bluuebunny/crossref_metadata_2025 huggingface dataset:
The Time-Accurate Numerical Simulation of a Centrifugal Compressor
Authors: Turunen-Saaresti Teemu , Reunanen Arttu , Larjola Jaakko
Published: February 2009

A fully 3-D, viscous, turbulent, time-accurate numerical simulation was carried out for a centrifugal compressor. The computational domain consisted of the entire compressor including the inlet pipe, inlet cone, full impeller, diffuser, volute, exit cone and exit pipe. A design operation point of the compressor was modelled. Turbulence is modelled with the low Reynolds number k-ε turbulence model. The time-accurate and quasi-steady computational results were compared with each other and with the experimental data. Computed isentropic total-total efficiency, pressure ratio and overall performance of the volute were compared with the measured data. Also the computed circumferential variations of the total and static pressure were shown and compared with the measured data. The variations of the mass flow and pressure in relation to time were shown.
Flow Studies on a Centrifugal Compressor Stage With Low Solidity Diffuser Vanes
Authors: Mukkavilli Prasad , Raju G. Rama , Dasgupta A. , Murty G. V. Ramana , Jagadeshwar Chary K. V.
Published: February 2009

Diffusers are found to play a significant role in the performance of centrifugal compressors. Extensive studies have been in progress in various research laboratories for improvement of performance with various types of diffusers. One such effort for study of performance of a centrifugal compressor stage with Low Solidity Diffuser (LSD) vanes is presented in this paper. The study was conducted at a tip mach number of 0.35. An exclusive test rig was set up for carrying out these flow studies. The LSD vane is formed using standard NACA profile with marginal modification at the trailing edge region. The study encompasses the variation of setting angle of the LSD vane and the vane solidity. The effect of solidity and the setting angle on overall stage performance is evaluated in terms of flow coefficient, head coefficient and efficiency normalised with respect to these parameters for the case of vaneless diffuser at design flow. Improvement in performance as well as static pressure recovery was observed with LSD as compared to vaneless diffuser configuration. It is concluded from these studies that there is an optimum solidity and stagger angle for the given stage with LSD vanes for the chosen configuration.
Investigation of Off-Design Performance of Vaned Diffusers in Centrifugal Compressors: Part II — A Low-Solidity Cascade Diffuser
Authors: Oh Jong-Sik
Published: February 2009

As the second part of the author’s study, off-design behavior of the design and performance parameters in the low-solidity cascade diffuser in a centrifugal compressor is investigated. The experimental flange-to-flange compressor map serves the validity of application of the present CFD work to the detailed investigation of the low-solidity cascade diffuser. Some meanline design and performance parameters as well as three-dimensional internal secondary flow fields are studied when the flow rate is changed from deep choke to stall.
The Use of Artificial Neural Networks for Performance Prediction of Return Channels for Industrial Centrifugal Compressors
Authors: Pazzi Simone , Martelli Francesci , Michelassi Vittorio , Giachi Marco
Published: February 2009

An innovative procedure for the preliminary design and optimization of return channels for centrifugal compressors is explained. A typical configuration of bladed return channel for industrial centrifugal compressors is analyzed by means of a well-known commercial Navier-Stokes solver. A set of geometrical parameters groups is chosen in order to represent the most significant changes in geometry with respect to the base configuration. A series of new return channel configurations is obtained as the result of variations of one or more geometrical parameters. Each geometry obtained with this procedure is analyzed by the flow solver which returns a set of accurately chosen performance indices quantifying aerodynamic losses and distortions at the eye of the downstream impeller. The results thus obtained are used to train a simple one-layer Neural Network (NN) which is afterwards interrogated to compute some performance maps linking the performance indices to the three most relevant geometrical parameters. A further computation is carried out on some return channel configurations which have not been previously analyzed. The results confirm that the interpolator is able to predict the return channels performances with a good accuracy. The resulting performance maps, validated by some random tests, seem to be a valid tool for performance prediction of this kind of return channels.
Effects of Co- and Counter-Rotating Inlet Distortions on a 5-Stage HP-Compressor
Authors: Peters Thomas , Fottner Leonhard
Published: February 2009

The HP-compressor of a twin-spool aero-engine experiences a rotating inlet distortion if a rotating stall in the upstream LP-compressor occurs. This may lead to HP-compressor instability like rotating stall or surge and has even more serious effects on the performance and behavior of the engine than rotating stall in the LP-compressor alone. Studies on compressor flow instabilities are carried out at the 5-stage HP-compressor Rig212, developed in the TurboUnion RB199 jet engine programme. In order to investigate rotating inlet distortions, the axial compressor test facility is equipped with a distortion generator rotating at high speeds in the compressor inlet duct. A disk with a sectorial total pressure loss screen simulates an upstream rotating stall. It produces a rotating inlet distortion with up to 65% of the compressor’s design speed in co- or counter-rotation direction. This paper extends the presentation of first results by Peters et al. [1] and covers both, co- and counter-rotating inlet distortions and their influence on the compressor surge margin. Hot-wire sensor data are analysed to investigate the stall inception process and the response of the compressor flow field to the excitation by the rotating inlet distortion. The experimental detection of aerodynamic eigenfrequencies of the compressor is compared with numerical results from a compressor model developed by Hu and Fottner [2].
Towards a Reduction of Compressor Blade Dynamic Loading by Means of Rotor-Stator Interaction Optimization
Authors: Benini Ernesto , Toffolo Andrea
Published: February 2009

