bluuebunny/crossref_metadata_2025 huggingface dataset:
Removing Tool Marks for Impellers in Five-Axis Machining With Improved Interference-Free Tool Paths
Authors: Chen Hsin-Pao , Kuo Hsin-Hung , Tsay Der-Min
Published: August 2009

The paper deals with the procedure of removing a gouge phenomenon on impeller surfaces in 5-axis machining. That is, when an impeller of a centrifugal compressor is being cut, tool marks on its surfaces may exist in finish milling due to reverse movements of moving axes along a 5-axis interference-free tool path. For generating interference-free cutter location (CL) data needed in rough and semi-finish 5-axis cutting processes, first, a simple yet useful approach is proposed. To identify the potential gouge area and to solve the problem for a tool path having reverse motion directions with its moving axes in finish milling, the CL data are further smoothed to remove the reverse movements about its rotating and tilting axes. The effectiveness of this procedure has been experimentally confirmed by successful 5-axis finish milling of an impeller without leaving tool marks on its surfaces.
Investigation of Blade Tip Interaction With Casing Treatment in a Transonic Compressor: Part 1—Particle Image Velocimetry
Authors: Voges M. , Schnell R. , Willert C. , Mo¨nig R. , Mu¨ller M. W. , Zscherp C.
Published: August 2009

A single-stage transonic axial compressor was equipped with a casing treatment (CT), consisting of 3.5 axial slots per rotor pitch in order to investigate the predicted extension of the stall margin characteristics both numerically and experimentally. Contrary to most other studies the CT was designed especially accounting for an optimized optical access in the immediate vicinity of the CT, rather than giving maximum benefit in terms of stall margin extension. Part 1 of this two-part contribution describes the experimental investigation of the blade tip interaction with casing treatment using Particle image velocimetry (PIV). The nearly rectangular geometry of the CT cavities allowed a portion of it to be made of quartz glass with curvatures matching the casing. Thus the flow phenomena could be observed with essentially no disturbance caused by the optical access. Two periscope light sheet probes were specifically designed for this application to allow for precise alignment of the laser light sheet at three different radial positions in the rotor passage (87.5%, 95% and 99%). For the outermost radial position the light sheet probe was placed behind the rotor and aligned to pass the light sheet through the blade tip clearance. It was demonstrated that the PIV technique is capable of providing velocity information of high quality even in the tip clearance region of the rotor blades. The chosen type of smoke-based seeding with very small particles (about 0.5 μm in diameter) supported data evaluation with high spatial resolution, resulting in a final grid size of 0.5 × 0.5 mm. The PIV data base established in this project forms the basis for further detailed evaluations of the flow phenomena present in the transonic compressor stage with CT and allows validation of accompanying CFD calculations using the TRACE code. Based on the combined results of PIV measurements and CFD calculations of the same compressor and CT geometry a better understanding of the complex flow characteristics can be achieved, as detailed in Part 2 of this paper.
Turbine Clashing Transient Analysis: Impact of Rotor Disk Stage Onto Static Vane Stage After Shaft Rupture
Authors: Frola Carlo , Vassallo Antonino , Degiovanni Marco , Mattone Massimiliano
Published: August 2009

Turbine shaft rupture is one of the most critical failures of aircraft engines. When rupture happens turbine work is no more equilibrated by compressor. By consequence the turbine rotor increases its angular velocity and moves axially downstream, leading to an impact between rotor and static parts. This impact may be used to limit angular velocity below the maximum admitted burst speed. On the other hand, the impact phenomena must be controlled in order to avoid that turbine components break into many damaging uncontrolled fragments. In this paper a complete transient analysis has been developed to evaluate the motion laws during these clashing phenomena. The impact dissipation coefficient, used into the motion laws, has been estimated by a non linear finite element analysis. An example of application of this methodology is also reported.
Transient Performance and Control System Design of Solid Oxide Fuel Cell/Gas Turbine Hybrids
Authors: Kroll Florian , Nielsen Annette , Staudacher Stephan
Published: August 2009

The presentation of a control strategy for the most important SOFC / gas turbine hybrid system maneuvers like start-up, shutdown or system-failures is one of the main issues of this paper. For a successful system simulation during different operational states, a coupled model of a gas turbine and a SOFC was combined with the proposed control system. To keep the model structure lean enough for real-time calculation, a non-linear lumped volume model with modular set up was chosen to achieve an accurate reflection of the dynamic effects. The control strategy takes into account the requirements of the gas turbine components but also necessitates safe operation of the SOFC. Specified boundary conditions are strictly to be considered within the control structure to ensure failure-free and safe operation during the entire operation range. In the presented hybrid cycle a possibility of bypassing both, the cold side of the recuperator and the cathode side of the SOFC is suggested. These two bypasses, which introduce two additional actuators to the system, allow the SOFC stack temperature to be kept in its limits more easily.
An Entropy Based Evaluation of Efficiency of a Transonic Compressor Rotor With Water Injection
Authors: Szabo Istvan , Turner Mark G.
Published: August 2009

