bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational Investigation of Flow and Heat Transfer for a Row of Circular Jets Impinging on a Concave Surface
Authors: Rama Kumar B. V. N. , Prasad B. V. S. S. S.
Published: September 2008

A computational investigation is carried out to study the flow and heat transfer from a row of circular jets impinging on a concave surface. The computational domain simulates the impingement cooling zone of a gas turbine nozzle guide vane. The parameters which are varied in the study include jet Reynolds number (Red = 5000 to 54000), inter-jet distance to jet diameter ratio (c/d = 3.33 and 4.67) and target plate distance to jet diameter ratio (h/d = 1, 3 and 4). The flow field, predicated with K- ω turbulence model (using Fluent 6.2), is characterized with the presence of a pair of counter rotating vortices, an upwash fountain flow and entrainment. The local pressure coefficient and Nusselt number variations along the concave plate are presented and these values are found to under predict the some available experimental data by about 12%.
Hybrid Kalman Filter Approach for Aircraft Engine In-Flight Diagnostics: Sensor Fault Detection Case
Authors: Kobayashi Takahisa , Simon Donald L.
Published: September 2008

In this paper, a diagnostic system based on a uniquely structured Kalman filter is developed for its application to inflight fault detection of aircraft engine sensors. The Kalman filter is a hybrid of a nonlinear on-board engine model (OBEM) and piecewise linear models. The utilization of the nonlinear OBEM allows the reference health baseline of the diagnostic system to be updated, through a relatively simple process, to the health condition of degraded engines. Through this health baseline update, the diagnostic effectiveness of the in-flight sensor fault detection system is maintained as the health of the engine degrades over time. The performance of the sensor fault detection system is evaluated in a simulation environment at several operating conditions during the cruise phase of flight.
Laboratory Studies of the Flow Field Characteristics of Low-Swirl Injectors for Adaptation to Fuel-Flexible Turbines
Authors: Cheng R. K. , Littlejohn D. , Nazeer W. A. , Smith K. O.
Published: September 2008

The low-swirl injector (LSI) is a simple and cost-effective lean premixed combustion method for natural-gas turbines to achieve ultra-low emissions (< 5 ppm NOx and CO) without invoking tight control of mixture stoichiometry, elaborate active tip cooling or costly materials and catalysis. To gain an understanding of how this flame stabilization mechanism remains robust throughout a large range of Reynolds numbers, laboratory experiments were performed to characterize the flowfield of natural gas flames at simulated partial load conditions. Also studied was a flame using simulated landfill gas of 50% natural gas and 50% CO2. Using Particle Image Velocimetry (PIV), the non-reacting and reacting flowfields were measured at five bulk flow velocities. The results show that the LSI flowfield exhibits similarity features. From the velocity data an analytical expression for the flame position as function of the flowfield characteristics and turbulent flame speed have been deduced. It shows that the similarity feature coupled with a linear dependency of the turbulent flame speed with bulk flow velocity enable the flame to remain relatively stationary throughout the load range. This expression can be the basis for an analytical model for designing LSIs that operate on alternate gaseous fuels such as slower burning biomass gases or faster burning coal-based syngases.
The Potential of Recuperated Semiclosed CO2 Cycles
Authors: Enge Yngvil O. , Wirsum Manfred , Wettstein Hans E.
Published: September 2008

Semi-closed cycles are characterized by firing a fuel with technically pure oxygen. The combustion gases mainly consist of CO2 and H2O. The use of the exhaust heat of the turbine in a steam bottoming cycle is the most common approach to achieve a sufficient thermal efficiency. In this paper it is shown that a semi-closed CO2 cycle with thermal recuperation avoids the complexity of a bottoming steam cycle and at the same time adds the potential of supercharging the cycle to high pressure. This allows both a very high power density and a discharge of fairly clean CO2 under sufficiently high pressure, which may be used directly or after separation of parasitic gases for enhanced oil recovery or other kind of disposal methods. We show in this paper preliminary cycle calculations, the optimization of pressure ratio, pressure level, turbine inlet temperature and recuperator assumptions. The real gas properties influence the cycle optimization and especially the temperature match within the recuperator.
Improved High Cycle Fatigue Damage Tolerance of Turbine Engine Compressor Components by Low Plasticity Burnishing (LPB)
Authors: Preve´y Paul S. , Jayaraman N. , Ravindranath Ravi A. , Shepard Michael
Published: September 2008

Significant progress has been made in the application of low plasticity burnishing (LPB) technology to military engine components, leading to orders of magnitude improvement in damage tolerance. Improved damage tolerance can facilitate inspection, reduce inspection frequency, and improve engine operating margins, all leading to improved military readiness at significantly reduced total costs. Basic understanding of the effects of the different LPB process parameters has evolved, and finite element based compressive residual stress distribution design methodologies have been developed. By incorporating accurate measurement of residual stresses to verify and validate processing, this combined technology leads to a total solutions approach to solve damage problems in engine components. An example of the total solution approach to develop LPB processing of a 1st stage Ti-6Al-4V compressor vane to improve the foreign object damage (FOD) tolerance from 0.002 in. to 0.025 in. is presented. The LPB process, tooling, and control systems are described, including recent developments in real-time process monitoring for quality control. Performed on CNC machine tools, LPB processing is easily adapted to overhaul and manufacturing shop operations with quality assurance procedures meeting military and industry standards, facilitating transition to military depots and manufacturing facilities.
Laser Cladding of 17-4PH Stainless Knife Edges
Authors: Cuddy Jonathan , Shanker Kartik
Published: September 2008

