bluuebunny/crossref_metadata_2025 huggingface dataset:
Radial Impeller Forces Using CFD: Part I — Model Development and Validation
Authors: Baun Daniel O. , Flack Ronald D.
Published: February 2009

In part one of this two part paper, CFD is used to predict the flow field in a laboratory centrifugal water pump. Multiple frame of reference simulations were conducted on a full pump model, a four vane impeller, a spiral volute and an axial inlet pipe, using water as the working fluid. The impeller angular position was systematically indexed relative to the volute to simulate the rotation of an impeller vane passage by the volute tongue. Relative tangential and meridional velocity profiles at the impeller exit and across the volute were reconstructed from the quasi-unsteady simulations and compared with directly and previously measured profiles obtained from laser velocimetry. In addition, the impeller slip at the design flow was evaluated from the CFD results and compared with the slip obtained using laser velocimetry. Average pressure profiles around the impeller circumference and around the outer wall of the volute were reconstructed from the quasi-static CFD simulations and compared with measured profiles. The pump hydraulic characteristic was evaluated from the CFD and compared with the measured characteristic. The CFD model developed and validated in Part I is used to predict impeller forces in the same geometry for both incompressible and compressible fluids in Part II.
Backward Traveling Rotating Stall Waves in Centrifugal Compressors
Authors: Spakovsky Z. S.
Published: February 2009

Rotating stall waves that travel against the direction of rotor rotation are reported for the first time and a new, low-order analytical approach to model centrifugal compressor stability is introduced. The model is capable of dealing with unsteady radially swirling flows and the dynamic effects of impeller-diffuser component interaction as it occurs in centrifugal compression systems. A simple coupling criterion is developed from first principles to explain the interaction mechanism important for system stability. The model findings together with experimental data explain the mechanism for first-ever observed backward traveling rotating stall in centrifugal compressors with vaned diffusers. Based on the low-order model predictions, an air injection scheme between the impeller and the vaned diffuser is designed for the NASA Glenn CC3 high-speed centrifugal compressor. The steady air injection experiments show an increase of 25% in surge-margin with an injection mass flow of 0.5% of the compressor mass flow. In addition, it is experimentally demonstrated that this injection scheme is robust to impeller tip-clearance effects and that a reduced number of injectors can be applied for similar gains in surge-margin. The results presented in this paper firmly establish the connection between the experimentally observed dynamic phenomena in the NASA CC3 centrifugal compressor and a first principles based coupling criterion. In addition, guidelines are given for the design of centrifugal compressors with enhanced stability.
Investigations of the Flow Through a High Pressure Ratio Centrifugal Impeller
Authors: Eisenlohr Gernot , Krain Hartmut , Richter Franz-Arno , Tiede Valentin
Published: February 2009

In an industrial research project of German and Swiss Turbo Compressor manufacturers a high pressure ratio centrifugal impeller was designed and investigated. Performance measurements and extensive laser measurements (L2F) of the flow field upstream, along the blade passage and downstream of the impeller have been carried out. In addition to that, 3D calculations have been performed, mainly for the design point. Results have been presented by Krain et al., 1995 and 1998, Eisenlohr et al., 1998 and Hah et al.,1999. During the design period of this impeller a radial blade at the inlet region was mandatory to avoid a rub at the shroud due to stress reasons. The measurements and the 3D calculations performed later, however, showed a flow separation at the hub near the leading edge due to too high incidence. Additionally a rather large exit width and a high shroud curvature near the exit caused a flow separation near the exit, which is enlarged by the radially transported wake of the already addressed hub separation. Changes to the hub blade angle distribution to reduce the hub incidence and an adaptation of the shroud blade angle distribution for the same impeller mass-flow at the design point were investigated by means of 3D calculations first with the same contours at hub and shroud; this was followed by calculations with a major change of the shroud contour including an exit width change with a minor variation of the hub contour. These calculations showed encouraging results; some of them will be presented in conjunction with the geometry data of the original impeller design.
Development of a Lean Direct Fuel Injector for Low Emission Aero Gas Turbines
Authors: Nickolaus Daniel A. , Crocker D. Scott , Black David L. , Smith Clifford E.
Published: February 2009

