bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Damping Analysis of a Vibrating Labyrinth Seal Structure With Frictional Contact
Authors: Coghlan R. P. , Green J. S. , Baron A. K.
Published: January 2011

Gas turbines incorporate throughout the engine many labyrinth air seals, which can suffer vibration excitation from a number of potential sources. This paper presents an analytical study of an example design of seal, for which vibration test data were available. Understanding of the observed vibration displacements was gained from (i) an investigation of the forcing excitation mechanism and (ii) non-linear vibration analysis of the seal structure, including estimates of work extracted by frictional contacts (mechanical damping). This paper presents only the mechanical damping analysis as an example of an industrial application of advanced multi-harmonic balance non-linear vibration techniques. The paper includes an overview of the non-linear model construction, including sensitivity studies in model reduction and contact element parameter choices. Once established, it is shown how the vibration model is used to assess the performance of a ring damper for the labyrinth seal in relation to the background mechanical damping provided by contact with adjacent components. The damping is a function of both friction coefficient and displacement amplitude and it is shown how the robustness of the damper design relates to friction assumptions.
Unsteady Forces Acting on the Rotor Blades and Shaft in the Control Stage for Different Steam Admission Variants
Authors: Rza˛dkowski Romuald , Solin´ski Marek
Published: January 2011

This paper concerns the unsteady high- and low-frequency excitation forces acting on the rotor blades and shaft in the control stage of a 200 MW steam turbine. An ideal gas flow through mutually moving stator and rotor blades was described in the form of unsteady Euler conservation equations, which were integrated using the Godunov-Kolgan explicit monotonous finite-volume difference scheme and a hybrid H-H grid. The effect of rotor blade mistuning on the unsteady forces acting on both the blades and the shaft was examined. Four different control stage steam admission variants were analysed. The actual levels of the stationary components of particular forces were determined by changes in the operating conditions of individual nozzle segments. Different mistuning variants generated different distributions of unsteady rotor blade force harmonics. The presented results show that the first harmonic does not always dominate the spectrum. When considering forces acting on the rotor blades and shaft, there exists an optimal procedure of turbine start-up.
A SOFC-Based Integrated Gasification Fuel Cell Cycle With CO2 Capture
Authors: Spallina Vincenzo , Romano Matteo C. , Campanari Stefano , Lozza Giovanni
Published: January 2011

Application of Solid Oxide Fuel Cells (SOFC) in gasification-based power plants would represent a turning point in the power generation sector, allowing to considerably increase the electric efficiency of coal-fired power stations. Pollutant emissions would also be significantly reduced in Integrated Gasification Fuel Cell cycles (IGFC) considering the much lower emissions of conventional pollutants (NOx, CO, SOx, particulate matter) typical of fuel cell-based systems. In addition, SOFC-based IGFCs appear particularly suited to applications in power plants with CO2 capture. This is evident by considering that SOFCs operate as air separators and partly oxidized fuel exiting the fuel cell does not contain nitrogen from air, like in conventional oxy-fuel processes. The aim of the present paper is the thermodynamic analysis of a SOFC-based IGFC with CO2 capture. In the assessed plant, syngas produced in a high efficiency Shell gasifier is used in SOFC modules after heat recovery and cleaning. Anode exhausts, still containing combustible species, are burned with oxygen produced in the air separation unit, also used to generate the oxygen needed in the gasifier; the product gas is cooled down in a heat recovery steam generator before water condensation and CO2 compression. The plant layout is carefully designed to best exploit heat generated in all the processes and, apart from the fuel cell, exotic components, far from industrial state-of-the-art, are not included. Detailed energy and mass balances are presented for a better comprehension of the obtained results.
Experimental Methodology to Characterize Mechanical Losses in Small Turbochargers
Authors: Payri Francisco , Serrano Jose R. , Olmeda Pablo , Paez Arlington , Vidal Fabrice
Published: January 2011

Turbocharging and turbocharger phenomena have been studied by many authors covering a wide range of subjects. One of these subjects, and objective of this work, is mechanical losses due to friction. Current work presents a methodology to characterize mechanical losses in small size turbochargers. Such methodology is based on low and constant operating temperature values for the turbine, lubricating oil, and compressor. In this way, a quasi-adiabatic operation of the turbocharger is achieved which allows separating friction power from heat transfer. The experiments performed have covered variations in turbocharger speed, lubricating oil pressure and temperature. Heat flows between turbine and compressor has been maintained as reduced as possible by means of the experiment conditions. The results obtained show satisfactory correlation between mechanical efficiency of the studied turbocharger and non-dimensional magnitudes.
Response of a Disk Cavity Flow to Gas Turbine Engine Transients
Authors: May David , Chew John W.
Published: January 2011

