bluuebunny/crossref_metadata_2025 huggingface dataset:
Design-Optimization Approach to Multistage Axial Contra-Rotating Turbines
Authors: Sozio Ernesto , Verstraete Tom , Paniagua Guillermo
Published: November 2013

Air Turbo Rocket engines, suitable for high-speed propulsion, require compact turbomachinery. This paper presents the design of an innovative multi-stage turbine mounted at the hub of a counter-rotating fan. Hence, the turbine airfoils are required to deliver high torque at low peripheral speeds. The design methodology specifically developed for this fourteen-stage turbine relies on two successive optimization cycles. The first one is based on a through-flow 1D code. This optimization cycle explores a vast set of possible design solutions. In a second step, an optimization using a 3D high fidelity RANS defines the 3D airfoil geometry. In order to accelerate the entire design procedure, a special routine was developed to morph the 1D results into the required info for the 3D optimization. Both the 1D and 3D optimizations are based on differential evolution algorithm.
Thermoacoustic Shape Optimization of a Subsonic Nozzle
Authors: Giauque Alexis , Huet Maxime , Clero Franck , Ducruix Sébastien , Richecoeur Franck
Published: November 2013

Indirect combustion noise originates from the acceleration of non-uniform temperature or high vorticity regions when convected through a nozzle or a turbine. In an recent contribution (Giauque et al., JEGTP, 2012), the authors have presented an analytical thermoacoustic model providing the indirect combustion noise generated by a subcritical nozzle when forced with entropy waves. This model explicitly takes into account the effect of the local changes in the cross-section area along the configuration of interest. In this article, the authors introduce this model into an optimization procedure in order to minimize or maximize the thermoacoustic noise emitted by arbitrary shaped nozzles operating under subsonic conditions. Each component of the complete algorithm is described in details. The evolution of the cross-section changes are introduced using Beziers splines which provide the necessary freedom to actually achieve arbitrary shapes. Beziers poles coordinates constitute the parameters defining the geometry of a given individual nozzle. Starting from a population of nozzles of random shapes, it is shown that a specifically designed genetic optimization algorithm coupled with the analytical model converges at will toward a quieter or noisier population. As already described by Bloy (JFM, 1979), results therefore confirm the significant dependence of the indirect combustion noise with respect to the shape of the nozzle, even when the operating regime is kept constant. It appears that the quietest nozzle profile evolves almost linearly along its converging and diverging sections leading to a square evolution of the cross-section area. Providing insight in the underlying physical reason leading to the difference in noise emission between two extreme individuals, the integral value of the source term of the equation describing the behavior of the acoustic pressure of the nozzle is considered. It is shown that its evolution with the frequency can be related to the global acoustic emission. Strong evidence suggest that the noise emission increases as the source term in the converging and diverging parts less compensate each other. The main result of this article is the definition and proposition of an Acoustic Emission Factor which can be used as a surrogate to the complex determination of the exact acoustic levels in the nozzle for the thermoacoustic shape optimization of nozzle flows. This Acoustic Emission Factor, much faster to compute, only involves the knowledge of the evolution of the cross-section area as well as the inlet thermodynamic and velocity characteristics to be computed.
Unsteady CFD Simulation of Control Valve in Throttling Conditions and Comparison With Experiments
Authors: Zanazzi Giorgio , Schaefer Ottmar , Sell Michael , Ridoutt Colin
Published: November 2013

The operational flexibility of steam power plant is becoming more important as power generation becomes increasingly decentralized, with a growing contribution from renewable energy sources. In a power plant the control valve is a key component to guarantee the control of the plant of which is increasingly demanded to extend the operational capability.

At specific operating conditions, the control valve could experience vibrations. In this paper, the physical phenomena of the unsteady aerodynamic excitation force have been investigated by means of CFD techniques.

An in-house code was used to simulate the flow-induced vibration. Unsteady transonic 3D simulation generally requires huge computational effort. A novel unsteady quasi-3D approach has been developed and applied as pre-design tool to establish the qualitatively operational map of the valve and to detect the critical operational range, to reduce the number of detailed 3D simulations.