This paper presents a two-dimensional procedure for minimizing dynamic loading and maximizing time-averaged isentropic efficiency in multi-stage compressors. The procedure arises from the combination of an evolutionary algorithm and a CFD code in which a sliding mesh technique and a time-dependent approach are implemented enabling the study of unsteady rotor stator interaction. The method is then applied to a two-stage compressor cascade (rotor-stator-rotor-stator). The results concerning the optimal set of geometrical parameters considered for optimization (axial distances between successive cascades, circumferential clocking between stators and between rotors) are finally presented and discussed.
Experimental Investigations Into Pressure Field in Tip Clearance of Shrouded Rotor Blades
Authors: Kosowski Krzysztof , Piwowarski Marian
Published: February 2009

The experimental investigations into the pressure field in the shroud clearance were performed on a one-stage air model turbine of impulse type. Measurements of pressure distribution were carried out for different rotor eccentricities, different values of axial gap and of rotor-stator misalignment, different rotor speeds and different turbine load. The experimental investigations proved that: a) the pressure in the blade tip clearance is not stationary but it pulsates, b) the effect of nozzle trailing edge can be observed in the blade shroud clearance, c) for a given turbine output, the rotor-stator eccentricity and rotor-stator misalignment appear the most important parameters influencing the pressure distribution in the shroud clearance. Aiming to investigate the pressure pulsation transmission through the leakage flow in the blade shroud clearances, pulsations of different amplitudes and frequencies were excited in the turbine inlet duct and corresponding changes of pressure were measured along the shroud width, followed by appropriate harmonic analysis. The investigations were performed for forced pulsations with frequencies ranging from 1Hz to 8 Hz. In all the examined cases, the frequency of pressure pulsations remained unchanged, while the amplitude of the pulsation decreased gradually along the tip clearance. The frequency of these pressure pulsations in the tip clearance was equal to the frequency of the pressure pulsation at the turbine stage inlet and to the frequency of pressure pulsation at the turbine flow passage’s exit.
Validation of a Three-Dimensional Linearized Euler Analysis for Classical Wake/Stator Interactions
Authors: Prasad Dilip , Verdon Joseph M.
Published: February 2009

A comprehensive validation of the linearized Euler analysis, LINFLUX, for wake/blade row interaction is carried out. The flow configuration is that of the benchmark problem for rotor-stator interaction proposed at the Third Computational Aeroacoustics Workshop. It consists of an unstaggered, annular, flat-plate blade row excited by the vortical gusts associated with the wakes shed from an upstream rotor. The LINFLUX numerical results for the unsteady pressure responses of the stator are compared with semi-analytic lifting surface and lifting line solutions. The validation is first conducted for narrow-annulus flows, where the numerical results are shown to agree well with classical two-dimensional solutions over a range of frequencies. We then carry out a detailed comparison of the three-dimensional LINFLUX results with the lifting surface results of Namba and Schulten for a blade row with a hub to tip ratio of 0.5. This study encompasses gust excitation frequencies for which the stator responses vary from cut off to propagating, as well as gusts with varying degrees of spanwise variation. The numerical and semi-analytical analyses yield results for the stator pressure response, including the complex amplitudes of the propagating and least attenuated, evanescent, pressure modes that are in very good agreement. The effect of increasing the spanwise phase variation of the gust is generally, but not necessarily, to reduce the power associated with the acoustic response of the blade row.
A Preliminary Study of an Inter-Cooled and Recuperative Microgasturbine Below 300 kW
Authors: Takase Kenjiro , Furukawa Hideo , Nakano Kimiaki
Published: February 2009

During the last few years, a number of small microturbines (<100kW) have been tested in commercial markets. These microturbines have demonstrated low emissions, increased fuel flexibility, and reasonable durability. However, if these microturbines are to compete economically with larger gas turbines and reciprocating engines, manufacturing costs will need to be significantly reduced and thermal efficiencies will need to be increased. A preliminary study has been completed that evaluated larger and more efficient microturbines (∼300 kW) that operate at higher pressure ratios based on an intercooled and recuperated cycle. The thermal efficiency of the proposed concept increases to 34–37% and is competitive with larger gas turbines and similarly rated diesel engines. Two-stage turbocharger compressors and intercoolers that were developed by the automotive industry for high volume manufacturing will further improve the specific fuel consumption and specific power of this proposed microturbine concept. An additional benefit of the higher pressure, intercooled cycle is that the temperature of the exhaust gases exiting the turbine and entering the recuperator is significantly lower facilitating the use of lower cost materials in the recuperator.
Proe 90™ Recuperator for Microturbine Applications
Authors: Proeschel Richard A.
Published: February 2009

