bluuebunny/crossref_metadata_2025 huggingface dataset:
Progress on the Advanced Turbine Technology Applications Project (ATTAP)
Authors: Berenyi S. G.
Published: February 2015

This technology project, sponsored by the U.S. Department of Energy, is intended to advance the technological readiness of the ceramic automotive gas turbine engine. Of the several technologies requiring development before such an engine becomes a commercial reality, structural ceramic components represent the greatest technical challenge, and are the prime project focus. The ATTAP aims at developing and demonstrating such ceramic components that have a potential for: (1) competitive automotive engine life cycle cost and (2) operating for 3500 hr in a turbine engine environment at turbine inlet temperatures up to 1371°C (2500°F).

Allison is addressing the ATTAP goal using internal technical resources, an extensive technology and data base from General Motors (GM), technical resources from several subcontracted domestic ceramic suppliers, and supporting technology developments from Oak Ridge and other federal programs.

The development activities have resulted in the fabrication and delivery of numerous ceramic engine components, which have been characterized through laboratory evaluation, cold spin testing, hot rig testing, and finally through engine testing as appropriate. These component deliveries are the result of the ATTAP design/process development/fabrication/characterization/test cycles.

Ceramic components and materials have been characterized in an on-going program using nondestructive and destructive techniques. So far in ATTAP, significant advancements include:

• evolution of a correlated design procedure for monolithic ceramic components

• evolution of materials and processes to meet the demanding design and operational requirements of high temperature turbines

• demonstration of ceramic component viability through thousands of hours of both steady-slate and transient testing while operating at up to full design speed, and at turbine inlet temperatures up to 1371°C (2500°F)

• completion of hundreds of hours of durability cyclic testing utilizing several “all ceramic” gasifier turbine assemblies

• demonstration of ceramic rotor survivability under conditions of extreme foreign object ingestion, high speed turbine tip rub, severe start-up transients, and a very demanding durability cycle

In addition to the ceramic component technology, progress has been made in the areas of low emission combustion technology and regenerator design and development.
Operating Experience and Economic Benefit of a 3-MW Gas Turbine in an Industrial Peak Shaving Application
Authors: Jones Michael H. , Nall L. M. (Matt)
Published: February 2015

In the late 1970’s, due to increasing electric energy costs and the potential for power interruption at Solar Turbines Incorporated’s Harbor Drive manufacturing facility, management evaluated several self-generating options available at the time. With large fluctuating loads and a very limited need for thermal energy, the appropriate solution was determined to be peak shaving.

In 1980, a 2.5-MW dual fuel industrial gas turbine generator set was installed. Its intended operating cycle was during on-peak billing periods, 5 days a week throughout the year. Through August 31, 1993, the system has accumulated 22,743 hours of use and 3879 starts. Its overall start reliability has been 99.9% with an availability of 98.2%. Payback on the installation was in 4.2 years. It has continued to generate savings since installation, with net savings for 1992 alone exceeding $470,000.

This paper highlights the key aspects of the economic methodology justifying installation of the peak shaving system, operating procedures, maintenance practices and system modifications put in place over the life of the installation.
Modelling of By-Pass Transition With Conditioned Navier-Stokes Equations and a K-E Model Adapted for Intermittency
Authors: Steelant J. , Dick E.
Published: February 2015

Turbomachinery flows are characterized by a very high intensity turbulent mean part. As a consequence, laminar flow in boundary layer regions undergoes transition through direct excitation of turbulence. This is the so-called bypass transition. Regions form that are intermittently laminar and turbulent. In particular in accelerating flows, as on the suction side of a turbine blade, this intermittent flow can extend over a very large part of the boundary layer. Classical turbulence modelling based on global time averaging is not valid in intermittent flows. To take correctly account of the intermittency, conditioned averages are necessary. These are averages taken during the fraction of time the flow is turbulent or laminar respectively. Starting from the Navier-Stokes equations, conditioned continuity, momentum and energy equations are derived for the laminar and turbulent parts of an intermittent flow. The turbulence is described by the classical k-ε model. The supplementary parameter introduced by the conditioned averaging is the intermittency factor. In the calculations, this factor is prescribed in an algebraic way.
Viscous Solutions for Transonic Oscillating Cascade Flows Using Dynamic Quadrilateral-Triangular Meshes
Authors: Hwang C. J. , Yang S. Y.
Published: February 2015