An integral part of the transient operation of a gas turbine engine is the behavior of the engine’s internal air system. It is desirable to model transient air system effects using a computationally efficient method, while accurate representation of these flows may require incorporation of the interactive effects of volume packing and swirl. Thus 1-D methods may need auxiliary relations to account for non-uniformity of properties in the cavity due to swirl or changes in the discharge coefficients of feed and exit holes to account for varying amounts of cross-flow. Consideration of the system response shows that flow spin-up times can be significant, suggesting the inclusion of the conservation of angular momentum in a 1-D volume modeling approach. To clarify the various contributions to the dynamics of these cavities, an axisymmetric rotor-stator disk geometry was modeled using CFD. Results are presented showing a notable effect of rotation. The presence of the rotor increased the time constant by a factor of about 2 for one case studied. The CFD results are compared to 1-D models. The results show improved accuracy of the 1-D model when the conservation of angular momentum is included in the formulation and recommendations for further improvement are made.
Results of an Advanced Fan Stage Operating Over a Wide Range of Speed and Bypass Ratio: Part I—Fan Stage Design and Experimental Results
Authors: Suder Kenneth L. , Prahst Patricia S. , Thorp Scott A.
Published: January 2011

NASA’s Fundamental Aeronautics Program is investigating turbine-based combined cycle (TBCC) propulsion systems for access to space because it provides the potential for aircraft-like, space-launch operations that may significantly reduce launch costs and improve safety. To this end, NASA and GE teamed to design a Mach 4 variable cycle turbofan/ramjet engine for access to space. To enable the wide operating range of a Mach 4+ variable cycle turbofan ramjet required the development of a unique fan stage design capable of multipoint operation to accommodate variations in bypass ratio (10X), fan speed (7X), inlet mass flow (3.5X), inlet pressure (8X), and inlet temperature (3X). In this paper, NASA has set out to characterize a TBCC engine fan stage aerodynamic performance and stability limits over a wide operating range including power-on and hypersonic-unique windmill operation. Herein, we will present the fan stage design, and the experimental test results of the fan stage operating from 15% to 100% corrected design speed. Whereas, in the companion paper [1], we will provide an assessment of NASA’s APNASA code’s ability to predict the fan stage performance & operability over a wide range of speed and bypass ratio.
Heat Transfer in Trailing Edge Wedge-Shaped Pin-Fin Channels With Slot Ejection Under High Rotation Numbers
Authors: Rallabandi Akhilesh P. , Liu Yao-Hsien , Han Je-Chin
Published: January 2011

The heat transfer characteristics of a rotating pin-fin roughened wedge shaped channel have been studied. The model incorporates ejection through slots machined on the narrower end of the wedge, simulating a rotor blade trailing edge. The copperplate regional average method is used to determine the heat transfer coefficient; pressure taps have been used to estimate the flow discharged through each slot. Tests have been conducted at high rotation (≈ 1 ) and buoyancy (≈ 2) numbers, in a pressurized rotating rig. Reynolds Numbers investigated range from 10,000 to 40,000 and rotational speeds range from 0–400rpm. Pin-fins studied are made of copper as well as non-conducting garolite. Results show high heat transfer coefficients in the proximity of the slot. A significant enhancement in heat transfer due to the pin-fins, compared with a smooth channel is observed. Even the non-conducting pin-fins, indicative of heat transfer on the end-wall show a significant enhancement in the heat transfer coefficient. Results also show a strong rotation effect, increasing significantly the heat transfer coefficient on the trailing surface — and reducing the heat transfer on the leading surface.
Effect of Inlet Temperature Non-Uniformity on High-Pressure Turbine Performance
Authors: Smith Craig I. , Chang Dongil , Tavoularis Stavros
Published: January 2011

The temperature of the flow entering a high-pressure turbine stage is inherently non-uniform, as it is produced by several discrete, azimuthally-distributed combustors. In general, however, industrial simulations assume inlet temperature uniformity to simplify the preparation process and reduce computation time. The effects of a non-uniform inlet field on the performance of a commercial, transonic, single-stage, high-pressure, axial turbine with a curved inlet duct have been investigated numerically by performing URANS (Unsteady Reynolds-Averaged Navier-Stokes equations) simulations with the SST (Shear Stress Transport) turbulence model. By adjusting the alignment of the experimentally-based inlet temperature field with respect to the stator vanes, two clocking configurations were generated: an aligned case, in which each hot streak impinged on a vane and a misaligned case, in which each hot streak passed between two vanes. In the aligned configuration, the hot streaks produced higher time-averaged heat load on the vanes and lower heat load on the blades. As the aligned hot streaks impinged on the stator vanes, they also spread spanwise due to the actions of the casing passage vortices and the radial pressure gradient; this resulted in a stream entering the rotor with relatively low temperature variations. The misaligned hot streaks were convected undisturbed past the relatively cool vane section. Relatively high time-averaged enthalpy values were found to occur on the pressure side of the blades in the misaligned configuration. The non-uniformity of the time-averaged enthalpy on the blade surfaces was lower in the aligned configuration. The flow exiting the rotor section was much less non-uniform in the aligned case, but differences in calculated efficiency were not significant.
Influence of Hydrodynamic Instability on the Heat Release Transfer Function of Premixed Flames
Authors: Hartmann Daniel , Schro¨der Wolfgang , Hemchandra Santosh
Published: January 2011