Laser cladding of 0.4 mm and 0.8 mm wide knife edges made from 17-4PH stainless steel was investigated, using two types of powder and two different post heat treatments. Acceptable cladding deposits of 0.5 to 0.9 mm height were obtained on both sizes of knife edge, and with both powder types. Powder manufactured by water atomization was more difficult to feed during cladding, and produced a substantially higher oxide content in the deposited clad. The clad dimensional results showed that increasing laser energy density into the knife edges caused an increase in both clad build-up height and parent melt-back. An optimal energy density was established for a given knife edge width and powder feed rate, which produced the most efficient cladding deposit. Full solution heat treatment and aging was effective in producing a uniform hardness profile across the clad and substrate materials, while direct aging resulted in a non-uniform profile. This repair technique is applicable to a variety of labyrinth seals used in gas turbine engines.
Comparative Evaluation of Advanced Gas Turbine Cycles With Modified Blade Cooling Models
Authors: Tabari Arian , Khaledi Hiwa , Benisi Ali Hajilouy
Published: September 2008

Advanced gas turbine cycles use advanced blade cooling technologies to reach high turbine inlet temperature. Accurate modeling and optimization of these cycles depend on blade cooling model. In this study, different models have been used to simulate gas turbine performance. The first model is the continuous model and the second is stage-by-stage model with alternative methods for calculating coolant, stagnation pressure loss and SPR. Variation of specific heat and enthalpy with temperature are included in both models. The composition of gas stream in turbine is changed step by step due to air cooling. These models are validated by two case study gas turbine results, which show good agreement with manufacture’s data. Then using these models, a comparison between continuous and stage by stage models is done. Results show that the stage by stage model can be improved to use in variable CPR by changing number of turbine stages. Also, the number of film cooled rows and coated rows change the number of cooled rows. This also increases power, efficiency and TET, while reduces coolant mass flow. For high TIT and with current blade cooling technology, efficiency seems to have no increase relative to lower TIT. CAP increases power but decreases efficiency, where with FP efficiency also increases, while power increases too.
Gasified Biomass Fuelled Gas Turbine: Combustion Stability and Selective Catalytic Oxidation of Fuel-Bound Nitrogen
Authors: Jayasuriya Jeevan , Manrique Arturo , Fakhrai Reza , Fredriksson Jan , Fransson Torsten
Published: September 2008

Low heating value of gasified biomass and its fuel bound nitrogen containing compounds challenge the efforts on utilizing gasified biomass on gas turbine combustor. Low heating value of the gas brings along combustion stability issues and pollutant emission concerns. The fuel bound nitrogen present in gasified biomass could completely be converted to NOx during the combustion process. Catalytic combustion technology, showing promising developments on ultra low emission gas turbine combustion of natural gas could also be the key to successful utilization of biomass in gas turbine combustor. Catalysts could stabilize the combustion process of low heating value gas while the proper design of the catalytic configuration could selectively convert the fuel bound nitrogen into molecular nitrogen. This paper presents preliminary results of the experimental investigations on combustion stability and nitrogen selectivity in selective catalytic oxidation of ammonia in catalytic combustion followed by a brief description of the design of catalytic combustion test facility. The fuel-NOx reduction strategy considered in this study was to preprocess fuel in the catalytic system to remove fuel bound nitrogen before real combustion reactions occurs. The catalytic combustion system studied here contained two stage reactor in one unit containing fuel preprocessor (SCO catalyst) and combustion catalysts. Experiments were performed under lean combustion conditions (λ value from 6 up to 22) using a simulated mixture of gasified biomass. The Selective Catalytic Oxidation approach was considered to reduce the conversion of NH3 into N2. Results showed very good combustion stability, higher combustion efficiency and good ignition performances under the experimental conditions. However, the selective oxidation of fuel bound nitrogen into N2 was only in the range of 20% to 30% under the above conditions.
Thermal-Mechanical Life Prediction System for Coated Anisotropic Turbine Components
Authors: Cunha F. J. , Seetharaman V. , Chyu M. K.
Published: September 2008

