bluuebunny/crossref_metadata_2025 huggingface dataset:
Technological Aspects of Ethanol Steam Reforming Processors for Molten Carbonate Fuel Cells
Authors: Freni S. , Frusteri F. , Mondello N. , Chiodo V. , Siracusano S. , Nevoso D.
Published: September 2008

Bioethanol, obtained by biomass fermentation, could be an important hydrogen supplier as a renewable source. The availability of active, selective and stable catalyst for bioethanol steam reforming is a key point for the development of processes suitable to this purpose. In this work, the performance of different supported catalysts in the steam reforming of bioethanol at molten carbonate fuel cell (MCFC) operative condition has been focused and a decreasing activity has been related to the formation of carbon. Furthermore catalytic behaviour of a Ni supported catalyst has been tested under reforming condition both distillation industry’s waste and ethanol-water mixture. Results revealed that, superior alcohols (fusel oil) arising from the distillation process influence carbon formation and the presence of oxygen (ATR condition) preserves the catalyst activity which otherwise significantly deactivate mainly due to the carbon formation.
Effect of Sonochemical, Regenerative Sol Gel and Microwave Assisted Synthesis Techniques on the Formation of Dense Electrolytes and Porus Electrodes for All Perovskite IT-SOFCs
Authors: Jena Hrudananda , Rambabu B.
Published: September 2008

The influence of preparation techniques on the microstructure, grain-size and consequently on the electrical transport properties of the ABO3 structured materials used as electrode and electrolytes in all perovskite IT-SOFC were investigated. Nano-crystalline powders of La1-xMxGa1-yNyO3±δ (M = Sr,; x = −0.10 to 0.15; N = Mg; y = −0.10 to 0.15) (LSGM) as electrolyte, porous La0.8Sr0.2Co0.8Fe0.2O3±δ (LSCF) or LaNi1-xFexO3±δ (x = 0–0.5) (LNF) as cathode, La0.8Sr0.2Cr0.7Mn0.3O3±δ (LSCM) as anode and LaCrO3 or substituted LaCrO 3 as interconnect were synthesized by various wet chemical methods. The wet chemical methods like metal-carboxylate gel decomposition, hydroxide co-precipitation, sonochemical and regenerative sol-gel process followed by microwave sintering of the powders have been used. Microwave sintering parameters were optimized by varying sintering time, and temperature to achieve higher density of LSGM pellets. The phase pure systems were obtained at sintering duration of 30 min at 1200 °C. The XRD, HR-TEM, and SEM measurements revealed the average grain size of these perovskites was ∼ 22 nm range. The electrical conductivities of the compositions were measured by ac (5Hz–13MHz) and dc techniques. The conductivity of the sintered pellets was found to be ∼0.01–0.21 S/cm at 550–1000°C range for electrolyte and 1.5–100 S/cm at 25–1000°C for electrodes respectively. The effect of sonochemical, and regenerative sol-gel methods in processing large quantities of nano-crystalline perovskites with multi-element substitutions at A- and B-sites to achieve physico-chemical compatibility for fabricating zero emission all perovskite IT-SOFCs are reported in this paper.
Experimental Investigation of Liquid Water Formation and Transport in a Transparent Single-Serpentine PEM Fuel Cell
Authors: Spernjak Dusan , Advani Suresh , Prasad Ajay K.
Published: September 2008

Liquid water formation and transport was investigated by direct experimental visualization in an operational transparent single-serpentine PEM fuel cell. We examined the effectiveness of various gas diffusion layer (GDL) materials in removing water away from the cathode and through the flow field over a range of operating conditions. Complete polarization curves as well as time evolution studies after step changes in current draw were obtained with simultaneous liquid water visualization within the transparent cell. At similar current density (i.e. water production rate), lower level of cathode flow field flooding indicated that liquid water had been trapped inside the GDL pores and catalyst layer, resulting in lower output voltage. No liquid water was observed in the anode flow field unless cathode GDLs had a microporous layer (MPL). MPL on the cathode side creates a pressure barrier for water produced at the catalyst layer. Water is pushed across the membrane to the anode side, resulting in anode flow field flooding close to the H2 exit.
Fast Design and Manufactured on Complex Flow Channel by Rapid Prototyping for Air-Breathing Polymer Electrolyte Membrane Fuel Cells
Authors: Lai Wei-Hsiang , Chen Cheng Yu , Chou Ming-Chang
Published: September 2008