CFD Research Corporation has developed a promising lean direct fuel injector for application to all sizes of aero gas turbine engines. The patented injector design utilizes a bifurcated flow pattern structure that produces low NOx emissions at full power conditions and low CO, UHC and smoke emissions at low power. The design consists of three swirlers and two fuel circuits, and a flow splitter that divides the airflow into two airstreams. Two concentric fuel circuits fuel the two airstreams, producing two distinct flames: a pilot flame and a main flame. This unique flame structure allows separate control of two flame regions, but still allows them to interact. A large percent of combustor airflow enters through the injector. At low power (idle and approach), only the pilot circuit is fueled. The pilot fuel flows into the pilot airstream, and a flame is anchored in the bifurcated recirculation zone. Lean blowouts at idle conditions as low as an injector equivalence ratio of 0.04 have been realized. Low CO, UHC and smoke emissions have been demonstrated at these conditions. For power settings above approach, the fuel flow through the pilot is reduced, and the main is fueled. At cruise to max power conditions, only 10% of the fuel goes through the pilot and 90% goes through the main to achieve both low NOx and good stability. At max power conditions, the injector equivalence ratio is approximately 0.60–0.65, and the flame is blue and non-luminous, resulting in reduced heat loads to the liner. NOx emission levels have been measured in single-injector tests that show this injector has the potential to reduce the Landing/Takeoff (LTO) NOx levels by 60–70% compared with 1996 ICAO standards. This paper presents an overview of how the fuel injector works and how overall performance was achieved. The most difficult aspect of injector performance, i.e. achieving low lean blowout (LBO) fuel-air ratio, is described at the end of the paper, including LBO data for a range of configurations.
Fluid Dynamics of a Pre-Swirl Rotor-Stator System
Authors: Yan Youyou , Gord Mahmood Farzaneh , Lock Gary D. , Wilson Michael , Owen J. Michael
Published: February 2009

In a “direct-transfer” pre-swirl supply system, cooling air flows axially across the wheel-space from stationary pre-swirl nozzles to receiver holes located at a similar radius in the rotating turbine disc. This paper describes a combined computational and experimental study of the fluid dynamics of such a system. Measurements of total and static pressures have been made using a purpose-built rotor-stator rig, with 24 pre-swirl nozzles on the stator and 60 receiver holes in the rotor. The number of pre-swirl nozzles could be reduced, and it was possible to calculate CD, the discharge coefficient of the receiver holes. Information on the flowfield was also obtained from three-dimensional, incompressible steady turbulent flow computations. The measurements showed that there was a significant loss of total pressure between the outlet from the pre-swirl nozzles and the rotating core of fluid in the wheel-space. This loss increased as the pre-swirl flow-rate and inlet swirl ratio increased, and as the number of nozzles decreased. CD increased as the swirl ratio at the receiver hole radius approached unity; for the experiments, CD varied in the range 0.2 to 0.45. Computed pressures and tangential velocities were in mainly good agreement with the measurements. The computations help to explain the reasons for the significant losses in total pressure and for the relatively low values of CD in this pre-swirl system.
Microturbines and Trigeneration: Optimization Strategies and Multiple Engine Configuration Effects
Authors: Campanari Stefano , Boncompagni Luca , Macchi Ennio
Published: February 2009

This paper investigates energy savings and economic aspects related to the use of microturbine generators in commercial buildings either for cogeneration (electricity+heat) or for trigeneration (electricity, heat and cold). In all calculations, reference is made to a 25 kWel–class commercial micro-turbine generator (MTG), tested by the authors. Various plant schemes are considered, based on one or several MTG sets. The possibility of generating heat and/or cold also by an electrically driven inverse-cycle air-to-water heat pump/chiller system is also considered. Calculations are based on the simulation code TRIGEN developed by the authors. The code provides detailed energy, economic and emission yearly balances. The plant operating mode is optimized in each time interval. The results indicate that, due to large load variations, (i) the optimum turbine nominal output is in the range of about 70% of the electric peak demand, (ii) energy savings are marginal, (iii) advantages related to splitting the overall capacity on more than one unit are marginal and (iv) the addition of an absorption machine improves the plant economics.
Turbine Mistuned Forced Response Prediction: Comparison With Experimental Results
Authors: Seinturier Eric , Lombard Jean-Pierre , Berthillier Marc , Sgarzi Olivier
Published: February 2009

It is currently a major challenge for aeroengines manufacturer to be able to predict early in the design process the dynamic response of bladed disk. To guaranty a good accuracy of prediction, it is necessary to define properly the excitation (unsteady aerodynamics) and to take into account some phenomenon such as mistuning. This paper proposes an application of Snecma prediction method for mistune forced response on an experimental test case. The method used is a component modes synthesis method similar to the one proposed by Castanier and Pierre in 1997 [1] and validated against experiment in [2]. Some improvement have been performed to take into account more accurately the centrifugal forces effects in the projection basis and to couple the method with unsteady Computational Fluids Dynamic (CFD) codes. It is now possible to use this method in an industrial process. The method is applied to a HP turbine representative case, for which experimental results are available. These experimental results have been obtained in a European Community funded project dedicated to forced response study [3]. Mistuning effects have been measured. Moreover, a full characterization, of unsteady aerodynamics, aeroelastic and structural dynamics aspects have been performed. The results obtained with the proposed method are then compared to the experimental one. This application shows the consistency of the method and its efficiency.
Axial-Flow Compressor Model Based on a Cascade Stacking Technique and Neural Networks
Authors: Benini Ernesto , Toffolo Andrea
Published: February 2009