Modern gas turbine engines provide large amounts of thrust and experience severe cyclic thermal gradients with sustained mechanical loads. Fatigue damage induced by cyclic thermal transients, along with creep and oxidation damage caused by quasi steady state, long hold-time periods, have emerged as critical life-limiting factors for coated turbine airfoils. It is, therefore, necessary to develop key thermal parameters for life prediction system for hot section components that accounts for operating thermal transients of anisotropic material properties for coated airfoils. Thermal cyclic deformations are determined as a function of the cyclic temperatures and sustained mechanical loads. This leads to the evaluation of local cyclic fatigue damage function, which can be compared against the strain energy density dissipated during monotonic deformation testing for damage assessment. Long hold-time periods at elevated temperatures also lead to cumulative effects of creep and oxidation. Key thermal-mechanical parameters, obtained from the formulation presented, arise as governing parameters, leading to analytical maps necessary to track the damage observed in cyclic thermomechanical test specimens. The contributing damage modes of thermal fatigue, creep and oxidation are summed by the traditional Miner’s rule of accumulated damage. This provides a way to determine the number of cycles remaining in the part.
Understanding Friction Factor Behavior in Liquid Annular Seals With Deliberately Roughened Surfaces: Roughness Geometric Characteristics Defining Flow Resistance
Authors: Villasmil L. A. , Childs D. W. , Chen H. C.
Published: September 2008

Multistage centrifugal pumps and compressors are among the most widely used pieces of rotating machinery in industry. A typical application demands the arrangement of several impellers mounted on a shaft that spin within a stationary case. Annular seals are the most common sealing devices used in this type of machinery. The annular seal design affects both (i) machinery performance in terms of energy conversion efficiency, and (ii) stability due to the interaction within the rotor and the stator through the fluid flow within the seals. Extensive numerical research of several liquid annular seal experiments is in progress, focusing on the patterns that experimentally and numerically provide larger resistance to flow, hexagonal cells (honeycomb) and equilateral triangular cells (isogrid), both constant depths. In the present paper, the geometric characteristics that define the leakage resistance of roughened seals are explored. First, the results of a parametric analysis are discussed, which include previous 2-D predictions and new simulations of multiple rectangular grooved seal geometries. The analysis is limited to the original clearance in the experiments, 0.175 mm. The results indicate that roughened surface to total area ratio, and the depth-to-length ratio are the primary parameters defining the leakage characteristics of these surfaces. Secondly, the effect of the roughness orientation on the friction factor characteristics of these surfaces is addressed. Previous numerical tests have shown that solving the flow up to the laminar sub-layer better captures the behavior of the friction-factor-to-clearance proportionality. Resolving this layer is demanding. Recent numerical studies show promise in reducing computational efforts by employing a simplified empirical model with extended wall functions, indeed avoiding including each roughness in the numerical domain. These studies evaluated the flow behavior in round-hole seals, a perfectly symmetric pattern. Contrary to round holes, nonsymmetric patterns; knurls, honeycombs, or isogrids, consistently provide larger friction factor values. The numerical evaluation of the leakage characteristics in the last two patterns indicates a non-negligible sensitivity to the pattern orientation in one of them.
Thermoeconomic Model Considering the Environment Impacts on Thermoelectric Power Plants: Natural Gas Versus Diesel
Authors: Villela Irai´des Aparecida de Castro , Silveira Jose´ Luz
Published: September 2008

In this paper a comparative analysis of the environmental impact caused by the use of natural gas and diesel in thermoelectric power plants utilizing combined cycle is performed. The objective is to apply a thermoeconomical analysis in order to compare the two proposed fuels. In this analysis, a new methodology that incorporates the economical engineering concept to the ecological efficiency once Cardu and Baica [1, 2], which evaluates, in general terms, the environmental impacts caused by CO2, SO2, NOx and Particulate Matter (PM), adopting as reference the air quality standards in vigour is employed. The thermoeconomic model herein proposed utilizes functional diagrams that allow the minimization the Exergetic Manufacturing Cost, which represents the cost of production of electricity incorporating the environmental impact effects to study the performance of the thermoelectric power plant [3,4]. It follows that it is possible to determine the environmental impact caused by thermoelectric power plants and, under the ecological standpoint, the use of natural gas as a fuel is the best option compared to the use of the diesel, presenting ecological efficiency values of 0.944 and 0.914 respectively. From the Exergoeconomic point of view of, it was found out that the EMC (Exergetic Manufacturing Cost) is better when natural gas is used as fuel compared to the diesel fuel.
A Unified Metric for Fault Detection and Isolation in Engines
Authors: DePold Hans R. , Rajamani Ravi , Morrison William H. , Pattipati Krishna R.
Published: September 2008

In this paper we make two key contributions. First, we formalize the effectiveness of fault detection and isolation (FDI) with a metric that globally considers the following: variance in engine parameter estimate residuals under normal conditions, costs of missed detections and false alarms, costs associated with misclassification of faults, fault frequencies and fault severities. Reducing the error variance increases the signal-to-noise ratio, thereby increasing the reliability and speed of fault-detection algorithms. Minimizing missed detections has enormous implications on operational safety, while minimizing false alarms and fault misclassifications has implications on downtime, asset management, cannot duplicates, and operational costs. This metric measures the trade off between reducing data error variances, between false and missed detects, and misclassification of faults. As a second contribution, we embed this metric in a systematic data-driven diagnostic optimization process for normative decisions on input parameter selection for residual generation, FDI methods and prediction/classification fusion techniques.
Conjugate Heat Transfer Analysis of a Cooled Turbine Vane Using the V2F Turbulence Model
Authors: Luo Jiang , Razinsky Eli H.
Published: September 2008

