bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of Equivalence Ratio Fluctuations in a Lean Premixed Gas Turbine Combustor Using an IR Absorption Technique
Authors: Lee Hyung Ju , Kim Kyu Tae , Lee Jong Guen , Quay Bryan D. , Santavicca Domenic A.
Published: January 2011

An experimental study was conducted to estimate and confirm equivalence ratio fluctuations at the inlet of a lean premixed gas turbine combustor. Fuel injectors were placed at several locations in the mixing section of the combustor, in order to produce different instability characteristics due to the equivalence ratio fluctuations. An IR absorption technique was used to measure the equivalence ratio fluctuations at the inlet of the dump combustor. The measured IR signals were processed in two different ways and the results were compared to confirm the two calibrated equivalence ratio signals. The processed data showed that the two processing methods gave very similar results, and the phase of the measured equivalence ratio fluctuations at the combustor inlet by the IR absorption technique agreed well with that of equivalence ratio fluctuations predicted by time lags in the mixing section. It was, however, not possible to accurately predict the magnitude of the equivalence ratio fluctuations at the combustor inlet by the time lag analysis because the equivalence ratio fluctuations generataed at the fuel injection location is changed by mixing and diffusion as the fuel is convected through the combustor.
Accuracy of Conventional Adiabatic Effectiveness and Heat Transfer Augmentation Factors in Predicting Heat Flux Into a Turbine Blade Leading Edge
Authors: Dobrowolski Laurene D. , Bogard David G. , Ravelli Silvia
Published: January 2011

This paper focuses on the legitimacy of using conventional predictions, based on adiabatic wall temperature (Taw) and heat transfer coefficient (HTC) augmentation, of heat flux into a film cooled leading edge. To answer this question, the heat flux predicted using Taw was compared to the heat flux into a conducting leading edge. The study used numerical simulations with the k-ε turbulence model of FLUENT. The model simulated was a three-row leading edge with one row of holes on the stagnation line and two additional rows located at ±25°, which has been experimentally studied extensively. The adiabatic wall temperature was obtained from an adiabatic simulation. External heat transfer coefficients were determined from a constant heat flux simulation using a density ratio of DR = 1.0, as is commonly done experimentally. A conjugate heat transfer simulation was also run to give the surface temperature and heat flux into the conducting leading edge. Overall, the heat transfer was well predicted with the use of Taw and HTC augmentation. However, between the holes, conventional predictions of heat transfer were poor, with disparity up to 30% when compared with the conducting wall heat flux obtained from the conjugate heat transfer simulation. Thermal boundary layer profiles were used to understand the disparity between the heat fluxes obtained from the conventional prediction and the conducting wall simulation.
An Advanced Multi-Configuration Stator Well Cooling Test Facility
Authors: Coren D. D. , Atkins N. R. , Turner J. R. , Eastwood D. E. , Davies S. , Childs P. R. N. , Dixon J. , Scanlon T. S.
Published: January 2011

Optimisation of cooling systems within gas turbine engines is of great interest to engine manufacturers seeking gains in performance, efficiency and component life. The effectiveness of coolant delivery is governed by complex flows within the stator wells and the interaction of main annulus and cooling air in the vicinity of the rim seals. This paper reports the development of a test facility which allows the interaction of cooling air and main gas paths to be measured at conditions representative of those found in modern gas turbine engines. The test facility features a two stage turbine with an overall pressure ratio of approximately 2.6:1. Hot air is supplied to the main annulus using a Rolls-Royce Dart compressor driven by an aero-derivative engine plant. Cooling air can be delivered to the stator wells at multiple locations and at a range of flow rates which cover bulk ingestion through to bulk egress. The facility has been designed with adaptable geometry to enable rapid changes of cooling air path configuration. The coolant delivery system allows swift and accurate changes to the flow settings such that thermal transients may be performed. Particular attention has been focused on obtaining high accuracy data, using a radio telemetry system, as well as thorough through-calibration practices. Temperature measurements can now be made on both rotating and stationary discs with a long term uncertainty in the region of 0.3 K. A gas concentration measurement system has also been developed to obtain direct measurement of re-ingestion and rim seal exchange flows. High resolution displacement sensors have been installed in order to measure hot running geometry. This paper documents the commissioning of a test facility which is unique in terms of rapid configuration changes, non-dimensional engine matching and the instrumentation density and resolution. Example data for each of the measurement systems is presented. This includes the effect of coolant flow rate on the metal temperatures within the upstream cavity of the turbine stator well, the axial displacement of the rotor assembly during a commissioning test, and the effect of coolant flow rate on mixing in the downstream cavity of the stator well.
Semi-Empirical Methods for the Analysis of Vertical Axis Wind Turbines With Helical Blades
Authors: Marini Martino , Gazzano Renato , Satta Antonio
Published: January 2011

