to variations of the feedback parameters. The intended state variable limitation of the original nonlinear system to defined thresholds has been achieved by applying floating functions between different controller parameter sets.
Fuel Flexibility Test Campaign on a GE10 Gas Turbine: Experimental and Numerical Results
Authors: Andreini Antonio , Facchini Bruno , Mangani Luca , Cocchi Stefano , Modi Roberto
Published: September 2008

Medium- and low-LHV fuels are receiving a continuously growing interest in stationary power applications. Besides that, since in many applications the fuels available at a site can be time by time of significantly different composition, fuel flexibility has become one of the most important requirements to be taken into account in developing power systems. A test campaign, aimed to provide a preliminary assessment of a small power gas turbine’s fuel flexibility, was carried over a full-scale GE10 prototypical unit, located at the Nuovo-Pignone manufacturing site, in Florence. The engine is a single shaft, simple cycle gas turbine designed for power generation applications, rated at 11 MW electrical power and equipped with a silos-type combustor. A variable composition gas fuel was obtained by mixing natural gas with CO2 to about 40% by vol. at engine base-load condition. Tests involved two different diffusive combustion systems: the standard version, designed for operation with natural gas, and a specific system designed for low-LHV fuels. Tests performed aimed to investigate both ignition limits and combustors’ performances, focusing on hot parts’ temperatures and pollutant emissions. Regarding NOx emissions, data collected during standard combustor’s tests were matched a simple scaling law (as a function of cycle parameters and CO2 concentration in the fuel mixture), which can be used in similar applications as a NOx predictive tool. In a following step, a CFD study was performed in order to verify in detail the effects of LHV reduction on flame structure and to compare measured and calculated NOx. STAR-CD™ code was employed as main CFD solver while turbulent combustion and NOx models were specifically developed and implemented using STAR’s user-subroutine features. Both models are based on classical laminar-flamelet approach. Three different operating points were considered at base-load conditions, varying CO2 concentration (0%, 20% and 30% vol. simulated). Numerical simulations point out the flexibility of the GE10 standard combustor to assure flame stabilization even against large variation of fuel characteristics. Calculated NOx emissions are in fairly good agreement with measured data confirming the validity of the adopted models.
The Effect of Obstacles in a Liquid Film
Authors: Eastwick Carol , Bertin Lucie , Johnson Graham
Published: September 2008

Cooling of bearing chamber walls is achieved by the through-flow of thin oil films, which are typically only a few millimeters thick. Support structures and other features disrupt both air and oil motion within such chambers, leading to localized variations in the oil film thickness, which in turn cause variation in local heat transfer coefficients. In extreme cases, the presence of wall protrusions may result in complete “dry-out” or thickening of the wall film. This paper describes an experimental study that has been undertaken to establish the range of conditions under which shear driven liquid films dry-out upstream and downstream of different obstacles. Three different sizes (0.5”, 1” & 1.5”) of cylindrical and square obstructions were employed. The effect of obstacle shape, size and orientation has been investigated. The interactions of waves and dry-out patches has also been investigated, as has the dependence on previous states (i.e. the liquid flow rate and the whether the surface was previously wetted). A number of conclusions have been drawn that provide a starting point for designers in specifying obstruction shapes that are less likely to cause film dry-out for obstacles that protrude through film flows.
Flashback Limit and Mechanism of Methane and Syngas Fuel
Authors: Xu Gang , Tian Ying , Song Quanbin , Fang Aibin , Cui Yufeng , Yu Bin , Nie Chaoqun
Published: September 2008