The locally implicit scheme and a rigid-deformable dynamic mesh algorithm are introduced to solve the unsteady Navier-Stokes equations with Baldwin-Lomax turbulence model in the Cartesian coordinate system. In this scheme, a new treatment of viscous flux function is developed on the quadrilateral-triangular meshes. To validate the present scheme, the viscous flow over an oscillating flat plate is studied. By using the above solution approach, turbulent flows around transonic oscillating cascade of four biconvex blades with different oscillation amplitudes and interblade phase angles are investigated. From the distributions of magnitude and phase angle of the first harmonic dynamic pressure difference coefficient, which include the experimental data and numerical results obtained by linearized theory, Euler and Navier-Stokes solvers, the present solution approach is reliable and acceptable. The instantaneous pressure and/or Mach number contours indicate the effects of oscillation amplitude and interblade phase angle on the unsteady flow phenomena, such as vortex-shedding, pressure waves, shocks and boundary layer interactions.
Transition Modeling Effects on Turbine Rotor Blade Heat Transfer Predictions
Authors: Ameri Ali A. , Arnone Andrea
Published: February 2015

The effect of transition modeling on the heat transfer predictions from rotating turbine blades was investigated. Three-dimensional computations using a Reynolds-averaged Navier-Stokes code were performed. The code utilized the Baldwin-Lomax algebraic turbulence model which was supplemented with a simple algebraic model for transition. The heat transfer results obtained on the blade surface and the hub end wall were compared with experimental data for two Reynolds numbers and their corresponding rotational speeds. The prediction of heat transfer on the blade surfaces was found to improve with the inclusion of the transition length model and wake induced transition effects over the simple abrupt transition model.
The Development of Fast Response Aerodynamic Probes for Flow Measurements in Turbomachinery
Authors: Ainsworth Roger W. , Allen John L. , Batt J. Julian M.
Published: February 2015

The advent of a new generation of transient rotating turbine simulation facilities, where engine values of Reynolds and Mach number are matched simultaneously together with the relevant rotational parameters for dimensional similitude (Dunn et al [1988], Epstein et al [1984]. Ainsworth et al [1988]), has provided the stimulus for developing improved instrumentation for investigating the aerodynamic flows in these stages.

Much useful work has been conducted in the past using hot-wire and laser anemometers. However, hot-wire anemometers are prone to breakage in the high pressure flows required for correct Reynolds numbers, Furthermore some laser techniques require a longer runtime than these transient facilites permit, and generally yield velocity information only, giving no data on loss production.

Advances in semiconductor aerodynamic probes are beginning to fulfil this perceived need. This paper describes advances made in the design, construction, and testing of two and three dimensional fast response aerodynamic probes, where semiconductor pressure sensors are mounted directly on the surface of the probes, using techniques which have previously been successfully used on the surface of rotor blades (Ainsworth, Dietz and Nunn [1991]). These are to be used to measure Mach number and flow direction in compressible unsteady flow regimes.

In the first section, a brief review is made of the sensor and associated technology which has been developed to permit a flexible design of fast response aerodynamic probe. Following this, an extensive programme of testing large scale aerodynamic models of candidate geometries for suitable semiconductor scale probes is described, and the results of these discussed. The conclusions of these experiments, conducted for turbine representative mean and unsteady flows, yielded new information for optimising the design of the small scale semiconductor probes, in terms of probe geometry, sensor placement, and aerodynamic performance.

Details are given of a range of wedge and pyramid semiconductor probes constructed, and the procedures used in calibrating and making measurements with them. Differences in performance are discussed, allowing the experimenter to choose an appropriate probe for the particular measurement required.

Finally, the application of prototype semiconductor probes in a transient rotor experiment at HP turbine representative conditions is described, and the data so obtained is compared with (PD solutions of the unsteady viscous flow-field.
A Fibre Optic Probe for Gas Total Temperature Measurement in Turbomachinery
Authors: Kidd S. R. , Barton J. S. , Meredith P. , Jones J. D. C. , Cherrett M. A. , Chana K. S.
Published: February 2015

This paper describes the design, operation, construction and demonstration of a new type of high bandwidth unsteady temperature sensor based on fibre optics, and capable of operating in a high speed multi-stage research compressor with flow representative of jet engine conditions. The sensing element is an optical coating of zinc selenide deposited on the end of an optical fibre. During evaluation in aerodynamic testing, a 1 K gas temperature resolution was demonstrated at 9.6 kHz and an upper bandwidth limit of 36 kHz achieved.
Laser Velocimeter Measurements in the Pump of an Automotive Torque Converter: Part I — Average Measurements
Authors: Gruver J. K. , Flack R. D. , Brun K.
Published: February 2015

A torque converter was tested for two turbine/pump rotational speed ratios, 0.065, and 0.800, and a laser velocimeter was used to measure three components of velocity within the pump. Shaft encoders were used to record the instantaneous pump angular position, which was correlated with the velocities. Average flow velocity profiles were obtained for the pump inlet, mid-, and exit planes. Large separation regions were seen in the mid- and exit planes of the pump for a speed ratio of 0.800. Strong counter-clockwise secondary flows were observed in the mid-plane and strong clockwise secondary flows were seen in the exit plane of the pump for all conditions; vorticities were evaluated and are reported. Velocity data was also used to find the torque distribution. For both speed ratios the torque was approximately evenly distributed between the inlet and exit. Finally, slip factors were evaluated at the mid- and exit planes. At the mid-plane they were approximately the same as for conventional centrifugal pumps; however, at the exit plane the slip factors are larger than for centrifugal pumps.
Turbulent Flow Between Two Discs Contra-Rotating at Differential Speeds
Authors: Kilic Muhsin , Gan Xiaopeng , Owen J. Michael
Published: February 2015

