bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Rotordynamic Modeling of Rolling Element Bearing Systems
Authors: Liew A. , Feng N. S. , Hahn E. J.
Published: July 2014

Non-linearity effects in rolling element bearings may arise from the Hertzian contact force deformation relationship, the presence of clearance between the rolling elements and the bearing races, and the bearing to housing clearance. Assuming zero bearing to housing clearance and ignoring rolling element centrifugal load effects, it has been shown in earlier work that Rotor Bearing Systems (RBSs) with deep groove ball bearings can give rise to non-linear behavior such as chaotic motion and jump. This paper extends the bearing model to include rolling element centrifugal load, angular contacts and axial dynamics. The effect of more sophisticated bearing models is illustrated in both a rigidly supported rigid RBS and a flexibly supported flexible RBS, the latter being a model of a test rig designed to simulate an aircraft mounted accessory drive unit. Results are presented on the effect of bearing preload on the unbalance response up to a speed of 18,000 rpm.
Investigation of Unsteady Aerodynamic Blade Excitation Mechanisms in a Transonic Turbine Stage: Part I — Phenomenological Identification and Classification
Authors: Laumert Björn , Mårtensson Hans , Fransson Torsten H.
Published: July 2014

Based on the results of time dependent 3D viscous computations the aerodynamic mechanisms that cause the unsteady pressure fluctuations on the vane and rotor blade surface of a high-pressure transonic turbine are identified and separately classified in a phenomenological manner. In order to be able to describe separately the influence of wake, potential and shock distortions on the blade surface pressure at design operation conditions, the stator exit Mach number is increased as to enhance the shock distortions and lowered as to enhance potential and wake distortions. In a comprehensive approach the observations from the off-design conditions are utilized to classify every major perturbation observed in the perturbation space-time maps at design operation conditions. The spanwise variations caused by the inherent 3D nature of the flow field and promoted by the 3D shape of the rotor blade are addressed.
Numerical Unsteady Flow Analysis of a Turbine Stage With Extremely Large Blade Loads
Authors: Jöcker Markus , Hillion Francois X. , Fransson Torsten H. , Wåhlén Ulf
Published: July 2014

This paper presents the detailed numerical analysis including parametric studies on the aerodynamic excitation mechanisms in a turbine stage due to the unsteady stator-rotor interaction. The work is part of the pre-design study of a high pressure subsonic turbine for a rocket engine turbopump. The pressure level in such turbines can be remarkably high (in this case 54 MPa inlet total pressure). Hence, large unsteady rotor blade loads can be expected, which impose difficult design requirements.

The parameter studies are performed at midspan with the numerical flow solver UNSFLO, a 2D/Q3D unsteady hybrid Euler/Navier-Stokes solver. Comparisons to 2D and steady 3D results obtained with a fully viscous solver, VOLSOL, are made.

The investigated design parameters are the axial gap (∼8%–29% of rotor axial chord length) and the stator vane size and count (stator-rotor pitch ratio ∼1–2.75). For the nominal case the numerical solution is analyzed regarding the contributions of potential and vortical flow disturbances at the rotor inlet using rotor gust computations.

It was found that gust calculations were not capable to capture the complexity of the detected excitation mechanisms, but the possibility to reduce excitations by enforcing cancellation of the vortical and potential effects has been elaborated. The potential excitation mechanism in the present turbine stage is found dominant compared to relatively small and local wake excitation effects. The parameter studies indicate design recommendations for the axial gap and the stator size regarding the unsteady rotor load.
Experimental Study of Aerodynamic and Structural Damping in a Full-Scale Rotating Turbine
Authors: Kielb Jason J. , Abhari Reza S.
Published: July 2014

Damping in turbomachinery blades has been an important parameter in the study of forced response and high cycle fatigue, but because of its complexity the sources and physical nature of damping are still not fully understood. This is partly due to the lack of published experimental data and supporting analysis of real rotating components. This paper presents the results of a unique experimental method and data analysis study of multiple damping sources seen in actual turbine components operating at engine conditions. The contributions of both aerodynamic and structural damping for several different blade vibration modes, including bending and torsion, were determined. Results of the experiments indicated that aerodynamic damping was a large component of the total damping for all modes. A study of structural damping as a function of rotational speed was also included to show the effect of friction damping at the blade and disk attachment interface. To the best of the authors’ knowledge, the present paper is the first report of independent and simultaneous structural and aerodynamic damping measurement under engine-level rotational speeds.
Experimental and Numerical Study of Forced Response in a Full-Scale Rotating Turbine
Authors: Kielb Jason J. , Abhari Reza S. , Dunn Michael G.
Published: July 2014