Defining the thermodynamic efficiency of the wet compression process in a compressor is not trivial, since the flow in this case has multiple phases present which interact with each other. In this paper, an approach is presented that calculates the overall entropy creation and thus the isentropic efficiency of a wet compression process in a transonic compressor rotor. The viscous dissipation function is calculated everywhere in the domain in the post-processing phase of the CFD simulation and integrated to the wall, with special treatment in the near-wall regions where high rates of entropy generation occur. The isentropic efficiency of the wet compression is then determined from the entropy generation rate. Analytical integration of wall functions and numerical integration of the viscous dissipation function allows for reasonable results even with relatively coarse grids and can be applied for single-phase flows. The methodology presented is also useful to quantify the efficiency of thermodynamic processes in devices that introduce streams into the flow path, such as cooled turbines and compressors with flow control.
Development of Gas Turbine Hot Gas Path Parts Maintenance Planning Support System
Authors: Fujii Tomoharu , Fujioka Terutaka
Published: August 2009

Since the hot gas path parts such as combustors, blades, and vanes are subject to extremely severe working conditions, the parts must be inspected and repaired at relatively short intervals. Therefore, it is essential to reduce the maintenance costs for economic reasons. Furthermore, since the hot gas path parts have cooling structures with advanced design and coated with various types of coatings, the prices of parts are usually very high. Therefore, using the parts efficiently and extending the service life of the parts are needed to significantly reduce the maintenance costs. In such a situation, a platform free system of “Gas Turbine Hot Gas Path Parts Maintenance Planning Support System” has been developed. This system can be used to decrease parts disposal loss by optimizing parts rotation plans. In this paper, main functions of this system and the results of some case studies by this system are described.
Experimental Study on Nonlinear Dynamics Characteristics of High-Speed Rotor-Gas Lubrication Bearing System
Authors: Chen Ce , Yang JinFu , Lou JianWei , Nie ChaoQun
Published: August 2009

An experimental study was done with the nonlinear dynamics characteristics of high-speed rotor-gas lubrication bearing system analyzed using the orbits of shaft center, 3D frequency coupling diagram, frequency spectrum and bifurcation diagram. Experimental results indicate that gas whirl is the main cause for the nonlinear instability of the high-speed rotor-gas lubrication bearing system, and the double periodic bifurcation resulting from gas whirl leads to the chaos vibration of the rotor-bearing system. It is therefore concluded that it is a new way to improve the nonlinear stability of a rotor-bearing system to keep the instability rotation speed far away from the design rotation speed by modulating the coupling between the natural frequency of the system and the gas whirl frequency, and to use the boundary nature of chaos verified through experiments to control the amplitude of vibration.
An Analytic Model of Oil-Film Force on Hydrodynamic Journal Bearing of Finite Length
Authors: Yang JinFu , Chen Ce , Yang ShengBo , Yu DaRen , Cui Ying , Yang Kun , Fu ZhongGuang
Published: August 2009

In order to more clearly express the interrelation between the oil-film force on hydrodynamic journal bearing of finite length and the wedging, whiling, and squeezing motions of journals, an analytic model with well-defined physical meaning is proposed in this paper by introducing the non-slip boundary condition for the oil-film velocity gradient without modifying the basic assumption for Reynolds equation to formulate the expression of oil-film pressure distribution, obtaining the analytic solution of oil-film force through integration of circumferential pressure, and defining the effect coefficients for wedging, whirling and squeezing motions, which are related to the clearance ratio and eccentricity ratio of bearings. The proposed model is compared with an existing model to show off its advantage. The proposed model was also applied to a 200MW steam turbine low-pressure rotor-bearing system to simulate the dynamic response of the rotor during the speed-up process. The analytic results of this application proved the validity of the proposed model.
A Criterion for Evaluation Stability of Journal Bearings-Rotor System
Authors: Yang Jin Fu , Yang Kun , Yang ShengBo , Chen Ce , Cui Ying , Yu DaRen , Wang YongJun , Wu WenFeng
Published: August 2009

A journal bearings-rotor system is under the influence of the interaction of nonlinear oil-film force, imbalance mass centrifugal force, journal whirling inertial force, rotor gravity and other external load (such as rub-impact force). A journal-oil film interaction balance equation is developed, which describes the correlation of journal whirling speed, rotating speed, oil supply pressure and bearing external load. Furthermore, a journal bearings-rotor system stability criterion and its application in the sense of engineering application are presented. According to a single-disk rotor supported on journal bearings experiment and micro turbine stability test, the mechanism of oil whirl and oil whip is illuminated and the practicability of journal bearing engineering stability criterion and its methodology is also validated.
Design of a Highly-Loaded Four-Stage Low-Speed Research Compressor
Authors: Clemen C. , Schrapp H. , Gu¨mmer V. , Mu¨ller R. , Ku¨nzelmann M. , Vogeler K.
Published: August 2009