The conjugate heat transfer methodology has been employed to predict the flow and thermal properties including the metal temperature of a NASA turbine vane at three operating conditions. The turbine vane was cooled internally by air flowing through 10 round pipes. The conjugate heat transfer methodology allows a simultaneous solution of aerodynamics and heat transfer in the external hot gas and the internal cooling passages and conduction within the solid metal, eliminating the need for multiple/decoupled solutions in a typical industry design process. The model of about three million computational meshes includes the gas path and the internal cooling channels, comprising hexa cells, and the solid metal comprising hexa and prism cells. The predicted aerodynamic loadings were found to be in close agreement with the data for all the cases. The predicted metal temperature, external and internal heat transfer distributions at the mid-span compared well with the measurement. The differences in the heat transfer rates and metal temperature under different running conditions were also captured well. The V2F turbulence model has been compared with a low-Reynolds-number k-ε model and a non-linear quadratic k-ε model. The V2F model is found to provide the closest agreement with the data, though it still has room for improvement in predicting the boundary layer transition and turbulent heat transfer, especially on the suction side. The overall results are quite encouraging and indicate that conjugate heat transfer simulation with proper turbulence closure has the potential to become a viable tool in turbine heat transfer analysis and cooling design.
Experimental Investigation of Spray Dynamics Under Jet Engine Augmentor-Like Conditions
Authors: Johnson Javier N. , Lubarsky Eugene , Zinn Ben T.
Published: September 2008

This paper describes an experimental investigation of fuel spray jet breakup mechanisms when it is injected across the high temperature air flow in low and high pressure jet engine augmentor-like conditions. Phase Doppler particle analyzer data and short exposure pulsed shadow graph images were taken of fuel jet injected into an air cross flow with liquid to air momentum ratios ranging from 5 to 180. Measured droplet diameters taken at atmospheric pressure and a flow Mach number of ∼0.15 show a progressive breakup of the droplets, gradually decreasing in size from 250μm to 150μm and finally to 25 μm as the spray moves downstream. The progressive breakup of droplets follows the classical Rayleigh-Helmholtz breakup mechanism. At higher pressure and Mach number tests, the fuel jet undergoes a different breakup process; i.e., the fuel jet breaks up instantaneously into a monodispurse spray of smaller droplets near the injector. High speed images of this process suggest that an aerodynamic breakup mechanism dominates this atomization process near the injector. In summary, the results of this study show the fuel jet breakup mechanism in augmentors varies significantly over the flight envelope.
Numerical Simulation of Aerodynamic Performances of Wet Compression Compressor Cascade
Authors: Zheng Qun , Shao Yan , Zhang Yinyong
Published: September 2008

The thermodynamic analyses and actual applications of wet compression have demonstrated its benefits for power augment. An aerodynamic flow field simulation of the wet compression compressor cascade can give more information about the cascade internal flow patterns. In this paper, a stage of wet compression compressor is simulated with computational fluid dynamics software. Three dimensional, two phases flows are numerically investigated under different water injected amount, different water droplet diameter etc. The CFD results present the details of wet compression compressor cascade flows. And the flow fields of wet compression are compared with those of dry compression.
Time-Resolved Heat Transfer Measurements on the Tip Wall of a Ribbed Channel Using a Novel Heat Flux Sensor: Part I — Sensor and Benchmarks
Authors: Roediger Tim , Knauss Helmut , Gaisbauer Uwe , Kraemer Ewald , Jenkins Sean , von Wolfersdorf Jens
Published: September 2008

A novel heat flux sensor was tested which allows for time-resolved heat flux measurements in internal ribbed channels related to the study of passages in gas turbine blades. The working principle of the Atomic Layer Thermopile (ALTP) sensor is based on a thermoelectric field created by a temperature gradient over an YBCO crystal (the transverse Seebeck effect). The sensors very fast frequency response allows for highly time-resolved heat flux measurements up to the 1 MHz range. This paper explains the design and working principle of the sensor, as well as the benchmarking of the sensor for several flow conditions. For internal cooling passages, this novel sensor allows for highly accurate, time-resolved measurements of heat transfer coefficients, leading to a greater understanding of the influence of fluctuations in temperature fields.
Preliminary Experimental Research to Develop a Combustor for Small Class Aircraft Engine Utilizing Primary Rich Combustion Approach
Authors: Makida Mitsumasa , Yamada Hideshi , Kurosawa Yoji , Yamamoto Takeshi , Matsuura Kazuaki , Hayashi Shigeru
Published: September 2008