Forced response predictive capabilities have advanced rapidly in the past decade because of increased emphasis on high cycle fatigue concerns. Progress in computation fluid dynamic (CFD) codes has allowed for the prediction of complex unsteady flows, but fidelity and accuracy of the unsteady solutions is uncertain. This uncertainty is due in part to a lack of representative experimental data to validate the forced response calculations. This study presents experimental results of both on-blade unsteady pressure and structural response in a full-scale rotating turbine at representative steady aerodynamic conditions. The primary focus of these experiments was on vane wake excited forced response in a subsonic turbine and its variation with axial rotor/stator spacing. Comparisons of data with quasi 3-D unsteady, multi-blade row CFD predictions showed good agreement for the unsteady pressure amplitude near the midspan. A significant increase in unsteady pressure level was seen for the experiments at a 10% closer axial rotor/stator spacing, particularly near the tip and on the suction surface. The study also included structural response characteristics for a bending, torsion, and axial vibration mode and the interaction with the aerodynamic response.
A Framework for Flutter Clearance of Aeroengine Blades
Authors: Khalak Asif
Published: July 2014

A framework for flutter operability assessment, based upon a new set of similarity parameters, has been developed. This set consists of four parameters which embrace both the performance characteristics in terms of corrected mass flow and corrected speed, and the flight condition in terms of inlet temperature and density (or, equivalently, inlet pressure). It is shown that a combined mass-damping parameter, g/ρ*, novel in the field of turbomachinery aeroelasticity, can summarize the individual effects of mechanical damping, g, and blade mass ratio, μ. A particular selection of four nondimensional parameters, including g/ρ* and a compressible reduced frequency parameter, K*, allows for a decoupling of corrected performance effects from purely aeroelastic effects, for a given machine and a specific modeshape. This view of flutter operability is applied to the analysis of full-scale engine data. The data exhibits the trend that increasing K* and increasing g/ρ* have stabilizing effects, which is consistent with previous work in flutter stability. We propose that these trends hold generally, and apply the trends towards constructing a flutter clearance methodology, a test procedure which satisfies the requirements for comprehensive flutter stability testing.
Forced Response of Turbine Engine Bladed Disks and Sensitivity to Harmonic Mistuning
Authors: Kenyon J. A. , Griffin J. H.
Published: July 2014

The mistuned forced response of turbine engine bladed disks is treated using harmonic perturbations in the properties of a continuous ring. A continuous shear spring is attached to the ring in which the stiffness is allowed to vary along the ring annulus. The modes of such a structure with a single harmonic mistuning pattern are shown to obey the Mathieu equation, which is solved to obtain the natural frequencies and modes of the mistuned system. The forced response of the system is then examined to determine the sensitivity of the system to small mistuning. The model is extended to include multiple harmonics, allowing for the possibility of general mistuning. An expression for the maximum amplitude magnification due to small mistuning is developed by showing that high response is caused by distortion of the structural modes. A method to intentionally mistune systems for maximum forced response is demonstrated, and numerical results demonstrate the accuracy of the analytical prediction. The intentionally mistuned system response is shown to be robust with respect to small random mistuning. Such a result might be useful for designing a test rotor for screening new bladed disk designs or for establishing root cause of fatigue problems.
Effects of Multi-Stage Coupling and Disk Flexibility on Mistuned Bladed Disk Dynamics
Authors: Bladh Ronnie , Castanier Matthew P. , Pierre Christophe
Published: July 2014

The effects of disk flexibility and multi-stage coupling on the dynamics of bladed disks with and without blade mistuning are investigated. Both free and forced responses are examined using finite element representations of example single- and two-stage rotor models. The reported work demonstrates the importance of proper treatment of interstage (stage-to-stage) boundaries in order to yield adequate capture of disk-blade modal interaction in eigenfrequency veering regions. The modified disk-blade modal interactions resulting from interstage-coupling-induced changes in disk flexibility are found to have a significant impact on (a) tuned responses due to excitations passing through eigenfrequency veering regions, and (b) a design’s sensitivity to blade mistuning. Hence, the findings in this paper suggest that multi-stage analyses may be required when excitations are expected to fall in or near eigenfrequency veering regions or when the sensitivity to blade mistuning is to be accounted for. Conversely, the observed sensitivity to disk flexibility also indicates that the severity of unfavorable structural interblade coupling may be reduced significantly by re-designing the disk(s) and stage-to-stage connectivity. The relatively drastic effects of such modifications illustrated in this work indicate that the design modifications required to alleviate veering-related response problems may be less comprehensive than what might have been expected.
Approach to Unidirectional Coupled CFD – FEM Analysis of Axial Turbocharger Turbine Blades
Authors: Filsinger D. , Szwedowicz J. , Schäfer O.
Published: July 2014

This paper describes an approach to unidirectional coupled CFD – FEM analysis developed at ABB Turbo Systems Ltd.. Results of numerical investigations concerning the vibration behavior of an axial turbocharger turbine are presented. To predict the excitation forces acting on the rotating blades, the time resolved two-dimensional coupled stator - rotor flow field of the turbine stage was calculated. The unsteady pressure, imposed on the airfoil contour, leads to circumferentially non-uniform and pulsating excitation forces acting on the rotating bladed disc.

