bluuebunny/crossref_metadata_2025 huggingface dataset:
Probabilistic Study of Fluid Structure Interaction
Authors: Gorla Rama S. R. , Pai Shantaram S. , Rusick Jeffrey J.
Published: February 2009

A combustor liner was computationally simulated and probabilistically evaluated in view of the several uncertainties in the aerodynamic, structural, material and thermal variables that govern the combustor liner. The interconnection between the computational fluid dynamics code and the finite element structural analysis codes was necessary to couple the thermal profiles with structural design. The stresses and their variations were evaluated at critical points on the liner. Cumulative distribution functions and sensitivity factors were computed for stress responses due to the aerodynamic, mechanical and thermal random variables. It was observed that the inlet and exit temperatures have a lot of influence on the hoop stress. For prescribed values of inlet and exit temperatures, the Reynolds number of the flow, coefficient of thermal expansion, gas emissivity and absorptivity and thermal conductivity of the material have about the same impact on the hoop stress. These results can be used to quickly identify the most critical design variables in order to optimize the design and make it cost effective.
3D Unsteady Forces of the Transonic Flow Through a Turbine Stage With Vibrating Blades
Authors: Rza˛dkowski Romuald , Gnesin Vitaly
Published: February 2009

Numerical calculations of the 3D transonic flow of an ideal gas through turbomachinery blade rows moving relatively one to another with taking into account the blades oscillations is presented. The approach is based on the solution of the coupled aerodynamic-structure problem for the 3D flow through the turbine stage in which fluid and dynamic equations are integrated simultaneously in time, thus providing the correct formulation of a coupled problem, as the blades oscillations and loads, acting on the blades, are a part of solution. An ideal gas flow through the mutually moving stator and rotor blades with periodicity on the whole annulus is described by the unsteady Euler conservation equations, which are integrated using the explicit monotonous finite-volume difference scheme of Godunov-Kolgan and moving hybrid H-H grid. The structure analysis uses the modal approach and 3D finite element model of a blade. The blade motion is assumed to be constituted as a linear combination of the first natural modes of blade oscillations with the modal coefficients depending on time. The algorithm proposed allows to calculate turbine stages with an arbitrary pitch ratio of stator and rotor blades, taking into account the blade oscillations by action of unsteady loads caused both outer flow nonuniformity and blades motion. There has been performed the calculation for the stage of the turbine with rotor blades of 0.765 m. The numerical results for unsteady aerodynamic forces due to stator-rotor interaction are compared with results obtained with taking into account the blades oscillations.
Fluid/Structure Coupled Aeroelastic Computations for Transonic Flows in Turbomachinery
Authors: Doi Hirofumi , Alonso Juan J.
Published: February 2009

The present study demonstrates the capabilities of a fluid/structure coupled computational approach which consists of an unsteady three-dimensional Navier-Stokes flow solver, TFLO, and a finite element structural analysis package, MSC/NASTRAN. The parallelized flow solver relies on a multi-block cell-centered finite volume discretization and the dual time stepping time integration scheme with multigrid for convergence acceleration. High accuracy is pursued with respect to load transfer, deformation tracking and synchronization between the two disciplines. As a result, the program successfully predicts the aeroelastic responses of a high performance fan, NASA Rotor 67, over a range of operational conditions. The results show that the unsteady pressure generated at the shock may act to damp or excite the blade motion mainly depending on the inter-blade phase angle. It is concluded that the level of sophistication in the individually sophisticated disciplines together with an accurate coupling interface will allow for accurate prediction of flutter boundaries of turbomachinery components.
A Microturbine Rotor-Bearing System Analysis
Authors: Chiang Hsiao-Wei D. , Hsu Chih-Neng , Jeng Wes , Tu Shun-Hsu , Li Wei-Chen
Published: February 2009

A microturbine of 12-pound thrust was developed for the Unmanned Aerial Vehicle (UAV) applications. Recent tests of the microturbines reveal problems associated with rear ball bearing integrity after extended run times. The microturbine rotor design originally calls for a critical speed margin of at least 15∼20% to prevent excessive vibrations. However, the microturbine was using an existing turbocharger rotor component with unknown margins. Therefore, the purpose of this paper is to perform both theoretical and experimental analyses of the dynamic characteristics of the 12-pound thrust microturbine rotor-bearing system. This rotor-bearing system analyses will start with a finite element (FEM) rotor-bearing system dynamic model, then using modal testing and dynamic engine test to verify the analysis results including critical speed map and bearing stiffness. In this paper, the rotor-bearing system dynamic model will be established under an inertia coordinate system. Through finite element method, this model can be used to predict natural frequencies, critical speed map, and bearing stiffness. Also, under free-free condition, a modal testing will be performed, and its results are used to compare with the FEM model. Then the gyroscopic moment effects are included in the FEM model to calculate the critical speed map. Finally the critical speed map is used to compare with the results of the dynamic experiments of the 12-pound thrust microturbine engine and the bearing stiffness is estimated through an optimization approach. Examination of the microturbine engine and recent product developments indicate that thrust performance and engine life goals can be improved to upgrade the present design. With the rotor-bearing system analysis, the goal of increasing the current engine life and improved performance is sought as a practical goal for the microturbine design.
Dynamic Response of Squeeze Film Dampers Operating With Bubbly Mixtures
Authors: San Andre´s Luis , De Santiago Oscar C.
Published: February 2009