Gas expansion across the premixed flame surface causes deformations induced on the flame surface to grow in time due to hydrodynamical coupling between the unsteady flow and flame surface motions. This phenomenon is the well known hydro-dynamical instability (also know as the Darrieus-Landau (D-L) instability) of premixed flames. It is well established from several experimental studies that premixed flames subject to acoustic forcing distort and wrinkle under the influence of the unsteady velocity field generated by the forcing, thereby, changing its surface area and causing the net heat-release rate of the flame to oscillate. The D-L instability mechanism influences this heat-release oscillation through its influence on the underlying flame surface wrinkling. An understanding of this mechanism is necessary to develop reliable reduced-order modelling tools to predict the onset of combustion instabilities in Lean Premixed (LPM) systems. This paper presents a computational study of the influence of the D-L instability on the heat release transfer function of premixed flames subjected to harmonic velocity forcing. The effect of varying Markstein length and gas temperature ratio is presented. It is shown that when the induced flame surface perturbations are unstable w.r.t the D-L instability, the net heat release response is dominated by the oscillation in total burning area. In the stable case, the net response is due to the resultant of contributions from the net burning area oscillation as well as the area-averaged mass burning rate oscillation induced by unsteady spatial variations in laminar flame speed, sL. The boundary between these two response regimes is determined by the Markstein number for which flame surface perturbations are neutrally stable.
Analysis of Secondary Flow Behavior in Low Solidity Cascade Diffuser of a Centrifugal Blower
Authors: Ishida Masahiro , Murakami Tengen , Sakaguchi Daisaku , Ueki Hironobu , Hayami Hiroshi , Senoo Yasutoshi
Published: January 2011

Aiming at reducing noise without deterioration of diffuser performance in a low solidity cascade diffuser (LSD) of a centrifugal blower, the authors have proposed to locate a shallow and short groove or a slot between the diffuser wall and the LSD blade tip limiting to near the blade leading edge. The effect of the LSD blade tip-groove on the blower characteristics and the noise characteristics were investigated experimentally as well as numerically. The mechanism being able to maintain the high LSD blade loading even at small flow rates was pursued in view points of the vortex formation and the induced secondary flow. In addition, the effect of the tip-groove length on the vortex formation in the shroud tip-groove and the secondary flow behavior in the LSD were analyzed numerically and an optimum tip-groove configuration was proposed. It is concluded that formations of the stable and intense vortex in the shroud tip-groove and the recirculating secondary flow along the shroud wall toward the impeller exit are the key factors for achieving a high LSD performance and reducing noise simultaneously at small flow rates.
An Experimental Ignition Delay Study of Alkane Mixtures in Turbulent Flows at Elevated Pressure and Intermediate Temperatures
Authors: Beerer David , McDonell Vincent , Samuelsen Scott , Angello Leonard
Published: January 2011

Autoignition delay times of mixtures of alkanes and natural gas were studied experimentally in a high pressure and intermediate temperature turbulent flow reactor. Measurements were made at pressures between 7 and 15 atm and temperatures from 785 to 935K. The blends include binary and ternary mixtures of methane, ethane and propane; along with various natural gas blends. Based on these data, the effect of higher hydrocarbons on the ignition delay time of natural gas type fuels at actual gas turbine engine conditions has been quantified. While the addition of higher hydrocarbons in quantities of up to 30% were found to reduce the ignition delay by up to a factor of four, the delay times were still found to be greater than 60 milliseconds in all cases which is well above the residence times of most engine premixers. The data were used to develop simple Arrhenius type correlations as a function of temperature, pressure and fuel composition for design use.
A Test Rig for Non-Contact Travelling Wave Excitation of a Bladed Disk With Underplatform Dampers
Authors: Berruti Teresa , Firrone Christian M. , Gola Muzio M.
Published: January 2011

The paper presents a static test rig called “Octopus” designed for the validation of numerical models aimed at calculating the nonlinear dynamic response of a bladed disk with underplatform dampers (UPDs). The test rig supports a bladed disk on a fixture and each UPD is pressed against the blade platforms by wires pulled by dead weights. Both excitation system and response measurement system are noncontacting. The paper features the design and the set-up of the noncontacting excitation generated by electromagnets placed under each blade. A travelling wave excitation is generated according to a desired engine order by shifting the phase of the harmonic force of one electromagnet with respect to the contiguous exciters. Since the friction phenomenon generated by UPDs introduces nonlinearities on the forced response, the amplitude of the exciting force must be kept constant at a known value on every blade during step-sine test to calculate Frequency Response Functions. The issue of the force control is therefore addressed since the performance of the electromagnet changes with frequency. The system calibration procedure and the estimated errors on the generated force are also presented. Examples of experimental tests that can be performed on a dummy integral bladed disk (blisk) mounted on the rig are described in the end.
Experimental Study of Vaned Diffusers in Centrifugal Compressor
Authors: Jaatinen Ahti , Gro¨nman Aki-Pekka , Turunen-Saaresti Teemu , Backman Jari
Published: January 2011