This paper describes a combined computational and experimental study of the turbulent flow between two contra-rotating discs for −1 ≤ Γ ≤ 0 and Reφ ≃ 1.2 × 106, where Γ is the ratio of the speed of the slower disc to that of the faster one and Reφ is the rotational Reynolds number. The computations were conducted using an axisymmetric elliptic multigrid solver and a low-Reynolds-number k-ε turbulence model. Velocity measurements were made using LDA at nondimensional radius ratios of 0.6 ≤ x ≤ 0.85. For Γ = 0, the rotor-stator case, Batchelor-type flow occurs: there is radial outflow and inflow in boundary layers on the rotor and stator, respectively, between which is an inviscid rotating core of fluid where the radial component of velocity is zero and there is an axial flow from stator to rotor. For Γ = −1, anti-symmetrical contra-rotating discs, Stewartson-type flow occurs with radial outflow in boundary layers on both discs and inflow in the viscid nonrotating core. At intermediate values of Γ, two cells separated by a streamline that stagnates on the slower disc are formed: Batchelor-type flow and Stewartson-type flow occur radially outward and inward, respectively, of the stagnation streamline. Agreement between the computed and measured velocities is mainly very good, and no evidence was found of nonaxisymmetric or unsteady flow.
Windage Heating of Air Passing Through Labyrinth Seals
Authors: Millward J. A. , Edwards M. F.
Published: February 2015

The viscous drag on rotating components in gas turbine engines represents both a direct loss of power from the cycle and an input of heat into the secondary (cooling) air system. Hotter cooling air in turn means increased flow requirements. The effects of windage on performance are therefore compounded.

To facilitate accurate temperature predictions of highly stressed components, information is needed on windage characteristics of all elements in the secondary cooling system. Much information is available in the literature for discs, cones, cylinders, bolts etc but little has been published on windage heating in high speed seals.

Results are presented for experiments carried out (at representative non-dimensional conditions) on different designs of labyrinth seals. The results are compared with values calculated from the simple momentum balance theory suggested by McGreeham and Ko (1989) and with several values determined from CFD analysis.
Vibration and Control of a Flexible Rotor in Magnetic Bearings Using Hybrid Method and H∞ Control Theory
Authors: Shiau Ting Nung , Sheu Geeng Jen , Yang Clann Dong
Published: February 2015

The vibration and active control of a flexible rotor system with magnetic bearings is investigated using Hybrid Method (HM) and H∞ control theory with consideration of gyroscopic effect. The hybrid method which combines the merits of finite element method (FEM) and generalized ploynomial expansion method (GPEM) is employed to model the flexible rotor system with small order of plant. The mixed sensitivity problem of H∞ control theory is applied to design the control of system vibration with spillover phenomena for the reduced order plant. The H2 control design is also employed for the comparison to the H∞ design.

The experimental simulation is used to illustrate the effects of control design. It is shown that the H∞ controller design can be very effective to suppress spillover phenomena. In addition, HM control design has robustness to the variation of the parameters of the model. The application of hybrid method (HM) together with H∞ control design is highly recommended for the vibration control of flexible rotor system with magnetic bearings.
Vibration Control of a Rotor System Utilizing a Bearing Housing With Controllable Spring Nonlinearity
Authors: Liu Baojiang , Yan Litang , Li Qihan , Zhu Zigen
Published: February 2015

On the basis of characteristics of vibration in the rotor system with spring nonlinearity, a new method for vibration control has been developed. In the method, the spring characteristics of a bearing housing are controlled to be of softening nonlinearity when the rotor supported on it is accelerated and to be of hardening one when it is decelerated. So vibratory amplitudes of the rotor system always vary along the smallest solution curve in the whole operating process. A model of vibration of the rotor system supported on the controllable hearing housing is derived. Its dynamic behaviour is predicted and verified by experiments. Both theoretical and experimental results show that not only vibratory amplitudes and transmitted forces are suppressed significantly but also nonlinear vibration performance of the rotor supported on squeeze film dampers, such as “lock up” at rotor pin-pin critical speeds and asynchronous vibration, can be avoided.
Numerical Investigations on the Optimum Design of Radial Inflow Turbine Guide Vanes
Authors: Reichert A. W. , Simon H.
Published: February 2015