Squeeze film dampers (SFDs) aid to attenuate vibrations in compressors and turbines while traversing critical speeds. In actual applications, gas ingestion from the environment may lead to the formation of a foamy lubricant that degrades the rotor/bearing system dynamic performance. Impact and imbalance response tests conducted on a rigid rotor supported on SFDs, and aimed to emulate the pervasive effect of air ingestion into the damper film lands, are reported. Two types of squeeze film damper support the test rotor, one is a conventional cylindrical design with a squirrel cage type elastic support, and the other is a compact four-pad damper with integral wire EDM elastic supports. Both dampers have identical diameter and radial clearance. Controlled (air in oil) mixtures ranging from pure oil to all air conditions are supplied to the SFDs, and measurements of the transient rotor response to calibrated impact loads are conducted. System damping coefficients, identified from acceleration/load transfer functions, decrease steadily as the air content in the mixture increases. However, measurements of the rotor synchronous imbalance response conducted with a lubricant bubbly mixture (50% air volume) show little difference with test results obtained with pure lubricant supplied to the dampers. The experimental results show that air entrainment is process and device dependent, and that small amounts of lubricant enable the effective action of SFDs when the rotor traverses a critical speed.
Unbalance Response of Rotors Supported on Hydrodynamic Bearings Placed Close to Nodal Points of Excited Vibration Modes
Authors: Zachariadis Demetrio C.
Published: February 2009

The traditional 8-coefficient bearing model, used in linear rotor dynamics, is shown here to be inadequate for the unbalance response calculation of rotor systems supported on hydrodynamic journal bearings placed close to nodal points of excited modes of vibration. In such situations, one cannot neglect the time varying tilt angle between journals and bearings, whose consideration leads to the adoption of a 32-coefficient bearing model. Numerical results indicate that the differences between vibration amplitudes calculated using both bearing models can be greater than 100%, while discrepancies in the predicted stability thresholds are small. The conclusions of the study are coherent with previously published theoretical and experimental results.
A Numerical Method for Turbomachinery Aeroelasticity
Authors: Cinnella P. , De Palma P. , Pascazio G. , Napolitano M.
Published: February 2009

This work provides an accurate and efficient numerical method for turbomachinery flutter. The unsteady Euler or Reynolds-averaged Navier–Stokes (RANS) equations are solved in integral form, the blade passages being discretised using a background fixed C-grid and a body-fitted C-grid moving with the blade. In the overlapping region data are exchanged between the two grids at every time step, using bilinear interpolation. The method employs Roe’s second-order-accurate flux difference splitting scheme for the inviscid fluxes, a standard second-order discretisation of the viscous terms, and a three-level backward difference formula for the time derivatives. The state-of-the-art second-order accuracy of numerical methods for unsteady compressible flows with shocks is thus carried over, for the first time to the authors knowledge, to flutter computations. The dual time stepping technique is used to evaluate the nonlinear residual at each time step, thus extending to turbomachinery aeroelasticity the state-of-the-art efficiency of unsteady RANS solvers. The code is proven to be accurate and efficient by computing the 4th Aeroelastic Standard Configuration, namely, the subsonic flow through a turbine cascade with flutter instability in the first bending mode, where viscous effect are found practically negligible. Then, the very severe 11th Aeroelastic Standard Configuration is computed, namely, the transonic flow through a turbine cascade at off-design conditions, where the turbulence model is found to be the critical feature of the method.
Calculation and Correlation of the Unsteady Flowfield in a High Pressure Turbine
Authors: Bakhle Milind A. , Liu Jong S. , Panovsky Josef , Keith Theo G. , Mehmed Oral
Published: February 2009

Forced vibrations in turbomachinery components can cause blades to crack or fail due to high-cycle fatigue. Such forced response problems will become more pronounced in newer engines with higher pressure ratios and smaller axial gap between blade rows. An accurate numerical prediction of the unsteady aerodynamics phenomena that cause resonant forced vibrations is increasingly important to designers. Validation of the computational fluid dynamics (CFD) codes used to model the unsteady aerodynamic excitations is necessary before these codes can be used with confidence. Recently published benchmark data, including unsteady pressures and vibratory strains, for a high-pressure turbine stage makes such code validation possible. In the present work, a three dimensional, unsteady, multi blade-row, Reynolds-Averaged Navier Stokes code is applied to a turbine stage that was recently tested in a short duration test facility. Two configurations with three operating conditions corresponding to modes 2, 3, and 4 crossings on the Campbell diagram are analyzed. Unsteady pressures on the rotor surface are compared with data.
The Effects of Lean and Sweep on Transonic Fan Performance
Authors: Denton J. D. , Xu L.
Published: February 2009