The present paper describes the design of a new set of blades for the four-stage axial-flow low-speed research compressor (LSRC) at the TU Dresden. The compressor contains nine blade rows: IGV, four rotors and four cantilevered stators designed as repeating stages. The compressor was originally designed and built in the German AG Turbo project. In recent years fourteen builds of the compressor were built and tested [1]. The new design of the NGV (Build A15) has increased pressure ratio and loading compared to the previous builds. The design was performed using a method giving three-dimensionally optimised blades achieving better efficiency than the previous builds with sufficient operating range despite increased loading. The numerical analysis was carried out using a Rolls-Royce 3D-Navier-Stokes solver at design and off-design inlet conditions. The experimental investigations were carried out by the Technical University of Dresden. Overall performance was measured for different speeds and different back-pressures up to compressor stall. Flow field details were measured at a design and a close-to-stall condition using static pressure probes on the blade suction and pressure surface and secondary flow measurements using 5-hole probes.
Instability Control by Premixed Pilot Flames
Authors: Albrecht Peter , Bade Stefanie , Lacarelle Arnaud , Paschereit Christian Oliver , Gutmark Ephraim
Published: August 2009

Premixed flames of swirl-stabilized combustors (displaced-half-cone) are susceptible to thermo-acoustic instabilities which should be avoided under all operating conditions in order to guarantee a long service life for both stationary and aircraft gas turbines. The source of this unstable flame behavior can e.g. be found in a transition of the premix flame structure between two stationary conditions that can be easily excited by fuel fluctuations, coherent structures within the flow and other methods. Pilot flames can alleviate this issue by either improving the dynamic stability directly or by sustaining the main combustion process at operating points where instabilities are unlikely. In the present study, the impact of two different premixed pilot injection on the combustion stability is investigated. One of the pilot injector (pilot flame injector, PFI) was located upstream of the recirculation zone at the apex of the burner. The second one was a pilot ring (PR) placed at the burner outlet on the dump plane. A noticeable feature of the pilot injector was that an ignition device allowed for creating pilot premixed flames. The present investigation evidenced that these premixed pilot flames were able to suppress instabilities over a wider fuel/air ratio range than when the conventional premixed pilot injection alone. Furthermore, it was possible to prevent instabilities and maintain the flame burning near the lean blow out when a percentage of the fuel was premixed with air and injected through the pilot ring. In the mean time, NOx emissions were significantly reduced.
Development of an Improved Desiccant-Based Evaporative Cooling System for Gas Turbines
Authors: Zadpoor Amir Abbas , Nikooyan Ali Asadi
Published: August 2009

The evaporative inlet cooling systems used for inlet cooling of gas turbines during hot summers do not work well in humid areas. However, desiccant wheels can be used to dehumidify the air before passing it trough the evaporative cooler. Since the desiccant wheels work adiabatically, the resulting air is hotter than the air introduced to the wheel and an evaporative cooling system is used to cool down the dehumidified air. Combined direct and indirect evaporative coolers have been already used to investigate the effects of dehumidification on the effectiveness of the evaporation cooling systems. It is shown that a single desiccant wheel does not offer much higher effectiveness compared to the multiple-stage evaporative systems. In this paper, an improved version of the desiccant inlet cooling system is presented. Additional dehumidification and indirect evaporative cooling stages are added to increase the effectiveness of the inlet cooling. A typical gas turbine cycle along with an industrial gas turbine with actual performance curves are used to simulate the thermal cycle in presence of the different inlet cooling systems. The simulations are carried out for three different climatic conditions. The improved and original desiccant-based systems are compared and it is shown that the added stages substantially improve the effectiveness of the desiccant-based inlet cooling.
Effect of Unsteadiness on the Performance of a Transonic Centrifugal Compressor Stage
Authors: Tre´binjac Isabelle , Kulisa Pascale , Bulot Nicolas , Rochuon Nicolas
Published: August 2009

Numerical and experimental investigations were conducted in a transonic centrifugal compressor stage composed of a backswept splittered unshrouded impeller and a vaned diffuser. The characteristic curves of the compressor stage resulting from the unsteady simulations and the experiments show a good agreement over the whole operating range. On the contrary, the total pressure ratio resulting from the steady simulations is clearly overestimated. A detailed analysis of the flow field at design operating point led to identify the physical mechanisms involved in the blade row interaction that underlie the observed shift in performance. Attention was focused on the deformation in shape of the vane bow shock wave due its interaction with the jet and wake flow structure emerging from the impeller. An analytical model is proposed to quantify the time-averaged effects of the associated entropy increase. The model is based on the calculation of the losses across a shock wave at various inlet Mach numbers corresponding to the moving of the jet and wake flow in front of the shock wave. The model was applied to the compressor stage performance calculated with the steady simulations. The resulting curve of the overall pressure ratio as a function of the mass flow is clearly shifted towards the unsteady results. The model in particular enhances the prediction of the choked mass flow.
Numerical and Experimental Study of the Performance Effects of Varying Vaneless Space and Vane Solidity in Radial Inflow Turbine Stators
Authors: Simpson Alister , Spence Stephen , Watterson John
Published: August 2009