The numerical results are compared with experimental test undertaken in the Central Research Institute of Electric Power Industry [4] and full 3D simulation performed with the commercial tool CFX, using the Scale-Adaptive Simulation (SaS) turbulence model. Different pressure drops at certain lift have been selected from the operational map and reproduced numerically. Different modes have been identified, from stochastic behavior with wide width of frequency to periodic flow with one dominant frequency.

Results indicate good agreement between the predicted frequency and amplitude and benchmark experiments. The quasi-3D simulation is able to reproduce the principle behavior of the flow field for different drop of pressure and capture the different operational mode. Similar behaviour has been detected also for the selected operating condition in the full 3D analysis.

In addition, flutter calculation of the downstream pipe is carried out. It has demonstrated that the implementation of oscillating discharge piping influences the amplitudes and frequency of the upstream flow region.
Adaption of Giles Non-Local Non-Reflecting Boundary Conditions for a Cell-Centered Solver for Turbomachinery Applications
Authors: Robens Sebastian , Jeschke Peter , Frey Christian , Kügeler Edmund , Bosco Arianna , Breuer Thomas
Published: November 2013

In contrast to external flow aerodynamics, where one-dimensional Riemann boundary conditions can be applied far up- and downstream, the handling of non-reflecting boundary conditions for turbomachinery applications poses a greater challenge due to small axial gaps normally encountered. For boundaries exposed to non-uniform flow in the vicinity of blade rows, the quality of the simulation is greatly influenced by the underlying non-reflecting boundary condition and its implementation. This paper deals with the adaptation of Giles’ well-known exact non-local boundary conditions for two-dimensional steady flows to a cell-centered solver specifically developed for turbomachinery applications. It is shown that directly applying the theory originally formulated for a cell-vertex scheme to a cell-centered solver may yield an ill-posed problem due to the necessity of having to reconstruct boundary face values before actually applying the exact non-reflecting theory.

In order to ensure well-posedness, Giles’ original approach is adapted for cell-centered schemes with a physically motivated reconstruction of the boundary face values, while still maintaining the non-reflecting boundary conditions. The extension is formulated within the original framework of determining the circumferential distribution of one-dimensional characteristics on the boundary. It is shown that, due to approximations in the one-dimensional characteristic reconstruction of boundary face values, the new approach can only be exact in the limiting case of cells with a vanishing width in the direction normal to the boundary if a one-dimensional characteristic reconstruction of boundary face values is used. To overcome the dependency on the width of the last cell, the new boundary condition is expressed explicitly in terms of a two-dimensional modal decomposition of the flow field. In this formulation, vanishing modal amplitudes for all incoming two-dimensional modes can easily be accomplished for a converged solution. Hence we are able to ensure perfectly non-reflecting boundary conditions under the same conditions as the original approach. The improvements of the new method are demonstrated for both a subsonic turbine and a transonic compressor test case.
Modelling Vortex Generating Jet-Induced Transition in Low-Pressure Turbines
Authors: Herbst Florian , Fiala Andreas , Seume Joerg R.
Published: November 2013

The current design of low-pressure turbines (LPTs) with steady-blowing vortex generating jets (VGJ) uses steady computational fluid dynamics (CFD). The present work aims to support this design approach by proposing a new semi-empirical transition model for injection-induced laminar-turbulent boundary layer transition. It is based on the detection of cross-flow vortices in the boundary layer which cause inflectional cross-flow velocity profiles. The model is implemented in the CFD code TRACE within the framework of the γ-Reθ transition model and is a reformulated, re-calibrated, and extended version of a previously presented model. It is extensively validated by means of VGJ as well as non-VGJ test cases capturing the local transition process in a physically reasonable way. Quantitative aerodynamic design parameters of several VGJ configurations including steady and periodic-unsteady inflow conditions are predicted in good accordance with experimental values. Furthermore, the quantitative prediction of end-wall flows of LPTs is improved by detecting typical secondary flow structures. For the first time, the newly derived model allows the quantitative design and optimization of LPTs with VGJs.
Aerodynamic Design and Testing of an Axial Flow Compressor for the GT24/26 Gas Turbines
Authors: Novak Damir , Loetzerich Michael , Boese Matthias
Published: November 2013