Microturbines are becoming increasingly important in the distributed power generation market. These machines are typically low pressure ratio gas turbines that require a recuperator to achieve the high, 30% or more, efficiency needed to compete in this market. However, the additional efficiency gained by a recuperator can easily be offset by its high initial cost. In response to this challenge, Proe Power Systems has developed, and has a U.S. patent pending on, the Proe 90™ gas turbine recuperator. The principal feature of the Proe 90™ recuperator is that it allows a high performance (high temperature, high effectiveness, low pressure drop) gas turbine recuperator to be manufactured by simply welding, brazing, or otherwise joining standard commercial tubing without the need for special tooling or manufacturing processes. The objective in developing the Proe 90™ recuperator was to provide a recuperator for gas turbine and related applications that can attain a minimum of 90% effectiveness with reasonable size and minimal cost. It meets those objectives by: having linear, counterflow, annular flow paths that avoid any thermal “short circuits”; by having sufficient margin to accommodate potential exhaust gas fouling of the low pressure flow passages; by having all surfaces either curved or stayed by flow tubes so that they can be made from commercially available tube and sheet stock while maintaining high margins of strength and creep resistance; and by avoiding thermal gradient stresses by having all non-isothermal portions of the recuperator able to freely expand and contract. The simple manufacturing process, design modeling techniques and predicted performance of the Proe 90™ recuperator are presented. Effects of tube length, diameter, and numbers of tubes on effectiveness and pressure losses are quantified. Additional parametric data show the effectiveness losses caused by axial conduction, flow misdistribution, manufacturing tolerances, and insulation losses. The Proe 90™ recuperator is ideally suited for microturbine distributed power applications in the 20–50 kW range. With properly sized tubes, the flow regime is laminar and results in a very small pressure loss while still producing very high heat exchanger effectiveness in a low cost, compact package.
Semi-Closed Cycle O2/CO2 Combustion Gas Turbines: Influence of Fluid Properties on the Aerodynamic Performance of the Turbomachinery
Authors: Roberts S. K. , Sjolander S. A.
Published: February 2009

Many gases, including carbon dioxide and argon, have been considered as alternatives to air as working fluids in a number of design studies for closed and semi-closed gas turbine engines. In many of these studies, it has been assumed that if the gas constant R and specific heat ratio (isentropic exponent) γ are included in the speed and flow parameters, the compressor map or turbine characteristic is applicable to other working fluids. However, similarity arguments show that the isentropic exponent itself is a criterion of similarity and that the turbomachinery characteristics, even when appropriately non-dimensionalized, will in principle vary as the γ of the working fluid varies. This paper examines the effect of γ on turbomachinery characteristics, mainly in terms of compressors. The performance of a centrifugal compressor stage was measured using air (γ = 1.4), CO2 (γ = 1.29), and argon (γ = 1.67). For the same values of the non-dimensional speed and mass flow, the pressure ratio, the efficiency, and the choking mass flow were found to be significantly different for the three test gases. The experimental results have been found to be consistent with a CFD analysis of the impeller. Finally, it is shown that the changes in performance can be predicted reasonably well with simple arguments based mainly on one-dimensional isentropic flow. These arguments form the basis for correction procedures that can be used to project compressor characteristics measured for one value of γ to those for a gas with a different value.
Exergy Analysis of Gas-Turbine Combined Cycle With CO2 Capture Using Pre-Combustion Decarbonization of Natural Gas
Authors: Kvamsdal Hanne M. , Ertesva˚g Ivar S. , Bolland Olav , Tolstad Tor
Published: February 2009

A concept for natural-gas fired power plants with CO2 capture has been investigated using exergy analysis. The present approach involves decarbonization of the natural gas by authothermal reforming prior to combustion, producing a hydrogen-rich fuel. An important aspect of this type of process is the integration between the combined cycle and the reforming process. The net electric power production was 47.7% of the Lower Heating Value (LHV) or 45.8% of the chemical exergy of the supplied natural-gas. In addition, the chemical exergy of the captured CO2 and the compression of this CO2 to 80 bar represented 2.1% and 2.7%, respectively, of the natural-gas chemical exergy. For a corresponding conventional combined cycle without CO2 capture, the net electric power production was 58.4% of the LHV or 56.1% of the fuel chemical exergy. A detailed breakdown of irreversibility is presented. In the decarbonized natural-gas power plant, the effect of varying supplementary firing (SF) for reformer-feed preheating was investigated. This showed that SF increased the total irreversibility and decreased the net output of the plant. Next, the effects of increased gas-turbine inlet temperature and of gas-turbine pressure ratio were studied. For the conventional plant, higher pressure led to increased efficiency for some cases. In the decarbonized natural-gas process, however, higher pressure ratio led to higher irreversibility and reduced thermal-plant efficiency.
The Employment of Hydrogenated Fuels From Natural Gas Reforming: Gas Turbine and Combustion Analysis
Authors: Bozza Fabio , Cameretti Maria Cristina , Tuccillo Raffaele
Published: February 2009