The aerodynamics of transonic fans is discussed with emphasis on the use of three-dimensional design techniques, such as blade sweep and lean, to improve their performance. In order to study the interaction of these 3D features with the shock pattern a series of five different designs is produced and analysed by CFD. It is found that the 3D features have remarkably little effect on the shock pattern near the tip where the shock must remain perpendicular to the casing. Lower down the blade significant shock sweep, and hence reduced shock loss, can be induced by 3D design but this is usually at the expense of reduced stall margin and increased loss elsewhere along the blade span. Overall, very little change in peak efficiency or pressure ratio is produced by blade sweep or lean. However, there are significant effects on stall margin with forwards sweep producing a better stall margin and maintaining a high efficiency over a wider range.
The Use of Sweep and Dihedral in Multistage Axial Flow Compressor Blading: Part II — Low and High Speed Designs and Test Verification
Authors: Gallimore Simon J. , Bolger John J. , Cumpsty Nicholas A. , Taylor Mark J. , Wright Peter I. , Place James M. M.
Published: February 2009

This paper describes the introduction of 3D blade designs into the core compressors of the Rolls-Royce Trent engine series with particular emphasis on the use of sweep and dihedral in the rotor designs. It follows the development of the basic ideas in a university research project, through multistage low-speed model testing, to their application to the high pressure engine compressor. An essential element of the project was the use of multistage CFD and some of the development of the method to allow the designs to take place is also discussed. Part I of the paper concentrated on the fundamental university-based research and the methods development. Part II describes additional low-speed multistage design and testing and the high-speed engine compressor designs and tests.
Transonic Flow Losses of Two Steam Turbine Blades at Large Incidences
Authors: Li S.-M. , Chu T.-L. , Yoo Y.-S. , Ng W. F.
Published: February 2009

A linear cascade experiment has been conducted to investigate transonic flow losses of two nozzle blade profiles for high-pressure steam turbines. Experimental incidences were changed from −34° to 35°, while exit Mach numbers were varied from 0.60 to 1.15. Reynolds numbers were tested between 7.4×105 and 1.6×106. Flow visualization techniques, such as shadowgraph, Schlieren, and surface color oil were used to document the flow. Measurements were made using downstream traverses with Pitot probe, upstream total pressure probe, and sidewall static pressure taps. Losses were found to be rather constant at subsonic flows. At transonic and low supersonic flows, the loss increased steeply, as high as 700% more when compared with the loss level at subsonic flows. For all the tested Mach numbers, the maximum relative increase of loss level was only about 100% due to the very large variation of incidences. Thus the effect of Mach numbers on losses is much greater than that of the very large incidences for the transonic and low supersonic flows. A frequently used shock wave loss correlation was found not suitable to predict the losses of the tested blades. Using the current experimental data, a modified loss correlation to account for the shock wave effects has been proposed for the transonic and low supersonic flows. Comparison was made between the modified loss correlation and the data of three other turbine cascades in the literature. Large improvement was obtained with the modified loss correlation as compared with the existing correlation.
Lateral Forces From Single Gland Rotor Labyrinth Seals in Turbines
Authors: Song Bum Ho , Song Seung Jin
Published: February 2009

Even though interest in labyrinth seal flows has increased recently, an analytical model capable of predicting turbine flow response to labyrinth seals is still lacking. Therefore, this paper presents a new model to predict flow response in an axial turbine stage with a shrouded rotor. A concentric model is first developed, and this model is used to develop an eccentric model. Basic conservation laws are used in each model, and a non-axisymmetric sealing gap is prescribed for the eccentric model. Thus, the two models can predict the evolution of a uniform upstream flow into a non-uniform downstream flow. In turbines with concentric shrouded rotors, the seal flow is retarded in the axial direction and tangentially underturned. In turbines with eccentric shrouded rotors, flow azimuthally migrates away from and pressure reaches its peak near the maximum sealing gap region. Finally, the rotordynamic implications of such flow non-uniformities are discussed and compared against eccentric unshrouded turbine predictions.
Performance Testing of a First and a Second Transonic Turbine Stage
Authors: Neumayer F. , Jericha H. , Kulhanek G. , Seyr A. , Rossi E. , Sanz W.
Published: February 2009

This paper describes the experimental activities aimed at developing two axial turbine stages. The first stage is representative of a high-pressure transonic design with stator and rotor cooling performed also in the experimental setup; the second is a low-pressure uncooled stage with strong transonic effects. The testing took place in the unique Graz University of Technology experimental facility. The present paper includes a description of the stage test configuration with particular reference to the cooling system, and the main outcomes of the test runs between January and June 2001 are presented. This activity was performed as part of the BRITE/EURAM Project ‘DITTUS’ under support from the European Union.
The Effect of End-Wall Profiling on Secondary Flow and Loss Development in a Turbine Cascade
Authors: Ingram Grant , Gregory-Smith David , Rose Martin , Harvey Neil , Brennan Graham
Published: February 2009