Improving the performance of a centrifugal compressor can lead to decreased energy consumption in industry. Vaned diffusers are known to narrow the operating range but increase the peak efficiency compared to vaneless diffusers. In this study, three vaned diffusers and one vaneless diffuser are studied experimentally to improve compressor performance. Attention is paid to the operating range and performance of the diffuser, specially close to stall, and therefore the vaned diffusers are designed to have large negative incidence (−8°) at the design conditions. Different vane numbers and vane turnings are used. Compressor performance maps are measured at different rotating speeds and diffuser flow fields at the design rotating speed. The results show that the vaned diffusers make the diffuser outlet flow field more uniform than the vaneless one. The peak efficiency of the vaned diffusers occur at lower mass flows, and the efficiency is also higher at the design operation point with the vaned diffusers. In general, the vaned diffusers are better at lower mass flows, but stall earlier.
Aerodynamic Performance of a Very High Lift Low Pressure Turbine Airfoil (T106C) at Low Reynolds and High Mach Number With Effect of Free Stream Turbulence Intensity
Authors: Micha´lek Jan , Monaldi Michelangelo , Arts Tony
Published: January 2011

A detailed experimental analysis of the effects of the Reynolds number and free-stream turbulence intensity on the aerodynamic performance of a very high-lift, mid-loaded low-pressure turbine blade (T106C) is presented in this paper. The study was carried out on a large scale linear cascade in the VKI S1/C high-speed wind tunnel, operating at high exit Mach number (0.65) with a range of low Reynolds numbers (80,000–160,000) and three levels of free-stream turbulence intensity (0.8–3.2%). In the first part of the paper, the overall aerodynamic performance of the airfoil is presented, based on mid-span measurements performed by means of static pressure taps, hot-film sensors and a 5-hole probe traversing downstream of the cascade. Some specific features of separated flow transition are also discussed for selected cases. The second part presents the analysis of the results in terms of correlations derived for the characteristic points of boundary layer separation and transition. A comparison with some previously published prediction models is shown. The large variety of boundary conditions provides a unique database for validating codes dealing with separated flow transition in turbomachinery.
Numerical Simulation as Design Optimization Tool for Gas Turbine Combustion Chambers
Authors: Kulshreshtha Digvijay B. , Channiwala S. A. , Dikshit Saurabh B.
Published: January 2011

In present study an attempt has been made through CFD approach using CFX 11 to analyze the flow patterns within the combustion liner and through different air admission holes, namely, primary zone, intermediate zone, dilution zone and wall cooling, and from these the temperature distribution in the liner and at walls as well as the temperature quality at the exit of the combustion chamber are predicted. The design optimization is carried out using the CFD results with validation using experimental investigations.
Performance of a Nozzle Guide Vane in Subsonic and Transonic Regimes Tested in an Annular Sector
Authors: Yasa Tolga , Paniagua Guillermo , Fridh Jens , Vogt Damian
Published: January 2011

The understanding of shock interactions and mixing phenomena is crucial to design and analysis of advanced turbines. A nozzle guide vane (NGV) is experimentally investigated at subsonic and transonic off-design conditions (M2is of 0.6 and 0.95) in an annular sector at the Royal Institute of Technology (KTH). The effect of cooling ejection (3% of main stream mass flow rate) on the downstream flow field is also studied. The airfoil loading is monitored with pneumatic taps. The downstream pressure field is characterized at four different axial locations using a 5-hole probe and a total pressure probe that contains a single piezo-resistive transducer. The probe with a piezo resistive transducer is also used as a virtual 3-hole probe to measure the flow angle. The time-averaged yaw angle measured with the virtual 3-hole probe is in agreement with the 5-hole probe data. At subsonic conditions the wake causes a pressure loss of 7% of the upstream total pressure and covers 25% of the pitch whereas the pressure deficit is doubled in transonic operation. The coolant ejection results in an additional loss of 2% of the upstream total pressure. The flow speed does not have a significant effect on the wake width at 7% Cax. However, the low pressure region has different width at far downstream depending on the flow velocity. The fillet at the hub region has a significant effect on the secondary flow development. The frequency spectrums at the different conditions clearly reveal the shear layers. The results aim to help the characterization of mixing phenomena downstream of the NGV.
Demonstration of a Palm-Sized 30 Watt Air-to-Power Turbine Generator
Authors: Sato S. , Jovanovic S. , Lang J. , Spakovszky Z.
Published: January 2011