Flashback is one of the major problems in lean premixed combustion of gas turbine combustor. Due to the effulgent future of co-product system and IGCC, lean premixed combustion, one of the approaches to ultra low NOx for rich hydrogen syngas fuel need farther research on anti-flashback and low pressure drop combustor. Mechanism and characteristics of methane and syngas flashback for 2 types of flame holders, i.e. ring shape and rod shape have been researched through experiment as well as numerical simulation. The partial premix model has been selected to simulate premixed combustion flashback process since it combined the advantage of PDF model and TFC model. Experiments demonstrate that, the flashback velocity of different fuel compositions or flame holder size generally can be correlated to the same dimensionless function by using Peclet number model if the structures of flame holders are the same. Peclet function curves were used to compare the anti-flashback performance of the 2 types of flame holders mentioned above with swirl holder. Boundary coaxial jet can change flashback through the wall into flashback in the core flow and significantly improve the anti-flashback performance of the ring-type flame holder on condition that the velocity of the boundary coaxial jet is in an optimal range. As the result, ring shape holder shows the best while swirl holder the worst on anti-flashback performance.
Development and Application of CFD-Based Analysis Methodology to Evaluate Efficiency of Low NOx Combustion Technologies
Authors: Kutsenko Yu. G. , Onegin S. F.
Published: September 2008

A combustor is a crucial unit of gas turbine engine because it should work reliably at high temperatures; provide a suitable temperature distribution at entry to the turbine and supply a low emission level of harmful substances. An operational development of combustors is a very complex process, involving a great volume of design and experimental work. The application of computational fluid dynamics (CFD) methods allows to decrease the volume of experimental works on operational development of combustors and to make changes to the design of combustors on early stages. This paper describes development and validation of CFD-based analysis methodology, used to predict NOx emission level for different types of gas turbine combustors. This methodology includes comprehensive modeling of physical and chemical processes that take place in gas turbine combustors: turbulent flow of reacting gases, heat transfer, chemical kinetics and formation of nitric oxide. To simulate these processes the following mathematical models were used and validated: • Navier-Stockes equations; k-ε RNG, k-ε RSM, k-ω SST turbulence models; • Flamelet and Flamefront combustion models; • Different chemical kinetics mechanisms, describing methane and aviation kerosene oxidation processes; • Diffusion radiation model and discrete ordinates method to calculate radiation heat fluxes; • Extended n-heptane oxidation mechanism to simulate PAH and soot formation; • Prompt and thermal NO formation mechanisms; • Wide band exponential model for gases and empirical correlation for soot to calculate radiation properties of medium. Different factors that affect NOx formation process are considered. They include O and OH prediction methods, influence of radiation heat transfer, and choice of combustion and turbulence models. Developed methodology was used to simulate combustion process in gas turbine combustors that use RQL, LPP, wet NO technologies of low NOx combustion. Merits, demerits and peculiarities of considered low NOx combustion technologies are discussed. According to the results of the analysis, the most efficient technology for NOx reduction was selected.
The Effects of Blade Passing on the Heat Transfer Coefficient of the Over-Tip Casing in a Transonic Turbine Stage
Authors: Thorpe Steven J. , Ainsworth Roger W.
Published: September 2008

In a modern gas turbine engine the outer casing (shroud) of the shroudless high-pressure turbine is exposed to a combination of high flow temperatures and heat transfer coefficients. The casing is consequently subjected to high levels of convective heat transfer, a situation that is complicated by flow unsteadiness caused by periodic blade-passing events. In order to arrive at an over-tip casing design that has an acceptable service life it is essential for manfacturers to have appropriate predictive methods and cooling system configurations. It is known that both the flow temperature and boundary layer conductance on the casing wall vary during the blade-passing cycle. The current article reports the measurement of spatially and temporally resolved heat transfer coefficient (h) on the over-tip casing wall of a fully-scaled transonic turbine stage experiment. The results indicate that h is a maximum when a blade-tip is immediately above the point in question, while lower values of h are observed when the point is exposed to the rotor passage flow. Time-resolved measurements of static pressure are used to reveal the unsteady aerodynamic situation adjacent to the over-tip casing wall. The data obtained from this fully-scaled transonic turbine stage experiment are compared to previously published heat transfer data obtained in low-Mach number cascade style tests of similar high pressure blade geometries.