The Vertical Axis Wind Turbine (VAWT) was not successful for large size installations but it is suitable for small size applications. It is likely to integrate better in an urban environment due to its architectural features and its intrinsic capability to exploit winds from any direction without an orientation system. The performances of these machines can be evaluated with enough accuracy by means of the semi-empirical models that allow to explore various configurations in a straightforward way. They need the support of experimental investigations for aerodynamic coefficients and they have to refer to a limited class of airfoils. However they can be matched with CFD tools usefully to enlarge the field of investigation keeping the above advantages. In the paper the performance of the H type (giromill) configuration as well as of the helical rotors are calculated and compared. The latter geometry has received recently a special attention on account of some aspects that are discussed.
Coupled Static/Dynamic Modeling of Wedge Dampers for Turbine Blades
Authors: Zucca Stefano , Firrone Christian M. , Gola Muzio
Published: January 2011

Friction damping is one of the most exploited systems of passive control of vibration of mechanical systems. A common type of blade-to-blade friction dampers are the so-called underplatform dampers (UPDs); they are metal devices placed under the blade platforms and held in contact with them by the centrifugal force acting during rotation. The effectiveness of underplatform dampers to dissipate energy by friction and reduce vibration amplitude depend mostly on the damper geometry and material and on the static pre-loads pressing the damper against the blade platforms. The common procedure used to estimate the static pre-loads acting on underplatform dampers consists in decoupling the static and the dynamic balance of the damper. A preliminary static analysis of the contact is performed in order to compute the static pressure distribution over the damper/blade interfaces, assuming that it does not change when vibration occurs. In this paper a coupled approach is proposed. The static and the dynamic displacements of blade and underplatform damper are coupled together during the forced response calculation. Both the primary structure (the bladed disk) and the secondary structure (the damper) are modelled by finite elements and linked together by contact elements, allowing for stick, slip and lift off states, placed between each pair of contact nodes, by using a refined version of the state-of-the-art friction contact model. In order to model accurately the blade/damper contact with a large number of contact nodes without increasing proportionally the size of the set of non-linear equations to be solved, damper and blade dynamics are modelled by linear superposition of a truncated series of normal modes. The proposed method is applied to a bladed disk under cyclic symmetric boundary conditions in order to show the capabilities of the method compared to the classical decoupled approaches.
Labyrinth Seal Technology Within the Dutch Aero Engine Cluster
Authors: Kool Gerrit , Kloosterman Arjen , Soemarwoto Bambang , Versluis Joris , Janssen Robert
Published: January 2011

Labyrinth honeycomb seals are regarded as very mature technology and seal flow performance improvements seem to be hardly achievable. However, since computational fluid dynamics have been successfully applied on the flow simulation through these seals, further seal performance optimization becomes within reach against acceptable development costs. This paper describes a staggered labyrinth seal design and is referenced against a two-knife edge stepped seal. Both seals have been evaluated with 3D CFD and tested in an advanced seal test rig facility under realistic conditions. The work described was done by the Dutch Aero Engine Cluster DAEC within the IMPACT-project for Improved Performance by Advanced Compressor Technology. The staggered seal has been selected initially based on potential performance gains, insensitive to axial excursion, good manufacturability, and robust design at acceptable development and manufacturing costs. The staggered labyrinth seal showed a performance improvement of over 30% compared with the baseline two knife edge stepped labyrinth seal. This was demonstrated by both, CFD-analyses and rig testing. In addition, the CFD and test data are consistent with each other.
Numerical Simulation of Pollutant Emissions in a Can-Type Low NOx Gas Turbine Combustor
Authors: Wang Di , Kong Wenjun , Ai Yuhua , Wang Baorui
Published: January 2011

A research program is in development in China in order to realize a demonstrator of combined cooling heating and power system (CCHP) with net electrical output around 100kW by using of a can-type micro gas turbine. In this paper, numerical simulations were completed to investigate the pollutant emissions in a can-type low NOx gas turbine combustor. Based on the analysis of the computational fluid dynamics (CFD) results, a Chemical Reactor Network (CRN) model was set up to simulate the pollutant emissions in the combustor with detailed gas-phase chemical kinetic mechanism of GRI-Mech 3.0. The CRN consists of a number of ideal reactors of the perfectly stirred reactors (PSR) and plug flow reactors (PFR) in series and parallel structures. Two types of CRN models were designed. One is relatively simple, another is more complex. The results show that the complex CRN model corresponds with the actual combustion process better. The trends of nitrogen oxides (NOx) and carbon monoxide (CO) varying with the equivalence ratio were conducted. Effects of the inlet temperature and pressure on NOx and CO emissions were also presented in this paper. At last, the numerical results are compared with the experimental results.
Refined Operating Profile Generation for Air Cushion Vehicles
Authors: Canilang Benjamin , Hampshire James
Published: January 2011