A compact, high power-density turbo-generator system was conceived, designed and experimentally tested. The air-to-power (A2P) device with a nominal design point of 50 W electric power output operates on high pressure air such as for example from a plant pneumatic system or a portable bottle of pressurized air. A concept design study was first carried out to explore the design space for a range of output power at cost efficiency levels specified in collaboration with industry. The cost efficiency is defined as the cost of electrical power over the cost of pressurized air. The key challenge in the design is the relatively low power demand of 50 W while operating at high supply pressures of nominally 5 to 6 bar. To meet the cost efficiency goal under these conditions, a high-speed turbine and generator (∼450,000 rpm) are required with small blade span (∼200 μm) minimizing the mass flow while achieving the highest possible turbine performance. Since turbines with such small turbomachinery blading aren’t commercially available, a silicon-based MEMS turbine was designed using 2-D and 3-D CFD computations. To reduce the development time, existing and previously demonstrated custom-made generator and ceramic ball-bearing technology were used, resulting in a compact A2P proof-of-concept demonstration. The cylindrical device of 35 mm diameter resembles a tube fitting with a standard M24 adapter. Without load, a top turbine speed of 475,000rpm was demonstrated exceeding the design specification. Using load resistors, the proof-of-concept A2P device achieved 30 W of electrical power at 360,000 rpm and a turbine efficiency of 47%, meeting the cost efficiency goal. Higher speeds under load could not be achieved due to thrust load limitations of the off-shelf ball bearings. The demonstrated performance is in good agreement with the projected CFD based predictions. To the authors’ knowledge, this is the first successful demonstration of a self-contained, 50 W-class turbo-generator of hybrid architecture where a MEMS turbine disk is joined with a precision machined titanium shaft and aluminum housing.
Endwall Effusion Cooling System Behaviour Within a High-Pressure Turbine Cascade: Part 2—Heat Transfer and Effectiveness Measurements
Authors: Facchini B. , Tarchi L. , Toni L. , Zecchi S.
Published: January 2011

The cooling performance of a micro-holed endwall of a large-scale high pressure turbine cascade has been investigated within the European Project AITEB-2. The experimental investigation has been performed for a baseline configuration, with a smooth solid endwall and with a micro-holed endwall providing micro-jets ejection from the wall. A micro-holed endwall made of two modules was adopted in order to reduce the compound angle between the main flow and the micro jets axes. The micro-holed endwall is provided with a total amount of 3294 micro-holes with a diameter of 0.1 per cent of the blade chord. Four different cooling flow rates, from 1.2% to 2.6% of the main flow mass flow rate respectively, were investigated and the experimental results are reported in the paper. Both adiabatic effectiveness and heat transfer coefficient have been measured employing a steady state technique with Thermo-chromic Liquid Crystals (TLC). A thin stainless steel heating foil was used to generate the surface heat flux for the HTC measurements and a data reduction procedure based on a Finite Element approach has been developed to take into account the non uniform heat generation along the endwall.
Combined Effect of Slot Injection, Effusion Array and Dilution Hole on the Heat Transfer Coefficient of a Real Combustor Liner: Part 1—Experimental Analysis
Authors: Facchini Bruno , Maiuolo Francesco , Tarchi Lorenzo , Coutandin Daniele
Published: January 2011

An experimental analysis of a real engine cooling scheme was performed on a test article replicating a slot injection and an effusion array with a central large dilution hole. Test section consists of a rectangular cross-section duct with a flat plate comprised of 270 holes arranged in 29 staggered rows (D = 1.65mm, Sx/D = 7.6, Sy/D = 6, L/D = 5.5, α = 30deg) and a dilution hole (D = 18.75mm) located at the 14th row. Both effusion and dilution holes are fed by a channel replicating combustor annulus, that allows to control cold gas side cross-flow parameters, especially in terms of Reynolds number of both annulus and effusion holes. Upstream the first row, a 6mm high slot, ensure the protection of the very first region of the liner. Final aim was the measurement of both heat transfer coefficient and Net Heat Flux Reduction of the cooling scheme, by means of a steady-state Thermochromic Liquid Crystals (TLC) technique with a thin Inconel heating foil. A data reduction procedure based on a Finite Element approach has been developed to take into account the non uniform heat generation and conduction due to the large amount of holes. Experiments were carried out considering the combined effects of slot, effusion and dilution holes. Three different effusion blowing ratios (BR = 3–5–7) are investigated, keeping constant the slot flow parameters (BR = 1.3). Results highlight a large influence of effusion blowing ratio on heat transfer coefficient. A steep increase was found in the first rows, while the large dilution hole does not influences significantly the heat transfer behaviour in the downstream area.
Time-Linearized and Time-Accurate 3D RANS Methods for Aeroelastic Analysis in Turbomachinery
Authors: Kersken Hans-Peter , Frey Christian , Voigt Christian , Ashcroft Graham
Published: January 2011

A computational method for performing aeroelastic analysis using either a time-linearized or an unsteady time-accurate solver for the compressible Reynolds averaged Navier-Stokes (RANS) equations is described. The time-linearized solver employs the assumption of small time-harmonic perturbations and is implemented via finite differences of the nonlinear flux routines of the time-accurate solver. The resulting linear system is solved using a parallelized Generalized Minimal Residual (GMRES) method with block-local preconditioning. The time accurate solver uses a dual time stepping algorithm for the solution of the unsteady RANS equations on a periodically moving computational grid. For either solver, and both flutter and forced response problems, a mapping algorithm has been developed to map structural eigenmodes, obtained from finite element structural analysis, from the surface mesh of the finite element structural solver to the surface mesh of the finite volume flow solver. Using the surface displacement data an elliptic mesh deformation algorithm, based on linear elasticity theory, is then used to compute the grid deformation vector field. The developed methods are validated first using standard configuration ten. Finally, for an ultra high bypass ratio fan the results of the time-linearized and the unsteady module are compared. The gain in prediction time using the linearized methods is highlighted.
Developing Data Mining-Based Prognostic Models for CF-18 Aircraft
Authors: Zaluski Marvin , Le´tourneau Sylvain , Bird Jeff , Yang Chunsheng
Published: January 2011