The potential for loss reduction by using non-axisymmetric end-wall profiling has been demonstrated in the so called “Durham” cascade (Hartland et al [1]) and in a turbine representative rig (Brennan et al [2] and Rose et al [3]). This paper aim to enhance the understanding of end-wall profiling. It describes detailed measurements from upstream to downstream through the Durham cascade. The measurements cover the profiled end-wall used by Hartland, a second generation end-wall design (Gregory-Smith et. al. [4]) and the planar reference case. Considerable effort has gone into refining the measurement technique used in the cascade and new results are presented for traverses downstream which capture more accurately the flow near the end-wall. These measurements show the development of loss and secondary flow throughout the blade row. It is shown that end-wall profiling has a dramatic effect on the flow patterns in the early part of the blade row which then translates to a loss reduction later in the blade row. Comparison with CFD results aids the understanding of the role of the reduced horseshoe vortex in this process.
The Investigation of Turbine and Exhaust Interactions in Asymmetric Flows: Part 2 — Turbine-Diffuser-Collector Interactions
Authors: Liu J. J. , Hynes T. P.
Published: February 2009

Part 2 of this paper describes the investigation of steam turbine and exhaust hood interactions in asymmetric flows by using a multiblock multigrid 3D Navier–Stokes solver incorporating an actuator disc model. The interactions among the turbine, diffuser and collector are analyzed by using a flow model. Numerical simulations for two exhaust hoods are performed to understand the flow details and to verify the flow model analysis. Based on the understanding of turbine and exhaust interactions, suggestions for the design of efficient exhaust systems are given.
Aerodynamic Performance Measurements of a Film-Cooled Turbine Stage: Experimental Results
Authors: Keogh R. C. , Guenette G. R. , Spadaccini C. M. , Sommer T. P. , Florjancic S.
Published: February 2009

Modern high performance gas turbine engines utilize film cooling to reduce the heat load on high-pressure turbine stage components, thereby increasing the maximum turbine inlet temperature at which the cycle can operate. However, increased turbine inlet temperature comes at the expense of a reduction in turbine efficiency. The objective of this research is to measure the aerodynamic performance of a film cooled turbine stage and to quantify the loss caused by film cooling. An un-cooled turbine stage was first fabricated with solid blading and tested using a newly developed short duration measurement technique. The stage was then modified to incorporate vane, blade and rotor casing film cooling. The film-cooled stage was then tested over a range of coolant-to-mainstream mass flow and temperature ratios for the same range of operating conditions (pressure ratios and corrected speeds) as the un-cooled turbine. This paper presents the experimental results for these two series of tests.
An Entropic Minimization Technique for Turbine Blade Profiles
Authors: Walsh Ed , Davies Mark , Myose Roy
Published: February 2009

The optimization of the boundary layer edge velocity distribution may hold the key to the minimization of entropy generation in the boundary layers of turbomachinery blades. A preliminary optimization analysis in the laminar region of a non film cooled turbine blade is presented, which demonstrates the concept of how the entropy generation rate may be reduced by varying the boundary layer edge velocity distribution along the suction surface, whilst holding the work done by the blade constant. In the laminar region the analytical technique developed by Pohlhausen and others to predict the boundary layer momentum thickness in the presence of pressure gradients has been adopted to predict the entropy generated as described in other papers by the same authors. The result gives an expression for the entropy generation rate in terms of the boundary layer edge velocity distribution for incompressible flows. The boundary layer edge velocity distribution may then be represented as a polynomial with undefined variables. This allows a minimization technique to be used to minimize the entropy generation rate on these variables. Constraints are included to keep the work output constant and the diffusion low to avoid separation. In this analysis it is only the laminar region that is considered for minimization, thus it is necessary to ensure that the modified boundary layer edge velocity distribution does not undergo transition earlier than the baseline boundary layer edge velocity distribution. This is accomplished by considering transition and separation criteria available in the literature. The result of this analysis indicates that the entropy generation rate may be reduced in the laminar boundary layers by using this technique.
Simulation of the Interaction of Labyrinth Seal Leakage Flow and Main Flow in an Axial Turbine
Authors: Anker Jan E. , Mayer Ju¨rgen F.
Published: February 2009

This paper presents the simulation of the flow in a 1.5 stage low-speed axial turbine with shrouded rotor blades and focuses on the interaction of the labyrinth seal leakage flow with the main flow. The presented results were obtained using the Navier-Stokes code ITSM3D developed at University of Stuttgart. A comparison of the computational results with experimental data of this test case gained at Ruhr-Universita¨t Bochum verifies that the flow solver is capable of reproducing the leakage flow effects to a sufficient extent. The computational results are used to examine the influence of the leakage flow on the flow field of the turbine. By varying the clearance height of the labyrinth in the simulations, the impact of the re-entering leakage flow on the main flow is studied. As demonstrated in this paper, leakage flow not only introduces mixing losses but can also dominate the secondary flow and induce severe losses. In agreement with the experimental data the computational results show that at realistic clearance heights the leakage flow gives rise to negative incidence over a considerable part of the downstream stator which causes the flow to separate.
Visualizations of the Unsteady Flow Field Near the Endwall of a Turbine Cascade
Authors: Ma Hongwei , Jiang Haokang , Qiu Yaxi
Published: February 2009