To improve the prediction of compressible flow in highly loaded turbomachinery components a modified high resolution scheme to solve the Navier Stokes equations has been developed. The scheme is based on the methods introduced by Osher and Roe. For high efficiency, an implicit iterative solution procedure is used. The code is validated, presenting highly accurate computational results. A structured grid is used during the investigations and a special grid topology for turbine vanes is presented. As the guide vanes are designed using CAD software the CFD code is coupled via the standard interface IGES (Smith et al., 1988). Starting with classical design principles, a first guide vane is designed. Based on flow field computations, the design of the guide vanes is improved successively. Resulting from the experiences gained during the improvement procedure general design principles are formulated.
Generalizing Circular Brush Seal Leakage Through a Randomly Distributed Bristle Bed
Authors: Chupp Raymond E. , Holle Glenn F.
Published: February 2015

Brush seals have established a niche in the gas-to-gas sealing against leakage in modern turbine engines. The variable nature of the brush during operation makes leakage prediction difficult. A simple semi-empirical model based on an effective brush thickness parameter has been successfully used to correlate and predict brush seal leakage in engine environments. The model was extended to correlate a range of brush densities using a physically realistic brush thickness. Later, the model was based on mean diametrical brush properties for a large range of circular brush seal geometries. However, the best basis for modeling bristle distribution was unknown. This paper proposes a solution to the distribution problem by assuming a randomly distributed bristle bed. A random distribution leads to a rectangular array model that is supported by the quality of leakage data generalization. Applying the resultant effective thickness parameter to predict brush seal performance in turbine engines is discussed.
The Differential Gas Turbine Using Electric Transmission
Authors: Balnes N. C. , Bressloff N.
Published: February 2015

This paper describes studies of simple gas turbine engines integrated with electrical transmission components. Recent developments in high-speed lightweight electrical machines and compact power electronics have enabled alternators and motors to be produced which can be coupled directly to the shaft of a gas turbine without an intermediate gearbox. For applications which require a wide range of power outputs, a single-shaft gas turbine with a high speed alternator can be run at constant speed while varying the current drawn from the alternator. This combines the flexibility of operation of a separate power turbine with the simplicity of a single-shaft engine. With this arrangement, in traction use high torques are obtained at low speed, while near-constant engine efficiency is sustained to about 50% of the design power. In the differential engine, the mechanical linkage between the compressor and the turbine is replaced with an electrical linkage. The turbine drives an alternator, and part of the alternator power is taken by a high-speed motor to drive the compressor. The excess alternator power forms the output of the engine. The compressor and turbine are now able to run at different speeds, and their operating points can be separately optimised at different engine conditions. For such an engine, studies show that high efficiency can be maintained to low power levels.
Sealing Flow Requirements for a Rotating Disk With External Swirling Flow
Authors: Izenson Michael G. , Swift Waiter L. , Aungier Ronald H.
Published: February 2015

Experiments have been performed to investigate the sealing flow requirements for a shrouded, rotating disk with external swirling flow. In some gas turbine applications, it is desirable to provide sealing flow to prevent ingress of process gas into the cavity between the turbine disk and its stator. The tangential or swirl component in flow leaving the nozzles can significantly affect the amount of flow required to seal the turbine disk. The experimental flow model used water as a working fluid and was hydrodynamically scaled to match conditions typical of hot gas expander turbines used for energy recovery in the petrochemical industry. Flow in the seal gap was observed using a stream of dye injected on the stator face near the periphery. Differential pressures were measured on the stator face and related to the observed direction of flow on the stator face. The pressures and sealing flows were normalized by the disk and gap geometry and the applied flow conditions, then compared to published data for shrouded, rotating disks with no applied, external flow. For tests where the external tangential velocity was roughly equal to twice the rim speed of the disk, sealing flow requirements were found to be 1.5 to 2.0 times greater than for a disk without the applied, external flow.
Adaptive Finite-Volume Solution of the Two-Dimensional Euler Equations on Unstructured Meshes
Authors: Irmisch Stefan
Published: February 2015

This paper presents a finite-volume method for solving the compressible, two-dimensional Euler equations using unstructured triangular meshes. The integration in time, to a steady-state solution, is performed using an explicit, multistage Runge-Kutta algorithm. A special treatment of the artificial viscosity along the boundaries reduces the production of numerical losses. Convergence acceleration is achieved by employing local time-stepping, implicit residual smoothing and a multigrid technique.

The use of unstructured meshes, based on Delaunay triangulation, automatically adapted to the solution, allows arbitrary geometries and complex flow features to be treated easily. The employed refinement criterion does not only detect strong shocks, but also weak flow features.