This paper introduces a cascade-stacking technique for the development of a gas turbine multi-stage axial-flow compressor model. A large database of stationary and rotating cascade performance is first obtained by quasi three-dimensional CFD simulations and used to train neural networks for the prediction of cascade performance under generalized conditions. Then the model directly calculates the operating point of a compressor having known geometry characteristics, including variable inlet guide/stator vane effects, as a function of mass flow rate and rotational speed. The model can also be used as a valuable preliminary design tool, obtaining geometry characteristics by imposing flow patterns.
A Combustion Test Facility for Testing Low NOx Combustion Systems
Authors: Wang Difei , Sahai Vivek , Cheng Dah Yu
Published: February 2009

Cheng Power Systems has designed and built an atmospheric pressure combustion test facility for gas turbines, which has the capability of testing the full size combustion systems of large gas turbines at atmospheric pressure while maintaining the adiabatic flame temperature at pressurized conditions. The uniqueness of the test facility is the method of preheating the air to the compressor discharge temperature of a gas turbine at high-pressure ratios using the combustion exhaust gas and a compact air-to-air heat exchanger. The exhaust dampers and dilution airflows control the preheated-air temperature. The other characteristic of the test facility is the competence of testing NOx reduction combustion systems using steam or inert gas. The facility has the capability to perform steam injection experiments to examine the combustion stability with massive steam injection rates of up to 20% of air mass flow rate. The test process is fully automated with computer data acquisition and digital control. Combustion systems such as GE Frame 5P, 6B, 7EA, and Westinghouse 501D5A have been tested. With Cheng Power’s unique NOx reduction system (CLN™ - Cheng Low NOx System), less than 5 ppm NOx and very low level of CO were obtained for these combustion systems without hardware modification. The facility is also capable of testing Dry-Low-NOx (DLN) combustion systems. The test system is also assisted by a commercial computer program (Star-CD) to estimate the pressurization effect for extrapolating the test results. The pressure dependence can be simulated with the unique combustion geometry, type of fuel, and onset of turbine inlet temperature, respectively. The results depict the detail of the flame structure under various combustion chamber design characteristics. The model pressurization results correlate well with our experimental results as well as results in the literature.
ICAS-GT: A European Collaborative Research Programme on Internal Cooling Air Systems for Gas Turbines
Authors: Smout Peter D. , Chew John W. , Childs Peter R. N.
Published: February 2009

The Internal Cooling Air Systems for Gas Turbines (ICAS-GT) research programme, sponsored by the European Commission, ran from January 1998 to December 2000, and was undertaken by a consortium of ten gas turbine manufacturing companies and four universities. Research was concentrated in five discrete but related areas of the air system including turbine rim seals, rotating cavity flow and heat transfer, and turbine pre-swirl system effectiveness. In each case, experiments were conducted to extend the database of pressure, temperature, flow and heat transfer measurements to engine representative non-dimensional conditions. The data was used to develop correlations, and to validate CFD and FE calculation methods, for internal fluid flow and heat transfer. This paper summarises the outcome of the project by presenting a sample of experimental results from each technical work package. Examples of the associated CFD calculations are included to illustrate the progress made in developing validated tools for predicting rotating cavity flow and heat transfer over an engine representative range of flow conditions.
A Program for the Evaluation of Pollutant Emissions in Combined Cycle Power Plants With Supplementary Firing
Authors: Bettocchi R. , Pinelli M. , Spina P. R.
Published: February 2009

In this paper, a one-dimensional program for evaluating pollutant emissions in combined cycle power plant with supplementary firing is presented. The program uses Chemical Reactors analysis based on a Perfectly Stirred Reactor approach in conjunction with an emission model that simulates a detailed chemical kinetic scheme for combustion process modelling. The program allows the evaluation of the main pollutant emissions deriving from natural gas and oil combustion. In order to simulate combustion systems that can be found in a fired combined cycle power plant, the developed program presents some extended features with respect to programs developed for gas turbine combustors only. In order to reproduce a wide typology of combustors, the combustor geometry is represented using two characteristic dimensions (hydraulic diameter and length) and the considered domain is divided into reactors in series (along the axial direction) and in parallel (along the radial direction). The temperature in each reactor is determined taking into account both the convective and the radiative heat transfer between hot gases and walls. The program has been applied to two cases. In the first the numerical predictions have been compared with available experimental data relative to two gas turbine combustors. In the second case the program has been instead applied to a cylindrical test burner designed in accordance with EN 267 European Standard. The obtained results are acceptable from an engineering point of view and have been considered sufficiently accurate for this preliminary set-up phase of the model.
Aerodynamic Optimisation of an Aeroengine Bypass Duct OGV-Pylon Configuration
Authors: Tschirner Thomas , Pfitzner Michael , Merz Ru¨diger
Published: February 2009