This paper examines the utilization of Landing Craft, Air Cushion (LCAC) historical operational data, empirical knowledge and emergent lifecycle topics to refine the operational profile of LCAC and other air cushion vehicles. Since 1986, the United States Navy’s (USN) LCAC vehicle has accumulated sizeable operational hours in a unique and rigorous environment. Such a distinctive operating environment prohibits singular application of a surface ship or aircraft operational profile. Addressing emergent lifecycle issues, such as fleet wide main engine 4th nozzle failures, the need for a refined operating profile has been identified. Presently, all component life limit forecasting and inspection criterion are dictated by an antiquated notional operating profile, which utilize inadequate cycling assumptions. Furthermore, existing practice records total operational hours and main engine start data. Neither variable correspond to cyclic data. Improved accuracy of the mission profile will assist in drive-train component life limit assessment and critical inspection criteria. This paper will expand upon generation of a refined operation profile tailored to air cushion vehicle operation based upon service history, mission requirements and testing.
The Effects of Wet Compression With Fuel Injection at the Geometry and the Design Point Performance of an Axial Flow Compressor
Authors: Antonogiannakis Emmanouil , Templalexis Ioannis
Published: January 2011

Over the past few years, an intensive effort has been put forth to reduce gas turbine engine generated pollutants, as well as fuel consumption. The current research team understanding the motives behind this effort, suggests an alternative method of wet compression that of using fuel as a cooling medium. Fundamentally, the method of wet compression with fuel injection is based on the same principles of wet compression incorporating water injection. However, there are some considerable differences between the two approaches. A thorough comparison has been carried out revealing each method’s advantages and disadvantages. Following the initial comparison of the two methods, the study goes a step further by investigating the applicability of wet compression incorporating fuel. The investigation has taken into account the characteristics of the axial flow compressor where a typical aviation fuel was injected. However, in order to acquire all the necessary information before putting method’s applicability into context, the differences between dry compression and wet compression with fuel injection were examined. In this new approach, the compressor is the engine component where the fuel is injected first, thus a preliminary design study was carried out along an axial compressor’s mean radius line. Finally the computation has been carried out for both dry and wet compression techniques. Compressor’s specifications were similar to J85’s compressor whereas fuel’s specifications were based on JP-8’s properties. Compressor’s geometry and design point performance, were computed using a mean line analysis domestic code. A brief analysis of the code will be given, including both the initial version that was used for the dry compression calculations, as well as the modified one that was used for the wet compression calculations. After that, the presentation of the results follows. Finally, the paper will be concluded with a discussion of the findings and wet compression’s with fuel injection perspectives.
Non-Destructive TBC Spallation Detection by a Micro-Indentation Method
Authors: Tannenbaum J. M. , Kang B. S.-J. , Alvin M. A.
Published: January 2011

In this research, a load-based depth-sensing micro-indentation method for spallation detection and damage assessment of thermal barrier coating (TBC) materials is presented. A non-destructive multiple loading/partial unloading testing methodology was developed where in stiffness responses of TBC coupons subjected to various thermal cyclic loading conditions were analyzed to predict the spallation site and assess TBC degradation state. The measured stiffness responses at various thermal loading cycles were used to generate time-series color maps for correlation with accumulation of TBC residual stress states. The regions with higher stiffness responses can be linked to a rise in out-of-plane residual stress located near or at the yttria stabilized zirconia (YSZ)/thermally grown oxide (TGO) interface, which is ultimately responsible for initiating TBC spallation failure. A TBC thermal exposure testing plan was carried out where time-series cross-sectional microstructural analyses of damage accumulation and spallation failure associated with the evolution of bond coat/TGO/top coat composite (e.g. thickness, ratcheting, localized oxidations, etc.) of air plasma sprayed (APS) TBCs were evaluated and correlated to the measured stiffness responses at various thermal cycles. The results show that the load-based micro-indentation test methodology is capable of identifying the spallation site(s) before actual occurrence. This micro-indentation technique can be viewed as a viable non-destructive evaluation (NDE) technique for determining as-manufactured and process-exposed TBCs. This technique also shows promise for the development of a portable instrument for on-line, in-situ spallation detection/prediction of industrial-size TBC turbine components.
Aerodynamic Measurements on a Vertical Axis Wind Turbine in a Large Scale Wind Tunnel
Authors: Battisti L. , Zanne L. , Dell’Anna S. , Dossena V. , Paradiso B. , Persico G.
Published: January 2011