Solutions are presented for several subsonic and transonic standard test cases and cascade flows that illustrate the capability of the algorithm.
Prediction of High Reynolds Number Compressible Flow Using an Explicit-Implicit Algorithm
Authors: Wang B. B. , Li F. , Lee W. C.
Published: February 2015

Based on the analysis of several time-marching finite-difference schemes, an improved explicit-implicit numerical algorithm MC-LB has been developed. The algorithm is shown to be successful in predicting a variety of high Reynolds number viscous interior flows. Further, the computational efficiency of the algorithm is significantly better than existing schemes.
High Stiffness Gas Journal Bearing Under Harmonic Excitation
Authors: Czolczynskl Krzysztof
Published: February 2015

This paper presents an analysis of the dynamic response of the high stiffness gas journal bearing to a harmonic load. The dependence between the frequency of the load, and the amplitude and phase angle of the shaft vibration are estimated from numerical simulation. Results of this simulation enable an attempt of identification of the high stiffness bearing as a linear system with two (or in simplification - one) degrees of freedom, to formulate simple dynamic models of the bearing. Stiffness and damping coefficients are calculated and compared with the simple gas journal bearing. The comparison suggests, that the investigated gas bearing retains high stiffness not only for slow changes of the load which appear in its application to grinding machines, but even when the frequency of the load is equal to several rad/s.
Effects of Frequency on Structural Stiffness and Damping in a Self-Acting Compliant Foil Journal Bearing
Authors: Ku C.-P. Roger , Heshmat Hooshang
Published: February 2015

This paper presents the results of an investigation into the dynamic structural properties of self-acting compliant foil journal bearings. A test facility with a journal supported by a compliant foil journal bearing was built. The nonrotating journal was driven by two shakers which were used to simulate the dynamic forces acting on the bump foil strips. The structural stiffness and equivalent viscous damping coefficients are calculated based on the experimental measurements for a wide range of operating conditions. The results are compared to the analytical predictions obtained by a theoretical model developed earlier, and the effects of frequency are investigated. Both theoretical and experimental results show that an increase in the excitation frequency decreases the direct damping term. The effect of frequency on the cross-coupling terms is much less than on the direct terms.
Influence of Radial Inflow on Rotor-Stator Cavity Pressure Distributions
Authors: Hart Kenneth J. , Turner Alan B.
Published: February 2015

Rig tests and computational fluid dynamic (CFD) modelling have been used to improve the understanding of the effects of component geometry and air bleed flows on the pressure and velocity variations in the rotor-stator cavity found typically behind the impeller of a gas turbine engine centrifugal compressor.

Ranges of axial gap ratio and bleed throughflow typical of those found in current gas turbine engine design have been investigated with close attention to radial inflow (centripetal) bleeds with and without initial swirl.

CFD models have been constructed corresponding to the test conditions to assist in the understanding of the test data and to validate the computational methods. These methods can be used to extend the ranges of geometry, rotational Reynolds number and throughflows studied with greater confidence, thereby providing a design tool for direct use in the gas turbine industry.
A Numerical Study of the Fatigue Life of a Gas Turbine Blade in Transient Operations
Authors: Hohlrieder M. , Irretier H.
Published: February 2015

A numerical study of the dynamical response and the life estimation of a gas turbine blade which is subjected to transient nozzle excitation is presented. The mechanical and mathematical model for the blade, the exciting unsteady aerodynamic forces and the life estimation techniques are described and the solution procedure and its realization in a computer code is discussed. For an axial gas turbine compressor blade subjected to unsteady lift and drag forces during a run-up and run-down process numerical results are presented and the relation between the damping ratios, the speed of the run-up/down and the estimated fatigue life is discussed.
Modelling and Analysis of the Dynamic Behavior of an Active Journal Bearing
Authors: Sun Linxiang , Krodkiewski Janusz M. , Zhang Nong
Published: February 2015

Modelling and analysis of a rotor-bearing system with a new type of active oil bearing are presented. The active bearing basically consists of a flexible sleeve and a pressure chamber. The deformation of the sleeve can be controlled by the chamber pressure during the operation, and so can the pressure distribution of the oil film.

Finite Element Methods (FEMs) and the Guyan condensation technique were utilised to create mathematical models for both the rotor and the flexible sleeve. The hydrodynamic pressure distribution of the oil film, for the instantaneous positions and velocities of the flexible sleeve and rotor, was approximated by Reynolds equation. The influence of the chamber pressure on the stability of the rotor system was investigated by numerical simulation based on the nonlinear model. The results showed that the stability of the rotor-bearing system can be improved effectively by implementation of the active bearing.
Identifying a Dynamic Model for a GE Frame 7 Gas Turbine
Authors: Kaufman Howard , Ravi R.
Published: February 2015

Several tests were conducted on a GE Frame 7 gas turbine to determine its dynamic characteristics. The objective is to obtain a model that can be used for controller design. The tests consisted of adding sequences of square waves to the two inputs — the fuel reference and the inlet guide vane angle reference — and recording the inputs and the outputs. This method of exciting the system afforded us with a way of separating the data sets into two categories, the first, in which the fuel reference was changed, and the second, in which the guide vane angle reference was changed. Least-squares system identification techniques were used to obtain linear models using a selection criterion that was a measure of how well a model fit both the sets of data. This brought in a measure of robustness to the models thus making them ideal for use in controller design. This paper summarizes the results from these tests, contains plots that show how well the linear models are able to fit the recorded data, and finally, provides some recommendations for others doing similar work.
Grid Orthogonality Effects on Predicted Turbine Midspan Heat Transfer and Performance
Authors: Boyle R. J. , Ameri A. A.
Published: February 2015