The unsteady flow field near the endwall of a turbine cascade was visualized in a water tunnel using the hydrogen bubble technique. With the help of a light sheet, the experiment was carried out at different incidences without a radial clearance. A fluctuating horseshoe vortex system of varying number of vortices is observed near the leading-edge endwall. The pressure-side leg of the vortex moves toward the suction side after it enters the passage, while the suction-side leg develops along the corner of the suction surface. With the incidence increase, the pressure-side leg of the horseshoe vortex becomes stronger and can directly kick on the suction surface, causing a considerable influence nearby. The interaction and the flow mixing among the counter-rotating horseshoe legs, the endwall boundary layer and the main flow occur in the passage, forming a vortex system traditionally called the passage vortex. The vortex patterns and the interactions are related to the incidence angle.
Improving 3D Flow Characteristics in a Multistage LP Turbine by Means of Endwall Contouring and Airfoil Design Modification: Part 1 — Design and Experimental Investigation
Authors: Eymann S. , Reinmo¨ller U. , Niehuis R. , Fo¨rster W. , Beversdorff M. , Gier J.
Published: February 2009

Endwall losses contribute significantly to the overall losses in modern turbomachinery, especially when aerodynamic airfoil load and pressure ratios are increased. Hence, reducing the extent and intensity of the secondary flow structures helps to enhance overall efficiency. This work focusses on secondary flow reduction in typical aero engine low pressure turbines. From the large range of viable approaches, a promising combination of axis symmetric endwall contouring and 3D airfoil thickening was chosen. Aerodynamic design, experimental verification and further analysis based on numerical simulation are described in a two part paper. In the first part, the aerodynamic design intent and the experimental setup embedded in the closed circuit test facility of the Institute of Aeronautical Propulsion at Stuttgart University are presented. For this work, a three stage turbine of realistic aero engine size was investigated with a conventional and a modified first stage. In order to gain detailed information about the complex flow different advanced measurement techniques were employed. In addition to multiple surface pressure tappings, extensive traverses were taken in several measurement planes with pneumatic probes, 3-component hot-wire probes and non-intrusive laser transit velocimetry. Time-averaged results of these measurements are reported for two different points of operation. By comparing the two configurations of the first stage the influencing of the secondary flow structure is made apparent through a variation in the radial extent and intensity of the endwall secondary flow motion.
Evolution of Upstream Propagating Shock Waves From a Transonic Compressor Rotor
Authors: Prasad Anil
Published: February 2009

The evolution of upstream propagating shock waves from the isolated transonic compressor designated NASA Rotor-35 is examined numerically. Results from the numerical simulations are compared with those from a semi-analytical two-dimensional model based on the nonlinear acoustic interaction of shock waves in the axial–tangential plane upstream of the rotor. The evolution determined from a two-dimensional viscous computational solution is found to agree well with the semi-analytical prediction and confirms that shock wave evolution is a primarily inviscid phenomenon. Radial variations are found to increase the rate of decay of the shock wave amplitude in comparison to the prediction from the semi-analytical two-dimensional model. The velocity field from the three-dimensional viscous solution compares well with experimental measurements, indicating that the initial shock strength and shock wave evolution immediately upstream of the rotor blade leading edge are accurately captured. The upstream-propagating shock system is found responsible for nearly 20% of the total loss attributable to the rotor, and is consistent with earlier transonic airfoil cascade studies. The axial decay rate of the upstream induced circumferential static pressure distortion is found to be an order of magnitude slower at spanwise locations with supersonic relative inlet Mach numbers than those at which it is subsonic. As a consequence of this slower decay rate, it is found that the axial gap to the upstream stator would need to be about twice that used for subsonic blade sections.
Assessing Viscous Body Forces for Unsteady Calculations
Authors: Xu L.
Published: February 2009

A strategy has been developed to model the three dimensional unsteady flows through turbomachines subject to non-axisymmetric flow/geometrical conditions such as low order distortions with relatively long length scale unsteadiness, by modelling the viscous effects as local source terms for a coarse computational mesh but not calculating them directly. In general full annulus multirow calculations are required for such flows but currently the computational resources are devoted to resolving detailed viscous flow very close to the walls, which in some cases is not the centre of concern. By avoiding resolving detailed viscous effects the model can accelerate the calculation by at least two orders of magnitude. The method has been illustrated to be able to resolve disturbances down to the blade passing frequency and give good estimates of overall unsteady blade forces due to blade row interactions. Obviously the correct modelling of the viscous body force as source terms in the governing equations is the key for accuracy of such calculations. Different ways of constructing/approximating the viscous body force term are discussed and their adequacy in unsteady flow calculations is assessed. It is found that in general the viscous force is relatively small compared to the total blade force, even smaller the unsteady fluctuation of the viscous force and a simple drag coefficient model is quite adequate to model both time mean and dynamic viscous effects. Whilst for the cases when separations are present variations in the drag coefficient may become large and more detailed modelling may be required.
Micro Air Injection and Its Unsteady Response in a Low-Speed Axial Compressor
Authors: Nie Chaoqun , Xu Gang , Cheng Xiaobin , Chen Jingyi
Published: February 2009