A 22-stage axial flow compressor with a pressure ratio 35:1 has been designed, built and successfully tested for a heavy-duty gas turbine application. Advanced technology and aero engine design tools have been used. The compressor has been designed using an “arbitrary” airfoil blading including 3D design features, like leading edge re-camber, lean, sweep and flowpath contouring.

The compressor performance and part load behavior have been improved by accurate stage matching based on whole compressor 3D analyses. The new compressor has been tested in a scaled down rig and validated in the Alstom Test Power Plant (ATPP).The compressor met all design objectives and demonstrated excellent performance.

This paper describes the aerodynamic design and test results.
Practical Controller Design for Rotors on Magnetic Bearings by Means of an Efficient Simulation Tool
Authors: Schmied Joachim , Kosenkov Alexander
Published: November 2013

This paper describes in detail by means of a realistic example and an efficient simulation tool the whole procedure of the magnetic bearing controller design. In a first step the suitability of the rotor is assessed. The objectives for the actual controller design to ensure a robust system, which is suited for the application, are then explained. In a first step of the design a controller structure, which is a series of proven filters with stable poles, is defined. The strategy to select the filters is determined by the rotor properties and the hardware characteristics of the bearing. The parameters of the controller are then optimized to fulfill the objectives. The optimization can be automated by the definition of suited goals, which are closely related to the objectives. Finally the performance of the resulting rotor-bearing system is assessed.
Consideration of Uncertainties in Compact Cross-Flow Heat Exchanger Design for Gas Turbine Engine Application
Authors: Manteufel Randall D. , Vecera Daniel G.
Published: November 2013

Recent experimental work characterized the performance of a unique cross-flow heat exchanger design for application of cooling compressor bleed air using liquid jet fuel before it is consumed in the gas turbine combustor. The proposed design has micro-channels for liquid fuel and cools air flowing in passages created using rows of intermittent fins. The design appears well suited for aircraft applications because it is compact and light-weight. A theoretical model is reported to be in good agreement with experimental measurements using air and water, thus providing a design tool to evaluate variations in the heat exchanger dimensions. This paper presents an evaluation of the heat exchanger performance with consideration of uncertainties in both model parameters and predicted results. The evaluation of the design is proposed to be reproduced by students in a thermal-fluids design class. The heat exchanger performance is reevaluated using the effectiveness–NTU approach and shown to be consistent with the method reported in the original papers. Results show that the effectiveness is low and in the range of 20 to 30% as well as the NTU which ranges from 0.25 to 0.50 when the heat capacity ratio is near unity. The thermal resistance is dominated by the hot gas convective resistance. The uncertainties attributed to fluid properties, physical dimensions, gas pressure, and cold fluid flow rate are less significant when compared to uncertainties associated with hot fluid flow rate, hot fluid inlet temperature, cold fluid inlet temperature, and convective correlation for gas over a finned surface. The model shows which heat transfer mechanisms are most important in the performance of the heat exchanger.
Transient Dynamics Analysis on Main Shaft of Wind Turbine
Authors: Chen Jie , Jiang Dongxiang
Published: November 2013