In a core-mounted high-bypass aero engine the fairing around the mount arm carrying the engine weight through the bypass duct has to be designed such that the aerodynamic losses induced by this thick structure are minimized to avoid an increase of specific fuel consumption. On the other hand, the overall engine length and weight needs to be kept to a minimum so that there is no negative impact on airplane payload. This paper describes the development of an automated 2-D CFD analysis procedure for fast investigation of aerodynamic losses generated in the fan outlet guide vanes (OGV’s) and the bypass duct by the introduction of a core mount arm. Design rules for the positioning and aerodynamic form of the mount arm fairing are presented. Different configurations are compared with respect to the pressure loss induced in the bypass duct and the additional contribution to fan back pressure. A combination of well adapted aerodynamic mount arm fairing and re-staggering of the struts is presented, which only marginally increases the overall total pressure loss in the bypass duct and has negligible effect on the fan backpressure distribution.
Computer Based Optimisation and Automation of Analysis and Design Processes in Aero Engine Development
Authors: Karl Alexander , Hansen Roland , Pfitzner Michael
Published: February 2009

Many variants of designs of different engine components have to be analysed in detail during the design and subsequent optimisation of modern aero engines. This often involves repetitive tasks and even today this process still contains a considerable amount of manual work for the majority of the tasks in the design process. Experts from different technical disciplines are involved and several different analysis tools are used. An automation of this process not only saves a lot of time during the design phase; it also increases the quality of the design since many more design variants can be screened. In the present paper the integration of different analysis codes and optimisation tools into an automated process using off-the-shelf software is described. A mix of commercial and in-house codes is integrated in a loose coupling way. Several applications from different areas of aero engine design are described. It is shown that in all cases the computer based optimisation and the process automation yields results of equal or better technical quality compared to the original hand optimised ones or improves the understanding of the design space. In addition, the necessary wall-clock time to reach the results was in all cases a fraction of that of the manual process.
Advances in the Development of Silicon Nitride and Other Ceramics
Authors: Carruthers W. Dave , van Roode Mark , Becher Paul F. , Ferber Mattison K. , Pollinger John
Published: February 2009

The use of silicon nitride for high temperature components in gas turbine engine and other heat engine applications continues to be sought due to the potential for significant improvements in both efficiency and emissions. However, low impact resistance and inadequate resistance to environmental degradation of current materials reduce its reliability for rotating and stationary components. Material improvements are needed to overcome these limitations. Potential and demonstrated methods to achieve improved fracture toughness, strength, and high temperature environmental resistance are reviewed.
Measurement and Prediction of the Influence of Catalytic and Dry Low NOx Combustor Turbulence on Vane Surface Heat Transfer
Authors: Ames Forrest E. , Wang Chao , Barbot Pierre A.
Published: February 2009

New combustion systems developed for low emissions have produced substantial changes to the characteristics of inlet turbulence entering nozzle guide vanes. This paper documents the characteristics of turbulence generated by mock combustion system configurations representative of recently developed catalytic and dry low NOx combustors. Additionally, heat transfer rates are determined on the surface of a vane subjected to inlet turbulence generated by these mock combustor configurations. Six different inlet turbulence conditions with levels ranging up to 14 percent are documented in this study and vane heat transfer rates are acquired at vane exit chord Reynolds numbers ranging from 500,000 to 2,000,000. Heat transfer distributions show the influence of turbulence level and scale on heat transfer augmentation and transition. Cascade aerodynamics are well documented and match pressure distributions predicted by a commercial CFD code for this large scale low speed facility. The vane pressure distribution could be characterized as a conventional or fully loaded distribution. This comprehensive data set on vane heat transfer is expected to represent an excellent test case for vane heat transfer predictive methods. Predictive comparisons are shown based on a two-dimensional boundary layer code using an algebraic turbulence model for augmentation as well as a transition model.
Advanced Thermochemical Cleaning Procedures for Structural Braze Repair Techniques
Authors: Stankowski Alexander
Published: February 2009

Hot gas path components of modern Industrial Gas Turbines (IGT) are exposed to extreme thermal, mechanical and chemical loading that ultimately leads to their deterioration. Modern GT designs provide for safe operation for a certain operation period. Higher firing temperatures and changing machine loads as a result of the deregulated markets call for highly sophisticated part designs and the use of cost-intensive superalloys. As the lifetime of critical parts is not infinite, they are reconditioned periodically or replaced to regain efficiency losses and to mitigate the risk of unscheduled outages due to hot gas path (HGP) failures. This paper presents advanced thermochemical preparation treatments that form the basis for the subsequent structural repairs, such as high temperature brazing. Before executing any repair step, coated components must be stripped of the consumed and degenerated coatings. Not all of the many techniques that are commonly used can guarantee reproducible and complete removal without damaging the substrate. Recently improved thermochemical techniques, such as a combination of advanced Chemical Stripping and Salt Bath Cleaning, enables the OEM to obtain clean components at low unit costs and for short processing times. In previous approaches, CrF2- and PTFE-based processes were used to clean surfaces and, principally, cracks from oxide scales before welding or brazing was carried out. These preparation techniques were indispensable for reworking superalloys, which cannot be cleaned sufficiently using conventional methods such as exposure under reducing atmospheres at high temperatures. Today, the high versatility of the “Dynamic Subatmospheric Fluoride Ion Cleaning” process (FIC) enables the OEM to run precisely tailored processes, allowing complete freedom to adjust the chemical activity of the gas phase and in so doing fulfil the specific conditions for any superalloy being reworked, even taking into account the varying grade of degradation sustained during service exposure. Weld repairs on superalloys are very sensitive to hot cracking, and high temperature brazing has established itself as a successful method for overcoming this problem. Furthermore, the intensively FIC cleaned surfaces can be regarded as the most important condition to enable a high quality bonding. Other key advantages of braze repairs are the uniform heat input that is possible, the high shape tolerance and the fact that multiple cracks can be simultaneously repaired. In addition, the brazing heat treatment allows controlled adjustment of the microstructural properties. Besides the economic benefits of the treatment, the brazed parts show excellent results in respect of their mechanical integrity. A schematic presentation of the repair sequence described in this paper is shown in the appendix (Fig. 17).
History of Development and Refinement of Gas-Static Bearings for Metal-Ceramic Gas Generator of 2.5 MW Power
Authors: Soudarev A. V. , Podgorets V. Ya. , Souryaninov A. A. , Molchanov A. S.
Published: February 2009