A series of experimental researches, including ignition and combustion tests at atmospheric pressure conditions, were conducted to develop a combustor for a small class aircraft engine (with pressure ratio about 20). Under restrictions of the combustor size and cost, in order to satisfy the requirement for ignition and blowout performance with sufficient combustion efficiency and NOx reduction for wide range of operating conditions, we applied single fuel nozzles and utilized the rich-burn-quick quench-lean-burn (RQL) combustion approach. Preliminary combustion tests were conducted to optimize the ignition and blowout characteristics, approximately determining positions of air holes and igniter, and selecting fuel nozzle parameters. Consequently, tubular combustor tests with exhaust gas analysis were also conducted to optimize the air mass flow ratio and the air holes’ positions to suppress NOx emissions. Obtained results showing the RQL characteristics of the combustion, decreasing NOx emissions at high equivalence ratio range, are presented in this report, and the optimized air mass flow ratio and position of air holes, which will be applied to a single sector combustor for the testing at practical pressure and temperature conditions, are also presented.
Preventing Hot Gas Ingestion by Film-Cooling Jets via Flow-Aligned Blockers
Authors: Shih T. I.-P. , Na S. , Chyu M.
Published: September 2008

Flow aligned blockers are proposed to minimize the entrainment of hot gases underneath film-cooling jets by the counter-rotating vortices within the jets. Computations, based on the ensemble-averaged Navier-Stokes equations closed by the realizable k-ε turbulence model, were used to assess the usefulness of rectangular prisms as blockers in increasing film-cooling adiabatic effectiveness without unduly increasing surface heat transfer and pressure loss. The Taguchi’s design of experiment method was used to investigate the effects of the height of the blocker (0.2D, 0.4D, 0.8D), the thickness of the blocker (D/20, D/10, D/5), and the spacing between the pair of blockers (0.8D, 1.0D, 1.2D), where D is the diameter of the film-cooling hole. The effects of blowing ratio (0.37, 0.5, 0.65) were also studied. Results obtained show that blockers can greatly increase film-cooling effectiveness. By using rectangular prisms as blockers, the laterally averaged adiabatic effectiveness at 15D downstream of the film-cooling hole is as high as that at 1D downstream. The surface heat transfer was found to increase slightly near the leading edge of the prisms, but reduced elsewhere from reduced temperature gradients that resulted from reduced hot gas entrainment. However, pressure loss was found to increase somewhat because of the flat rectangular leading edge, which can be made more streamlined.
Using Diagnostics and Prognostics to Minimize the Cost of Ownership of Gas Turbines
Authors: DePold Hans R. , Siegel Jason
Published: September 2008

In general, health management technologies observe features associated with anomalous system behavior and relate these features to useful information about the system’s condition. In the case of prognostics, this information is then related to the expected condition at some future time. The ability to estimate the time to conditional or to mechanical failure is of great benefit in health management systems. Inherently probabilistic in nature, prognostics can be applied to system/component failure modes governed by material condition and by functional loss. Like diagnostic algorithms, prognostic algorithms tend to be generic in design but specific in application. Today, elements of turbine gas generator condition based maintenance, module and part life analysis, and soft removal times play essential roles in sustaining safe operations and effective equipment maintenance. When intelligently combined with value chain analysis they provide the decision support system needed to undertake the maintenance actions which minimize total cost of ownership. The methodologies and mathematical constructs for performing optimization require the system designer to clearly define a useful cost or objective function, which when minimized mathematically produces the parametric design combination that we call optimized. In the specific cases where parametric constraints exist, our optimized system typically will be found along those boundary conditions.
Experimental and Numerical Study of Mass/Heat Transfer on an Airfoil Trailing-Edge Slots and Lands
Authors: Cakan M. , Taslim M. E.
Published: September 2008

Proper cooling of the airfoil trailing edge is imperative in gas turbine designs since this area is often one of the life limiting areas of an airfoil. A common method of providing thermal protection to an airfoil trailing edge is by injecting a film of cooling air through slots located on the airfoil pressure side near the trailing edge, thereby providing a cooling buffer between the hot mainstream gas and the airfoil surface. In the conventional designs, at the breakout plane, a series of slots open to expanding tapered grooves in between the tapered lands and run the cooling air through the grooves to protect the trailing edge surface. In this study, naphthalene sublimation technique was used to measure area averaged mass/heat transfer coefficients downstream of the breakout plane on the slot and on the land surfaces. Three slot geometries were tested: a) a baseline case simulating a typical conventional slot and land design, b) same geometry with a sudden outward step at the breakout plane around the opening, and c) the sudden step was moved one-third away from the breakout plane in the slot. Mass/heat transfer results were compared for these slots geometries for a range of blowing ratios (M = (ρu)s/(ρu)m) from 0 to 2. For the numerical investigation, a pressure-correction based, multi-block, multi-grid, unstructured/adaptive commercial software was used in this investigation. Several turbulence models including the standard high Reynolds number k-ε turbulence model in conjunction with the generalized wall function were used for turbulence closure. The applied thermal boundary conditions to the CFD models matched the test boundary conditions. Effects of a sudden downward step (Coanda) in the slot on mass/heat transfer coefficients on the slot and on the land surfaces were compared both experimentally and numerically.
Comparative Study Between a Cut-Back and Conventional Trailing Edge Film Cooling System
Authors: Telisinghe Janendra C. , Ireland Peter T. , Jones Terry V. , Barrett David , Son Changmin
Published: September 2008