A harmonic transformation of the excitation forces into the rotating co-ordinate system of a single blade was elaborated and the complex Fourier amplitudes were determined. The bladed rotor was modeled by a single symmetric segment with complex circumferential boundary conditions. With respect to different nodal diameter numbers free vibration analyses of the disc assembly were then effectively performed. For calculated resonance conditions, the steady state responses of the turbocharger bladed disc were computed. By using this coupled CFD - FEM analysis, the dynamic loading of the turbine blades can be determined in the design process.
Estimation of Contact Stiffness and its Role in the Design of a Friction Damper
Authors: Szwedowicz J. , Kissel M. , Ravindra B. , Kellerer R.
Published: July 2014

The use of under-platform friction dampers is a common practice for the elimination of high cycle fatigue failures of turbomachinery blading. Damper performance curves and damper optimization curves are used for the design of friction dampers. It is establishedAAfrom the previous work that apart from damper mass, the contact stiffness between damper and the blade platform is an important parameter in achieving a good damper design. Several methods for the estimation of damper stiffness have been proposed in the literature. Some of them include: 1. Curve fitting approach to a measured frequency response function, 2. Compliance measurement, 3. Measurement of hysteresis loop etc. However, it is not possible to carry out extensive sets of experiments to observe the influence of various parameters on the contact stiffness. Numerical and/or analytical models for contact stiffness evaluation are the present needs for a damper designer. This paper addresses a detailed investigation of the contact stiffness computation. Finite element modeling of the damper and the platform is carried out to study the effect of various parameters such as friction coefficient, centrifugal load, material properties etc. on the contact stiffness. The role of surface roughness and wear are neglected in the present analysis. The reliability of the applied finite element meshes is verified by simulating Hertz’s contact problems. The parametric study indicates that the contact stiffness builds up with increase in friction coefficient, centrifugal force and elastic modulus of the damper material. The results received from a pilot experiment are also presented for further evaluation of the computed results. Finally, a very good agreement between the numerical and experimental performance curves (resonance response amplitude of the blade versus excitation amplitude for the constant damper mass; Cameron et. al, 1987) of the blade with the damper is found for the tangential contact stiffness obtained from the finite element calculation. The present work extends the quest for a rational approach to damper design.
Analysis of the Worst Mistuning Patterns in Bladed Disc Assemblies
Authors: Petrov E. P. , Ewins D. J.
Published: July 2014

In the paper, the problem of determining of the worst mistuning patterns is formulated and solved as an optimization problem. Maximum resonant amplitudes searched across the many nodes of a large-scale finite element model of a mistuned bladed disc and across all the excitation frequencies in a given range are combined into an objective function. Individual blade mistuning is controlled by varying design parameters, whose variation range is constrained by manufacture tolerances.

Detailed realistic finite element models, which have so far only been used for analysing tuned bladed discs, are used for calculation of the forced resonant response of mistuned assemblies and for determination of its sensitivity coefficients with respect to mistuning variation.

Results of the optimum search of mistuning patterns for some practical bladed discs are analysed and reveal higher worst cases than those found in previous studies.
Fail Safe, High Temperature Magnetic Bearing for High Efficiency Gas Turbine Engine Applications
Authors: Palazzolo Alan , Montague Gerald T. , Kim Yeonkyu , Kenny Andrew , Tucker Randall , Na Uhn Joo , Lei Shuliang , Lingenfelter Nathan , Provenza Andy , Kascak Albert F.
Published: July 2014

This paper contributes to the magnetic bearing literature in two distinct areas: high temperature and redundant actuation. Design considerations test results are given for the first published combined 538°C (1000°F)-high speed rotating test performance of a magnetic bearing. Secondly, a significant extension of the flux isolation based, redundant actuator control algorithm is proposed to eliminate the prior deficiency of changing position stiffness after failure.
Experimental and Numerical Investigation of Blade Pressure Fluctuations on a CFK-Bladed, Counterrotating Propfan
Authors: Schnell Rainer
Published: July 2014