An extensive experimental program has been carried out on a 135 mm tip diameter radial turbine using a variety of stator designs, so as to facilitate direct performance comparisons of varying stator vane solidity and the effect of varying the vane-less space. A baseline nozzle was designed using commercial blade design software, having 15 vanes and a vane trailing edge to rotor leading edge radius ratio (Rte/rle) of 1.13. Two additional sets were designed and manufactured; one set having varying vane numbers of 12, 18, 24 and 30, and a further set with Rte/rle ratios of 1.05, 1.175, 1.20 and 1.25. As part of the design process a series of CFD simulations were carried out in order to guide design iterations towards achieving a matched flow capacity for each stator. In this way the variations in measured stage efficiency could be attributed to the stator passages only, thus allowing direct comparisons to be made. Inter-stage measurements were taken to capture the static pressure distribution at rotor inlet, and these measurements then used to validate subsequent numerical models. The overall losses for different stators have been quantified, and the variations in measured and computed efficiency used to recommend optimum values of vane solidity and Rte/rle.
Lean Premixed Combustion of Undiluted Syngas at Gas Turbine Relevant Conditions: NOx Emissions and Lean Operational Limits
Authors: Daniele S. , Jansohn P. , Boulouchos K.
Published: August 2009

The experimental work presented in this paper focuses on the characterization of four syngas mixtures, primarily in terms of NOx emissions and Lean Blow Out (LBO) limits; these mixtures were selected to simulate various syngas types derived from coal, refinery residues, biomass and co-firing of syngas with natural gas. These fuel mixtures are all of interest for applications in gasturbine processes for power generation. The experiments were carried out in a High Pressure Test Rig. Preheating of the fuel/air mixture to a temperature of 673 K, inlet bulk velocities between 40 and 80 m/s and operating pressures between 5 and 15 bars have been applied. The results show the expected strong difference between the CH4 containing mixture and all the other “pure” syngas mixtures concerning the “operational window”. As the focus of this paper is on lean extinction limits and NOx emissions, flashback phenomena are not discussed in further detail. Lean Blow Out limits were found to have weak pressure dependence for the methane containing mixture whereas for the other mixtures this dependence is slightly stronger: “Lean Blow Out” limits move to less lean condition with increasing pressure. No significant dependence on the Inlet velocity was found. Lean blow out occurs at much leaner conditions, ΦLBO≈0.25, for the pure syngas mixtures than for the methane containing fuel mixture (simulating co-firing of syngas with natural gas) which shows flame extinction already at ΦLBO≈0.38. NOx emissions show also a significant difference between the CH4 containing mixture and all other “pure” syngas mixtures with higher NOx emissions for the latter fuel gas mixtures. The difference can be attributed to the different O2 concentration in the hot exhaust gas after the flame front (for a given flame temperature) and to the difference in the flame length which leads to longer residence times in the post flame zone (for the much more compact syngas flames).
LES of Vortex Breakdown in Swirled Bluff-Body Flows
Authors: Olbricht Clemens , Hahn Frederik , Janicka Johannes
Published: August 2009

In this work the large-eddy simulation (LES) technique is used to investigate swirl configurations with different swirl intensities. The main aim is to shed light on the formation of swirl induced flow instabilities which affect the mixing of fuel and oxidiser in the nozzle region. LES is applied to the isothermal, unconfined Sydney Bluff-Body flow cases, with swirl numbers of 0.54 (low-swirl case, N29S054) and 1.59 (high-swirl case, N16S159). All computations are performed with the second order accurate, finite-volume CFD code, FASTEST, on an elliptically-smoothed, boundary-fitted, multi-block, hexahedral grid. For the low-swirl case, numerical results with different turbulence models (Smagorinsky and Germano) are compared with experimental data; both models perform very well. The prediction of different flow features had varying success. The computation of the high-swirl case is performed with the Germano turbulence model and compared to experimental data. A study of flow structures is carried out using a vortex identification technique. The onset of vortex breakdown was obtained for the low-swirl case only.
Study of Various Configurations Under Variable Density Mixing Conditions Aiming on Gas Turbine Combustion Using LES
Authors: Hahn Frederik , Olbricht Clemens , Janicka Johannes
Published: August 2009

In most technical applications involving mixing, density variation is of importance, while acoustic effects are normally considered to be unimportant. CFD models of such of such applications benefit from a low Mach number based formulation, which significantly reduces the computational effort when compared to fully compressible, variable density approaches. Within LES, which relies on accurate high-order numerics, problems arise due to the tendency of these pressure correction based formulations to oscillate for variable density flows. Damping of these oscillations is contrary to accuracy and predictability, regardless of wether it is done by numerics or adopted models. In this work, a high order approach which prevents the development of unphysical oscillations is described. This approach is then applied to several test cases of increasing complexity. Therefore the geometry flexible flow solver, FASTEST, is extended and used as a research tool. As test cases, several configurations were used. These are, in order of increasing flow complexity: a convected density wave, a mixing layer, a multi jet in cross flow, and, as a swirl configuration, a model gas turbine combustor. The results of the different test cases are discussed in detail. Where available, comparison between experiment and simulation will be made.
Shorten the Intermediate Turbine Duct Length by Applying an Integrated Concept
Authors: Marn A. , Go¨ttlich E. , Cadrecha D. , Pirker H. P.
Published: August 2009