This paper presents the first results of a wide experimental investigation on the aerodynamics of a vertical axis wind turbine. Vertical axis wind turbines have recently received particular attention, as interesting alternative for small and micro generation applications. However, the complex fluid dynamic mechanisms occurring in these machines make the aerodynamic optimization of the rotors still an open issue and detailed experimental analyses are now highly recommended to convert improved flow field comprehensions into novel design techniques. The experiments were performed in the large-scale wind tunnel of the Politecnico di Milano (Italy), where real-scale wind turbines for micro generation can be tested in full similarity conditions. Open and closed wind tunnel configurations are considered in such a way to quantify the influence of model blockage for several operational conditions. Integral torque and thrust measurements, as well as detailed aerodynamic measurements were applied to characterize the 3D flow field downstream of the turbine. The local unsteady flow field and the streamwise turbulent component, both resolved in phase with the rotor position, were derived by hot wire measurements. The paper critically analyses the models and the correlations usually applied to correct the wind tunnel blockage effects. Results evidence that the presently available theoretical correction models does not provide accurate estimates of the blockage effect in the case of vertical axis wind turbines. The tip aerodynamic phenomena, in particular, seem to play a key role for the prediction of the turbine performance; large-scale unsteadiness is observed in that region and a simple flow model is used to explain the different flow features with respect to horizontal axis wind turbines.
Gaseous and Particulate Emissions Results of the NASA Alternative Aviation Fuel Experiment (AAFEX)
Authors: Bulzan Dan , Anderson Bruce , Wey Changlie , Howard Robert , Winstead Edward , Beyersdorf Andreas , Corporan Edwin , DeWitt Matthew J. , Klingshirn Chris , Herndon Scott , Miake-Lye Richard , Timko Michael , Wood Ezra , Tacina Kathleen M. , Liscinsky David , Hagen Donald , Lobo Prem , Whitefield Phillip
Published: January 2011

The Aircraft Alternative Fuels Emissions experiment (AAFEX) was conducted at National Aeronautic and Space Administration (NASA) Dryden Flight Research Center (DFRC) Aircraft Operations Facility (DAOF) in Palmdale, California, during January and February 2009. The purpose was to systematically investigate the effect of alternative fuels on both gas-phase and particle emissions from a CFM56-2C1 engine on NASA’s DC-8 aircraft parked on the ground as functions of engine power, fuel composition, and exhaust plume age. Emissions parameters were measured at 6 engine power settings, ranging from idle to maximum thrust, in samples collected at 1, 30, and 145 meters (m) downstream of the exhaust plane as the aircraft burned three pure fuels and two fuel blends. The fuels included JP-8, two fuels produced using the Fischer-Tropsch process and 50/50 blends by volume of the F-T fuels with JP-8. The 1 m sampling rakes contained multiple gas and particle inlet probes and could also be traversed in order to measure the spatial variation of emissions across the engine exhaust plane. The #2 inboard engine on the left side always burned JP-8 while the #3 inboard right side engine was fueled with the various fuels and fuel blends. In addition, emissions from the Auxiliary Power Unit (APU) were also evaluated with both JP-8 and one pure F-T fuel. Both gaseous and particulate emissions are presented. Results show that the synthetic fuels reduced pollutant emissions while having relatively little effect on engine operation or performance.
A Method to Determine the Exact Time Period of Oscillations of a Bifilar Pendulum
Authors: Sharma Sheshadri , Jettappa Richard Rodrigues
Published: January 2011

A novel method to determine the exact time period of oscillations of a class of non-linear systems is presented. Taking the bifilar pendulum as an example, and employing the conservation of total energy concept, the free oscillations of the system is studied. The governing equation of motion of a bifilar pendulum is non-linear. The integration of this equation to obtain the time period of oscillation is highly complicated and only numerical solution is available. This is because the integral is singular at the extremities of the motion where the velocity will be zero. But, what cannot be achieved by integral calculus can be obtained easily by employing the definition of velocity taught in the high school curriculum. By employing this simple mathematical trick, this intractable equation is recast in a different but exact form. This leads to the identification of what is called the “Geometric Inertia” in bifilar pendulums. This Geometric Inertia is the additional inertia displayed by the system due to the constraint imposed by the two filaments as a result of the geometry of the pendulum. In the proposed method, the total displacement of the system is considered and divided into small equal segments. At the end points of each such segment, the corresponding velocity is calculated from the energy equation. Noting that the velocities are zero at the extremities of the system, an average velocity to each segment is calculated, and this average velocity is positive in each segment. The “delta” time spent by the system in each segment is now calculated by dividing the segment length by the average velocity of that segment. (From, time = displacement/velocity). The linear sum of such “delta” times gives the time period of oscillation. As the number of segments is increased, thereby reducing the segment length, the estimate becomes increasingly accurate. The proposed approach avoids a direct integration of complex, and often singular expressions that complicate the determination of time periods of oscillations of non-linear systems.
A Simple Thermal Model of Bearings With Transient Effects
Authors: Justice Karleine M. , Halliwell Ian , Dalton Jeffrey S.
Published: January 2011