In order to investigate pressure fluctuations on the blade surface experimentally, a CFK - bladed Counterrotating Prop-fan CRISP with an outer diameter of 1m has been instrumented with 20 piezoresistive pressure sensors on each rotor. An accompanying two-dimensional numerical simulation has been conducted using the unsteady code TRACE-U. The flowfield was subsonic in both rotors because of a chosen operating point of approximately 52% of the design speed at a corrected mass flow of 108 kg/s. Upstream potential effects upon the first rotor where found to be relatively small at this operating point. The paper focuses on downstream effects on the second rotor of both viscous and potential nature. The main sources causing fluctuations in blade pressure were to be found wake shedding from the first rotor, pressure perturbations caused by the wake of the first rotor impinging on the leading edge of the second rotor and reflections of these pressure perturbations on adjacent blade ro ws running upstream. An analysis of these unsteady flow phenomena taking into account both experimental and numerical data will be presented including a detailed comparison of both sets of data.
Effects of Rotating Inlet Distortion on a 5-Stage HP-Compressor
Authors: Peters Thomas , Bürgener Thomas , Fottner Leonhard
Published: July 2014

In a twin-spool jet engine the HP-compressor experiences a rotating inlet distortion if rotating stall in the upstream LP-compressor occurs. This destabilizing effect on the compressor operating behavior may lead to HP-compressor instabilities like rotating stall or surge. In order to investigate this specific type of unsteady inlet distortion a 5-stage HP-compressor is operated with a newly developed high rotation speed distortion generator in the inlet duct. It produces a rotating inlet distortion with up to 65% of the compressor design speed rotating clockwise or counterclockwise with the compressor rotor. Kulite pressure sensors as well as hot-wire probes are installed to resolve the unsteady character of the inlet distortion, to define the compressor map and to analyse the stall inception process. Describing the rotating inlet distortion and its influence on the compressor operating behavior will be the major objective of this paper. In the experiment the distortion speed of an inlet distortion rotating clockwise with the compressor rotor is varied at different compressor speeds and the effects on the surge margin are analysed.
Stall Inception in a High-Speed Centrifugal Compressor
Authors: Kang Jeong-Seek , Kang Shin-Hyoung
Published: July 2014

Stall inception in a high-speed centrifugal compressor has been examined. The main objective was to find stall precursor and to develop a reliable stall warning method. Eight equally spaced fast-response pressure transducers in the inducer detected the spatial structure of small amplitude perturbations, via spatial Fourier transform, as stall is approached. Near the stall inception point, the phase of spatial Fourier coefficients increased linearly with the speed of impeller rotation for several impeller revolutions at all test speeds, and the spectrum at impeller frequency increased as stall is approached. This is the clear evidence that the impeller frequency participates in the stalling process.

For stall warning, a method which uses the spectrum at impeller frequency is suggested. The use of spectrum at impeller frequency as a stall warning method showed a warning time of about two hundreds impeller revolutions. This method uses only one sensor that it has made the stall warning method more useful. And the well-known traveling wave energy method proved to be a good method for stall warning also in a high-speed centrifugal compressor. The warning time was about one hundred impeller revolutions at lower speeds, and about one thousand impeller revolutions at higher speeds. The stall warning methods used here were found to be robust and reliable. Therefore, it seems to be promising to set up a reliable stall avoidance control based on this analysis.
Wake-Wake Interactions and its Potential for Clocking in a Transonic High Pressure Turbine
Authors: Hummel Frank
Published: July 2014

Two-dimensional unsteady Navier-Stokes calculations of a transonic single stage high pressure turbine were carried out with emphasis on the flow field behind the rotor. Detailed validation of the numerical procedure with experimental data showed excellent agreement in both time-averaged and time-resolved flow quantities. The numerical time-step as well as the grid resolution allowed the prediction of the Kármán vortex streets of both stator and rotor. Therefore the influence of the vorticity shed from the stator on the vortex street of the rotor is detectable. It was found that certain vortices in the rotor wake are enhanced while others are diminished by passing stator wake segments. A schematic of this process is presented. In the relative frame of reference the rotor is operating in a transonic flow field with shocks at the suction side trailing edge. These shocks interact with both rotor and stator wakes. It was found that a shock-modulation occurs in time and space due to the stator wake passing. In the absolute frame of reference behind the rotor a 50% variation in shock strength is observed according to the circumferential or clocking position. Furthermore a substantial weakening of the rotor suction side trailing edge shock in flow direction is detected in an unsteady flow simulation when compared to a steady state calculation which is caused by convection of upstream stator wake segments. The physics of the mentioned unsteady phenomena as well as their influence on design are discussed.
Numerical Investigation of Airfoil Clocking in a Three-Stage Low Pressure Turbine
Authors: Arnone Andrea , Marconcini Michele , Pacciani Roberto , Schipani Claudia , Spano Ennio
Published: July 2014

A quasi–three–dimensional, blade–to–blade, time–accurate, viscous solver w as used for a three–stage LP turbine study Due to the low Reynolds number, transitional computations were performed. Unsteady analyses were then carried out by varying the circumferential relative position of consecutive vanes and blade rows to study the effects of clocking on the turbine’s performance. A clocking strategy developed in order to limit the number of configurations to be analyzed is discussed. The optimum analytically–determined clocking position is illustrated for two different operating conditions, referred to as cruise and takeoff.