The demand of further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters which rotate at lower speed. Therefore, it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at larger diameters minimising the losses and providing an adequate flow at the LP-turbine inlet. Due to costs and weight this intermediate turbine duct has to be as short as possible. This would lead to an aggressive (high diffusion) s-shaped duct geometry. It is possible to shorten the duct simply by reducing the length but the risk of separation is rising and losses increase. Another approach to shorten the duct and thus the engine length is to apply a so called integrated concept. These are novel concepts where the struts, mounted in the transition duct, replace the usually following LP-vane row. This configuration should replace the first LP-vane row from a front bearing engine architecture where the vane needs a big area to hold bearing services. That means the rotor is located directly downstream of the strut. This means that the struts have to provide the downstream blade row with undisturbed inflow with suitable flow angle and Mach number. Therefore, the (lifting) strut has a distinct three dimensional design in the more downstream part while in the more upstream part it has to be cylindrical to be able to lead through supply lines. In spite of the longer chord compared with the base design this struts have a thickness to chord ratio of 18%. To apply this concept a compromise must be found between the number of struts (weight), vibration, noise and occurring flow disturbances due to secondary flows and losses. The struts and the outer duct wall have been designed by ITP. The inner duct was kept the same as for the base line configuration (designed by MTU). The aim of the design was to have similar duct outflow conditions (exit flow angle and radial mass flow distribution) as the base design with which it is compared in this paper. This base design consists of a single transonic HP-turbine stage, an aggressive s-shaped intermediate turbine duct and an LP-vane row. Both designs used the same HP-turbine and were run in the continuously operating Transonic Test Turbine Facility (TTTF) at Graz University of Technology under the same engine representative inlet conditions. The flow field upstream and downstream the LP-vane and the strut, respectively has been investigated by means of five hole probes. A rough estimation of the overall duct loss is given as well as the upper and lower weight reduction limit for the integrated concept. This work is part of the EU-project AIDA (Aggressive Intermediate Duct Aerodynamics, Contract: AST3-CT-2003-502836).
Investigation of the Unsteady Aerodynamics of an Annular Combustor Using PIV and LES
Authors: Spencer Adrian , Hollis David , Gashi Sara
Published: August 2009

Experimental measurements have been carried out which have been used for specifying both boundary conditions of CFD predictions and for validation of the results. Combustor aerodynamics were therefore investigated in the same geometry, using LDA, PIV and LES. Three different LES simulations were performed in order to assess the flow field sensitivity to different boundary conditions. In the first run steady state boundary conditions are specified; in the second run, unsteady conditions at the injector exit and steady conditions in the annuli entry are specified; and in the third run unsteady boundary conditions at both injector exit and annuli entry are specified. A standard RANS simulation is also performed for comparison. The different simulations gave considerably different results. LES results with white noise scaled to give correct inlet turbulence intensities agree reasonably well with experimental data. With steady inflow conditions incorrect prediction of combustor aerodynamics resulted. Introduction of unsteady inflow conditions at the fuel injector exit plane were shown to have a significant effect on the flow interaction between the injector and the primary ports. LES is thus shown to be a good predictive tool for unsteady combustor flow fields. It is still questioned what level of fidelity is required in representing the inlet conditions to best use the predictive ability of LES. It offers significant improvement over standard RANS techniques but LES is more costly and requires detailed experimental data, used carefully, to correctly specify the inflow conditions.
Comparison of URANS and LES CFD Methodologies for Air Swirl Fuel Injectors
Authors: Dunham David , Spencer Adrian , McGuirk James J. , Dianat Mehriar
Published: August 2009

It is well documented that various large scale quasi-periodic flow structures, such as a Precessing Vortex Core (PVC) and multiple vortex helical instabilities, are present in the swirling flows typical of air swirl fuel injectors. Prediction of these phenomena requires time-resolved computational methods. The focus of the present work was to compare the performance and cost implications of two CFD methodologies — Unsteady Reynolds Averaged Navier Stokes (URANS – using a k-ε model) and Large Eddy Simulation (LES) for such flows. The test case was a single stream radial swirler geometry, which has been the subject of extensive experimental investigation. Both approaches captured the gross (time-mean) features of strongly swirling confined flows in reasonable agreement with experiment. The temporal dynamics of the quadruple vortex pattern emanating from within the swirler and observed experimentally were successfully predicted by LES, but not by URANS. Spectral analysis of two flow configurations (with and without a central jet), revealed various coherent frequencies embedded within the broadband turbulent frequency range. LES reproduced these characteristics, in excellent agreement with experimental data, whereas URANS predicted the presence of coherent motions but at incorrect amplitudes and frequencies. For the no jet case, LES-predicted spectral data indicated the occurrence of a PVC, which was also observed experimentally for this flow condition; the URANS solution failed to reproduce this measured trend. On the evidence of this study, although k-ε based URANS offers considerable computational savings, its inability to capture the temporal characteristics of the flows studied here sufficiently accurately suggests that only LES-based CFD, which captures the stochastic nature of the turbulence much more faithfully, is to be recommended for fuel injector flows.
Economical Benefits of Highly Efficient Three-Stage Intake Air Filtration for Gas Turbines
Authors: Schroth Thomas , Cagna Michele
Published: August 2009