The present experimental study investigates the aero performance differences between a conventional turbine blade trailing edge and a trailing edge with a sharp cut-back. Both geometries include trailing edge film cooling. A scaled model of a conventional turbine blade trailing edge and the trailing edge with a sharp cut-back including the scaled film cooling hole geometries were incorporated into flat plates. Experiments were conducted in a low speed wind tunnel to establish the performance change caused by introducing such a cut-back system on the trailing edge. Experiments were conducted at a Reynolds number of 1.9 × 106 at the trailing edge and for blowing ratios from 0.9 to 2.4. The experimental data presented include; static pressure variation on the plate surfaces; the change in discharge coefficient due to the cut-back; detailed total pressure measurements via a 2D traverse mechanism at a plane 40mm downstream of the flat plates. The total pressure measurements were used to establish the mixed out loss for both configurations.
Measurement of Flow Pattern Within a Rotating Stall Cell in an Axial Compressor
Authors: Lepicovsky J. , Braunscheidel E. P.
Published: September 2008

Effective active control of rotating stall in axial compressors requires detailed understanding of flow instabilities associated with this compressor regime. Newly designed miniature high frequency response total and static pressure probes as well as commercial thermoanemometric probes are suitable tools for this task. However, during the rotating stall cycle the probes are subjected to flow direction changes that are far larger than the range of probe incidence acceptance, and therefore probe data without a proper correction would misrepresent unsteady variations of flow parameters. A methodology, based on ensemble averaging, is proposed to circumvent this problem. In this approach the ensemble averaged signals acquired for various probe setting angles are segmented, and only the sections for probe setting angles close to the actual flow angle are used for signal recombination. The methodology was verified by excellent agreement between velocity distributions obtained from pressure probe data, and data measured with thermoanemometric probes. Vector plots of unsteady flow behavior during the rotating stall regime indicate reversed flow within the rotating stall cell that spreads over to adjacent rotor blade channels. Results of this study confirmed that the NASA Low Speed Axial Compressor (LSAC) while in a rotating stall regime at rotor design speed exhibits one stall cell that rotates at a speed equal to 50.6% of the rotor shaft speed.
Efficiency Entitlement for Bottoming Cycles
Authors: Hofer Douglas C. , Gulen S. Can
Published: September 2008

A significant portion of the new electrical generating capacity installed in the past decade has employed heavy-duty gas turbines operating in a combined cycle configuration with a steam turbine bottoming cycle. In these power plants approximately 1/3 of the power is generated by the bottoming cycle. To ensure that the highest possible combined cycle efficiency is realized it is important to optimize the bottoming cycle efficiency and doing so requires a solid understanding of the efficiency entitlement. This paper describes a new technique for calculating the theoretical efficiency entitlement for a bottoming cycle that corresponds to the maximum possible bottoming cycle work and maximized combined cycle work and efficiency. This new method accounts for the decrease in ideal efficiency as the gas turbine exhaust is cooled as it transfers heat energy to the working fluid in the bottoming cycle. The new definition is compared to conventional definitions, including that of Carnot and an Exergy based second law efficiency, and shown to provide a simple and accurate analytical expression for the entitlement efficiency in a bottoming cycle. For representative cycle conditions, the entitlement efficiency for the bottoming cycle is calculated to be ∼45% compared to the Carnot efficiency for the same conditions of ∼67%. Although the new method is applicable to any power cycle obtaining its heat input from the exhaust stream of a topping cycle, special attention is given to the steam bottoming cycle traditionally used in modern gas turbine combined cycle power plants. Comparisons are made between the ideal bottoming cycle and variants of a steam cycle including a single pressure non-reheat and a three pressure reheat cycle. These comparisons explore the unavoidable loss in efficiency associated with constant temperature heat addition that occurs in the steam cycle.
Experimental and Computational Flow Field Studies of an Integrally Cast Cooling Manifold With and Without Rotation
Authors: Ieronymidis Ioannis , Gillespie David R. H. , Ireland Peter T. , Kingston Robert
Published: September 2008

This paper presents detailed pressure measurements and discharge coefficient data for a long, low aspect ratio manifold; part of a novel blade cooling scheme. The cooling geometry, in which a series of racetrack passages are connected to a central plenum, provides high heat transfer coefficients in regions of the blade in good thermal contact with the outer blade surface. The Reynolds number changes along its length because of the ejection of fluid through a series of 19 transfer holes in a staggered arrangement, which are used to connect ceramic cores during the casting process. For rotation number RN = 0 the velocity down each hole remains almost constant. A correlation between hole discharge coefficient and Velocity Head Ratio is also presented. Pressure loss coefficients in the passage and through the holes are also discussed. A High Pressure (HP) rig was tested to investigate compressibility effects and expand the inlet Reynolds number range. A CFD model was validated against the experimental data, and then used to investigate the effects of rotation on the hole discharge coefficients. Results are presented for an inlet Reynolds number of 43477. At an engine representative rotation number of 0.08 corresponding buoyancy number of 0.17 there was little effect of rotation. However, at high rotational speeds secondary flows in the cooling passage and the exit plenum greatly reduce the hole discharge coefficient by increasing the local cross flow at the hole entrances and capping the hole exits in a manner similar to that seen in leading edge film-cooling geometries.
Evolution of Surface Deposits on a High Pressure Turbine Blade: Part I — Physical Characteristics
Authors: Wammack James E. , Crosby Jared , Fletcher Daniel , Bons Jeffrey P. , Fletcher Thomas H.
Published: September 2008