The miniature and air-breathing fuel cell has become the globally major design concepts of fuel cell development recently. In this paper, the authors used 3-D drafting software for fast design and utilize rapid prototyping (RP) technology to accelerate the prototype development of new stack designs and optimize the assembly method. A fast design and convenient manufacture tool, i.e., rapid prototyping, has been first successfully applied to the fabrication of the complicated flow channels of both DMFC and PEMFC in this paper. The honeycomb shape methanol reservoir and honeycomb cathode structure design of DMFC and a complex flow distributor design of mono-polar PEMFC stack, which are almost impossibly manufactured by traditional CNC manufacturing, is fabricated by rapid prototyping technology and illustrated for the extraordinary advantages of RP technology. This paper shows that the fast design and manufacture characteristics are more important for the feasibility study of a complicated structure and any new design ideas. Although the performance of air-breathing pseudo-polar DMFC is only 2.16 mW/cm2 in peak power density by using 50% of hydrophobic carbon paper; this poor performance is resort to the MEA of DMFC is not well prepared. The other example of the power density of 188 mW/cm2 (at 0.425 V) in parallel-connection and 123mW/cm2 (at 4.25V) in serial-connection for the air-breathing mono-polar PEMFC stack are achieved. The performance of the stack is close to the state-of-the-art comparing to recently published literatures [6–9].
Compatible Cathode Materials for High Performance Low Temperature (300–600°C) Solid Oxide Fuel Cells
Authors: Zhu Bin , Sun Juncai , Sun Xueli , Li Song , Gao Wenyuan , Liu Xiangrong , Zhu Zhigang
Published: September 2008

We have made extensive efforts to develop various compatible electrode materials for the ceria-based composite (CBC) electrolytes, which have been, reported as most advanced LTSOFC electrolyte materials (Zhu, 2003). The electrode materials we have investigated can be classified as four categories: i) LSCCF (LaSrCoCaFeO) and BSCF perovskite oxides applied for our CBC electrolyte LTSOFCs; ii) LFN (LaFeO-based oxides, e.g. LaFe0.8Ni0.2O3) perovskite oxides; iii) lithiated oxides: e.g. LiNiOx, LiVOx or LiCuOx are typical cathode examples for the CBC LTSOFCs; iv) other mixed oxide systems, most common in a mixture of two-oxide phases, such CuOx-NiOx, CuO-ZnO etc. systems with or without lithiation are developed for the CBC systems, especially for direct alcohol LTSOFCs. These cathode materials used for the CBC electrolyte LTSOFCs have demonstrated excellent performances at 300–600°C, e.g. 1000 mWcm−2 was achieved at 580°C. The LTSOFCs can be operated with a wide range of fuels, e.g. hydrogen, methanol, ethanol etc with great potential for applications.
A New Design for Tip Injection in Transonic Axial Compressors
Authors: Beheshti Behnam H. , Ghorbanian Kaveh , Farhanieh Bijan , Teixeira Joao A. , Ivey Paul C.
Published: September 2008

This paper presents a state of the art design for the blade tip injection. The design includes the means to inject high-pressure gas jet directly into a circumferential casing groove formed in the shroud adjacent to the blade tip. The casing groove is positioned over the blade tip and exceeds 30% of the blade axial chord beyond the impeller to both upstream and downstream directions. In order to validate the multi block model used in the tip gap region, main flow characteristics are verified with the experimental data for smooth casing with a design clearance of 0.5% span. Three arbitrary mass flow rates (1.75%, 2.45%, and 4.35% of choked mass flow) have been studied. The results indicate remarkable advantageous effects on the compressor stability margin. Further, compared to classical design for tip injection, the current design can significantly improve the compressor stall margin due to direct injection of flow. An increase of the injected air may enhance the stall margin improvement. Furthermore, results for injection at different angles, shows that the compressor stability margin reaches a maximum when the bleed air in the relative coordinates is aligned with the mean camber line of the blade leading edge. The main objective of this research is to present an improved design for tip injection as well as to determine its effect on the stability enhancement of the compressor. The current research also provides guidelines to an optimum design of tip injection.
Unsteady Flow Field of an Axial-Flow Turbine Rotor at a Low Reynolds Number
Authors: Matsunuma Takayuki
Published: September 2008

The unsteady flow field of an annular turbine rotor was investigated experimentally using a laser Doppler velocimetry (LDV) system. Detailed measurements of the time-averaged and time-resolved distributions of the velocity, flow angle, and turbulence intensity, etc. were carried out at a very low Reynolds number condition, Reout = 3.5 × 104. The data obtained were analyzed from the viewpoints of both an absolute (stationary) frame of reference and a relative (rotating) frame of reference. The effect of the turbine nozzle wake and secondary vortices on the flow field inside the rotor passage was clearly captured. It was found that the nozzle wake and secondary vortices are suddenly distorted at the rotor inlet, because of the rotating potential field of the rotor. The nozzle flow (wake and passage vortices) and the rotor flow (boundary layer, wake, tip leakage vortex, and passage vortices) interact intensively inside the rotor passage.
The Effect of an Entraining Diffuser on the Performance of Circular-to-Slot Exhaust Ducts With a 90 Degree Bend
Authors: Bottenheim S. , Birk A. M. , Poirier D. J.
Published: September 2008