Wind turbine operates in harsh environment so that wind turbine breaks down frequently. As the altering loads on wind turbine are complicated, finding abnormity through the parameters of performance is difficult to achieve. How to find the faults of wind turbine in early time effectively is a practical problem confronted by researchers. In this paper, the method for detecting and distinguishing several faults of wind turbine using transient dynamics analysis on main shaft of wind turbine is presented. Firstly, a finite element model of wind turbine is established. Secondly, loads on blades and rotor of the model would be calculated using GH Bladed. Thirdly, transient dynamics analysis is carried out based on the finite element model, using the loads mentioned above. As the displacements of the shaft vary with the operating conditions, we can get the characters of the different faults of wind turbine through the vibration, and even judge the fault type of the wind turbine. Perhaps this method could be a practical way to detect the abnormity of wind turbine and prevent it from failing.
Effect of Circumferential Static Pressure Non-Uniformity Caused by a Volute on Flow in High Pressure Ratio Centrifugal Compressor With Vaneless and Vaned Diffuser
Authors: Tamaki Hideaki , Unno Masaru , Zheng Xinqian , Zhang Yangjun
Published: November 2013

Centrifugal compressors are deemed to have a wide operating range. Recirculation devices, which comprise a bleed slot, an upstream slot and an annular cavity connecting them, are often used particularly compressors for turbochargers. They remove low energy fluid at the inducer and improve the incidence angle of the impeller leading edge, i.e. the blade loading of the inducer, at low flow rates due to the recirculation flow supplied to the compressor inlet. The impeller of a centrifugal compressor is often housed in a volute. Since the geometry of the volute is not axisymmetric, the impeller might be surrounded by an asymmetric flow field, hence there is the potential to enlarge the compressor operating range and improve efficiency using a recirculation device with an asymmetrically-distributed bleed slot, referred to here as a non-axisymmetric recirculation device.

The authors [1] applied non-axisymmetric recirculation devices to a compressor with a vaneless diffuser. The results showed the effectiveness of a non-axisymmetric recirculation device with a bleed slot partially channeled in the circumferential direction. They also showed that the surge line of the compressor characteristics, which is the line connecting the operational points of the smallest flow rates on all peripheral Mach numbers, was significantly affected by the change in the circumferential position of the bleed slot relative to the volute tongue. The tested compressor was originally designed to feature a vaned diffuser [2]. Enhancing the compressor operating range is the key for marine use turbochargers, integrally geared compressors, multistage compressors and gas turbines as well as automotive turbochargers. These compressors normally use vaned diffusers. In this study the authors tried to apply non-axisymmetric recirculation devices developed in their previous study [1] to compressors with a vaned diffuser. Moreover different circumferential positions of the bleed slot relative to the volute tongue were tested as well as the vanelss diffuser case. The change in the surge line of the compressor characteristics was much smaller compared to the compressor with the vaneless diffuser. The circumferential static pressure distributions in the compressors in combination with vaneless and vaned diffusers were measured to determine the above reason as well as conducting unsteady calculations with a simplified outlet boundary condition. These measurements and calculations showed that the impeller with the vaned diffuser was surrounded by a less distorted static pressure field than that with the vaneless diffuser. These results implied that the vaned diffuser depresses the spread of the circumferential static pressure non-uniformity effect caused by a volute to the impeller.
Developement of a Turning Mid Turbine Frame With Embedded Design: Part I — Design and Steady Measurements
Authors: Spataro Rosario , Göttlich Emil , Lengani Davide , Faustmann Christian , Heitmeir Franz
Published: November 2013

The paper presents a new setup for the two-stage two-spool facility located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology. The rig was designed in order to simulate the flow behavior of a transonic turbine followed by a counter rotating low pressure stage like the spools of a modern high bypass aero engine. The meridional flow path of the machine is characterized by a diffusing S-shaped duct between the two rotors. The role of turning struts placed into the mid turbine frame is to lead the flow towards the LP rotor with appropriate swirl.

Experimental and numerical investigations performed on the setup over the last years, which were used as baseline for this paper, showed that wide chord vanes induce large wakes and extended secondary flows at the LP rotor inlet flow. Moreover, unsteady interactions between the two turbines were observed downstream of the LP rotor.

In order to increase the uniformity and to decrease the unsteady content of the flow at the inlet of the LP rotor, the mid turbine frame was redesigned with two zero-lifting splitters embedded into the strut passage.