The effect of five different C type grid geometries on the predicted heat transfer and aerodynamic performance of a turbine stator is examined. Predictions were obtained using two flow analysis codes. One was a finite difference analysis, and the other was a finite volume analysis. Differences among the grids in terms of heat transfer and overall performance were small. The most significant difference among the five grids occurred in the prediction of pitchwise variation in total pressure. There was consistency between results obtained with each of the flow analysis codes when the same grid was used. A grid generating procedure in which the viscous grid is embedded within an inviscid type grid resulted in the best overall performance.
Parameter Identification With Noncollocation of Force and Measurement Locations Using Nonsynchronous Perturbation and Optimization Techniques
Authors: Franklin Wesley D. , Muszynska Agnes , Bently Donald E.
Published: February 2015

Nonsynchronous perturbation techniques developed over the last few years have proven to be a very powerful tool for parameter identification of rotating systems. In order to obtain interpretable results, some limitations have had to be imposed on the analytical models and rotor systems used in the process, such as applied forces, and measurement transducers had to be located near major masses on the rotor. In the laboratory environment these limitations can usually be accommodated, but not always, while in the field, compliance is almost impossible. This paper explores the use of finite element modeling, measured vibration response data, and optimization techniques to extend the applicability of parameter identification through nonsynchronous perturbation techniques to those systems in which the perturbation forces and/or resultant response measurements cannot be conveniently located at the mass centers. In this technique, a finite element model of the rotor system is constructed, and all known information about the system parameters input to a computer program designed to operate on a personal computer. The program then computes the theoretical response of the system, by processing user-supplied initial conditions for the unknown system parameters, and compares these results with the vibration responses measured on the machine, and collected by the data acquisition system. The unknown parameters are then modified using local convergence optimization techniques until the error between the theoretical and measured responses is acceptably small. If the system parameters under investigation coincide with the unknown parameters in the computer program, they are identified in the process.

This technique was applied to an experimental rotor system constructed such that the parameters under investigation, the direct and quadrature dynamic stiffness components for a plain oil-lubricated journal bearing operating at low eccentricity, could be determined by both this technique and conventional unbalance force testing. The results of the nonsynchronous tests are presented in the paper.
Unbalance Response of Rotors Considering the Distributed Bearing Stiffness and Damping
Authors: Sekhar A. S. , Prabhu B. S.
Published: February 2015

Usually while modelling rotor-bearing systems the bearings are treated as point supports. In the present paper, using the finite element technique, the unbalance response of rotors is studied by considering distributed bearing stiffness and damping. The bearing stiffness and damping terms are derived by the principle of virtual work. Unbalance responses of rotors with bearing distributed effects are compared with the model using point supports and for different supports Viz., cylindrical journal bearings, tilting pad journal bearings, offset and three lobe journal bearings.
Pressure Oscillations Occurring in a Centrifugal Compressor System With and Without Passive and Active Surge Control
Authors: Jungowski Wiktor M. , Weiss Marvin H. , Price Glenn R.
Published: February 2015

A study of pressure oscillations occurring in small centrifugal compressor systems without a plenum is presented. Active and passive surge control were investigated theoretically and experimentally for systems with various inlet and discharge piping configurations. The determination of static and dynamic stability criteria was based on Greitzer’s (1981) lumped parameter model modified to accommodate capacitance of the piping. Experimentally, passive control using globe valves closely coupled to the compressor prevented the occurrence of surge even with the flow reduced to zero. Active control with a sleeve valve located at the compressor was effective but involved a significant component of passive throttling which reduced the compressor efficiency. With an oscillator connected to a short side-branch at the compressor, effective active control was achieved without throttling. Both methods of active control reduced the flow rate at surge onset by about 30%. In general, the experiments qualitatively confirmed the derived stability criteria.
An Experimental and Computational Investigation of Flow in a Radial Inlet of an Industrial Pipeline Centrifugal Compressor
Authors: Flathers M. B. , Bache G. E. , Rainsberger R.
Published: February 2015

The flowfield of a complex three dimensional radial inlet for an industrial pipeline centrifugal compressor has been experimentally determined on a half scale model. Based on the experimental results, inlet guide vanes have been designed to correct pressure and swirl angle distribution deficiencies. The unvaned and vaned inlets are analyzed with a commercially available fully 3D viscous Navier-Stokes code. Since experimental results were available prior to the numerical study, the unvaned analysis is considered a postdiction while the vaned analysis is considered a prediction. The computational results of the unvaned inlet have been compared to the previously obtained experimental results. The experimental method utilized for the unvaned inlet is repeated for the vaned inlet and the data has been used to verify the computational results. The paper will discuss experimental, design and computational procedures, grid generation, boundary conditions, and experimental versus computational methods. Agreement between experimental and computational results is very good, both in prediction and postdiction modes. The results of this investigation indicate that CFD offers a measurable advantage in design, schedule and cost and can be applied to complex, three dimensional radial inlets.
A Quasi Unsteady Study on Wake Interaction of Turbine Stator and Rotor Cascades
Authors: Yamamoto Atsumasa , Murao Rin-ichi , Suzuki Yuji , Aoi Yoshihiro
Published: February 2015