Turbine blade coupons with three different surface treatments were exposed to deposition conditions in an accelerated deposition facility. The facility simulates the flow conditions at the inlet to a first stage high pressure turbine (T = 1150°C, M = 0.31). The combustor exit flow is seeded with dust particulate that would typically be ingested by a large utility power plant. The three coupon surface treatments included: (1) bare polished metal, (2) polished thermal barrier coating with bondcoat, and (3) unpolished oxidation resistant bondcoat. Each coupon was subjected to four successive 2 hour deposition tests. The particulate loading was scaled to simulate 0.02 ppmw (parts per million weight) of particulate over three months of continuous gas turbine operation for each 2 hour laboratory simulation (for a cumulative one year of operation). Three-dimensional maps of the deposit-roughened surfaces were created between each test, representing a total of four measurements evenly spaced through the lifecycle of a turbine blade surface. From these measurements the surface topology and roughness statistics were determined. Despite the different surface treatments, all three surfaces exhibited similar non-monotonic changes in roughness with repeated exposure. In each case, an initial build-up of isolated roughness peaks was followed by a period when valleys between peaks were filled with subsequent deposition. This trend is well documented using the average forward facing roughness angle in combination with the average roughness height as characteristic roughness metrics. Deposition-related mechanisms leading to spallation of the thermal barrier coated coupons are identified and documented.
Advanced Labyrinth Seals for Steam Turbine Generators
Authors: Vakili Ahmad D. , Meganathan Abraham J. , Ayyalasomayajula Sricharan , Hesler Stephen , Shuster Lewis
Published: September 2008

A new class of knives (C-Shaped) for reduced labyrinth seal discharge has been designed and assessed through two dimensional numerical modeling of the seal’s internal flow passages. Modeling procedures used for the analysis have been previously validated by comparison with static labyrinth seal experiments. The objectives of the new seal are to: 1) reduce flow leakage through the seal and 2) introduce structural flexibility in the knives so that design clearances could be maintained even after rub events during startup. The baseline chosen for comparative evaluation is an N2 packing used in GE steam turbines. The new seals have compliant C-shaped knives instead of the straight knives, found in an N2 packing. The best performing configuration has one tall ‘C’ shaped long knife and three ‘C’ shaped short knives in each stage. It was found that the best configuration at clearances similar to the baseline seal reduces flow leakage by 42%. Two dimensional numerical structural analyses showed that the new seal knife is more flexible than a straight knife. This is also intuitive by virtue of its geometric profile. A non-dimensional geometric parameter correlates with the degree of flexibility in the knife. These results indicate a potential for design of labyrinth seals that maintain lower design clearances throughout their life time by carefully selecting the knives’ geometric parameters and incorporating high performance composite materials. Then, the new design would result in significantly lower steam leakage.
Effect of Jet Pulsing on Film Cooling: Part 2 — Heat Transfer Results
Authors: Coulthard Sarah M. , Volino Ralph J. , Flack Karen A.
Published: September 2008

Pulsed film cooling was studied experimentally to determine its effect on film cooling effectiveness and heat transfer. The film cooling jets were pulsed using solenoid valves in the supply air line. Cases with a single row of cylindrical film cooling holes inclined at 35 degrees to the surface of a flat plate were considered at blowing ratios of 0.25, 0.5, 1.0, and 1.5 for a variety of pulsing frequencies and duty cycles. Temperature measurements were made using an infrared camera and thermocouples. The plate was equipped with constant flux surface heaters, and data were acquired for each flow condition with the plate both heated and unheated. The local film cooling effectiveness, Stanton numbers, and heat flux ratios were calculated and compared to baseline cases with continuous blowing and no blowing. Stanton number signatures on the surface provided evidence of flow structures including horseshoe vortices wrapping around the film cooling jets and vortices within the jets. Pulsing tends to increase Stanton numbers, and the effect tends to increase with pulsing frequency and duty cycle. Some exceptions were observed, however, at the highest frequencies tested. Overall heat flux ratios also show that pulsing tends to have a detrimental effect with some exceptions at the highest frequencies. The best overall film cooling was achieved with continuous jets and a blowing ratio of 0.5. The present results may prove useful for understanding film cooling behavior in engines, where mainflow unsteadiness causes film cooling jet pulsation.
Development and Demonstration of Engine-Ready Surface-Stabilized Combustion System
Authors: Arellano Leonel O. , Bhattacharya Arun K. , Smith Kenneth O. , Greenberg Steven J. , McDougald Neil K.
Published: September 2008