In recent years, users and OEMs of gas turbines are focusing more and more on the quality of the combustion air, since turbo machines have become more sensitive to fouling of the compressor blades. High-quality air filters are able to reduce the fouling on the blades and enable stable power output P and efficiency η. Continuous development of filter media and filter construction have improved the filter performance in the past. Will there be further steps towards even better air filtration for gas turbines or has the development reached a plateau? The answer to this question can be found in an economic analysis taking into account a reduction of fouling due to better combustion air quality on the one hand and higher investment costs and higher pressure drop in the air intake on the other hand. The evaluations and calculations are accomplished at so-called static filter systems where air filters with depth loading characteristics are used. With static filter systems several steps of filtration are arranged in a sequence and therefore the examined upgrades of the filtration efficiencies can be implemented relatively easy so that the effect could be studied. A comparison of two- and three-stage filter systems for intake air filtration at gas turbines produces important findings regarding the most operationally cost-efficient filter sequence overall. The upgrade of the air intake system on the one hand resulted in an increased static pressure loss in the air intake causing reduced turbine efficiency and less power output. On the other hand at the same time the soiling of the blades mainly in the compressor section (compressor fouling) is lowered and as a consequence efficiency and power output are enhanced. The effects of a higher pressure drop entailed by three-stage filtration are compared with those arising from reduced soiling on the blades. In the cases examined, including case studies from actual operation, definite advantages are found for three-stage filtration with the filter sequence F6-F9-H11 in conformity with EN 779 and EN 1822. Even the modification costs for installing another filter stage can be amortized in what will sometimes be significantly less than two years.
Partload Fuel Economy Characteristics of 300 kW Class Gas Turbines
Authors: Rodgers Colin , Stone Aubrey
Published: August 2009

The partload fuel consumption characteristics of single and, two shaft recuperated, and two spool intercooled recuperative small 300 kw class gas turbines were studied in order to compare with an advanced diesel engine. With variable speed and either constant turbine inlet temperature or constant turbine exhaust temperature these three engines were judged to potentially possess a normalized fuel consumption versus load characteristic comparing favorably with that of a Diesel engine. This is moreover without the complications of many past patented Brayton cycle novel concepts conceived to achieve nearly constant thermal efficiency. Fundamentally part load optimization for a specific gas turbine engine focuses upon the slope of its fuel consumption versus power from the design point to the idle condition. The idle condition is typically set by a specified accessory load above that of the no load, or self sustaining speed, and or lean blow out limit of the combustor. It is shown that although this fuel flow slope can be slightly changed with component efficiency fall off characteristics, or with dual engine packs, for a single engine it is dominated by the two end points, the design and no load fuel flows. The premise that such 300 kw class gas turbines could however challenge the manufacturing, and direct operating costs of an advanced technology Diesel engine, besides meeting future emissions regulations remains to be aggressively pursued.
Modeling of Turbulent Combustion Process and Lean Blow Out Using Combined Approach
Authors: Kutsenko Yu. G. , Onegin S. F. , Gomzikov L. Y.
Published: August 2009

Most of the modern combustor’s designs use staged concepts for reducing thermal NO emissions. Usually, a combustion process takes place inside the main zone, which uses very lean premixed fuel/air mixtures. A diffusion pilot zone supports combustion process inside a lean main zone. Thermal NO formation process takes place predominantly inside hot diffusion flame. So, operation modes of pilot and main zones must be arranged to provide low NO emissions of pilot zone and maintain flame stability inside the main zone simultaneously. In this paper a concept of new turbulent model combustion model is presented. This model allows to model diffusion and premixed flames and takes into account various physical processes, which lead to flame destabilization. The model uses an equation for reaction progress variable. In the frameworks of considered approach this equation has three source terms. These terms are responsible for different conditions of combustion process: diffusion flames, premixed flames and distributed reaction zones. A proposed model was widely validated for different types of combustion chambers such as: 1) Bluff-body flameholder (lean premixed combustion: modeling of lean blow out); 2) Conventional diffusion regime of combustion chamber of gas turbine engine (modeling of flame stabilization and NO emissions); 3) Combined combustion regime of combustion chamber: burning process is inside pilot diffusion and main premixed zones (NO emissions and lean blow out limits for several operational modes). These tests had shown a good agreement of experimentally obtained data with results of simulations.
Design Optimization of a HP Compressor Rotor Blade and Its Hub Endwall
Authors: Iliopoulou Vicky , Lepot Ingrid , Geuzaine Philippe
Published: August 2009