Detailed flow measurements were made to study cascade interaction of turbine stator and rotor, by using two linear cascades installed in series. The upstream cascade was traversed at several times in the cascade pitchwise direction in order to change the relative location between the two cascades, and measurements were made in the downstream cascade. The result shows that the net total pressure loss generated in the downstream cascade becomes maximum when wakes of the upstream cascade pass the suction side of the downstream cascade passage, while the tip leakage loss generated in the downstream cascade does not change with the relative location th cascades. The upstreaof born cascade wakes interact with the secondary flows, and most strongly with the endwall flow in the downstream cascade passage, making the loss distributions in both cascades fairly unsteady.
Computation and Simulation of Wake-Generated Unsteady Pressure and Boundary Layers in Cascades: Part 2 — Simulation of Unsteady Boundary Layer Flow Physics
Authors: Fan S. , Lakshminarayana B.
Published: February 2015

The unsteady pressure and boundary layers on a turbomachinery blade row arising from periodic wakes due to upstream blade rows are investigated in this paper. Numerical simulations are carried out to understand the effects of the wake velocity defect and the wake turbulence intensity on the development of unsteady blade boundary layers. The boundary layer transition on the blade is found to be strongly influenced by the unsteady wake passing. Periodic transitional patches are generated by the high turbulence intensity in the passing wakes and transported downstream. The time dependent transition results in large unsteadiness in the instantaneous local skin friction coefficient and a smoother time averaged transition curve than the one observed in the steady boundary layer. A parametric study is then carried out to determine the influence of wake parameters on the development of the unsteady blade boundary layers. It is shown that the unsteadiness in the blade boundary layer increases with a decrease in the axial gap, an increase in wake/blade count ratio or an increase in the wake traverse speed. The time averaged boundary layer momentum thickness at the trailing edge of the blade is found to increase significantly for higher wake/blade count ratio and larger wake traverse speed. Increase of the wake/blade count ratio also results in higher frictional drag of the blade.
Experimental and Numerical Study of Orifice Discharge Coefficients in High Speed Rotating Disks
Authors: Wittig S. , Kim S. , Jakoby R. , Weißert I.
Published: February 2015

Experimental and numerical results of the flow through orifices in rotating disks are presented, with emphasis on basic physical phenomena. It is shown, that rotational effects strongly influence the massflow discharged, a phenomenon which cannot be modelled by a stationary setup.

The study includes the determination of discharge coefficients under variation of the length to diameter ratio, pressure ratio and rotational speed. The pressure ratio covers low as well as critical values, the maximum rotational speed is 10000 rpm which is equivalent to a tangential velocity of 110 m/s. In order to understand the flow structure, local flow velocities were measured by means of a 2D Laser-Doppler-Velocimeter. Phase-resolved measurements have been carried out in front of and behind the orifices.

A 3D Finite-Volume-Code with bodyfitted coordinates in a rotating frame of reference is employed for the numerical analysis and the verification of its possibilities and limitations. The results reveal a very complex flow field, which is dominated by high velocity gradients in close vicinity to the orifices. The comparison of the computational solutions with the experimental data shows good agreement. Based on the measurements in combination with the numerical solution, a detailed insight into the physical properties of the flow is achieved.
The Development of a Doppler Global Velocimeter for Transonic Turbine Applications
Authors: Ainsworth Roger W. , Thorpe Steven J.
Published: February 2015

The development of a Doppler Global Velocimeter (DGV) for the measurement of transonic turbo-machinery flows in the Oxford Isentropic Light Piston Tunnel rotor facility is described. A novel optical arrangement for capturing both reference and iodine cell discriminated images with a single CCD camera and frame grabber is presented. Practical arrangements for determination of the iodine cell transmission properties as a function of temperature and light frequency are discussed in the context of using an argon ion continuous wave laser for illumination. Flow seeding aspects of the experiment are described with particular emphasis on particle dynamics and light scattering. Error bounds for the DGV measurements are assessed and quantified in respect to the frame grabber resolution and Gaussian beam profile. Results of measurements of the velocity of a rotating disc with tip speed of nominally 90 m/s, obtained with 0.5 W single mode argon ion laser illumination are presented. Practical aspects for employing the DGV on the established Oxford rotor facility, such as seeding of the flow, optical access and synchronisation of data acquisition are addressed.
Steady and Unsteady Boundary Conditions for Numerical Simulations of Flows in Turbomachines
Authors: Dorney Daniel J. , Davis Roger L.
Published: February 2015