An experimental study has been undertaken on a 3-stage entraining diffuser with a distorted inlet flow. Two different circular-to-slot transition ducts were used as driving nozzles. Both transition ducts included a 90 degree bend. Varying degrees of inlet swirl were also considered. A 7-hole pressure probe was used to traverse the diffuser outlets. With a longitudinal duct the measured flows showed severe impingement of the primary flow on the walls of the entraining diffuser. Similar outlet flow distributions were observed for all cases of inlet swirl considered. In contrast, only minimal primary flow impingement was observed with a transverse duct. The use of the transverse duct also resulted in significant secondary flows including multiple large-scale vortices. These secondary flows intensified when swirl was added. Four performance parameters were calculated: the entrainment ratio, back pressure coefficient, pressure recovery coefficient and the entraining diffuser efficiency. The results showed that peak performance was attained at 20° of inlet swirl for both configurations. The addition of an entraining diffuser was found to result in minimal improvements of performance for the longitudinal duct configuration and significant improvements for the transverse orientation.
Computation of the Acoustic Field in an Annular Gas Turbine Combustion Chamber Using a Hybrid Approach
Authors: Szasz Robert Z. , Mihaescu Mihai , Fuchs Laszlo
Published: September 2008

The acoustic field generated by flow unsteadiness in a model annular gas turbine (GT) combustion chamber is determined using a hybrid approach. In the flow solver the semi-compressible Navier-Stokes equations are resolved using LES as turbulence model. The acoustic solver is based on an inhomogeneous wave equation, where the instantaneous source terms are computed from the LES data in each time-instant. The flow and the acoustics in a GT combustor with co- and counter-rotating swirler burners have been considered. The results have shown that significant differences can be observed between the co- and counter-rotating configurations both in the flow and acoustic fields.
A Three-Dimensional Unsteady CFD Model of Compressor Stability
Authors: Chima R. V.
Published: September 2008

A three-dimensional unsteady CFD code called CSTALL has been developed and used to investigate compressor stability. The code solved the Euler equations through the entire annulus and all blade rows. Blade row turning, losses, and deviation were modeled using body force terms which required input data at stations between blade rows. The input data was calculated using a separate Navier-Stokes turbomachinery analysis code run at one operating point near stall, and was scaled to other operating points using overall characteristic maps. No information about the stalled characteristic was used. CSTALL was run in a 2-D throughflow mode for very fast calculations of operating maps and estimation of stall points. Calculated pressure ratio characteristics for NASA stage 35 agreed well with experimental data, and results with inlet radial distortion showed the expected loss of range. CSTALL was also run in a 3-D mode to investigate inlet circumferential distortion. Calculated operating maps for stage 35 with 120 degree distortion screens showed a loss in range and pressure rise. Unsteady calculations showed rotating stall with two part-span stall cells. The paper describes the body force formulation in detail, examines the computed results, and concludes with observations about the code.
Time-Linearized Quasi-3D Tone Noise Computations in Cascade Flows
Authors: Boncinelli Paolo , Marconcini Michele , Poli Francesco , Arnone Andrea , Schipani Claudia
Published: September 2008

A time-linearized quasi-3D solver for flutter analysis in turbomachinery flows was modified in order to deal with incoming perturbations due to unsteady interactions with upstream/downstream rows. To do this, exact two-dimensional single-frequency non-reflecting boundary conditions of Giles were implemented at inlet/outlet boundaries. A matrix dissipation model was used to reduce the artificial damping of propagating waves in the computational domain. Various applications for both uniform and non-uniform steady mean flows are presented for cascade configurations of turbomachinery interest, and results are compared with quasi-analytical and numerical data available in literature. Analyses of preliminary results are promising for future applications to turbomachinery configurations and fully three-dimensional flows.
Effects of Boundary Layer Suction on the Performance of Compressor Cascades
Authors: Chen Fu , Song Yanping , Chen Huanlong , Wang Zhongqi
Published: September 2008

The effects of boundary layer suction on the aerodynamic performance of compressor cascade are mainly determined by: (1) the location of the suction slot; (2) the suction flow rate; (3) the suction slot geometry; and (4) the aerodynamic parameters of the cascade (e.g. solidity and incidence). In this paper, an extensive numerical study has been carried out to investigate the effects of these influencing factors in a highly-loaded compressor cascade by comparing the aerodynamic performance of the cascade in order to give guidance for the application of boundary layer suction to improve the performance of modern highly-loaded compressors. The results show that boundary layer suction alleviates the accumulation of low-energy fluid at suction surface corners and enhances the ability of flow turning, and this improvement in flow behavior depends on the location of the suction slot and the suction flow rate. When the location of the suction slot and the suction flow rate are fixed, as the cascade solidity decreases from 1.819 to 1.364 and 1.091, the cascade total pressure loss is reduced at most by 25.1%, 27.7% and 32.9% respectively, and the cascade exit flow deviation is decreased by 3.1°, 4.2° and 5.0° accordingly. Moreover, boundary layer suction also has the largest effect in the cascade with smaller solidity at large positive incidences, which means that boundary layer suction is an effective way to widen the stable operating range of the highly-loaded compressor cascade. The suction slot geometry is described by the suction slot width and the suction slot angle with respect to the direction normal to the blade suction surface. The results show that the flow behavior is improved and the endwall loss is reduced further as the increase of the suction slot width. The suction slot angle has an obvious influence on the pressure inside the slot, therefore, should be considered in the design of the suction slot since the maximum pressure inside the slot is usually required.
Clearance Effects on the Onset of Instability in a Centrifugal Compressor
Authors: Schleer Matthias , Song Seung Jin , Abhari Reza S.
Published: September 2008