The present contribution focuses on the design of a non axisymmetric hub endwall of a HP compressor single-row rotor blade in order to improve its performance at nominal conditions. First, the validation of the optimization chain is performed with a blade shape optimization based on 48 parameters with the aim to maximize the isentropic efficiency of the HP compressor at two different operating points and with two different tip gap values. The non axisymmetric hub surface is then parameterized with 16 design parameters that can create circumferential 3D bumps and hollows of variable amplitude and length at two main control sections that follow the blade curvature. The optimized non axisymmetric hub yields a 0.4% increase of the isentropic efficiency compared to the axisymmetric case by influencing more the shock mechanism close to the wall rather than the secondary flows.
Forced Response of a Large Civil Fan Assembly
Authors: Green J. S.
Published: August 2009

Forced response analysis has become commonplace for predicting the vibration amplitude of turbomachinery blading. These analyses are usually limited because they rely on predicting a well defined source of flow distortion, such as blade wakes and shocks etc. However, the sources of excitation of civil fans are not well defined and yet are able to produce high levels of force. The objective of the work described in this paper is to investigate the forced response of a large civil fan assembly using CFD. An unsteady, time accurate, 3D CFD model of the complete low pressure compression system has been used to calculate the modal response of a large civil fan. The mesh consists of the ground plane, intake, fan, OGV, bypass duct and compressor inlet stator, with every aerofoil passage modelled. The analysis tool allows calculation of a time history of modal response for a range of modes simultaneously to provide a description of the overall vibration behaviour. The results of the analyses have been used to investigate the modal contributions to the off-resonant first engine order response at a range of operating conditions to assess the contribution of various geometric features. The response is shown to compare well with measured strain gauge data for both ground and altitude conditions. The response of the majority of resonances was found to be heavily influenced by the presence of the ground plane, which is consistent with the available experimental data.
Effect of Fuel Dilution on the Stability Characteristics of Syngas Diffusion Flames
Authors: Mo Kejin , Zhang Yongsheng , Zhang Zhedian , Wang Yue , Xiao Yunhan , Hui Xin
Published: August 2009

In order to investigate the effects of fuel dilution on flame stability characteristics, open syngas diffusion flames are established and H2O, N2 and CO2 are employed respectively as diluents. The burner configuration used in this study consists of a bluff body with a central jet flow of the fuel and a surrounding coflow of the air. The syngas is composed of 50% of H2 and 50% of CO (by volume). The experiments are conducted at 1 atmospheric pressure, and the temperatures of the fuel and the air are kept constant at about 400 K. The results show that the flame tapers inward and becomes more cylindrical in the shape as after the dilution, the flame becomes unstable due to dilution effects. It has been found that there is a maximum flow rate of diluents responsible for the flame extinction. Among these three dilutions, H2O diluted flames exhibit a highest stability, while CO2 diluted flames have the lowest one due to its large specific heat. Planar Laser-Induced Fluorescence (PLIF) measurements of the OH radical are applied to study the behavior of the OH radical in the flames. The results show that as the diluents introduced into the flame increases, the overall OH mole fraction significantly decreases, and the flame width also decreases. The structures of flame bases are also studied to obtain a better understanding of fuel dilution effects on the flame stability. The radial stabilization distance is decreased and the local flame extinctions in the reaction zones are found as dilution increases. For operating conditions close to the flame extinction limit, the flame reaction zones in the flame bases take on a more intermittent, shredded appearance.
The Effects of Steady Injection on an Ultra High Lift Vane in a LP Turbine
Authors: Schumann Thomas , Rose Martin G. , Staudacher Stephan , Gier Jochen , Schro¨der Th.
Published: August 2009

The application of steady flow injection to control flow separation on the suction side of an ultra high lift low pressure turbine airfoil is presented. The blade lift coefficient of the ultra high lift airfoil at 1.46 Zweifel coefficient is considerably higher than those of conventional airfoils. Blade Reynolds numbers and blade dimensions are comparable to the first stages of aero engine low pressure turbines. The ultra high lift vane row is installed into a three stage low Mach number turbine test rig. Steady flow injection through suction side streamwise holes is investigated: with an angle to the surface of 45 deg. The pitch to diameter ratio is 10. The variation of the blowing ratio allows a closer study of the influence and effects occuing due to flow injection. Results show that steady flow injection can almost completely eliminate separation on the suction side. For four different blowing ratios blade pressure distribution and exit flow area traverse shows rising stage loading. A maximum of one percent change in flow exit angle was measured. The experimental results reveal that the injection jets only locally suppress the separation. This results in a spanwise variation in lift and trailing edge shed vortical structures.
Effects of Sand Ingestion Through an Axial Fan With Blade Staggering
Authors: Ghenaiet Adel
Published: August 2009