The effects of clocking on wake interaction mechanisms and unsteady blade loadings is presented and discussed. For low Reynolds number turbine flows, the importance of taking transition into account in clocking analysis is demonstrated by a comparison with a fully turbulent approach.
Unsteady Aerodynamical Blade Row Interaction in a New Multistage Research Turbine: Part 1 — Experimental Investigation
Authors: Gombert Ralf , Höhn Wolfgang
Published: July 2014

Exploitation of stator–stator interaction phenomena can increase overall efficiency in axial turbomachines. The first part of this paper sets out to present results of steady and unsteady flow experiments obtained in a new three stage cold flow low pressure turbine. Observation and understanding of boundary layer development and transition phenomena on the vanes dependent on relative stator position will be the focal point. In addition to this, stator position influence on profile loss, turbine efficiency and the development of secondary flow are examined.

The experiments were carried out in the closed circuit test bed of the Institute of Aeronautical Propulsion at Stuttgart University. Annulus geometry and blading design of the research turbine were taken from the low pressure turbine of a modern commercial jet engine. The three stage test rig had identical blade counts for all stators or rotors respectively, whilst the circumferential position of each stator row could be individually adjusted. The second and third stators were optimised with respect to the radial alignment of the vanes. Surface mounted hot film gauges on the vanes and hot film probes were employed to assess the unsteady interaction phenomena. For steady measurements, pneumatic five hole probes and multiple kielhead pressure and temperature probes were used.

For both the second and third stator, circumferential position was varied in eight steps over one pitch. Whereas the design point forms the basis of this detailed investigation, some attention was also paid to variations in Reynolds number and wheel speed. The results, such as quasi wall shear stress, stochastic and periodic fluctuations, total pressure etc., are presented in the form of chordwise ensemble-averaged distributions and contour plots and should be compared with the corresponding numerical studies presented in the second part of this paper.
Unsteady Aerodynamical Blade Row Interaction in a New Multistage Research Turbine: Part 2 — Numerical Investigation
Authors: Höhn Wolfgang , Gombert Ralf , Kraus Astrid
Published: July 2014

This paper is the second part of a two part paper, which describes in part one the experimental setup and results of a new multistage turbine. Part two presents results of unsteady viscous flow calculations based on cold flow experiments of that three stage low pressure turbine. The present paper emphasizes the investigation of stator-stator interaction of a low pressure turbine section of a commercial jet engine. Different positions for the second and third stator are studied numerically and experimentally with respect to the blade row interaction, unsteady blade loading and unsteady boundary layer effects.

A time accurate Reynolds averaged Navier-Stokes solver is applied for the computations. Turbulence is modeled using the Spalart-Allmaras one equation model turbulence model and the influence of modern transition models on the unsteady flow predictions is investigated. The integration of the governing equations in time is performed by a four stage Runge-Kutta scheme, which is accelerated by a two grid method in the viscous boundary layer around the blades and alternatively by a dual time stepping method. At the inlet and outlet reflecting or non-reflecting boundary conditions are used. The quasi 3D calculations are conducted on a stream surface around midspan allowing a varying stream tube thickness.

In particular, the flow field with respect to time averaged and unsteady quantities such as surface pressure, vorticity, unsteady velocity field and skin friction are compared with the experiments conducted in the cold air flow test rig.
An Analysis of the Spatial Fluctuations at the Stator-Rotor Interface in a Transonic Turbine
Authors: Callot Stanislas , Ferrand Pascal
Published: July 2014

This paper analyses the flow in a transonic turbine stage, using numerical results from a full 3D Navier-Stokes computation over the whole stage. This analysis, based on the combination of time and space Fourier transforms, points out how a spatio-temporal periodicity phenomenon is involved in the so-called stator-rotor interaction.

A first comparison is made between the computational results using geometrical approximation and the results achieved by the complete simulation. This analysis points out how the signal is enforced by the numerical conditions at the circumferential boundaries.

The stator-rotor interaction produces low spatial harmonics which are identified as spinning modes by means of Fourier series. The analytical theory from Tyler and Sofrin (1962) is then used to define a general model of stator-rotor interaction. This model allows the determination of the angular speed of rotation of the spinning modes, and results are compared with the global numerical simulation.