This report intends to shed an insight into the effect of large relative tip clearances on the onset of instability in a highly loaded centrifugal compressor. Time-resolved pressure measurements have been performed along the casing of a scaled-up model of a small compressor for two clearances at a wide range of operating conditions. Based on these time-resolved measurements the pressure distribution along the meridional length and the blade loading distribution are calculated for each operating condition. In addition, the phase locked pressure fluctuation and its deviation are computed. The results show the behavior of each sub-component of the compressor at different flow conditions and explain the role of the relative tip clearance on the onset of instability. For high mass flow rates the steady pressure distribution along the casing reveals that the inducer acts as an accelerating nozzle. Pressure is only built up in the radial part due to the centrifugal forces and in the subsequent diffuser due to area change. For off-design conditions incidence effects are seen in the blade loading distribution at the leading edge while the inducer is unloaded. A region of high pressure deviation originates at the leading edge of the main blade and convects downstream. This feature is interpreted as the trajectory of the leakage vortex. The trajectory of these vortices is strongly affected by the mass flow coefficient. If the mass flow rate is sufficiently small the trajectory of the leakage vortex becomes perpendicular to the axis of rotation, the leakage vortex interacts with the adjacent blade, and inlet tip recirculation is triggered. If the flow rate is further reduced, the leakage vortex vanishes and rotating stall is initiated in the diffuser. For larger clearances, stronger vortices are formed, stall is triggered at higher flow rates and the overall compressor performance deteriorates.
An Effective Turbine Blade Parameterization and Aerodynamic Optimization Procedure Using an Improved Response Surface Method
Authors: Chen Naixing , Zhang Hongwu , Ning Fangfei , Xu Yanji , Huang Weiguang
Published: September 2008

This paper describes a procedure for a rapid and accurate 3D aerodynamic optimization of high performance turbine blades. This procedure has been developed to account for the complicated geometrical aspects and the complex nature of the associated fluid flow, while remaining simple, practical and demanding less computing power. The focus has been placed on the blade geometrical representation using a set of simple algebraic equations (blade parameterization) and on the aerodynamic optimization methodology based on the numerical computations by a N.S. solver. The turbine blade, including thickness distribution and camber line for each section of the blade span and radial stacking line, has been defined by polynomials, allowing investigation of the influence of any single-parameter change on blade performance. An improved response surface method, by incorporating a simulated annealing algorithm (RS-SAM), has been found to improve the accuracy and to strengthen the optimum-searching ability. A multi-objective response surface method (MORSM) has also been included for testing. One example is given here to demonstrate the effectiveness of the procedure.
Experimental and Numerical Investigation of Varying Stator Design Parameters for a Radial Turbine
Authors: Simpson Alister , Spence Stephen W. T. , Artt David W. , McCullough Geoffrey
Published: September 2008

The experimental and numerical investigations of five different vaned stators for a radial turbine are reported. Three different stator vane numbers and three different vane shapes were tested and modelled. The experimental tests were conducted at matched mass flow rates and pressure ratios, using the same 86 mm diameter turbine rotor, allowing direct comparison of the losses arising from each stator configuration. Stator vane number was found to have a small impact on measured stage efficiency (less than 1%), while vane shape was found to have a more significant effect (up to 4%). A commercial CFD code was used to construct a combination of full stage and single passage numerical models of the test turbine. Flow separation as a result of excessive incidence angle at stator inlet was shown to be a significant factor for some of the stators. Predicted pressure loss coefficients for the vaned stators were in the range 7–11%.
Design Optimization of Transonic Compressor Rotor Using CFD and Genetic Algorithm
Authors: Yi Weilin , Huang Hongyan , Han Wanjin
Published: September 2008

The paper describes a new optimization strategy for computationally expensive design optimization problems of turbomachinery, combined with design of experiment (DOE), response surface models (RSM), genetic algorithm (GA) and a 3-D Navier-Stokes solver. Data points for response evaluations were selected by Latin hypercube design (LHD) and 3-dimensional Navier-Stokes analysis was carried out at these sample points. The quadratic response surface model was used to approximate the relationships between the design variables and flow parameters. The genetic algorithm was applied to the response surface model to perform global optimization to obtain the optimum design. The above method was applied to the optimization design of NASA rotor37. The object was to maximize the adiabatic efficiency. An optimum leading edge line was found which produced a new 3-dimensional blade combined with sweep and composite bowing. As a result of this optimization, the adiabatic efficiency was successfully increased by 1.58%. It was found that the strategy of this paper provides a reliable design optimization method for turbomachinery blades at reasonable computing cost.
The Development of an Aerodynamic Performance Prediction Tool for Modern Axial Flow Compressor Profiles
Authors: Bruna Dario , Cravero Carlo , Turner Mark G.
Published: September 2008