Since 1990, by the order of the Joint-Stock Company “GAZPROM” the Research-Engineering Center “Ceramic Heat Engines” has been involved in the development of the stationary ceramic gas-turbine engine (CGTE) of 2.5 MW, efficiency 42% which is notably in excess of the characteristics of the serial-production engines of the similar power. Alongside the application of the ceramic materials, a goal to increase the fire and explosion safety of CGTE through use of journal and thrust oil beatings was set up. The refinement of the embodied design of the CGTE gas-static bearings was carried out on specially designed test beds, initially on simplified and then on baseline test beds. On all stages, the rotors were “rigid”, the balancing accuracy ensured the residual imbalance not exceeding 5–7 g*mm, the air cleaning provided the moisture separation of at least 90% with the filtration being not worse than 80μm. The tests were carried out by two stages: initially the journal beatings without the axial load applied and then the thrust bearing component with variation of the axial load within the 0.2 ≤ Presi/Pbase ≤ 1.2 were developed. The maximum speed was 30,000 rpm (noper = 23,000–24,000 rpm). Thus, the performed complex of the computation-experimental operations allowed the development of the gas-static thrust-journal beatings for the 250 N mass CGTE rotor.
The R-ATR and the R-REF Gas Turbine Power Cycles With CO2 Removal: Part 2 — The R-REF Cycle
Authors: Fiaschi Daniele , Lombardi Lidia , Tapinassi Libero
Published: February 2009

The relatively innovative gas turbine based power cycles R-ATR and R-REF (Recuperative – Auto Thermal Reforming GT cycle and Recuperative – Reforming GT cycle) here proposed, are mainly aimed to allow the upstream CO2 removal by the natural gas fuel reforming. The 2nd part of the paper is dedicated to the R-REF cycle: the power unit is a Gas Turbine (GT), fuelled with reformed and CO2 cleaned gas, obtained by the addition of several sections to the simple GT cycle, mainly: • Reformer section (REF), where the reforming reactions of methane fuel with steam are accomplished: the necessary heat is supplied partially by the exhausts cooling and, partially, with a post–combustion. • Water Gas Shift Reactor (WGSR), where the reformed fuel is, shifted into CO2 and H2 with the addition of water. • CO2 removal unit for the CO2 capture from the reformed and shifted fuel. No water condensing section is adopted for the R-REF configuration. Between the main components, several heat recovery units are applied, together with GT Cycle recuperator, compressor intercooler and steam injection into the combustion chamber. The CO2 removal potential is close to 90% with chemical absorption by an accurate choice of amine solution blend: the heat demand for amine regeneration is completely self-sustained by the power cycle. The possibility of applying steam blade cooling (the steam is externally added) has been investigated: in these conditions, the RREF has shown efficiency levels close to 43–44%. High values of specific work have been observed as well (around 450–500 kJ/kg). The efficiency is slightly lower than that found for the R–ATR solution, and 2–3% lower than CRGTs with CO2 removal and steam bottoming cycle, not internally recuperated. If compared with these, the R-REF offers higher simplicity due to absence of the steam cycle, and can be regarded as an improvement to the simple GT. In this way, at least 5–6 points efficiency can be gained, together with high levels of CO2 removal. The effects of the reformed fuel gas composition, temperature and pressure on the amine absorption system for the CO2 removal have been investigated, showing the beneficial effects of increasing pressure (i.e. pressure ratio) on the specific heat demand.
Fuel Atomization in Small Jet Engines
Authors: Levy Yeshayahou , Lipkin Semion , Nadvany Valery , Sherbaum Valery
Published: February 2009