In this first part paper the design process of the splitters and its critical points are presented, while the time-averaged field is discussed by means of five-hole probe measurements and oil flow visualizations. The comparison between the baseline case and the embedded design configuration shows that the new design is able to reduce the flow gradients downstream of the turning struts, providing a more suitable inlet condition for the low pressure rotor. The improvement in the flow field uniformity is also observed downstream of the turbine and it is consequently reflected in an enhancement of the LP turbine performance.

In the second part of this paper the influence of the embedded design on the time-resolved field is investigated.
Control of a Supercritical CO2 Electro-Thermal Energy Storage System
Authors: Wright S. A. , Z’Graggen A. , Hemrle J.
Published: November 2013

Transcritical CO2 power systems are being investigated for site independent electro-thermal energy storage (ETES). The storage plant uses electrical energy with a standard vapor-compression heat pump/refrigeration cycle to store thermal energy as hot water and ice over a period of approximately 8 hours during low power demand. The power cycle is then reversed and operated as a simple Rankine cycle to produce ∼100 MWe for about 4.5 hours during peak demand. During the power generation cycle the storage plant uses the heat stored in the hot water tanks, together with ice melting, plus ambient heat rejection for the heat sink. For 100 MWe class power plants, the round trip efficiency is estimated to be up to 60%. CO2 was selected as the working fluid because it improves the ability of the plant to operate with high reversibility. In addition, it is compact and can operate below the freezing point of water.

This report describes the major control characteristics of the plant, together with methods, tools, and results of the model. Because the plant is nearly “closed”, it must operate only by consuming electrical energy during the charging cycle and by producing electrical energy plus some waste heat during the discharge cycle. All other heat transfer processes occurs solely within the storage plant itself and consists of either heating or cooling water and by making or melting ice. For the plant to operate continuously, both the water thermal storage and ice storage must be returned to their initial conditions after every 24 hour period. Otherwise, small changes in the thermal environment during waste heat rejection or performance variations of internal components will cause the storage system to drift from its designed operating temperature, pressure and energy storage capability, challenging its ability to operate.

The control concept for the storage plant addresses both the operation of the plant during charging and discharging. It also addresses strategies for control during off-design situations or due to disturbances such as load following or changes in ambient heat rejection conditions. The process simulations described in the paper include models for the main physical components of the plant including the turbomachinery, the heat exchanger network, states of charge of the cold and hot storage, and CO2 inventory.
Journal Bearing Design Retrofit for Better Rotordynamic Characteristics of Process Large Motor-Generator
Authors: Lee An Sung , Kim Byung Ok
Published: November 2013

In this study, for the purpose of improving the rotordynamic characteristics of a large power recovery train, PRT, motor-generator rotor fundamentally by design, firstly, a bearing improvement analysis is carried-out by retrofitting from plain partial journal bearings, originally applied for an operation at a rated speed of 1,800 rpm, to final tilting pad journal bearings. Results show that satisfying evenly key basic lubrication performances such as the minimum lift-off speed and maximum oil-film temperature, a careful design solution of 5-pad tilting pad journal bearings may effectively result in enhancing the direct stiffness of bearings by about two times at such a relatively low rated speed. Next, a detailed rotordynamic analysis is performed, applying both of the original plain partial and retrofitted tilting pad journal bearings, in order to confirm the effect of rotordynamic improvement after the suggested bearing retrofit. Results show that the rotor unbalance response vibrations with the tilting pad journal bearings are greatly reduced to as much as about 11% of those with the plain partial journal bearings. In addition, for the tilting pad journal bearings there is no critical speed up to the rated speed while for the plain partial journal bearings there is one critical speed close to the rated speed with some damping but not sufficiently enough.
Regeneration-Induced Forced Response in Axial Turbines
Authors: Aschenbruck Jens , Meinzer Christopher E. , Pohle Linus , Panning-von Scheidt Lars , Seume Joerg R.
Published: November 2013

The regeneration of highly loaded turbine blades causes small variations of their geometrical parameters. To determine the influence of such regeneration-induced variances of turbine blades on the nozzle excitation, an existing air turbine is extended by a newly designed stage. The aerodynamic and the structural dynamic behavior of the new turbine stage are analyzed. The calculated eigenfrequencies are verified by an experimental modal analysis and are found to be in good agreement.