The development of a computational tool (MP-LOS) for the aerodynamic loss modeling and prediction for axial-flow compressor blade sections is presented in this paper. A state-of-the-art quasi 3-D flow solver, MISES, has been used for the flow analysis on existing airfoil geometries in many working conditions. Different values of inlet flow angle, inlet Mach number, AVDR, Reynolds number and solidity have been chosen to investigate a possible working range. The target is a loss prediction formulation that will be introduced into throughflow or axisymmetric Navier-Stokes codes for the performance prediction of multistage axial flow compressors. The loss coefficient has been correlated to the flow parameters that have shown an influence on the profile loss for the blades under study. The proposed correlation, using the described computational approach, can be extended to any profile family with the aid of any code for the parametric design of blade profiles.
Unsteady Flows in the Last Stator Rows of Axial Compressor of Gas Turbine Working in Coal Gasification Combined Cycle
Authors: Cyrus V. , Rehak K. , Polansky J.
Published: September 2008

Fatigue failure of the last three stator row vanes of the Alstom gas turbine axial compressor occurred in Vresova power plant. The plant uses syngas, produced by the brown coal gasification, as fuel. Experimental investigation of non-steady flow in the axial compressor was carried out by means of the static and total pressure probes. Flow pulsations, in the rear part of compressor, at a frequency of (380–400) Hz were found. This frequency is near the first natural frequency of the damaged stator vanes. The stalled flow on vane surfaces with vortex structure shedding off is responsible for the flow pulsation origin. The results of flow simulations in cascades of last three stator rows support such conclusion.
Short Length-Scale Rotating Stall Inception in a Transonic Axial Compressor: Experimental Investigation
Authors: Bergner Jo¨rg , Kinzel Matthias , Schiffer Heinz-Peter , Hah Chunill
Published: September 2008

To improve the understanding of spike-type stall inception of a transonic axial compressor, measurements of the unsteady static pressure in the rotor endwall region are analyzed. At design speed, a detailed experimental investigation of the unsteadiness of the pressure field at the rotor endwall at near stall condition shows a strong fluctuation of the tip clearance flow. Both vortex strength and -trajectory oscillate randomly. Analysis of the wall pressure time histories during stall inception suggests that spike-type disturbances of the flow field correlate with an upstream motion of one blade passages shock front. In addition, the evolution of a stall cell could be visualized by means of static wall-pressure contour plots.
Unsteady Flow Modeling Across the Rotor/Stator Interface Using the Nonlinear Harmonic Method
Authors: Vilmin S. , Lorrain E. , Hirsch Ch. , Swoboda M.
Published: September 2008

The paper presents results of the incorporation of the harmonic nonlinear method into an existing turbomachinery Navier-Stokes code. This approach, introduced by He and Ning in 1998, can be considered as a bridge between classical steady state and full unsteady calculations, providing an approximate unsteady solution at affordable calculation costs. The unsteady flow perturbation is Fourier decomposed in time, and by a casting in the frequency domain transport equations are obtained for each time frequency. The user controls the accuracy of the unsteady solution through the order of the Fourier series. Alongside the solving of the time-averaged flow steady-state equations, each frequency requires the solving of two additional sets of conservation equations (for the real and imaginary parts of each harmonic). The method is made nonlinear by the injection of the so-called deterministic stresses, resulting from all the solved frequencies, into the time-averaged flow solver. Because of the transposition to the frequency domain, only one blade channel is required like a steady flow simulation. The presented method also features a new improved treatment that enhances the flow continuity across the rotor/stator interface by a reconstruction of the harmonics and the time-averaged flow on both sides of the interface. A non-reflective treatment is applied as well at each interface. Validation for analytical and turbomachinery test cases are presented. In particular, results are compared between the harmonic method, steady-state mixing plane and full unsteady calculations. The comparison with the reference full unsteady calculation provides a quantitative indication of the accuracy of the approach, as well as the significant gain in CPU time, whereas the comparison with classical quasi-steady state solutions indicates the gain of accuracy. A multistage compressor flow is also presented to show the capabilities of the method.
Forward Sweep in a Four-Stage High-Speed Axial Compressor
Authors: Braun Michael , Seume Joerg R.
Published: September 2008

The present paper provides a comparison of a CDA-bladed four-stage high-speed axial compressor and a configuration in which the first three rows are replaced with forward swept blades and vanes. The blades are designed with sweep from mid-span to tip, the vanes from mid-span to the hub. The non-swept portion of the leading edge is kept radial and identical to the CDA blading. The overall performance of the compressor with both configurations is measured at five engine speeds. The flow fields of each rotor and stator at two operating points (“Design Point” and “Near Stall”) of both configurations are investigated at the design speed. On the suction and the pressure side of the third stage vane, static surface pressures are measured to determine the local Mach number distribution and to identify zones of separation. Multistage CFD-computations are carried out for both configurations. The numerical and experimental results of both configurations are compared and show the effect of sweep on the operating map of the compressor from choke to stall: Sweep reduces corner stall and the end-wall losses at high aerodynamic loads. It is shown that the reduction of separation due to sweep leads to an increase of total pressure rise towards lower mass flow so that the present swept compressor achieves higher total pressure ratios at and near the stall limit. An analysis along streamlines suggests that the performance of the compressor could have been improved further by a more uniform total pressure distribution in the front stages and a better match of the sweep in stages 2 and 3.
Modelling the Streamline Curvature Effects in Turbomachinery Flows
Authors: Kozˇulovic´ Dragan , Ro¨ber Thomas
Published: September 2008