Small and inexpensive jet engines are usually equipped with vaporizing fuel supply systems. This is in order to deliver low fuel flow-rates from relatively low-pressure fuel supply systems and the need for simple configuration. The difficulties associated with small engines are mainly during ignition or at high altitude re-lights, when the combustor is cold, air supply is poor, and fuel demand and pressure are low. Such conditions lead to poor atomization within the vaporizer resulting in very large droplets at its exit tip or even to a pool of liquid fuel within the combustor. Thus, there is no fuel vapor for ignition. Ignition is very difficult or even impossible under such conditions. Therefore, small engines are commonly equipped with dual fuel supply systems, either in the form of gaseous fuel for the ignition stage or with an additional higher-pressure supply line to the dedicated fuel nozzles for the purpose of ignition. Additional solutions involve the use of a large glow plug or high-energy pyrotechnic cartridges in the kilo-Joule range, to heat the combustor casing prior to ignition. The present work is concerned with the development of alternative and novel atomization systems, which would improve atomization at low pressures and consequently facilitate the ignition process, thus minimizing the need for supporting systems. The work refers to an alternative design for an existing vaporizer system of a small jet engine with 400 Nt of thrust. It focuses on an alternative design for the fuel injection within the vaporizer housing while maintaining all external dimensions and operating conditions unchanged. Three types of fuel nozzles were investigated: • a special impact atomizer, • a miniature pressure swirl atomizer, • a doublet atomizer involving two swirling nozzles (preliminary study only). Droplet size distribution under various nozzle pressure drops and air velocities were measured with Phase Doppler Particle Anemometry (PDPA) and global spray characteristics were obtained by photography. All modified atomization systems demonstrated improved performance and better atomization than the existing system. Initially, water was used as a liquid. At a later stage, the modified impact atomizer was tested and successful spark ignition was demonstrated.
Analysis and Optimization of Transonic Centrifugal Compressor Impellers Using the Design of Experiments Technique
Authors: Bonaiuti Duccio , Arnone Andrea , Ermini Mirco , Baldassarre Leonardo
Published: February 2009

The turbomachine industry is increasingly interested in developing automated design procedures that are able to summarize their current design experience, to take into account the manufacturing limitations and to define new rules for improving their machines’ performance. In this paper, a strategy for the parametric analysis and optimization of transonic centrifugal impellers was developed, using the technique of the Design of Experiments coupled with a 3–D fluid-dynamic solver. The geometrical parameterization was conducted using Bezier curves and a few geometrical parameters, chosen after a screening analysis in order to determine the most significant ones. The range of variation of the parameters was defined taking into account the manufacturing requirements. The analysis of the influence of such parameters on the main impeller performance was subdivided into two steps: first, the effect of the parameters acting on the blade shape was investigated and an optimum configuration was chosen, then the influence of three functional parameters was analyzed, fixing the already optimized variables. The whole strategy aimed at an industrial design approach, and attention was focused on the time required in the design process. From the present analysis it is possible not only to define an optimum geometry, but also to understand the influence of the input parameters on the main machine performance.
An Overview of High Temperature Electronics and Sensor Development at NASA Glenn Research Center
Authors: Hunter Gary W. , Neudeck Philip G. , Okojie Robert S. , Beheim Glenn M. , Powell J. A. , Chen Liangyu
Published: February 2009

This paper gives a brief overview of the status of high temperature electronics and sensor development at NASA Glenn Research Center supported in part or in whole by the Ultra Efficient Engine Technology Program. These activities contribute to the long-term development of an intelligent engine by providing information on engine conditions even in high temperature, harsh environments. The technology areas discussed are: 1) High temperature electronics, 2) Sensor technology development (Pressure sensor and High temperature electronic nose), 3) Packaging of harsh environment devices and sensors, and 4) Improved Silicon Carbide electronic materials. A description of the state-of-the-art and technology challenges is given for each area. It is concluded that the realization of a future intelligent engine depends on the development of both hardware and software including electronics and sensors to make smart components. When such smart components become available, an intelligent engine composed of smart components may become a reality.
Characterization of the Cohesive Strengths of Environmental Barrier Coatings to Ceramic Substrates Using Compression Tests
Authors: Nair Shanti V. , Eaton Harry E. , Sun Ellen Y. , Ojard Greg C.
Published: February 2009

The cohesive strengths of environmental barrier coatings applied to silicon carbide substrates were characterized using a compression test containing a strip of coating along a portion of the gage length. The substrate sample design and test fixture are similar to that described in ASTM D 695-96. The theory needed to extract the cohesive/adhesive strengths from the data is presented. The results of the compression tests are compared to the standard test method for the determination of the cohesive/adhesive strengths by the tension-adhesion test (TAT) (ASTM C 633-79). The preliminary results indicate that the onset of failure in the compression tests can be correlated with TAT test results, allowing for the extraction of the cohesive strength of the coating. For this system, this strength was found to be 15–20 MPa. The compression test has the advantage that it can be conducted at elevated temperature without the use of adhesives and, furthermore, is not limited by the adhesive strengths of polymeric adhesives.
Investigation of a Fuel Cell-Powered Blended Wing Body Airliner With Boundary Layer Re-Energization
Authors: Pachidas Vassilios A. , Singh Riti
Published: February 2009