Alzeta Corporation has developed surface-stabilized fuel injectors for use in lean-premixed low-emissions combustion systems. These injectors use a patented technique to form interacting high-flow and low-flow flame zones immediately above a selectively-perforated porous metal surface. This allows stable operation at low reaction temperatures conducive for preventing high NOx formation. Solar Turbines and Alzeta had previously worked together to evaluate single-injector and full-scale proof-of-concept test hardware. This paper presents results of a combustion system developed for evaluation on an engine. The next-generation hardware has evolved to include a pilot to handle low engine speeds, and flow circuits have been adjusted to meet low-pressure drop requirements. Screening tests of the full-scale system have been completed at simulated engine conditions in a full-scale rig. Single-digit NOx and CO emissions have been achieved without encountering combustion-driven instabilities. The combustion system demonstrated adequate power turndown with the assistance of the pilot module, and studies to predict the service life of burners have been initiated.
Examination of Ambient Pressure Effects on Hybrid Solid Oxide Fuel Cell Turbine System Operation Using Hardware Simulation
Authors: Tucker David , Lawson Larry , VanOsdol John , Kislear Jordan , Akinbobuyi Ayodeji
Published: September 2008

The effect of ambient inlet air pressure variations on the compressor performance in a direct fired solid oxide fuel cell gas turbine hybrid power system has been studied using the Hybrid Performance (Hyper) project hardware simulation facility at the U.S. Department of Energy, National Energy Technology Laboratory (NETL). The Hyper facility at NETL makes use of a high speed numerical model which controls a burner and a series of pressure vessels and piping to collectively simulate a direct-fired, high-temperature fuel cell. The hardware simulating the fuel cell is integrated into the system with a modified single shaft turbine driven compressor and a pair of recuperates to provide cathode air preheat from the turbine exhaust. Orifice plates were employed at the compressor inlet of the facility to parametrically vary the inlet pressure. The compressor inlet temperature for all tests conducted was held within a 2 Kelvin range. Variation in inlet pressure was shown to have a significant effect on many hybrid system performance parameters. Some system parameters were shown to have a linear dependency on the inlet pressure, leading to the implementation of correction factors. Similar dependence of compressor discharge pressure and temperature on compressor inlet pressure was predicted by dynamic models based on isentropic compression principles. Transient operation was also impacted by changes in compressor inlet pressure. Startup profiles are shown against the compressor stall line for indication of changes in surge margin.
Design and Off-Design Characteristics of the Alternative Recuperated Gas Turbine Cycle With Divided Turbine Expansion
Authors: Hwang Sung Hoon , Yoon Soo Hyung , Kim Tong Seop
Published: September 2008

In order to fully address the characteristics of the alternative recuperated cycle with divided turbine expansion, both the design and off-design analyses have been performed. Two types of mechanical design are assumed: two-shaft and single-shaft. In particular, optimal pressure ratio division between the high and low pressure turbines is evaluated for the single shaft configuration. It is predicted that the alternative recuperated cycle hardly exhibits sensible design efficiency advantage over the conventional recuperated cycle for moderate turbine inlet conditions and with usual component performances. An advantage of the alternative cycle with single shaft design is that thermal efficiency is less sensitive to compressor pressure ratio compared with other configurations and we can also have flexibility in the turbine division without much efficiency loss. The part load analyses have been carried out with the aid of realistic component maps and models for off-design operation. In addition to the general fuel only control, a variable speed control is assumed as the part load operating strategy of the single shaft configuration. Obvious advantage with the alternative cycle is observed in the variable speed operation of the single shaft design. With this strategy, the part load efficiency of the alternative cycle is far superior to the conventional cycle. Almost constant efficiency is predicted for a wide power range.
The Role of Leading-Edge Contouring on End-Wall Flow and Heat Transfer: Computations and Experiments
Authors: Saha Arun K. , Mahmood Gazi I. , Acharya Sumanta
Published: September 2008

Numerical predictions and measurements of the flow structure and the Nusselt number behavior are presented for the endwall region of a linear blade cascade with contoured leading edge fillets. Two types of fillet profiles are employed: (a) a linear profile and (b) a circular profile. The fillets are placed at the junction of the blade leading edge and bottom endwall. The results with the fillets are also compared with the baseline case (predicted and measured) without any leading edge fillet. The pitchwise pressure gradient and shear stress on the endwall region are reduced for the filleted blades compared to the baseline case where there is no fillet. The flow turning from the axial direction (yaw angle) and the pitchwise flow velocity at the endwall boundary layer are also reduced in the vicinity of the fillets. In addition, the fillets weaken the leading edge horseshoe vortex by significantly reducing its vorticity and turbulent kinetic energy. Because of such changes in the endwall boundary layer, especially in the region where the fillets are located, the streamwise vorticity, turbulence kinetic energy, and total pressure losses in the passage vortex and the suction side leg vortex are reduced compared to the baseline. Endwall Nusselt numbers for the filleted cases are reduced upstream of the throat region.