Turbomachinery flows show significant streamline curvature with corresponding effects on turbulence development. Generally, linear eddy viscosity turbulence models, which are widely used in industrial aerodynamic design, do not predict these effects accurately, leading to less reliable RANS-simulations. In this work, therefore, a modification is made to the two-equation turbulence model of Wilcox [1]. Although this extension is a simple and pragmatic approach, the effects of streamline curvature are accurately reproduced for many presented applications, ranging from simple generic test cases to multistage compressor flows. Improved predictions of performance maps are achieved, which is mainly due to improved modelling in regions with higher streamline curvature, e.g. tip vortex and end-wall boundary layers. The curvature correction enables a greater mass flow range to be simulated and increases the numerical stability. Furthermore, the new approach requires only local variables, which makes it applicable to complex flows and easy to implement in existing codes.
Investigation of Unsteady Flow Field in Vaned Diffuser of a Transonic Centrifugal Compressor
Authors: Ibaraki Seiichi , Matsuo Tetsuya , Yokoyama Takao
Published: September 2008

Transonic centrifugal compressors are used with high-load turbochargers and turboshaft engines. These compressors usually have a vaned diffuser to increase the efficiency and the pressure ratio. To improve the performance of such a centrifugal compressor, it is required to optimize not only the impeller but also the diffuser. However the flow field of the diffuser is quite complex and unsteady because of the impeller located upstream. Although some research on vaned diffusers has been published, the diffuser flow is strongly dependent on the particular impeller exit flow, and some of the flow physics remain to be elucidated. In the research reported here, detailed flow measurements within a vaned diffuser were conducted using a particle image velocimetery (PIV). The vaned diffuser was designed with high subsonic inlet conditions marked by an inlet Mach number of 0.95 for the transonic compressor. As a result, a complex three-dimensional flow with distortion between the shroud and the hub was observed. Also, unsteady flow accompanying the inflow of the impeller wake was confirmed. Steady computational flow analysis was performed and compared with the experimental results.
Numerical Simulation of the Flow Interaction Between Turbine Main Annulus and Disc Cavities
Authors: Boudet Je´roˆme , Hills Nickolas J. , Chew John W.
Published: September 2008

This paper presents numerical simulations of the unsteady flow interactions between the main annulus and the disc cavity for an axial turbine. The simulations show the influence of the main annulus asymmetries (vane wakes, blade potential effect), and the appearance of rim seal flow instabilities. The generation of secondary frequencies due to non-linear interactions is observed, and the possibility of further low frequency effects and resonance is noted. The computations are compared to experimental results, looking at tracer gas concentration and mass-flows. Results are further analysed to investigate the influence of the rim seal flow on the blading aerodynamics. The flow that is ejected through the rim seal influences the unsteady flow impinging the blades. The influence of this rim-seal flow is even observed downstream of the blades, where it distorts the radial profile of stagnation temperature.
Unsteady Flow and Aeroelasticity Behaviour of Aero-Engine Core Compressors During Rotating Stall and Surge
Authors: Vahdati M. , Simpson G. , Imregun M.
Published: September 2008

The paper will focus on two core-compressor instabilities, namely rotating stall and surge. Using a 3D viscous time-accurate flow representation, the front bladerows of a core-compressor were modelled in a whole-annulus fashion whereas the rest of bladerows were represented in single passage fashion. The rotating stall behaviour at two different compressor operating points was studied by considering two different variable-vane scheduling conditions for which experimental data were available. Using a model with 9 whole bladerows, the unsteady flow calculations were conducted on 32-CPUs of a parallel cluster, typical run times being around 3–4 weeks for a grid with about 60 million points. The simulations were conducted over several engine rotations. As observed on the actual development engine, there was no rotating stall for the first scheduling condition while mal-scheduling of the stator vanes created a 12 band rotating stall which excited the rotor blade 1st flap mode. In a separate set of calculations, the surge behaviour was modelled using a time-accurate single-passage representation of the core compressor. It was possible to predict not only flow reversal into the low pressure compression domain, but also the expected hysteresis pattern of the surge loop in terms of its mass flow vs pressure characteristic.
Development and Demonstration of a Stability Management System for Gas Turbine Engines
Authors: Christensen D. , Cantin P. , Gutz D. , Szucs P. N. , Wadia A. R. , Armor J. , Dhingra M. , Neumeier Y. , Prasad J. V. R.
Published: September 2008

Rig and engine test processes and in-flight operation and safety for modern gas turbine engines can be greatly improved with the development of accurate on-line measurement to gauge the aerodynamic stability level for fans and compressors. This paper describes the development and application of a robust real time algorithm for gauging fan/compressor aerodynamic stability level using over-the-rotor dynamic pressure sensors. This real time scheme computes a correlation measure through signal multiplication and integration. The algorithm uses the existing speed signal from the engine control for cycle synchronization. The algorithm is simple and is implemented on a portable computer to facilitate rapid realtime implementation on different experimental platforms as demonstrated both on a full-scale high-speed compressor rig and on an advanced aircraft engine. In the multi-stage advanced compressor rig test, the compressor was moved toward stall at constant speed by closing a discharge valve. The stability management system was able to detect an impending stall and trigger opening of the valve so as to avoid compressor surge. In the full-scale engine test, the engine was configured with a one-per-rev distortion screen and transients were run with a significant amount of fuel enrichment to facilitate stall. Test data from a series of continuous rapid transients run in the engine test showed that in all cases the stability management system was able to detect an impending stall and manipulated the enrichment part of the fuel schedule to provide stall free transients.
Assessment of Unsteady Behavior in Turbocharger Turbines
Authors: Costall Aaron , Szymko Shinri , Martinez-Botas Ricardo F. , Filsinger Dietmar , Ninkovic Dobrivoje
Published: September 2008