An integrated method for power plant analysis, including rotating component matching and CFD simulation of the combustion process, is applied to the study of gas turbines supplied with hydrogenated fuels originating from the natural gas reforming. The method proposed by the authors allows estimation of the power plant performance and emission in the gas turbine operating range. A comparison is then carried out between the plant behaviour with conventional fuelling and with decarbonised fuel supply. Attention is also paid to the study of the combustion regimes with either natural gas or fuels with increasing hydrogen contents, in order to achieve a realistic insight of both the temperature distributions and the growth of nitric oxides throughout the combustion chamber.
Pre-Design Studies of Cycles With Energy, Exergy, Thermoeconomy and ELCA Analysis
Authors: Azimian Ahmad R. , Olausson Pernilla L. , Assadi Mohsen
Published: February 2009

High efficiency, environmental friendliness, low operation and maintenance (O&M) costs, and lowest possible impact on the surroundings are some requirements of sustainable energy production. In selection of new power generation systems, a number of steps have to be taken into account to meet these requirements. Here the first law analysis has been implemented and investigated followed by a combination of the first and second law analyses (exergy analysis), and thermoeconomics, and finally an Exergetic Life Cycle Assessment (ELCA) is carried out for two different power cycles. The two cycles, investigated here, are a two-pressure level combined cycle, hereafter called (CC), and a Humid Air Turbine or (HAT-cycle). The main goal of this study is to point out the advantages and the difficulties related to the usage of each and every method and their combinations, and to identify the target groups that can gain knowledge and information using these methods. Since the operators of power plants often do not have access to detailed information about component materials, characteristics, etc., of the power cycle, assumptions have to be made when comparing different cycle configuration with each other. This limited type of data and information has also been used here to create a plausible scenario of how different pre-design methods can differ from each other. One major conclusion that has been drawn is that the two cycles investigated here are favorable in different situations and that the results from application of the three methods mentioned above indicate differences in which cycle is the preferable one. However, using a combination of different analysis methods illuminates the plant strengths and limitations during pre-design studies, but conflicting results need to be resolved to obtain the most cost effective and environmentally-friendly power cycle.
U.S. Navy Large Deck Amphibious Assault Ship: Steam to Gas Turbine Conversion
Authors: Hatcher Shaun , Oswald Alan , Boughner Abe
Published: February 2009

This paper will discuss the conversion of the US Navy LHD assault ship from conventional steam propulsion to gas turbine mechanical drive with all electric auxiliaries. The LHD 8 will provide gas turbine mechanical drive and electric propulsion via Controllable Pitch Propellers (CPP) in a Combined Operation Diesel Electric or Gas Turbine (CODLOG) configuration. The primary propulsion is from gas turbine engines with an auxiliary electric drive to provide economical low speed operations while the ship is operating in the littoral zone. The paper will discuss how the gas turbine drive in concert with an electric “loiter” motor drive will be used to provide the most efficient drive combination for each operating scenario. The paper will also discuss the process, trade-offs, and constraints placed on the designers of incorporating a new propulsion plant into an existing ship design. Interfaces with other ship systems presented significant challenges. The text presents the constraints and issues involved in the design process by addressing all major design impacts and significant design concerns. Since the Navy first introduced the General Electric LM2500, the standard gas turbine installation has changed very little and all major surface combatants since the early 1970s have utilized a very similar design. The paper will discuss how the LM2500+ installation on LHD 8, the first of its kind in a military application, will capitalize on the existing design while at the same time changing to meet new requirements, standards and regulations. The paper will also discuss the changes brought about by adopting commercial practices and standards and capitalizing on commercial experiences particularly in areas such as engine qualification.
The Identification of the Unbalance of a Flexible Rotating Machine From a Single Run-Down
Authors: Lees A. W. , Sinha J. K. , Friswell M. I.
Published: February 2009

The reliable estimation of a flexible foundation model and the state of unbalance (both amplitude and phase) of a turbogenerator from machine run-down measured vibration data is an active research area. Earlier studies on the estimation of both these quantities used the whole frequency range of the run-down as a single band. However, such an identification may be inaccurate for large flexible foundations having many modes in the run-down frequency range. For reliable identification, the whole frequency range has to be divided into a number of frequency bands and the frequency dependent foundation models have to be estimated together with the unbalance. This paper combines the unbalance estimation with the split frequency range for the foundation model, and the highlights the limitations observed during estimation of foundation models and state of unbalance. Having established the method in simulation, experimental data from a 3 m long test rig, with four journal bearings, is used to test the method. The robustness of the unbalance estimates to a number of errors in the bearing and shaft model is demonstrated. The approach seems to give reliable estimates of the machine unbalance.
Predicting Engine Whirl Instability Via Equivalent 2D Mechanisms
Authors: Klompas Nicholas
Published: February 2009