In thermal management, system-level models provide an understanding of interactions between components and integration constraints — issues which are exacerbated by tighter coupling in both real life and simulation. A simple model of the steady-state thermal characteristics of the bearings in a two-spool turbofan engine has been described in previous work [1], where it was compared with a more comprehensive tribology-based simulation. Since failure is more likely to occur during transient rather than steady-state operating conditions, it is important that transient behavior is also studied. Therefore, development of models capable of capturing transient system-level performance in air vehicles is critical. In the current paper, the former simple model is used for the generation of a method to replicate the transient effects of heat loads within the lubrication system of a gas turbine engine. The simple engine model that defined the lubrication system is representative of a twin-spool, mid-size, high bypass ratio turbofan used in commercial transport. In order to demonstrate the range and versatility of the parametric heat load model, the model is now applied to the transient operation of a low-thrust unmanned aerial vehicle (UAV) engine, similar to that found on the Global Hawk. There are five separate bearings in the oil loop model and four separate oil sump locations. Contributions to the heat load calculations are heat transfer through the bearing housings and friction caused by station temperatures and shaft speeds, respectively. The lubrication system has been simplified by applying general assumptions for a proof-of-concept of the new transient parametric model. The fuel flow rate for the fuel-cooled oil cooler (FCOC) is set via the full authority digital electronic control (FADEC) in the transient engine model which is coupled to the parametric heat load model. Initially, it is assumed that total heat transfer from the bearings to the oil correspond to oil temperature changes of 150–250°F (83–139°C). The results show that successful modeling of the transient behavior on the thermal effects in the bearings of a gas turbine engine using the MATLAB/Simulink environment have been achieved. This is a valuable addition to the previous steady-state simulation, and the combined tools may be used as part of a more sophisticated thermal management system. Because it is so simple and scalable, the tool enables thermal management issues to be addressed in the preliminary design phase of a gas turbine engine development program.
A Method for Evaluating the Effect of Circumferential Inlet Distortion on the Aerodynamic Stability of Multi-Stage Axial-Flow Compressors
Authors: Nakano Tsuguji , Breeze-Stringfellow Andy
Published: January 2011

A simple engineering parameter to evaluate the stability of high-speed multi-stage compressors with distorted inlet flow has been derived based on a simplified semi-compressible linear stability model. The parameter consists of steady-state flow quantities and geometric parameters of the compressor and it indicates that the circumferential integral of the slope of the steady-state individual blade row static pressure rise characteristics is important in the determination of the compressor stability limit in the presence of distortion. The parameter reduces to the author’s rotating stall inception parameter in the limit of non-distorted inlet flow. Since the model includes a downstream plenum and throttle, a condition for pure surge inception with undistorted inlet flow has been deduced. The pure surge conditions can be reduced to the classical dynamic and static instability conditions in the limit of a constant annulus area incompressible compressor. The results indicate that rotating stall always precedes surge instability, as many engineers and researchers would expect from experience. The parameter for instability with inlet distortion was calculated using test data measured in a high-speed 5-stage compressor with two different types of circumferential inlet distortion, and the results show that the parameter has a strong correlation with the data and is an improvement over the classical incompressible stability parameter. The results demonstrate that the parameter captures much of the physics important during the instability inception in a high-speed multi-stage compressor subjected to circumferential inlet distortion. The parameter clearly shows how each compressor component’s characteristics contribute to the overall stability in a high speed axial multi-stage compressor, therefore, it will aid engineers and designers in their understanding and prediction of the aerodynamic instability inception phenomena.
A Physically Enhanced Method for Sub-Idle Compressor Map Generation and Representation
Authors: Aslanidou Ioanna , Zachos Pavlos K. , Pachidis Vassilios , Singh Riti
Published: January 2011