Finally, a first analysis of the axial propagation of the spinning modes is proposed, and attention is focused on the fact, that only few parameters are necessary to reproduce the unsteady signal.
Investigation of Acoustic Phenomena at the Inlet and the Outlet of a Centrifugal Compressor for Pressure Ratio 4.5
Authors: Feld H.-J. , Aschenbrenner S. , Girsberger R.
Published: July 2014

The effects of the interaction between impeller and diffuser and the influence of distortions in the inlet flow on noise generation in a high speed centrifugal compressor were investigated. Therefore, an existing test rig was modified to allow acoustic measurements in the upstream and downstream ducts of the compressor. Anechoic ends designed according to the standards for low speed fans were inserted at both sides of the compressor in order to prevent disturbing reflections. Three slit tube microphone probes were installed in each duct to determine the noise level at the compressor inlet and the compressor outlet. In addition, a measurement plane for microphone traverses was set to allow the evaluation of the sound field. The tests provided fundamental insight into the main noise sources and the structure of the sound field at the inlet and the outlet of a high speed compressor stage.
Instability Analysis of a Centrifugal Compressor Stage Near Peak Pressure Rise
Authors: Jahnen Werner , Breugem Wim-Paul , Ribi Beat
Published: July 2014

It is often observed that radial compressor stages exhibit different types of instabilities dependent on the rotor-diffuser matching. The onset of instability may be before, at, or after the slope of the pressure rise characteristic becomes zero during throttling. In this study the flow conditions in the individual stage components at instability onset have been investigated experimentally and theoretically to allow an improvement of present prediction methods.

Within the scope of the experimental study separate characteristics of the rotor and the diffuser have been recorded in detail while unsteady measurements have been performed simultaneously. The measurement results show that rotor and/or diffuser instability affects overall stage stability. The nature of stage component stability suggests that rotor and diffuser can be excited as subsystems.

For an improved understanding, numerical investigations based on the Moore-Greitzer (1986) model have been performed. In order to account for the observed subsystem properties of rotor and diffuser, the model had to be extended, and was adapted to the geometry of the investigated radial compressor stage. By implementing inner stage mass storage and flow redistribution capability into the model, a decoupled treatment of stage components was accomplished. The numerical results are in qualitative agreement with the measurements, and prove that a decoupled treatment of rotor and diffuser in radial compressor stages is able to describe stall inception more accurately.
Analytical and Test Experiences Using a Rib Diffuser in a High Flow Centrifugal Compressor Stage
Authors: Sorokes James M. , Kopko Jason A.
Published: July 2014

The paper addresses the use of a rib style (partial height) vaned diffuser to improve the flowfield downstream of a high flow coefficient centrifugal impeller. Empirical and analytical (3-D CFD) results are presented for both the original vaneless diffuser and the replacement rib configuration. Comparisons are made between the CFD results and the data obtained through single stage rig (SSTR) testing. Comments are offered regarding the qualitative and quantitative agreement between the empirical and analytical results.
Numerical Investigation of Tandem-Impeller Designs for a Gas Turbine Compressor
Authors: Roberts Douglas A. , Kacker Suresh C.
Published: July 2014

The tandem-bladed impeller centrifugal compressor, which may offer potential aerodynamic benefits over conventional designs, is rarely employed in production gas-turbine applications. Conventional impeller designs are often favored because of concerns for both significant performance losses and increased manufacturing costs associated with tandem configurations. In addition, much of the available literature concerning the characteristics of tandem-impellers is inconclusive, and at times contradictory. Because of the scarcity of tandem-impellers, rules for their design are nearly non-existent. Also, the effects of inducer/exducer clocking upon tandem-impeller performance and exit flow characteristics are not fully understood. In the present study, a numerical investigation was performed to investigate the aerodynamic characteristics of a tandem-impeller design for the rear-stage of a gas-turbine compressor (target impeller PRt-t≈3.0). A parametric study of tandem-impeller inducer/exducer clocking was performed in order to explore its effect upon performance and exit flow quality. Because the tandem impeller was designed to be retrofittable for an existing conventional impeller, it was also compared to predictions for the baseline conventional design.

Results of the study indicated that the tandem-impeller was less efficient than the conventional design for all clocking configurations studied. Tandem-impeller blade clocking was found to have a significant effect upon predicted pressure-ratio, temperature-ratio, efficiency, and slip-factor; the maximum values for these parameters were predicted for the in-line tandem configuration. The minimum predicted tandem-impeller isentropic efficiency occurred at a clocking fraction of 50%, falling 3.8 points below that of the in-line case. Although the tandem-impeller performance was predicted to diminish as blade clocking was increased, significant improvements in the uniformity of impeller exit velocity profiles were observed. Profiles of both total pressure and swirl at impeller exit indicated that the tandem-impeller design may offer both improved diffuser recovery and stalling margin over the conventional design.
Numerical Investigation of Different Tip Gap Shape Effects on Aerodynamic Performance of an Axial-Flow Compressor Stator
Authors: Jia Xicheng , Wang Zhengming , Cai Ruixian
Published: July 2014