A new approach, steady micro air injection from the casing, is proposed to improve the stability of a three-stage low-speed axial compression system. Although the injection rate is designated to be only a few ten thousandth of the compressor flow rate, such an injection is able to trigger the unsteady response and thus lower the mass flow rate at stall for up to 5.83%. At the same time, it keeps the steady compressor characteristic with no injection unchanged. In order to verify that the compressor response is indeed unsteady, experiments at various injection configurations are performed, which include different injection angles, axial gaps between injector and blade leading edge, radial penetration of injector and the amount of injected air. Evidences of the unsteady response are further demonstrated through dynamic signal analysis using a wavelet-based method to show the behavior of early flow disturbances under the influence of injection. Numerical analyses performed at near stall condition show that the tip clearance vortices do response to the micro injection and thus delay the inception of stall.
Development of New High Load/High Lift Transonic Shrouded HP Gas Turbine Stage Design: A New Approach for Turbomachinery
Authors: Haller Brian , Anderson James
Published: February 2009

This paper details some of the recent developments that ALSTOM has made, in collaboration with QinetiQ, to develop and test highly loaded high pressure turbine stage designs. A new approach was used for the preliminary design of the stage (adapted from the Denton U3 method) and this is described. For the first time the standard empirical loss correlations were abandoned. The targets for the stage are very aggressive. The stage incorporates many innovative features to address aerodynamic and other parasitic losses, including “Controlled Flow” technology to address secondary flow losses. This new approach is then validated against detailed steady performance measurements. Additional unsteady traverse measurements taken have been used to validate the predicted rotor flow field. These unsteady traverse measurements have also been used to resolve the unsteady flow field. Although detailed interpretation of these results has not yet been completed, some understanding is drawn from these results.
Investigation of the 3D Unsteady Rotor Pressure Field in a HP Turbine Stage
Authors: Valenti E. , Halama J. , De´nos R. , Arts T.
Published: February 2009

This paper presents steady and unsteady pressure measurements at three span locations (15, 50 and 85%) on the rotor surface of a transonic turbine stage. The data are compared with the results of a 3D unsteady Euler stage calculation. The overall agreement between the measurements and the prediction is satisfactory. The effects of pressure ratio and Reynolds number are discussed. The rotor time-averaged Mach number distribution is very sensitive to the pressure ratio of the stage since the incidence of the flow changes as well as the rotor exit Mach number. The time-resolved pressure field is dominated by the vane trailing edge shock waves. The incidence and intensity of the shock strongly varies from hub to tip due to the radial equilibrium of the flow at the vane exit. The decrease of the pressure ratio attenuates significantly the amplitude of the fluctuations. An increase of the pressure ratio has less significant effect since the change in the vane exit Mach number is small. The effect of the Reynolds number is weak for both the time-averaged and the time-resolved rotor static pressure at mid-span, while it causes an increase of the pressure amplitudes at the two other spans.
Simulations of Aeroelasticity in an Annular Cascade Using a Parallel 3-Dimensional Navier-Stokes Solver
Authors: McBean Ivan , Liu Feng , Hourigan Kerry , Thompson Mark
Published: February 2009

A parallel multi-block Navier-Stokes solver with the k-ω turbulence model is developed to simulate the 3-dimensional unsteady flow through an annular turbine cascade. Results at mid-span are compared with the experimental results of Standard Test Case 4. Comparisons are made between 3-dimensional and 2-dimensional, and inviscid and viscous simulations. The inclusion of a viscous flow model does not greatly affect the stability of the configuration.
Numerical Investigation of the Wake-Boundary Layer Interaction on a Highly Loaded LP Turbine Cascade Blade
Authors: Cardamone Pasquale , Stadtmu¨ller Peter , Fottner Leonhard
Published: February 2009