The flow through most turbomachinery blade rows is dominated by unsteady phenomena. Accurately predicting the behavior of complex unsteady flows with computational analyses can require enormous computer resources. To make the computational problem more tractable, the time dependence of the solution has traditionally been removed. Thus, during the past decade many steady flow procedures have been developed and validated for turbomachinery applications. Less attention has been given to the rigorous development of unsteady flow computational procedures. The purpose of this investigation is to extend, validate, and perform numerical experiments with two existing computational procedures for the study of inviscid, compressible, unsteady flow in axial turbomachinery. Results are presented for unsteady subsonic and transonic flows subject to inlet vortical distortions.
The Flow and Rotation Characteristics of a Centrifugal Compressor During Surge
Authors: Jin D. , Hasemann H. , Haupt U. , Rautenberg M.
Published: February 2015

Unsteady flow and the rotor rotational behavior during surge in a single stage centrifugal compressor have been investigated to study the physical mechanism of this special operating period. The experiments were performed for the compressor with vaneless and vaned diffuser at different rotational speed. The centrifugal compressor was driven by a 1350 kw dc-motor with Leonard-control. Unsteady pressure was measured with fast response dynamic transducers while rotor speed was simultaneously measured with a capacitive impulser. At the beginning and the end of the surge, the pressure signals measured in the meridional direction from the impeller inlet to the diffuser exit show obvious pressure oscillation. During the whole surge period, the pressure signal at the impeller exit shows periodic fluctuations with very large amplitudes at a high frequency. The further pressure analyses indicate that these pressure fluctuations is produced by the pressure difference across blade pitch. The pressure side and the suction side of the blade are inversed compared with that in the normal compressor operating condition. This reverse pressure difference produces an additional torque on the impeller blades in the impeller rotation direction. The rotating speed of the compressor rotor during surge was also studied. It is shown that during the surge the rotor speed increases slowly until the surge stops. Since the compressor-motor system is controlled by the Leonard-set, the increase in rotor speed indicates the torque reduction of the compressor.
A Numerical Study of the Interaction of a Transonic Compressor Rotor Overtip Leakage Vortex With the Following Stator Blade Row
Authors: Dawes W. N.
Published: February 2015

This paper presents a numerical simulation of the unsteady flow in a transonic compressor stage. The simulations were performed using an unstructured mesh, 3D Navier-Stokes solver with a sliding interface between the mesh blocks containing the rotor and stator blades to permit a time-resolved calculation. The focus in the simulation is the endwall flow, its contrast with the mid-span flow and, in particular, the interaction of the rotor overtip leakage flow with the downstream stator.

The endwall region of both the rotors and the stators was predicted to be proportionally responsible for much more loss production than the mid-span sections of the blading. Unsteady effects were predicted to be responsible for rather more of the total loss production in the rotors than in the stators but the unsteady loss production in the rotors did not seem to be associated with the endwall flow but rather occurred over the bulk of the blade span caused by unsteady shock motion. By contrast, the rotor overtip leakage flow was shown to cause a considerable degradation of the stator performance near the casing. In the stators nearly a third of the loss production near the endwall was predicted to be directly due to unsteady effects associated with the rotor vortex interaction and a number of individual physical loss generating mechanisms were identified.
The Influence of Secondary Flows Near the Endwall and Boundary Layer Disturbance on Convective Transport From a Turbine Blade
Authors: Goldstein R. J. , Wang H. P. , Jabbari M. Y.
Published: February 2015

A naphthalene sublimation technique is used to investigate convective transport from a simulated turbine blade in a stationary linear cascade. In some of the tests undertaken a trip wire is stretched along the span of the blade near the leading edge. The disturbance produced by tripping the boundary layers on the blade near the leading edge causes early boundary layer transition, creates high mass transfer rate on the pressure side and in the laminar flow region on the suction side, but lowers the transfer rate in the turbulent flow region on the suction side. Comparison is made with other heat and mass transfer studies in the two dimensional region far from the endwall and good agreement is found.

Near the endwall, flow visualization indicates a strong secondary flow pattern. The impact of vortices initiated near the endwall on the laminar-turbulent transition extends three dimensional effects to about 0.8 chord lengths on the suction side and to about 0.2 chord lengths on the pressure side away from the endwall. The effect of the passage vortex and the new vortex induced by the passage vortex on mass transfer is clearly seen and can be traced along the suction surface of the blade. Close to the endwall the highest mass transfer rate on the suction surface is not found near the leading edge. It occurs at about 27% of the curvilinear distance from the stagnation line to the trailing edge where a strong main flow and the secondary passage flow from the pressure side of the adjacent blade interact. The influences of some small but very intense corner vortices and the passage vortex on mass transfer are also observed on both surfaces of the blade.