This paper presents the numerical results of sand particle trajectories and erosion patterns in a single stage axial fan used in industrial air ventilation, and the subsequent deterioration of the blade geometry. Attention is focused in particular on the effects of rotor blade staggering and the operating flow rates. By adopting the Lagrangian formulation to study the dynamics of particulate air-flow, the flow-field within the blade passage is solved separately. Particle trajectories computation is based on a stochastic tracking algorithm, which includes eddy-lifetime concept for turbulence, and accounts for the complex flow patterns near walls, random particle rebound factors, in addition to particle size, shape and fragmentation. The equations of motion are solved in a stepwise manner, whereas, particle tracking in different cells of the computational domain is based on the finite element method. The computation of the particle trajectories yields the impact locations along the blade surfaces, where the corresponding erosion patterns are calculated by using experimental correlations. The results of the numerical simulations carried out at low and high concentrations of MIL-E5007E sand particles, for different fan blade staggering and mass flow rates, revealed that the main impacted areas are found along the blade leading edge, over a strip of the blade suction side and a large area of the pressure side, in addition to the tip and casing, but with rare impacts on the hub. The rates of erosion in this axial fan are found to depend strongly on the air flow condition and the blade staggering. In all operating conditions of this axial fan, the rates of erosion are lower in comparison to high speed fans and compressors. Erosion analysis could be used in aerodynamic and mechanical design procedures to produce turbomachinery blading that would be less susceptible to erosion.
Heat Transfer in Trailing Edge, Wedge Shaped Cooling Channels With Slot Ejection Under High Rotation Numbers
Authors: Liu Yao-Hsien , Huh Michael , Wright Lesley M. , Han Je-Chin
Published: August 2009

Heat transfer coefficients are experimentally measured in a rotating cooling channel with slot ejection. This test section is used to model an internal cooling passage near the trailing edge of a gas turbine blade where the spent coolant exhausts through the slot to the mainstream flow. The regionally averaged heat transfer coefficients are measured in a wedge-shaped cooling channel (Dh = 2.22cm, Ac = 7.62cm2). Due to the discharging of coolant through the slots, the local mass flow rate decreases along the streamwise direction. The effect of slot ejection enhances the heat transfer near the narrow side of the channel, while heat transfer on the wide side decreases. The inlet Reynolds number of the coolant varies from 10000 to 40000 and the rotational speeds varies from 0 to 500 rpm. The inlet rotation number is from 0 – 1.0. The local rotation number and buoyancy parameter vary by the rotational speeds and the local Reynolds number in each region. The effect of rotation in this wedge-shaped channel with slot ejection is presented in this paper. This study shows that the rotation number and buoyancy parameter are good parameters to quantify the effect of rotation with slot ejection over the extended ranges achieved in this study.
Aircraft Engine On-Line Diagnostics Through Dual-Channel Sensor Measurements: Development of an Enhanced System
Authors: Kobayashi Takahisa , Simon Donald L.
Published: August 2009

In this paper, an enhanced on-line diagnostic system which utilizes dual-channel sensor measurements is developed for the aircraft engine application. The enhanced system is composed of a nonlinear on-board engine model (NOBEM), the hybrid Kalman filter (HKF) algorithm, and fault detection and isolation (FDI) logic. The NOBEM provides the analytical third channel against which the dual-channel measurements are compared. The NOBEM is further utilized as part of the HKF algorithm which estimates measured engine parameters. Engine parameters obtained from the dual-channel measurements, the NOBEM, and the HKF are compared against each other. When the discrepancy among the signals exceeds a tolerance level, the FDI logic determines the cause of discrepancy. Through this approach, the enhanced system achieves the following objectives: 1) anomaly detection, 2) component fault detection, and 3) sensor fault detection and isolation. The performance of the enhanced system is evaluated in a simulation environment using faults in sensors and components, and it is compared to an existing baseline system.
Effect of Different Economic Support Policies on the Optimal Definition and Operation of a CHP and RES Distributed Generation Systems
Authors: Casisi Melchiorre , Castelli Lorenzo , Pinamonti Piero , Reini Mauro
Published: August 2009

This paper deals about the application of MILP for economic optimization of complex cogenerative systems. In particular, it optimizes both the size and operating strategy of CHP systems and the lay-out of micro district heating networks applied to a urban contest. The proposed model considers the possible adoption of a set of micro-cogeneration gas turbines located in different buildings, and of a centralized cogeneration system thus allowing part of the required thermal energy to be produced in a single site. In addition, thermal and photovoltaic panels can be integrated into the system to improve thermal and electrical energy production, respectively. Each site can be connected to the others through district heating micro-grids. Hence thermal energy can be distributed inside the system. A further objective of the paper is to evaluate the effect of different economic support policies on the optimal solution, and to relate the economic effort implied in each support policy with the expected results in terms of CO2 emissions reduction and primary energy savings.