The flow in turbocharger turbines is highly unsteady in nature as it responds to the exhaust manifold of an internal combustion engine. This paper investigates the significance of unsteadiness by examining first its relevance to real engine situations and then its effect on turbocharger turbine operation. The engine simulations carried out show the relevance of the Strouhal number effect for real turbocharger applications, which has been demonstrated experimentally on a turbine stage test stand. Therefore, for realistic multiple-cylinder-engine configurations with different exhaust gas pipe lengths and firing frequencies the importance of the actual unsteady behavior needs careful assessment. The effect upon the turbine itself is examined by modeling the laboratory arrangement to replicate the test stand configuration and operation using a one-dimensional wave action code. The 1D model is validated against experimental results obtained using a new permanent magnet eddy-current dynamometer for a mixed flow turbine suitable for a medium-sized automotive application covering an equivalent speed range of 50–100%, U2/Cis of 0.3–1.1 and a pulse frequency of 20–80 Hz. The turbine model has been refined using unsteady experimental data and so enables the capture of unsteady effects in engine design codes. The beneficial effect of the ability of this model to predict turbine mass flow is discussed.
Optimal Design of Swept, Leaned and Skewed Blades in a Transonic Axial Compressor
Authors: Jang Choon-Man , Samad Abudus , Kim Kwang-Yong
Published: September 2008

Shape optimization of a transonic axial compressor rotor operating at the design flow condition has been performed using the response surface method and three-dimensional Navier-Stokes analysis. The three design variables, blade sweep, lean and skew, are introduced to optimize the three-dimensional stacking line of the rotor blade. The objective function of the shape optimization is adiabatic efficiency. Throughout the shape optimization of the rotor, the adiabatic efficiency is increased by reducing the hub corner and tip losses. Separation line due to the interference between a passage shock and surface boundary layer on the blade suction surface is moved downstream for the optimized blade compared to the reference one. Among the three design variables, the blade skew is most effective to increase the adiabatic efficiency in the compressor rotor.
Behavior of Tip Leakage Flow in an Axial Flow Compressor Rotor
Authors: Wu Yanhui , Chu Wuli , Lu Xingen , Zhu Junqiang
Published: September 2008

The current paper reports on investigations with an aim to advance the understanding of the flow field near the casing of a small-scale high-speed axial flow compressor rotor. Steady three dimensional viscous flow calculations are applied to obtain flow fields at various operating conditions. To demonstrate the validity of the computation, the numerical results are first compared with available measured data. Then, the numerically obtained flow fields are analyzed to identify the behavior of tip leakage flow, and the mechanism of blockage generation arising from flow interactions between the tip clearance flow, the blade/casing wall boundary layers, and non-uniform main flow. The current investigation indicates that the “breakdown” of the tip leakage vortex occurs inside the rotor passage at the near stall condition. The vortex “breakdown” results in the low-energy fluid accumulating on the casing wall spreads out remarkably, which causes a sudden growth of the casing wall boundary layer having a large blockage effect. A low-velocity region develops along the tip clearance vortex at the near stall condition due to the vortex “breakdown”. As the mass flow rate is further decreased, this area builds up rapidly and moves upstream. This area prevents incoming flow from passing through the pressure side of the passage and forces the tip leakage flow to spill into the adjacent blade passage from the pressure side at the leading edge. It is found that the tip leakage flow exerts little influence on the development of the blade suction surface boundary layer even at the near stall condition.
Effect of Pre-Whirl on Unstable Flow Suppression in a Centrifugal Impeller With Ring Groove Arrangement
Authors: Ishida Masahiro , Sakaguchi Daisaku , Ueki Hironobu
Published: September 2008

In order to obtain a wider operating range in a centrifugal impeller with inducer, the effect of the pre-whirl induced by the inlet recirculation flow on the flow incidence and the impeller characteristics were analyzed numerically and compared with the experimental results. In order to control the swirl intensity of the recirculation flow, guide vanes were installed circumferentially in the annular bypass of the ring groove arrangement, and the setting angle of the guide vane was changed. The fundamental concept for surge suppression is to achieve the flow incidence less than or close to the critical one. A too large-positive flow incidence can be reduced by increasing the recirculation flow rate determined by the pressure difference between the two ring groove positions, on the other hand, a higher pressure rise in the inducer can be obtained at the flow incidence close to the critical one by suppressing the pre-whirl induced by the recirculation flow. It is clearly shown that the better impeller characteristics and the large recirculation flow rate can be achieved by giving a suitable setting angle of the guide vane. The unstable flow rate range of the tested impeller was reduced by about 53% almost without deterioration of the impeller efficiency in the whole flow rate range.
Design Methodology and Predicted Performance for a Supersonic Compressor Stage
Authors: Grosvenor Allan D. , Brown Paul M. , Lawlor Shawn P.
Published: September 2008