The effects of wake passing on the development of the profile boundary layer of a highly loaded low-pressure turbine cascade are studied using the RANS code TRACE-U. The numerical results are compared with available experimental data to verify the accuracy of the code in predicting the periodic-unsteady transition and separation mechanisms at low Reynolds number conditions. The experimental investigations have been carried out on a turbine cascade called T106D-EIZ subjected to wakes generated by an up-stream moving bar-type generator. The cascade pitch was increased by about 30% with respect to design conditions without modifying the blade geometry in order to obtain a large separation bubble on the suction surface. The extensive database containing time-averaged as well as time-resolved results was presented in a separate paper by Stadtmu¨ller and Fottner (2001) and is discussed only briefly. The time-accurate multistage Navier-Stokes solver TRACE-U developed by the DLR Cologne used for the numerical simulations employs a modified version of the one-equation Spalart-Allmaras turbulence model coupled with a transition correlation based on the work of Abu-Ghannam and Shaw in the formulation of Drela. The objective of this paper is to provide further insight into the aerodynamics of the wake-induced transition process and to rate the application limits of the numerical approach for exit Reynolds numbers as low as 60.000. The CFD predictions for two different flow conditions are compared with the measurements. Plots of wall-shear stress, blade loading, shape factor and loss behaviour are used to verify the reliability of the code. The periodic-unsteady development of the boundary layer as well as the loss behaviour is well reproduced for higher Reynolds numbers. For the case with massive separation, large discrepancies between numerical and experimental results are observed.
Self-Recirculating Casing Treatment Concept for Enhanced Compressor Performance
Authors: Hathaway Michael D.
Published: February 2009

A state-of-the-art CFD code (APNASA) was employed in a computationally based investigation of the impact of casing bleed and injection on the stability and performance of a moderate speed fan rotor wherein the stalling mass flow is controlled by tip flow field breakdown. The investigation was guided by observed trends in endwall flow characteristics (e.g., increasing endwall aerodynamic blockage) as stall is approached, and based on the hypothesis that application of bleed or injection can mitigate these trends. The “best” bleed and injection configurations were then combined to yield a self-recirculating casing treatment concept. The results of this investigation yielded: 1) identification of the fluid mechanisms which precipitate stall of tip critical blade rows, and 2) an approach to recirculated casing treatment which results in increased compressor stall range with minimal or no loss in efficiency. Subsequent application of this approach to a high speed transonic rotor successfully yielded significant improvements in stall range with no loss in compressor efficiency.
Aerodynamic Design and Performance of Aspirated Airfoils
Authors: Merchant Ali
Published: February 2009

The impact of boundary layer aspiration, or suction, on the aerodynamic design and performance of turbomachinery airfoils is discussed in this paper. Aspiration is studied first in the context of a controlled diffusion cascade, where the effect of discrete aspiration on loading levels and profile loss is computationally investigated. Blade design features which are essential in achieving high loading and minimizing the aspiration requirement are described. Design studies of two aspirated compressor stages and an aspirated turbine exit guide vane using three dimensional Navier-Stokes calculations are presented. The calculations show that high loading can be achieved over most of the blade span with a relatively small amount of aspiration. Three dimensional effects close to the endwalls are shown to degrade the performance to varying degrees depending on the loading level.
Experimental Investigation of an Aspirated Fan Stage
Authors: Schuler Brian J. , Kerrebrock Jack L. , Merchant Ali
Published: February 2009

This paper addresses the use of viscous flow control by suction to improve compressor stage performance. The pressure ratio can be significantly increased by controlling the development of the airfoil and endwall boundary layers. This concept has been validated through an aspirated fan stage experiment performed in the MIT Blowdown Compressor Facility. The fan stage was designed to produce a pressure ratio of 1.6 at a throughflow adiabatic efficiency of 89% at a corrected rotor tip speed of 750 ft/s (229 m/s). Aspiration was applied to the airfoil surface of both the rotor and stator at a design suction rate of 0.5% of the inlet flow. Aspiration was also used on the endwall boundary layers. The measured performance of the stage agrees well with the design intent and predicted performance. An incompressible, vortex shedding model calibrated to the experimental data shows that the vortex shedding induces radial flows that redistribute flow properties in the spanwise direction.
Development of Secondary Flow Field in a Low Solidity Diffuser in a Transonic Centrifugal Compressor Stage
Authors: Bonaiuti Duccio , Arnone Andrea , Hah Chunill , Hayami Hiroshi
Published: February 2009

In the present paper, the flow structure inside a low-solidity diffuser of a transonic compressor was investigated in detail. Steady computations were carried out and compared to experimental data. The secondary flow development inside the diffuser was analyzed and the reason for the stall inception was detected. Unsteady calculations were performed for two operating points, one close to the choke and the other one close to the stall of the compressor, in order to assess the effect of the unsteadiness in the diffuser secondary flow development.
Aerodynamics of a Transonic Centrifugal Compressor Impeller
Authors: Ibaraki Seiichi , Matsuo Tetsuya , Kuma Hiroshi , Sumida Kunio , Suita Toru
Published: February 2009

High pressure ratio centrifugal compressors are applied to turbochargers and turboshaft engines because of their small dimensions, high efficiency and wide operating range. Such a high pressure ratio centrifugal compressor has a transonic inlet condition accompanied with a shock wave in the inducer portion. It is generally said that extra losses are generated by interaction of the shock wave and the boundary layers on the blade surface. To improve the performance of high pressure ratio centrifugal compressor it is necessary to understand the flow phenomena. Although some research works on transonic impeller flow have been published, some unknown flow physics are still remaining. The authors designed a transonic impeller, with an inlet Mach number is about 1.3, and conducted detailed flow measurements by using Laser Doppler Velocimetry (LDV). In the result the interaction between the shock wave and tip leakage vortex at the inducer and flow distortion at the downstream of inducer were observed. The interaction of the boundary layer and the shock wave was not observed. Also computational flow analysis were conducted and compared with experimental results.
The Impact of Volute Versus Collector on Centrifugal Compressor Performance
Authors: Biba Y. I.
Published: February 2009