Sub-idle is a very challenging operating region, as the performance of a gas turbine engine changes significantly compared to design conditions. In addition, the regulations for new and existing engines are becoming stricter and the prediction of engine relight capability is essential. In order to predict the performance of an engine, detailed component maps are required. The data obtained from rig tests is insufficient at low speeds, creating the need for generation of maps within the sub-idle regime. The first step towards this direction is the use of an extrapolation process. This is a purely mathematical process and the results are not usually of sufficient accuracy. In addition, this method does not provide any insight on the physical phenomena governing the operation of the compressor at low speeds. The accuracy of the resulting compressor map can be increased with a better low speed region definition; this can be achieved via the thorough study of a locked rotor compressor, enabling the derivation of the zero rotational speed line and allowing an interpolation process for the generation of the low speed part of the characteristic. In this work an enhanced sub-idle compressor map generation technique is proposed. The suggested methodology enables the generation of characteristics at far off-design conditions with enhanced physical background. Alternative parameters for map representation are also introduced. Provided that the all the blade rows of the compressor are of known geometry, a numerical analysis is used for the calculation of the characteristic of the half stage and a stage stacking method is employed to create the entire compressor characteristic. This way, the sub-idle region of the map can be calculated through interpolation, which provides a more accurate and predictive technique. The application to compressor maps showed that the methodology proposed is robust and capable to enhance any performance simulation tool used for the prediction of transient altitude relight or groundstarting manoeuvres.
Separation Control on a Very High Lift Low Pressure Turbine Airfoil Using Pulsed Vortex Generator Jets
Authors: Volino Ralph J. , Kartuzova Olga , Ibrahim Mounir B.
Published: January 2011

Boundary layer separation control has been studied using vortex generator jets (VGJs) on a very high lift, low-pressure turbine airfoil. Experiments were done under high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in the suction surface boundary layer. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000 and 50,000. Jet pulsing frequency, duty cycle, and blowing ratio were all varied. Computational results from a large eddy simulation of one case showed reattachment in agreement with the experiment. In cases without flow control, the boundary layer separated and did not reattach. With the VGJs, separation control was possible even at the lowest Reynolds number. Pulsed VGJs were more effective than steady jets. At sufficiently high pulsing frequencies, separation control was possible even with low jet velocities and low duty cycles. At lower frequencies, higher jet velocity was required, particularly at low Reynolds numbers. Effective separation control resulted in an increase in lift and a reduction in total pressure losses. Phase averaged velocity profiles and wavelet spectra of the velocity show the VGJ disturbance causes the boundary layer to reattach, but that it can re-separate between disturbances. When the disturbances occur at high enough frequency, the time available for separation is reduced, and the separation bubble remains closed at all times.
Thermally Sprayed Abradable Coatings in Steam Turbines: Design Integration and Functionality Testing
Authors: Sporer Dieter , Wilson Scott , Fiala Petr , Schuelein Ruediger
Published: January 2011

The concept of thermally sprayed abradable sealing technology has successfully been used in aero engines and industrial gas turbines for several decades now. More recently efforts were undertaken to implement the concept of seal coatings in steam turbine designs. As these typically use labyrinth type sealing, the application and test methods for sprayed seals applied to improve efficiency and reduce emissions need to be tailored to this particular seal configuration. This paper reviews how steam turbines can benefit from abradable coating technology and how it can be implemented into existing labyrinth seal designs for various seal locations in a steam turbine. A detailed review of high temperature rig abradability testing capabilities for labyrinth seal layouts using abradable coatings will be provided. Coating materials and their performance in a high temperature steam environment at 650 °C ( 1200 °F ) will be discussed. The application of coatings to various steam turbine components including large casings will be reviewed.
Effect of Unsteady Wakes on Boundary Layer Separation on a Very High Lift Low Pressure Turbine Airfoil
Authors: Volino Ralph J.
Published: January 2011

Boundary layer separation has been studied on a very high lift, low-pressure turbine airfoil in the presence of unsteady wakes. Experiments were done under low (0.6%) and high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Wakes were produced from moving rods upstream of the cascade. Flow coefficients were varied from 0.35 to 1.4 and wake spacing was varied from 1 to 2 blade spacings, resulting in dimensionless wake passing frequencies F = fLj-te/Uave (f is the frequency, Lj-te is the length of the adverse pressure gradient region on the suction surface of the airfoils, and Uave is the average freestream velocity) ranging from 0.14 to 0.56. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in the suction surface boundary layer and downstream of the cascade. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000 and 50,000. In cases without wakes, the boundary layer separated and did not reattach. With wakes, separation was largely suppressed, particularly if the wake passing frequency was sufficiently high. At lower frequencies the boundary layer separated between wakes. Background freestream turbulence had some effect on separation, but its role was secondary to the wake effect.
Trailing Edge Film Cooling of Gas Turbine Airfoils: External Cooling Performance of Various Internal Pin Fin Configurations
Authors: Horbach T. , Schulz A. , Bauer H.-J.
Published: January 2011