Aspects of the aerodynamic design of a unique supersonic high pressure ratio compressor rotor, termed the Rampressor, are presented. The design of this shock wave compression system is based on principles employed in supersonic intake design with a multi-shock compression system and boundary layer treatment. One of the unique features of this configuration is the way these techniques have been applied to the design of a high-speed rotor, as opposed to a system designed for linear flight. The rotor consists of three blade-rows within which the shock system is produced by a ramp, throat, and diffuser on the hub. The technology has been previously demonstrated in a 2.3:1 pressure ratio experimental test compressor. The present study concentrates on applying the same techniques to achieve pressure ratios in the range of 8–10:1. Estimated performance is supported by mean-line and method of characteristics calculations, as well as 3D viscous Computational Fluid Dynamics (CFD) simulations. Validation of the employed CFD scheme is provided through test cases that represent the physics of boundary layers, diffusing flows and separation, shock wave / boundary layer interaction, and compressor aerodynamics. The study concentrates on the predicted effect of hub contour on the rotor shock system, and subsequent impact on compressor performance.
Experimental Investigation of Flow Control in Compressor Cascades
Authors: Hergt A. , Meyer R. , Engel K.
Published: September 2008

A large part of the total pressure losses in a compressor stage is caused by secondary flow effects like the separation between the wall and the vane i.e., a corner separation. An experimental and numerical investigation in a highly loaded compressor cascade was performed to understand the fluid mechanic mechanism of this corner separation in order to control it by using vortex generators. The experiments were carried out with a compressor cascade at a high-speed test facility at DLR in Berlin. The cascade consisted of five vanes and their profiles represent the cut at 10% of span distance from the hub of the stator vanes of a single stage axial compressor. The experiments were accomplished at Reynolds numbers up to Re = 0.6 × 106 (based on 40 mm chord) and Mach numbers up to M = 0.7. To measure the total pressure losses of the cascade (caused by the corner separation) a wake rake was used. It consisted of 26 pitot probes to measure the total pressure distribution of the outflow and 4 Conrad probes to determine the outflow angles. To detect the separation area on the vane, a flow visualisation technique was used. In addition to the experiments, numerical computations were carried out with the URANS TRACE, which has been developed at DLR for the simulation of steady and unsteady turbomachinery flow. The computations were performed with identical geometrical conditions as in the experiments, including the measured inflow boundary layer conditions at the side walls. The experiments were performed with the aim of controlling the corner separation. In this case, vortex generators as a passive flow control device were used. The vortex generators were attached at the surface of the suction side of the vanes. The flow control device is producing a strong vortex, which enhances the mixing between the main flow and the retarded boundary layer at the side wall. Thus, the corner separation is reduced on the vanes. The experiments were carried out at the peak efficiency (design point) of the cascade in order to optimize the design of the vortex generators for an application in turbomachines.
Tonal Noise Generation in an Inlet Vaned Axial Blower at Several Axial Gaps
Authors: Argu¨elles Di´az K. M. , Ferna´ndez Oro J. M. , Santolaria Morros C. , Ballesteros Tajadura R.
Published: September 2008

The main objective is the numerical study of the noise generation in a single stage axial flow blower. For the present work, just the discrete noise generation (tonal noise) is dealt with. A numerical methodology based on a generalization of Lighthill’s aero-acoustic analogy, the so-called Ffowcs Williams and Hawkings aero-acoustic analogy (FFWH), is developed. The numerical methodology has been tested with two different operational configurations of the blower: a first one, with a reduced axial gap between the rows of the stage (i.e. 50 mm) and a second one with a higher axial distance (i.e. 70 mm). The specific contribution of every tonal noise source term will be analyzed for both configurations.
Experimental Investigation of a Generic Compressor Bleed System
Authors: Gomes Reinaldo A. , Schwarz Carsten , Pfitzner Michael
Published: September 2008

Extensive experimental studies on axial compressor bleed-flow systems have been carried out on a three dimensional model of a generic bleed-flow configuration typical for aero engines. The compressor flow is modeled as a clean annular flow. One row of stator vanes is used to impart a constant swirl upstream of the bleed system. The rig is designed modularly in order to allow for inexpensive changes in all of its components and therefore to enlarge the variability of the model. The research is focused onto the generation of an experimental data base, which can be used to derive correlations for the calculation of effective areas and pressure losses. Those data are gained using steady pneumatic measurement technique. In addition, the highly complex flow field in the manifold, which has an important effect onto the bleed-flow, is analyzed using Doppler-Global-Velocimetry (DGV). These measurements were conducted in collaboration with DLR Cologne, who have developed the DGV technique. In this paper the flow field in the manifold is analyzed in detail for two different configurations featuring two and four bleed ducts, respectively. Furthermore the use of a flush design of the slot is compared with a lip design. These data are compared to results from the literature achieved using 2-dimensional configurations.