The following study was undertaken on the assumption that hydrocarbon-based fuels may not be acceptable in the very long term, because of environmental concerns. A possible future fuel is hydrogen, and this study explores a novel proposition for a civil airliner using hydrogen fuel. The technical challenges of this preliminary investigation were: a) the integration of an electric power plant (Fuel Cell) into a Blended Wing Body (BWB) aircraft, and b) to investigate the possibility of reducing the aircraft’s profile drag by boundary layer re-energization. For the re-energization of the boundary layer and for propulsion during cruise, the study considered High-Speed/High Specific Power (HS/HSP) motors, situated at the trailing edge (TE) of the center body, driving fans. Re-energizing the boundary layer of the center body, would reduce the profile drag of the aircraft and hence, the total fuel burn. The take-off requirements of the aircraft were met, by high by-pass ratio (BPR) turbofan lift engines, operating on hydrogen, for a V/STOL (Pachidis, 2000b).
A Tip-Turbine Driven Propulsion Fan Concept
Authors: Casado H. , Cristobal E. , Lorido A. , Ramsden K. W.
Published: February 2009

The current drive for low specific fuel consumption (SFC) has resulted in increasing the bypass ratio (BPR) to improve the propulsive efficiency. Conventional high BPR engines face several practical limits when augmenting BPR i.e. an increase in the number of low-pressure turbine stages and in weight of the engine. This paper is an account of an investigation of the tip-turbine driven propulsion fan (TTDPF) as one potential solution. In particular, the TTDPF is considered as the main propulsion source for the Blended Wing Body Aircraft (BWB) developed by the College of Aeronautics at Cranfield University. The concept combines a gas generator(s) in the fuselage in combination with three or four over-wing mounted propulsion fans driven by tip-turbines. A double pass single stage configuration for the tip-turbine is assessed. This comprises two partial admission segments sharing the same circular annulus. The paper considers some special features of this novel engine concept. For example, the complex ducting (volutes) between the two passes and the aerodynamic arrangement of a two-pass turbine with a single rotor are investigated. Mechanical integrity issues and nacelle sizing are also considered. Finally, estimates are made of the noise generated by the fan and the exhaust configuration and a comparison is made with a traditional high by-pass ratio turbofan. The study concludes that the potential benefits in terms of SFC are somewhat overshadowed by the less favourable outcomes in terms of weight, nacelle size, noise and tip-turbine efficiency.
Influence of Co and Counter Swirl on Lean Stability Limits of an Airblast Nozzle
Authors: Merkle Klaus , Bu¨chner Horst , Zarzalis Nikolaos , Sara Osman N.
Published: February 2009

This paper presents the reacting flow field and the temperature distribution of two different airblast nozzles, namely co and counter swirl. To support the interpretation of the obtained results, previous measurements of the isothermal flow and mixture field of methane and combustion air are summarized. Velocities within the turbulent flow field were measured by using 3D-LDA, measurements of the field distribution of temperature were performed by means of thermocouple probes. The results show that the counter swirl arrangement provides formation of an additional vortex in the immediate vicinity of the nozzle, which has been observed as well within the isothermal as within the reacting flow. Furthermore, a dampening effect of the tangential velocity profiles towards turbulent exchange of momentum has been observed within the counter swirl configuration. Both effects cause preferential mixing of the fuel with the inner combustion air flow, thereby performing higher concentrations of methane in the near nozzle mixture field. As a consequence the counter swirl flow field exhibits larger areas of near-stoichiometric composition of fuel and air, resulting in an elevated temperature level within the stabilization zone at otherwise identical operation conditions. Therefore, application of a counter swirl nozzle allows a higher thermal load than the co swirl configuration, which offers a satisfying explanation for the wider operating range of the counter swirl burner.
CFD Prediction of Secondary Airflow Through Holes in Rotating Shafts
Authors: Young Colin , Snowsill Guy D.
Published: February 2009

Internal cooling of gas turbine engines is achieved by bleeding air off from various compressor stages and delivering it, via a complex network of flow passages, to the desired location. In modern gas turbines the air bled off for such purposes may account for up to 20% of the core airflow and is controlled by static and rotating restrictions such as orifices and seals. As this secondary air makes no direct contribution to engine thrust, there are strong economic incentives for acquiring a detailed knowledge of the flow characteristics of such devices under engine operating conditions, so that secondary air consumption can be minimised. In the present work the behaviour of secondary airflow through radial drillings in concentric shaft assemblies undergoing co- and contra-rotation is investigated using CFD techniques. The results of this work compare well with previously published orifice flow data and provide qualitative and quantitative information on these complex flows to support future air system component design.
The Influence of Leading-Edge Geometry on Secondary Losses in a Turbine Cascade at the Design Incidence
Authors: Benner M. W. , Sjolander S. A. , Moustapha S. H.
Published: February 2009