The present paper describes an experimental study on trailing edge film cooling of modern high-pressure turbine blades using coolant ejection through planar slots on a pressure side cutback. The experimental test section consists of a generic scaled-up trailing edge model in an atmospheric open loop wind tunnel, which has been used in earlier studies by Martini et al. (e.g. [1]). An infrared thermographic measurement technique is employed, which allows for the application of engine-realistic density ratios around 1.6 by increasing the main flow temperature. The effects of different geometric configurations on the structure and performance of the cooling film are investigated in terms of film cooling effectiveness, heat transfer, and discharge behavior. Among other issues, the interaction between internal turbulators, namely an array of pin fins, with the ejection slot lip is of major interest. Therefore, different designs of the coolant ejection lip are studied. Four different ratios of lip thickness to ejection slot height (t/H = 0.2, 0.5, 1.0, 1.5) are investigated as well as three different lip profiles representing typical manufacturing imperfections and wear. Other geometric variations comprise elliptic pin fins with spanwise and streamwise orientation and the application of land extensions from the internal coolant cavity onto the cut-back surface. The blowing ratio is varied between 0.2 < M < 1.25. In terms of film cooling effectiveness the results show a strong dependency on ejection lip thickness and minor improvements are obtained with a rounded ejection lip profile. Significant improvements are achieved using land extensions. The elliptic pin fins have a strong effect on discharge behavior as well as on film cooling effectiveness and heat transfer. Except for the elliptic pin fins, the geometric variations have only a minor influence on heat transfer.
Fault Diagnosis of Gas Turbine Engines by Using Dynamic Neural Networks
Authors: Mohammadi Rasul , Naderi Esmaeil , Khorasani Khashayar , Hashtrudi-Zad Shahin
Published: January 2011

This paper presents a novel methodology for fault detection in gas turbine engines based on the concept of dynamic neural networks. The neural network structure belongs to the class of locally recurrent globally feed-forward networks. The architecture of the network is similar to the feed-forward multi-layer perceptron with the difference that the processing units include dynamic characteristics. The dynamics present in these networks make them a powerful tool useful for identification of nonlinear systems. The dynamic neural network architecture that is described in this paper is used for fault detection in a dual-spool turbo fan engine. A number of simulation studies are conducted to demonstrate and verify the advantages of our proposed neural network diagnosis methodology.
Elimination of Wire-Generated Error Signals From Dynamic Strain Measurements
Authors: Hockaday Bruce D.
Published: January 2011

Legacy processes sometimes include steps that have no clear justification and add unnecessary cost that too often no one can explain. An example of this is the costly step of adding temporary copper leads for engine strain gage calibration. In an attempt to eliminate temporary leads, gage calibration was performed with the permanent type-K thermocouple engine lead wire. This cost saving effort resulted in uncovering a source of measurement noise and error signals in engine development data. Subsequent laboratory studies showed that type-K thermocouple wire produces sinusoidal error signals as a function of vibration input. These error signals have the potential to add coherently to the strain gage information causing the measured amplitude to be either higher or lower as a function of phase between the signals. The laboratory studies also compared different wire alloys and their associated signal generating properties in order to identify suitable replacement wire. Final validation of the new lead wire was accomplished by running an engine test and producing a back-to-back comparison of type-K to the replacement lead wire. This test compared pairs of dynamic strain gages on separate airfoils installed at the same locations. Test data recorded with the gage excitation current turned off showed the replacement wire eliminated all wire-generated signals above 0.25 ksi (1,724 kPa), while the type-K leads generated signals up to 2.5 ksi (17,237 kPa). Test data with strain gages energized showed a dramatic reduction in false signals and noise with the replacement lead wire. The data collected through the type-K wire illustrates the potential for making poor design choices when wire-generated signals are undetected in the data. This work resulted in measurable cost savings (millions of dollars) by introducing a replacement for type-K wire which eliminated the need for temporary leads. While the cost avoidance here can be difficult to estimate, preventing a field failure resulting from erroneous data could result in orders of magnitude more cost saving.
Experimental Investigation of the Forcing Function and Forced Pitching Blade Oscillations of an Annular Compressor Cascade in Transonic Flow
Authors: Belz Joachim , Hennings Holger , Kahl Gerhard
Published: January 2011

The interaction between rotor blades and non-rotating stator blades is the most significant blade excitation mechanism in turbomachines. It is well documented in various numerical and experimental investigations for turbine cascades. Like turbine blades, also compressor blades are excited as well by potential fields of the following stator, the downstream flowfield of the stator of the previous stage or struts and incoming flow distortions. In this paper, experimental investigations of the excitation of a transonic compressor cascade due to gust generating struts upstream are presented. The experiments were performed in the test facility of non-rotating annular cascades at EPFL using a compressor cascade, which consists of 20 blades (NACA3506 profile) mounted on elastic spring suspensions for torsional motions at the midchord. For the non-rotating annular cascade, relative flow conditions similar to those present in a rotating cascade are generating by swirling the flow in front of the test test section. The struts are rotating in order to create a periodic excitation upstream of the cascade. The so generated pressure distribution on the cascade’s profiles as well as the measured vibration response of the blades are presented and compared for a pure subsonic and a transonic flow case.
Benchmarking CD-Adapco’s Star-CCM+ in a Production Design Environment
Authors: Grigoriev Mikhail M. , Swiatek Chester V. , Hitt James A.
Published: January 2011