Analysis to predict whirl instability of a whole engine, including flexible bladed disks, due to both linear and nonlinear destabilizing mechanisms at any speed, not only the critical, is advanced. The basis is the previously published, and now extended, equivalent two-dimensional mechanism (E2dM). Proven through physical logic are the principles: (1) a deflection or slope with a phase angle greater than 90 deg lead in response to an external disturbing force or moment respectively signals instability; (2) response of a system absorbing energy is modulated at speeds below onset of instability. Tactics to exploit these principles through fundamental analyses of response are devised.
Eigen Solutions of an Orthotropy Composite Blade Solved by the Differential Quadrature Method
Authors: Kuang J. H. , Hsu M. H.
Published: February 2009

The eigenvalue problem of an orthotropy composite blade is formulated by employing the differential quadrature method (DQM). The Euler-Bernoulli beam model is used to characterize the orthotropy composite blade. The differential quadrature method is used to transform the partial differential equations of an orthotropy composite blade into a discrete eigenvalue problem. The Chebyshev-Gauss-Lobatto sample point equation is used to select the sample points. In this study, the effects of the fiber orientation, internal damping, external damping, inclined angle and the rotation speed on the eigen solutions for an orthotropy composite blade are investigated. The effect of the number of sample points on the accuracy of the calculated natural frequencies is also discussed. The integrity and computational efficiency of the DQM in this problem will be demonstrated through a number of case studies. Numerical results indicated that the differential quadrature method is valid and efficient for an orthotropy composite blade formulation.
Effects of the Nature of Excitation on the Response of a Mistuned Bladed Disk Assembly
Authors: Cha D. , Sinha A.
Published: February 2009

In this paper, responses of a mistuned bladed disk assembly are examined and compared for three types of excitations: uncorrelated narrow band random excitations, correlated narrow band random excitations and sinusoidal excitations with unknown (time-invariant and random) amplitudes. Analytical techniques are also developed to compute the statistics of responses for these types of excitations. Effects of correlations of narrow band excitations are investigated in details. It has been found that the response statistics for correlated narrow band random excitations can be viewed in terms of the concepts related to the response to a deterministic engine order excitation.
Machinery Management: The New Paradigm
Authors: Harker Roger G. , Sabin Steven J.
Published: February 2009

This paper addresses the topic of machinery management by describing what it is, how it is performed, and what benefits those who employ machinery management practices can expect to derive. The practice has evolved since its inception in the 1960s, and a historical perspective is provided showing the roots of machinery management practices, its growth to currently adopted practices, and the limitations of such current practices. A new method of machinery management is presented, using currently available off-the-shelf products, and the advantages of this new method are shown. Machinery management is also placed within the broader context of Plant Asset Management, an emerging focus in the process industries to obtain competitive advantage through an integration of condition monitoring, maintenance management, and reliability management practices applied to all plant production assets, not just machinery.
A Design Method for the Profiling of End Walls in Turbines
Authors: Hartland Jonathan , Gregory-Smith David
Published: February 2009

The profiling of end walls in turbines has proved to be effective in reducing secondary flows and losses in turbines, both in cascades and in a turbine representative rig. This paper presents a simple method for the design of end walls using the philosophy that the blade (or rather flow) curvature causes the cross passage pressure gradient, so that mirroring the blade curvature on the end-wall should assist in canceling this effect. Three alternative end-wall profiles have been designed based on the camber line of the blades. From a CFD investigation into the effects of these profiles, they should all be effective in reducing the secondary flow within the cascade. The best profile extended upstream and downstream of the blades to attempt to overcome the problems associated with sharp curvature at inlet and exit from the blade row. For the best profile the CFD predicts a 6% reduction in secondary loss and a 61% reduction in secondary kinetic energy. Whilst the loss predictions are not expected to be accurate, the reduction in secondary kinetic energy is likely to be similar to that achieved if the profile were tested experimentally. Experience with testing of an earlier end wall (Hartland et al [1]) suggests that there is likely to be a substantial reduction in secondary loss accompanying this level of reduction in secondary kinetic energy.
Wake, Shock and Potential Field Interactions in a 1.5 Stage Turbine: Part I — Vane-Rotor and Rotor-Vane Interaction
Authors: Miller R. J. , Moss R. W. , Ainsworth R. W. , Harvey N. W.
Published: February 2009