An efficient numerical method is applied to investigate the influence of different tip gap shapes on the performance of an axial-flow compressor stator under the condition of rotating hub or stationary hub. Tip gap shapes considered in this paper include zero gap, uniform gap, and linearly varying gap. The analysis of the results shows, at least for these test cases, tip leakage vortex can be found to generate earlier for stationary hub cases than for rotating hub cases. On the same working conditions, the blade row with zero gap has not the highest efficiency, while the blade row with smaller tip gap can attain higher efficiency due to the role of tip leakage flow the direction of which is opposite to the secondary flow in the passage near the hub. For the same circumferential leakage area in the tip region, the blade row with linearly expanding gap can obtain higher efficiency. The work of this paper can provide a useful reference for optimum design of compressor stator.
Experimental and Numerical Investigation of the Flow in a 5-Stage Transonic Compressor Rig
Authors: Lecheler Stefan , Schnell Rainer , Stubert Bertram
Published: July 2014

The flow in a 5-stage transonic compressor rig was experimentally and numerically investigated. The rig is geometrically scaled from the front part of an existing heavy duty gas turbine compressor with CDA-blading.

At several operating points pressures and temperatures were measured in order to get the performance map of the compressor, radial distributions at vane leading edges and static pressures at vanes and casing.

In order to identify shock locations and to get information about the rotor-stator interactions and the flow angles, 3D L2F-measurements were done in the first and second rotor at two speeds. A newly developed double periodic measuring L2F-system was employed in order to analyze the results with respect to up- and downstream effects of both rotors.

The experimental data were used for the validation and calibration of two steady 3D multistage Navier-Stokes codes with mixing plane models between the blade rows.

With STAGE3D, calculations were mainly done for the first 2 transonic stages in order to compare shock locations, velocities, inlet and outlet flow angles with measurements. Furthermore the code was calibrated, which means, that grid sizes and numerical parameters were adjusted to give the best fit to the experiments while having acceptable calculation times. A set of parameters was found, which will be used for the design of new transonic multistage compressors. However not all flow quantities fit well to the measurements. Mass flow and pressures could not be fulfilled at the same time.

The other code used was TRACE-S. A procedure for a fast calculation of the whole performance map for all 9 blade rows together was developed and tested. The shape of the calculated speed lines fit well to the measured ones, but the mass flow is predicted too high at off-design conditions. The reason is a too low calculated loss production which is confirmed by the higher calculated radial total pressure distributions.
A New Multistage Axial Compressor Designed With the Apnasa Multistage CFD Code: Part 1 — Code Calibration
Authors: Mansour M. , Hingorani S. , Dong Y.
Published: July 2014

The NASA Average-Passage multistage turbomachinery flow analysis code “APNASA” by J.J. Adamczyk (1985) has been validated, calibrated, and demonstrated at Honeywell Engines and Systems for the design of multistage axial compressors. APNASA was first calibrated against test data of two existing compressors and then used as a design tool in the design of a new modern multistage axial compressor. The results of the calibration, design effort, and the data measurements are presented in this two-part paper. In the present paper (Part 1) the results of the calibration for two multistage axial compressors are presented. The first compressor consists of four axial stages that were designed in the mid 1980s. The second compressor consists of three axial stages and was designed in the mid 1990s using viscous, three-dimensional CFD code, with airfoil optimization performed in single blade row fashion. The calibration work was aimed at developing meshing and modeling best practices and validating the code capability to simulate flow behavior in a multistage environment. Predictions are compared with test data for the axial compressor overall performance, individual stage performance, and detailed radial profiles at the stator vanes leading edge planes, throughout the compressor. Results show good agreement between APNASA predictions and measurement data. In particular, the results clearly demonstrate the ability of APNASA to capture the stage matching of multistage machines. As a result of this calibration/validation work, a new multistage axial compressor was subsequently designed, by using APNASA as the primary source of information for airfoil optimization (presented as Part 2 of this paper). Test results for the new compressor reveal that the design achieved its performance and operability goals in its first build. Details of the compressor design philosophy using APNASA and the comparison between APNASA simulation results and test data are presented in Part 2.
A New Multistage Axial Compressor Designed With the APNASA Multistage CFD Code: Part 2 — Application to a New Compressor Design
Authors: Dong Y. , Mansour M. , Hingorani S. , Hayes J.
Published: July 2014

In this second part of a two-part paper on the application of the NASA multistage aerodynamic simulation CFD tool, the APNASA code, work is presented on how the code was used successfully in the design of a brand new, four-stage axial compressor aimed for a modern turbofan engine. In particular, the code was used to guide the blade geometry changes such that the right stage matching throughout the compressor was achieved. The overall performance is shown to be in good agreement with the map generated prior to the detailed design from a one-dimensional model, including the surge line. This success is attributed to the fact that the compressor has been successfully matched at its design intention. More detailed comparisons of the measurements with the prediction demonstrate capability of APNASA in capturing details of flow, such as the rotor exit pressure and temperature profiles and the stator exit flow angle. Largely as a result of the application of APNASA, the compressor described in this paper has been designed “right the first time”, resulting in significant cost savings in a new engine development program for Honeywell Engines and Systems.
Analysis of the Aerodynamic Behavior of the Swept Leading Edge Shock Surfaces in High Loading Axial Flow Compressors
Authors: Shan Peng , Liu Xueying , Luo Yunhe
Published: July 2014