As part of a revamp or rerate study, an investigation was undertaken to assess the impact of a collector design versus a volute on compressor performance. The subject compressor was a single stage, axial inlet configuration with a discharge collector rather than the more commonly used scroll volute. The primary distinction between the collector and volute is that the collector cross sectional area is constant at all circumferential locations. A complex 3D model containing the inlet, impeller, low solidity diffuser (LSD), and collector was built. A similar model was also created where the volute was substituted for the collector. Computational Fluid Dynamics (CFD) analyses were performed using these models with results generated at different flow rates. Computational results are presented and compared to test data for collector configuration. The test included standard performance measurements as well as more detailed internal flow data, allowing a credible comparison with the CFD results. Conclusions are drawn with respect to potential compromises in choosing a collector versus a volute.
Effect of Suction Elbow and Inlet Guide Vanes on Flow Field in a Centrifugal Compressor Stage
Authors: Cui Michael M.
Published: February 2009

Suction elbows and inlet guide vanes (IGVs) are typical upstream components in front of first-stage impellers in centrifugal compressors. The three-dimensional distortion induced by elbows and IGVs affects the flow field behind the IGV housing. Since the flow field in front of the impeller is subsonic, the flow motion induced by the rotating impeller will interact with the elbow and IGVs as well. The flow field resulting from these interactions is three-dimensional. The nature of this flow field defines design requirements of upstream components and impact overall performance of the compressor. To understand the mechanism controlling the interactions of up-steam components and optimize the compressor design for better efficiency and reliability, a numerical simulation of the flow field inside the entire first stage of the compressor was conducted. The stage studied includes suction elbow, IGV housing with vanes, and first-stage impeller. HFC 134a was used as the working fluid. The thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws respectively. The three-dimensional flow field was simulated with a Navier-Stokes solver using the k-ε turbulence model. The overall performance parameters are obtained by integrating the field quantities. The force, torque, and arm of moment acting on the IGVs were then calculated. The results can be used to improve centrifugal compressor design to achieve higher efficiency and improve reliability. The methodology developed in the current study can be applied to centrifugal compressor design and optimization.
A Study on Impeller-Diffuser Interaction: Part I — Influence on the Performance
Authors: Ziegler Kai U. , Gallus Heinz E. , Niehuis Reinhard
Published: February 2009

The interaction between impeller and diffuser is considered to have strong influence on the flow in highly loaded centrifugal compressors. However, the knowledge about this influence is still not satisfying. This two-part paper presents an experimental investigation of the effect of impeller-diffuser interaction on the unsteady and the time averaged flow configuration in impeller and diffuser and the performance of these components. The flat wedge vaned diffuser of the investigated stage allows an independent adjustment of diffuser vane angle and radial gap between impeller exit and diffuser vane inlet. Attention is mainly directed to the radial gap, as it determines the intensity of the impeller-diffuser interaction. Part I deals with the integral flow losses and the diffusion in impeller, diffuser and the entire compressor. An extensive test series with steady probe measurements at impeller exit and diffuser exit was performed at 10 different diffuser geometries and different operating points. The results show that in most cases smaller radial gaps are leading to a more homogeneous flow field at diffuser vane exit and to a higher diffuser pressure recovery resulting in a higher compressor efficiency. On the other hand, impeller efficiency is hardly affected by the radial gap. In part II measurements with a laser-2-focus velocimeter are presented illuminating the reasons for the effects found. The experimental results are intended to be published as an open CFD testcase under the name “Radiver”.
Application of an Improved Streamline Curvature Approach to a Modern, Two-Stage Transonic Fan: Comparison With Data and CFD
Authors: Boyer Keith M. , O’Brien Walter F.
Published: February 2009

A streamline curvature method with improvements to key loss models is applied to a two-stage, low aspect ratio, transonic fan with design tip relative Mach number of approximately 1.65. Central to the improvements is the incorporation of a physics-based shock model. The attempt here is to capture the effects of key flow phenomena relative to the off-design performance of the fan. A quantitative analysis regarding solution sensitivities to model parameters that influence the key phenomena over a wide range of operating conditions is presented. Predictions are compared to performance determined from overall and interstage measurements, as well as from a three-dimensional, steady, Reynolds-averaged Navier-Stokes method applied across the first rotor. Overall and spanwise comparisons demonstrate that the improved model gives reasonable performance trending and generally accurate results. The method can be used to provide boundary conditions to higher-order solvers, or implemented within novel approaches using the streamline curvature method to explore complex engine-inlet integration issues, such as time-variant distortion.