The composition of the time-resolved surface pressure field around a high-pressure rotor blade caused by the presence of neighboring blade rows is investigated, with the individual effects of wake, shock and potential field interaction being determined. Two test geometries are considered: first, a high-pressure turbine stage coupled with a swan-necked diffuser exit duct; secondly, the same high-pressure stage but with a vane located in the downstream duct. Both tests were conducted at engine-representative Mach and Reynolds numbers, and experimental data was acquired using fast-response pressure transducers mounted on the mid-height streamline of the HP rotor blades. The results are compared to time-resolved computational predictions of the flowfield in order to aid interpretation of experimental results and to determine the accuracy with which the computation predicts blade interaction. The paper is split into two parts, the first investigating the effect of the upstream vane on the unsteady pressure field around the rotor (vane-rotor interaction) and the second investigating the effect of the downstream vane on the unsteady pressure field around the rotor (rotor-vane interaction). The paper shows that at typical design operating conditions shock interaction from the upstream blade row is an order of magnitude greater than wake interaction and that with the design vane-rotor inter-blade gap the presence of the rotor causes a periodic increase in the strength of the vane trailing edge shock. The presence of the potential field of the downstream vane is found to affect significantly the rotor pressure field downstream of the Mach one surface within each rotor passage.
The Tip and Hub Leakage Flow of a Repeated Two Stage Compressor
Authors: Wang Songtao , Wang Zhongqi
Published: February 2009

End wall flow of a repeated two stage compressor at design and choke condition were studied by numerical simulation. The vortex near the hub depends on the traverse pressure gradient and sheer force induced by the hub rotation. At the design and the choke condition the hub leakage vortex is the dominant secondary flow. The position and trajectory of the tip leakage vortex at design and choke condition were also studied. At the design condition the tip leakage vortex traverse the blade channel and impinge on the middle chord of the suction surface of the adjacent blade. At the near choke condition the tip leakage vortex would go downstream along the streamwise direction. The composition of the tip vortex was also studied. It is clearly to distinguish the strong and weak part of the tip leakage vortex for design condition while at the near choke condition there is no evident weak part of the tip leakage vortex.
Time Resolved Measurements in an Annular Compressor Cascade With High Aerodynamic Loading
Authors: Weidenfeller Jo¨rg , Lawerenz Martin
Published: February 2009

In order to identify unsteady flow phenomena this paper presents experimental investigations inside an isolated compressor cascade under off-design conditions. The results of extensive time resolved measurements, which were performed by piezo-resistive pressure sensors and hot wire anemometry show an interaction of aerodynamic and acoustic mechanisms. For a certain operating range the measurements indicate, that vortices, caused by boundary layer separations, oscillate with the pipe mode of the test section. In addition so-called rotating instabilities occur at high blade loading. They rotate with 48% of the circumferential component of the inlet velocity.
Influence of Endwall Contouring on the Transonic Flow in a Compressor Blade
Authors: Hoeger M. , Cardamone P. , Fottner L.
Published: February 2009

Endwall contouring is successfully applied to compressor rotors to reduce boundary layer loading and to control endwall flow. Over-speeds resulting from large relative thickness and curvature of the rotor root section are compensated by the increase in open flow area which is generated by the concave hub shape. In transonic flow this area increase promotes higher Mach numbers and has a considerable impact on the shock system. To investigate endwall contouring experimentally at engine like flow conditions a novel cascade technique is introduced: A contracting endwall is designed in a way to enable homogenious flow conditions in Mach number and flow angle at the inlet plane of the cascade. For a given blade shape now several endwall contours may be investigated. Experiments are performed at the High Speed Cascade Windtunnel of the University of the Armed Forces, Munich for a linear and a concave endwall for a given blade section. Inlet Mach number level is around Ma1 = 0.9 at typical turning and profile thickness. The results show an increase in pre-shock Mach number and a change in shock pattern from an oblique shock for the linear contour to a normal shock for the concave one. Endwall contouring is demonstrated not only to influence the flow in the vicinity of the endwall but to extend up to a considerable distance in spanwise direction.
An Improved Streamline Curvature Approach for Off-Design Analysis of Transonic Axial Compression Systems
Authors: Boyer Keith M. , O’Brien Walter F.
Published: February 2009

A streamline curvature throughflow numerical approach is assessed and modified to better approximate the flow fields of transonic axial compression systems. Improvements in total pressure loss modeling are implemented, central to which is a physics-based shock model, to ensure accurate and reliable off-design performance prediction. The new model accounts for shock geometry changes, with shock loss estimated as a function of inlet relative Mach number, blade section loading (flow turning), solidity, leading edge radius, and suction surface profile. Data from a single-stage, isolated rotor provide the basis for experimental comparisons. Improved performance prediction is shown. The importance of properly accounting for shock geometry and loss changes with operating conditions is demonstrated.
Carbon Dioxide Emission Analysis With Energy Payback Effect
Authors: Utamura Motoaki
Published: February 2009

Analytical model is proposed to account for carbon emission behaviour during replacement of power source from fossil to renewable energy in which sustainability of energy supply is stressed. Analyses show that energy payback time (EPT) should be much shorter than the doubling time of manufacturing cycle to secure adequate available energy during as well as after the replacement. Nuclear, small hydropower and photovoltaic cell are taken as representative candidates and investigated as an option to replace fossil power until mid-century. Nuclear and small hydropower can be a promising candidate but photovoltaic cell needs further development efforts to reduce EPT to avoid energy expense after the replacement.
Forced Response Experiments in a High Pressure Turbine Stage
Authors: Hennings Holger , Elliott Robert
Published: February 2009