This paper is Part III of a comprehensive study on the blade leading edge sweep/bend of supersonic and transonic axial compressors. For the curved leading edge shock surfaces generated by high loading swept axial flow rotors, using an analytical structure model of 3-D shock surface, this paper investigated the characteristics of the shock surface structure, then calculated the distributions of the flow variables in front of and behind the shock. The research focused on the influences of the relatively forward- or backward-swept rotors on the flow field behind but near the leading edge shock surface. By the analytical model, this paper answered the one hand of the question of the swept rotors’ functions. For the first time it quantitatively showed the existence of the phenomenon of 3-D shock induced span-wise and circumferential mixing in the primary flow.
Compact Low-Temperature Analogue of Aero Engine Fire-Certification Burner
Authors: Talib Abd. Rahim Abu , Neely Andrew J. , Ireland Peter T. , Mullender Andrew J.
Published: July 2014

The paper describes the compact low-temperature analogue burner designed for fire integrity testing. The low-temperature analogue burner has been improved in order to make the test procedures easier, faster and more accurate. The use of a thermally thin faceplate at the burner nozzle eliminates the requirement for a warm up phase that was previously required and thus negates the need for a shutter. Less helium and time is needed for the whole operation. The new compact burner also provides improved accessibility for instrumentation and camera views. A new image processing technique has been developed to simultaneously map the distributions of heat transfer coefficient (h) and adiabatic wall temperature (Taw) across the surface of the model using multiple liquid crystal coatings and varying gas temperatures. Measurements of h and Taw distributions made on a flat plate using the compact burner are reported.
Thermodynamic, Economic and Environmental Benefits of the Integration Between Oil Refineries and IGCCs
Authors: Consonni Stefano , Pelliccia Giampaolo
Published: July 2014

IGCC technology enables environmentally-friendly generation of electricity from high sulphur content refinery residuals and, at the same time, higher production of light and middle distillates over a wide range of crude quality. The latter represents a particularly valuable feature because environmental regulations are driving toward larger market shares of lighter and cleaner distillates and, at the same time, crude quality is declining.

This paper illustrates how the integration between a refinery process and an IGCC can reduce primary energy consumption and emissions, as well as improve the economic prospects of the refinery. The analysis moves from the specific case of the ISAB-Energy plant recently completed in Priolo (Italy) and then assesses the thermodynamic, economic and environmental benefits achievable by the upgrade of the whole Italian refinery system under three sets of assumptions: IGCC with the same features and cost of the ISAB plant; advanced IGCC (LHV efficiency 46%) with a specific cost of 1400 $/kW; advanced IGCC with a specific cost of 1200 $/kW.

If all Italian refineries were integrated with advanced IGCCs (with natural gas fired Combined Cycles covering the deficit of electricity production), national primary energy consumption would decrease by more than five millions tons of oil equivalent per year, CO2 emissions would decrease by almost 15 million t/y and there would be substantial reductions of SOx, NOx and particulate emissions. If the overall cost of this restructuring were totally charged to the reduction of CO2 emissions, each ton of avoided CO2 emissions would costs between 4,5 to 29,3 $.
Performance Analysis of Evaporative Biomass Air Turbine Cycle With Gasification for Topping Combustion
Authors: Wolf Jens , Barone Federico , Yan Jinyue
Published: July 2014

This paper investigates the performance of a new power cycle, a so called Evaporative Biomass Air Turbine (EvGT-BAT) cycle with gasification for topping combustion. The process integrates an externally fired gas turbine (EFGT), an evaporative gas turbine (EvGT) and biomass gasification. Through such integration, the system may provide the potential for adapting features from different advanced solid-fuel based power generation technologies, e.g. externally fired gas turbine, integrated gasification combined cycle (IGCC) and fluidized bed combustion, thus improving the system performance and reducing the technical difficulties. In the paper, the features of the EvGT-BAT cycle have been addressed. The thermal efficiencies for different integrations of the gasification for topping combustion and the heat recovery have been analyzed. By drying the biomass feedstock, the thermal efficiency of the EvGT-BAT cycle can be increased by more than 3 percentage points. The impact of the outlet air temperature of the high temperature heat exchanger has also been studied in the present system. Finally, the size of the gasifier for topping combustion has been compared with the one in IGCC, which illustrates that the gasifier of the studied system can be much smaller compared to IGCC. The results of the study will be useful for the future engineering development of advanced solid fuel power generation technologies.