The CF-18 aircraft is a complex system for which a variety of data are systematically being recorded: operational flight data from sensors and Built-In Test Equipment (BITE) and maintenance activities recorded by personnel. These data resources are stored and used within the operating organization but new analytical and statistical techniques and tools are being developed that could be applied to these data to benefit the organization. This paper investigates the utility of readily available CF-18 data to develop data mining-based models for prognostics and health management (PHM) systems. We introduce a generic data mining methodology developed to build prognostic models from operational and maintenance data and elaborate on challenges specific to the use of CF-18 data from the Canadian Forces. We focus on a number of key data mining tasks including: data gathering, information fusion, data pre-processing, model building, and evaluation. The solutions developed to address these tasks are described. A software tool developed to automate the model development process is also presented. Finally, the paper discusses preliminary results on the creation of models to predict F404 No. 4 Bearing and MFC (Main Fuel Control) failures on the CF-18.
One and Three-Dimensional Analysis of Centrifugal Compressor for 600 kW Simple Cycle Gas Turbine Engine
Authors: Gutie´rrez Vela´squez Elkin I. , Nascimento Marco A. R. , Miranda Carrillo Ruben A. , Moura Newton R.
Published: January 2011

Currently, industrial countries generate most of their electricity in large centralized plants. These plants have excellent economies of scale, however, they usually transmit electricity through long distances and can affect the environment. Distributed generation is another approach that reduces the amount of lost energy during transmission as the electricity is generated closely to where it is used, this way reducing the size and number of power lines to be constructed. The current technologies in DG include small gas turbine engines, internal combustion reciprocating engines, photovoltaic panels, fuel cells, solar thermal conversion and Stirling engines using fossil fuels and bio-fuels. Among them, small gas turbine engines are a promising technology for the implementation of distributed generation systems in the near future. This work presents the results of the preliminary compressor design of a simple cycle gas turbine engine, obtained with the use of a straightforward one-dimensional FORTRAN code, which enables to calculate the main characteristics of a centrifugal compressor by means of the application of non-dimensional parameters, with a vast reduction of computational time. The results obtained were compared with a CFD analysis and with experimental results taken from specialized literature; therefore a reasonable agreement was reached. The main contribution of this paper is to demonstrate that by the use of a simple code it is feasible to obtain fairly close results in comparison with those which can be obtained by laborious iterative processes such as those developed through the analysis using CFD techniques.
Numerical Calculation of the Structural Stiffness of Gas Foil Bearings
Authors: Geng Haipeng , Qi Shemiao , Yu Lie
Published: January 2011

The dynamics of a rotor supported in Gas Foil Bearings is strongly influenced by stiffness and damping properties of the bearings. In order to obtain the structural stiffness properties of Gas Foil Bearings, a coupled finite element method (FEM) is developed in this paper. The compressible gas lubricated Reynolds equation is transformed into a typical elliptic partial differential equation and solved by FEM. The elastic deformation equation and the contact boundary conditions between foils are solved by nonlinear contact finite method. A generalized numerical solving method for the elasto-aerodynamically coupled lubrication problem in the foil bearing is given with mesh mapping relationship between the two kind of finite element solving process above mentioned. The structural stiffness of the foil bearings with different parameters is estimated by using the numerical method. It is helpful to decide the structural parameters of the foil bearing.
Design of a Test Rig for Organic Vapours
Authors: Spinelli A. , Dossena V. , Gaetani P. , Osnaghi C. , Colombo D.
Published: January 2011