An experimental investigation was conducted on a single stage high pressure turbine in order to gain a deeper unterstanding of turbine blade forced response. In particular the main objective of this experiment was to obtain good quality validation data for the prediction methods used by major engine manufacturers. The stage investigated consists of an uncooled nozzle guide vane (NGV) and a rotor with 64 blades. To study the complete forced response problem a so called Flexible Rotor was designed and manufactured. This rotor has three modes of interest in the operating range of the stage: first torsion, second flap and second edge. The design of the experiment was supported by detailed CFD and structural analysis. The mechanical behavior of the Flexible Rotor is well known. In order to identify all interesting modes all blades are equipped with strain gauges individually calibrated. To check the unsteady pressures 18 unsteady pressure transducers were mounted at midspan. This paper deals with experiments only with the Flexible Rotor. Forced response results are presented for the first torsion mode at two different pressure ratios. The results obtained show a large scatter for the maximum response amplitudes at each pressure ratio. The distribution of the amplitudes around the disk is controlled by the mechanical properties of the rotor.
Ceramic Matrix Composite Material in Highly Loaded Journal Bearings
Authors: Leuchs M. , Mu¨hlratzer A.
Published: February 2009

Conventional sintered silicon carbide (SSiC) has been applied in journal bearings of pumps for more than 20 years with the pumped medium itself being the lubricant. High corrosion and wear resistance of SSiC have contributed to this success. The brittle failure of that material quite often is a problem, though, and limits the application of SSiC in highly loaded bearings. In contrast, ceramic matrix composites (CMC) based on C- or SiC-fiber-reinforced SiC-ceramics show strongly improved fracture toughness on the level of cast iron and are applicable in cases where conventional ceramics due to their lack of reliability cannot be used. These CMC-materials have been developed in several programs primarily for space and military applications and are also beeing successfully used in journal bearings for pumps in power plants [1] and for tubular casing pumps [2]. In power plant pumps, low viscosity water of up to 160°C can be the lubricant. In tubular casing pumps quite often water loaded with abrasive sand particles lubricates the bearings. CMC-journal bearings for pumps in cryogenic rocket engines for reusable launch vehicles (RLVs), where the lifetime of mechanical components is a critical issue, are presently tested. Journal bearings of the type introduced in water pumps could replace ball bearings presently in use. Improved stiffness and damping properties, reduced wear, increased reliability and no limitations in speed times diameter would be some of the expected advantages [3]. Journal bearings for hot hinges in re-entry systems are foreseen for the space vehicle CRV (crew rescue vehicle) and have successfully been tested under close to real conditions. They are envisaged to be flight-tested on the experimental NASA vehicle X38. The bearing faces run under dry conditions and temperatures of more than 1600°C in air of about 50 mbar pressure [4]. Presently, only CMCs based on carbon fibers have potential to operate successfully under such conditions.
Combustion Control by Extended EV Burner Fuel Lance
Authors: Paschereit Christian Oliver , Flohr Peter , Kno¨pfel Hanspeter , Geng Weiqun , Steinbach Christian , Stuber Peter , Bengtsson Karin , Gutmark Ephraim
Published: February 2009

Flame stabilization in a swirl-stabilized combustor occurs in an aerodynamically generated recirculation region which is a result of vortex breakdown. The characteristics of the recirculating flow are dependent on the swirl number and on axial pressure gradients. Coupling to downstream pressure pulsations is also possible. In order to fix the position of the recirculation zone, an extended fuel lance was inserted into the burner. An additional benefit of the extended lance was to enable secondary fuel injection directly into the recirculation zone where the flame is stabilized. Tests were conducted with and without secondary fuel injection. The measurements included optimization of the location of the extended lance in the mixing chamber and variation of the amount of secondary fuel injection at different equivalence ratios and output powers. Flow visualizations showed that stabilization of the recirculation zone was achieved. The effect of the extended lance on pressure and heat release oscillations and on emissions of NOx, UHC and CO was investigated. The results were confirmed in high pressure single burner pressure tests and in a full scale land-based test gas-turbine. The lance has been successfully implemented in engines with sufficient stability margins and good operational flexibility. This paper shows the careful development process from lab scale tests to full scale engine tests until the implementation into the field engines.
Construction of Low NOx and High Stability Flames Aiming at Micro Gas Turbine Combustion
Authors: Shiotani Hitoshi , Takagi Toshimi , Okamoto Tatsuyuki , Kinoshita Shinichi , Teraoka Hironobu
Published: February 2009