It has been well-known that many industrial applications that use centrifugal compressors have continuously demanded for more and more efficient machines in the past decade or so. However, the current market trend indicates that there is a strong demand among the end users for reduced delivery times of these efficient compressors. This, in turn, requires that the aerodynamic design of highly efficient centrifugal stages be completed within shorter time frames. In order to meet these challenges, it is mandatory to involve modern computational analysis tools such as Computational Fluid Dynamics (CFD) as a routine design tool for the aerodynamic engineer. This presentation discusses a hierological structure for CFD analysis along with an overview of limitations and benefits for each classification within this structure. Usage and results pertaining to the implementation of this structure at Cameron’s Compression System will also be covered. Accordingly, a discussion of aerodynamic design practices (both current and historical) will be offered. It should be obvious to the reader that the goal of design integration would require the primary focus to be towards validation of the commercial CFD code. Results presented were obtained using the StarCCM + CFD package developed by CD-Adapco. As mentioned earlier, CFD analysis can be described as a hierological structure consisting of 4 levels. At level 1, the analysis component consists of an impeller coupled with a vaneless diffuser region under a steady state flow condition. On level 2, the model involves an impeller and low solidity diffuser row analysis using a mixing plane interface. Level 3 facilitates the consideration of entire impeller and an entire diffuser with a full set of diffuser blades within a transient framework. These levels (1 through 3) include the assumption of a dump collector and imply a circumferential periodicity at the exit. Also, models for level 2 and level 3 incorporate the use of a 1-d modeling to predict overall stage performance. Level 4, the most sophisticated model, involves a full-stage analysis of an unsteady turbulent flow through the entire centrifugal stage, all the way from impeller inlet to the discharge of the scroll/volute/collector. At this level, the overall stage performance is predicted directly from the CFD analyses. The paper compares the results of each level of analyses with the test data and discusses the potential benefits as well as limitations of each level of analyses.
Challenges for Implementing a Distributed-Control System for Turbine Engines
Authors: Berner Andrew W.
Published: January 2011

For several years, the potential benefits of implementing a distributed-control system on an airborne gas-turbine engine have been discussed and analyzed. However, after many years of trade studies and lab demonstrations, it appears that the airborne gas-turbine community is no closer to implementing this type of distributed architecture. The NASA-sponsored Distributed Engine Control Working Group is attempting to unify the efforts of engine manufacturers, their system integrators, and sub-tier suppliers. In order to collectively move forward, it is necessary to understand the issues that have impeded the progress of this approach. In so doing, the industry can focus on the near-term work required to develop programs that would create the necessary infrastructure to make airborne turbine-engine-based distributed-control systems a reality. This paper will present some proposed distributed-control architectures, advantages and disadvantages of some of these approaches, and will discuss the major technical challenges that have, to date, prevented these architectures from becoming viable. Some of the architectural approaches range from a fully distributed system (one distributed-control module per actuator loop) to a “hybridized” system that has a data concentrator and a reduced FADEC. The technical challenges that will be discussed include: high-temperature electronics, robust serial-communication bus in a high-temperature environment, power distribution, and certification.
Techno-Economic Evaluation of a Tri-Generation Energy Supply System for a Non-Interconnected Island Using Single-Shaft Gas-Turbine
Authors: Polyzakis A. L. , Malkogianni A. K.
Published: January 2011

In this paper, is presented a realistic simulation of the techno-economic performance of a tri-generation power plant, helping the potential investor to evaluate the profits of his future investment. The paper includes an overall techno-economic analysis including the following steps: Firstly, the research concerns the energy demands of an energy autonomous island. The second part, deals with the prime mover (namely the Gas Turbine, GT) modeling and simulation. The technical part of the assessment includes the Design Point (DP) and Off-Design (OD) analysis of the GT. The third part includes the simulation of the absorption cooling system alone and/or in cooperation with the prime mover. Finally, an evaluation methodology of tri-generation plants is introduced taking into account, both technical facts and economic data helping the potential users to decide whether it is profitable to use such technology or not. The economic scene will include the basic economic facts such as initial cost, handling and operational cost (fuel prices, maintenance etc), using methodology based on Net Present Value (NPV). The results are valuated using suitable sensitivity analysis. The results of the analysis generally shown, that the tri-generation plant is more profitable than the conventional way of energy supply.