A blow-down wind tunnel for real gas applications has been designed to characterize an organic vapour stream by independent measurements of pressure, temperature and velocity. Experiments are meant to investigate flow fields representative of expansions taking place in Organic Rankine Cycles (ORC) turbines. Strong real gas effects, high Mach numbers and approximations affecting the calculated properties of novel compounds, make the knowledge of ORC turbine blade passage flow field still rather limited. A significant enhancement of turbines efficiency is expected from detailed investigations on expansion streams. Despite Organic Cycles have attracted large research efforts in recent years, present days design tools still suffer from a lack of relevant experimental data. So far, ideal gas test cases and equilibrium measurements have supported separately CFD and thermodynamic model validations. These considerations prove the relevance of such a test rig. This paper discusses the design and the final layout of the facility, whose construction is currently in progress. A straight axis supersonic nozzle has been chosen as test section for early tests; investigations on blade cascades are foreseen in the future. Due to high stream densities and temperatures, a throat size compatible with probes intrusion made a continuous cycle plant unaffordable, requiring an input thermal power of around 2.5 MW. A reduction to 30 kW has been achieved by adopting a blow-down tunnel: the fluid, slowly vaporized in a high pressure vessel, feeds the nozzle at a lower pressure. The vapour is then collected in a low pressure tank and condensed. The loop is closed by liquid compression through a pump. Such a batch operating system also offers the option to select test/condensation pressures and temperatures, allowing experimentation of a wide variety of working fluids, even though new ORC compounds (e.g. Siloxanes, Fluorocarbons) remain of major interest. Maximum temperature and pressure are 400 °C and 50 bar. Despite the unsteady operational mode, the inlet nozzle pressure can be kept constant by a control valve. Depending on the fluid and test pressure, experiments may last from 20 seconds to several minutes, while their set-up requires a few hours. Fast response pressure transducers, pressure probes and thermocouples have been selected for thermodynamic measurements; Laser Doppler Velocimetry (LDV) and Schlieren techniques allow direct measurements of velocity and flow visualization. The design has been carried out with a lumped parameter approach, using Siloxane MDM and Hydrofluorocarbon R245fa as reference compounds and FluidProp® for properties calculation.
Influence of Transversal Acoustic Excitation of the Burner Approach Flow on the Flame Structure
Authors: Hauser Martin , Lorenz Manuel , Sattelmayer Thomas
Published: January 2011

Modern large gas turbines for power generation have multiple burners, which are distributed around the circumference of the engine and which generate flames in combustors of either annular or can-annular geometry. In both cases considering only the axial modes has proven to be insufficient for the assessment of the thermoacoustic stability. An adequate analysis requires consideration of the circumferential acoustic coupling, generated by the acoustic field in the upstream and downstream annuli and the open passages between the cans, respectively. As in annular combustors the particularly critical eigenmodes with low frequencies are predominantly of circumferential nature, the stability of annular combustors is often governed by the onset of circumferential acoustic oscillations. To determine the influence of these circumferential acoustic modes on the dynamic flame behavior, a new single burner test rig was developed. The unique acoustic properties of the test rig allow the exposure of a single swirl burner to a two-dimensional acoustic field that resembles the circumferential mode in an annular combustor. Measurements were performed for axial as well as transversal excitation of the burner and the combination of both. To investigate the dynamic flame structure phase-resolved flame images have been evaluated in terms of amplitude and phase distribution. Under transversal excitation the flame structure becomes highly asymmetrical. A region of higher OH*-intensity is generated in the combustion chamber which rotates with the excitation frequency. From phase-resolved PIV measurements of the isothermal flow it is concluded that the transversal excitation modulates the swirl generation leading to an asymmetrical velocity distribution in the burner nozzle and the combustion chamber, respectively.
Mechanical Design of a Variable Pitch Fan for Turbofan Engines
Authors: Violette John A. , Loos Eric S.
Published: January 2011

The mechanical design of a new variable pitch fan system for high bypass turbofan engines is presented, offering 10–14% fuel savings for next generation turbofan engines. Comparable in weight to current fans, the new design incorporates a compact pitch change mechanism that fits within a current fan’s center body. The key to compactness is the use of multiple high strength tension/torsion straps, which support blade centrifugal loads with unique structural efficiency and redundancy, while allowing ten to fifteen degrees of blade pitch rotation. The new retention system also offers significant reduction of pitch control forces by balancing blade centrifugal twisting loads with strap restoring moments, achieving a desired pitch setting. The use of a pin root fan blade facilitates on-wing blade replacement. Fan blade incidence angles are decreased at low aircraft speeds to avoid fan stall flutter problems. Therefore, advanced engines no longer need the addition of a variable area nozzle to the exit of the fan duct to prevent flutter, saving additional weight, complexity, and cost. This new fan system offers the best solution for achieving a major improvement in turbofan engine efficiency, at the lowest weight.
Effects of an Axisymmetric Contoured Endwall on a Nozzle Guide Vane: Convective Heat Transfer Measurements
Authors: Thrift A. A. , Thole K. A. , Hada S.
Published: January 2011

Heat transfer is a critical factor in the durability of gas turbine components, particularly in the first vane. An axisymmetric contour is sometimes used to contract the cross sectional area from the combustor to the first stage vane in the turbine. Such contouring can lead to significant changes in the endwall flows thereby altering the heat transfer. This paper investigates the effect of axisymmetric contouring on endwall heat transfer of a nozzle guide vane. Heat transfer measurements are performed on the endwalls of a planar and contoured passage whereby one endwall is modified with a linear slope in the case of the contoured passage. Included in this study is upstream leakage flow issuing from a slot normal to the inlet axis. Each of the endwalls within the contoured passage presents a unique flowfield. For the contoured passage, the flat endwall is subject to an increased acceleration through the area contraction while the contoured endwall includes both increased acceleration and a turning of streamlines due to the slope. Results indicate heat transfer is reduced on both endwalls of the contoured passage relative to the planar passage. In the case of all endwalls, increasing leakage mass flow rate leads to an increase in heat transfer near the suction side of the vane leading edge.
Part-Span Application of Sweep and Lean at Turbine Blade Tips: A Low Speed Experimental Cascade Study
Authors: Roy Bhaskar , Prajapati Anoop
Published: January 2011