For the micro gas turbine combustor, low NOx emission, high stability and complete combustion are requested. The objective of this study is to construct the flame to establish the above targets. The concepts of the combustor are (1) to use the circulation zone by swirl flow to ensure the flame stability and complete combustion and (2) to induce lean premixed combustion by mixing fuel and air at the inlet of combustor to ensure low NOx emission and prevention of flashback. Town gas is used as the fuel. We conduct experiments using three types of combustor design to investigate the characteristics of NOx and CO emission together with the investigation of the flame stability and visualization of the flame configuration. By improving the premixing of the fuel and air the NOx emission was minimized to get 3ppm (at 0% O2) with sufficiently low CO emission.
Aerodynamic Evaluation of Double Annular Combustion Systems
Authors: Denman Paul A.
Published: February 2009

Legislation controlling the permitted levels of pollutant emissions from aircraft gas turbines has been an increasingly important design driver for the combustion system for some time, particularly with respect to oxides of nitrogen. This has lead to many suggestions for radical departures from the geometry of the classical combustor configuration involving, for example, lean premixed module technology, or staging (axially or radially) of combustor pilot and main zones. The optimum operation of any combustor also requires, however, appropriate and efficient distribution of compressor delivery air to the various flametube features (fuel injectors, dilution ports, for cooling and for air bleed purposes). Radial staging, leading to double annular combustor configurations, poses a particularly difficult challenge. The radial depth of the combustor increases to a level where the external aerodynamics of the combustor involves large flow turning after the pre-diffuser. Careful design is then needed to achieve acceptable levels of loss coefficient in the outer annulus. If these aspects are not properly addressed then inadequate penetration and mixing in the combustor interior can result, rendering low emissions performance impossible. This paper will report on the design, instrumentation and operation of a fully annular isothermal test facility, which has been developed specifically to enable this important issue of external flow quality in double annular combustor systems to be assessed. Representative inlet conditions to the combustion system are generated using a single stage axial compressor; modular construction enables quick and inexpensive changes to components of the combustor (pre-diffuser, cowl shape, liner port locations and geometrical details). Computerised rig control and data acquisition allows the collection of large amounts of high quality data. In addition to the calculation of overall system performance, it is then possible to identify flow mechanisms and loss-producing features in various zones and suggest appropriate modifications.
Safety Developments in Gas Turbine Power Applications
Authors: Santon Roger C. , Kidger Jasper W. , Lea Chris J.
Published: February 2009

Gas turbine driven power plants are subject to a number of new European Directives. The paper refers to the ATEX Directives and contains recommendations from a UK perspective of particular relevance to suppliers and users of gas turbines. It describes specifically the application of demonstrably effective dilution ventilation as a basis of safety and includes CFD methodology recommendations and a leak size determination method. It includes detail on the development and progress of the new ISO/European gas turbine safety standard intended to give further guidance and form a basis of compliance with Directives. It includes details of an extensive Industry funded research project intended to provide a better founded ventilation design basis. Its scope includes micro turbines as well as the full range of industrial and aero-derivatives. This paper follows from ASME 98-GT-215 [1].
Pressure-Side Bleed Film Cooling: Part I — Steady Framework for Experimental and Computational Results
Authors: Holloway D. Scott , Leylek James H. , Buck Frederick A.
Published: February 2009

This study combines both experiments and computations to investigate pressure-side bleed on the trailing edge of a turbine blade. Realistic engine conditions are considered with a lip thickness to slot height ratio of 0.9 and mainstream Mach numbers of 0.7 at the coolant injection point expanding to sonic conditions at the exit plane of the test section. The purpose of this study is to understand the complex physics of pressure-side bleed, in particular, the unusual behavior that occurs with increasing blowing ratio. Experimentally, it is shown that as the blowing ratio increases, the film cooling effectiveness at a point near the end of the test section increases for blowing ratios less than 0.8, while decreasing over the range of blowing ratios from 1.0 through 1.25. For blowing ratios higher than 1.25, effectiveness increases. This phenomenon has been repeated experimentally for many years without being fully understood. Parts I and II of this paper describe the mechanism responsible for the unusual experimental results. This mechanism is unsteady vortex shedding. Experimental results are from a row of jets with the use of foreign gas injection that simulates the engine conditions that would be seen by the pressure side of an airfoil with pressure-side bleed. These results consist of the pressure distribution due to the nozzle and the effectiveness along the test surface downstream of the injection site. The computational model is designed to replicate the experimental setup. High-quality grids, high-order discretization schemes, and an advanced turbulence model are employed to ensure that the computational results can be used to explain the complex physics of transonic pressure-side bleed film cooling. The grid consists of 2.2 million cells and a high-quality, unstructured, multi-topology, super-block mesh with the resolution of the viscous sub-layer and y+ < 1 on all surfaces. The simulations are fully converged and grid-independent. Effects of blowing ratio are examined, with blowing ratio ranging from 0.5 to 2.0 and a density ratio of 1.52. The geometry consists of not only the transonic mainstream flow and the jet, but also the creeping plenum flow. As a result of the significant lip thickness to slot height ratio, it is shown that unsteady effects are the dominant mechanism in the physics of pressure-side bleed film cooling.