The paper presents detailed experimental results of the secondary flows from two large-scale, low-speed linear turbine cascades. The aerofoils for the two cascades were designed for the same inlet and outlet conditions and differ mainly in their leading-edge geometries. Detailed flow field measurements were made upstream and downstream of the cascades using three- and seven-hole pressure probes and static pressure distributions were measured on the aerofoil surfaces. All measurements were made exclusively at the design incidence. The results from this experiment suggest that the strength of the passage vortex plays an important role in the downstream flow field and loss behaviour. It was concluded that the aerofoil loading distribution has a significant influence on the strength of this vortex. In contrast, the leading-edge geometry appears to have only a minor influence on the secondary flow field, at least for the design incidence.
The Development of Turbine Exit Flow in a Swan-Necked Inter-Stage Diffuser
Authors: Miller R. J. , Moss R. W. , Ainsworth R. W. , Harvey N. W.
Published: February 2009

This paper describes both the migration and dissipation of flow phenomena downstream of a transonic high-pressure turbine stage. The geometry of the HP stage exit duct considered is a swan-necked diffuser similar to those likely to be used in future engine designs. The paper contains results both from an experimental programme in a turbine test facility and from numerical predictions. Experimental data was acquired using three fast-response aerodynamic probes capable of measuring Mach number, whirl angle, pitch angle, total pressure and static pressure. The probes were used to make time-resolved area traverses at two axial locations downstream of the rotor trailing edge. A 3D time-unsteady viscous Navier-Stokes solver was used for the numerical predictions. The unsteady exit flow from a turbine stage is formed from rotor-dependent phenomena (such as the rotor wake, the rotor trailing edge recompression shock, the tip-leakage flow and the hub secondary flow) and vane-rotor interaction dependant phenomena. This paper describes the time-resolved behaviour and three-dimensional migration paths of both of these phenomena as they convect downstream. It is shown that the inlet flow to a downstream vane is dominated by two corotating vortices, the first caused by the rotor tip-leakage flow and the second by the rotor hub secondary flow. At the inlet plane of the downstream vane the wake is extremely weak and the radial pressure gradient is shown to have caused the majority of the high loss wake fluid to be located between the mid-height of the passage and the casing wall. The structure of the flow indicates that between a high pressure stage and a downstream vane simple two-dimensional blade row interaction does not occur. The results presented in this paper indicate that the presence of an upstream stage is likely to significantly alter the structure of the secondary flow within a downstream vane. The paper also shows that vane-rotor interaction within the upstream stage causes a 10° circumferential variation in the inlet flow angle of the 2nd stage vane.
Trigeneration: Thermodynamic Performance and Cold Expander Aerodynamic Design in Humid Air Turbines
Authors: Genrup Magnus , Thern Marcus , Assadi Mohsen
Published: February 2009

Improving electrical efficiency has been proposed as the most convenient means of reducing, e.g. CO2 emission from power plants. Increasing fuel utilization through combined heat and power generation is another useful measure for emission reduction. Trigeneration technology for the production of heat, power and cooling is an interesting alternative for further improvement of fuel utilization. Previous studies at The Department of Heat and Power Engineering in Lund, Sweden, have shown that wet cycles are the best candidates, with a high potential to achieve fuel utilization higher than 100%, based on the fuel’s lower heating value [1, 2, 8]. Apart from high fuel utilization, trigeneration technology can produce cooling without the use of harmful cooling agents. The basic principle of trigeneration is to interrupt the expansion at an elevated pressure level and extract heat from the working medium. The final expansion then takes place at low temperature admission levels resulting in a very low temperature at the turbine exhaust. In this paper results from both thermodynamic analysis of the humid air turbine concept in conjunction with trigeneration, and the expander design criterion required for realization of the last section of the expander are presented. The thermodynamic study gives the boundary conditions for the cold turbine design. Optimum conditions for the inlet to the cold expander are a pressure of 2 to 3 bar and a temperature of 47°C. This may put serious loading constraints on the final cold expander design due to Mach and Reynolds number effects. This problem has been investigated and a detailed study of the aerodynamic loading and efficiency levels achievable is presented, using a mid-span and SCM-throughflow approach. This paper will address the cycle performance and the cold turbine aerodynamic limitations on the thermodynamic optima.
Experimental Investigation and Characterization of the Rotating Stall in a High Pressure Centrifugal Compressor: Part IV — Impeller Influence on Diffuser Stability
Authors: Cellai A. , Ferrara G. , Ferrari L. , Mengoni C. P. , Baldassarre L.
Published: February 2009

Vaneless diffuser rotating stall is a major problem for centrifugal compressors since it is a limit to their working range. In particular the last stage seems to be the most critical. In the literature some good correlations for predicting stall inception can be found but they do not adequately cover the case of the last stage configuration, especially for very low blade-outlet-width-to-impeller-radius-ratio impellers typically used in high-pressure applications. Extensive research has been performed to define diffuser stall limits for this family of stages: three impellers characterized by different blade-outlet-width-to-impeller-radius-ratios are tested with different diffuser configurations (different pinch shapes, diffuser widths and diffusion ratios). Part I and II report the results of these geometry modifications on diffuser stability for the first impeller. Part III, those for the second impeller. In this part the comparison of these results in terms of impeller influence on diffuser stability is reported.