This study is aimed at exploring the possibility of aerodynamic performance improvement by providing part-span forward sweep and lean near the tip regions of axial flow turbine rotor blades. Such aerodynamic benefits may have application potential in the uncooled LPT blades. The curved forward sweep and curved lean have been provided to 25% of the blade span near the tip in cascade, Three sets of cascades of the same turbine airfoil have been studied — (i) straight blades, (ii) part span swept blades and (iii) part span leaned blades. The cascade results show that swept blade gives a recovery of 20–25% loss in blade performance near the tip region at 0° and 10° incidences. The swept and leaned blades suppress the Cp perturbations (as seen in straight blades) at 0° and at 10° incidences, on the suction surfaces of turbine blade cascades. Comparatively the leaned blades show blade unloading, largely on the pressure surface, which leads to some performance reduction. The wake loss study shows reduction in wake losses for swept turbine blade at near tip region. The end-wall boundary layer measurements across the open tips demonstrate some aerodynamic improvement, near the tip regions, for parts-span swept and leaned blades.
Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System: Part 2—Predictions Versus Test Data
Authors: San Andre´s Luis , Kim Tae Ho , Ryu Keun
Published: January 2011

Implementation of gas foil bearings (GFB) in micro gas turbines relies on physics based computational models anchored to test data. This two-part paper presents test data and analytical results for a test rotor and GFB system operating hot. A companion paper (Part 1) describes a test rotor-GFB system operating hot to 157°C rotor OD temperature, presents measurements of rotor dynamic response and temperatures in the bearings and rotor, and including a cooling gas stream condition to manage the system temperatures. The second part briefs on a thermoelastohydrodynamic (TEHD) model for GFBs performance and presents predictions of the thermal energy transport and forced response, static and dynamic, in the tested gas foil bearing system. The model considers the heat flow from the rotor into the bearing cartridges and also the thermal expansion of the shaft and bearing cartridge and shaft centrifugal growth due to rotation. Predictions show that bearings’ ID temperatures increase linearly with rotor speed and shaft temperature. Large cooling flow rates, in excess of 100 L/min, reduce significantly the temperatures in the bearings and rotor. Predictions, agreeing well with recorded temperatures given in Part 1, also reproduce the radial gradient of temperature between the hot shaft and the bearings ID, largest (37°C/mm) for the strongest cooling stream (150 L/min). The shaft thermal growth, more significant as the temperature grows, reduces the bearings operating clearances and also the minimum film thickness, in particular at the highest rotor speed (30 krpm). A rotor finite element (FE) structural model and GFBs force coefficients from the TEHD model are used to predict the test system critical speeds and damping ratios for operation at increasing shaft temperatures. In general, predictions of the rotor imbalance show good agreement with shaft motion measurements acquired during rotor speed coastdown tests. As the shaft temperature increases, the rotor peak motion amplitudes decrease and the system rigid-mode critical speed increases. The computational tool, benchmarked by the measurements, furthers the application of GFBs in high temperature oil-free rotating machinery.
Temperature Predictions and Comparison With Measurements for the Blade Leading Edge and Platform of a 1-1/2 Stage Transonic HP Turbine
Authors: Mathison R. M. , Wishart M. B. , Haldeman C. W. , Dunn M. G.
Published: January 2011

A series of computational predictions generated using FINE/Turbo are compared with data to investigate implementation techniques available for predicting temperature migration through a turbine stage. The experimental results used for comparison are from a one-and-one-half stage turbine operating at design-corrected conditions in a short-duration facility. Measurements of the boundary conditions are used to set up the computational models, and the predicted temperatures are compared to measured fluid temperatures at the blade leading edge and just above the blade platform. Fluid temperature measurements have not previously been available for these locations in a transonic turbine operating at design-corrected conditions, so this represents a novel comparison. Accurate predictions for this short-duration turbine experiment require use of the iso-thermal wall boundary condition instead of an adiabatic boundary condition and accurate specification of the inlet temperature profile all the way to the wall. Predictions using the harmonic method agree with the temperatures measured for the blade leading edge from 65% to 95% span to within 1% normalized temperature data. Agreement over much of the rest of the leading edge is within 5% of the measured value. Comparisons at 5–10% span and for the blade platform show larger differences up to 10%, which indicates that the flow in this region is not fully captured by the prediction. This is not surprising since the purge cavity and platform leading edge features present in the experiment are treated as a smooth hub wall in the current simulation. This work represents a step towards the larger goal of accurately predicting surface heat-flux for the complicated environment of an operational engine as it is reproduced in a laboratory setting. The experiment upon which these computations are based includes realistic complications such as one-dimensional and two-dimensional inlet temperature profiles, a heavily film-cooled vane, and purge cooling. While the ultimate goal is to accurately handle all of these features, the current model focuses on the treatment of a subset of experiments performed for a one-dimensional radial inlet temperature profile and no cooling.