Typical geometric variances of overhauled turbine blades are then applied to stator vanes of the newly designed turbine stage. A forced response analysis of these vanes is conducted using a uni-directional fluid-structure interaction approach. The effects of geometric variances on the forced response of the rotor blade are evaluated. It is shown that the vibration amplitudes of the response are significantly higher for some modes due to the additional wake excitation that is introduced by the geometrical variances e.g. 56 times higher for typical MRO-induced variations in stagger-angle.
Damping Identification and its Comparison for Various Types of Blade Couplings
Authors: Kubin Zdenek , Polreich Vaclav , Cerny Vaclav , Babkova Petra , Prchlik Lubos
Published: November 2013

Regarding steam turbine blade vibrations, damping of blade as well as bladed disc mode shapes is one of the most important parameters in terms of steam turbine operation. A value of the parameter depends on properties of material used for manufacturing and construction elements of the blades and the discs such as blade roots, shrouds, tiebosses (snubbers) and dampers.

This article deals with a comparison of damping of mode shapes for particular blade couplings and shows which methods are suitable for determination of the damping in individual cases. The whole identification procedure of the damping together with its specifics is also presented. At first, an identification technique of material damping ratio is introduced and its results are given for different materials. The material damping ratio is assessed as material strain dependent. Subsequently, damping ratio of bladed disc mode shapes under bladed disc rotation is identified taking into account two alternatives. The alternatives differ in such a way that blades have been free for the first time and then coupled with friction dampers.

Outcomes presented in the article illustrate good agreement between damping ratio of bladed disc mode shapes with free blades and material used for manufacturing of the blades. On the other hand, damping ratio of bladed disc mode shapes with friction dampers is significantly different and strongly dependent on blade vibration amplitudes as well as nodal diameters of bladed disc mode shapes. Finally, nonlinear behavior of the bladed disc has been revealed along large blade vibration amplitudes and higher nodal diameters of the disc. The non-linear behavior manifests itself in such a way that values of natural frequencies of the disc have become dependent on blade vibration amplitudes.
Hybrid Analysis of Gas Annular Seals With Energy Equation
Authors: Migliorini Patrick J. , Untaroiu Alexandrina , Witt William C. , Morgan Neal R. , Wood Houston G.
Published: November 2013

Annular seals are used in turbomachinery to reduce secondary flow between regions of high and low pressure. In a vibrating rotor system, the non-axisymmetric pressure field developed in the small clearance between the rotor and the seal generate reactionary forces that can affect the stability of the entire rotor system.

Traditionally, two analyses have been used to study the fluid flow in seals, bulk-flow analysis and computational fluid dynamics (CFD). Bulk-flow methods are computational inexpensive, but solve simplified equations that rely on empirically derived coefficients and are moderately accurate. CFD analyses generally provide more accurate results than bulk-flow codes, but solution time can vary between days and weeks. For gas damper seals, these analyses have been developed with the assumption that the flow can be treated as isothermal. Some experimental studies show that the difference between the inlet and outlet temperature temperatures is less than 5% but initial CFD studies show that there can be a significant temperature change which can have an effect on the density field. Thus, a comprehensive analysis requires the solution of an energy equation.

Recently, a new hybrid method that employs a CFD analysis for the base state, unperturbed flow and a bulk-flow analysis for the first order, perturbed flow has been developed. This method has shown to compare well with full CFD analysis and experimental data while being computationally efficient. In this study, the previously developed hybrid method is extended to include the effects of non-isothermal flow. The hybrid method with energy equation is then compared with the isothermal hybrid method and experimental data for several test cases of hole-pattern seals and the importance of the use of energy equation is studied.
Accuracy of Centrifugal Compressor Stages Performance Prediction by Means of High Fidelity CFD and Validation Using Advanced Aerodynamic Probe
Authors: Satish K. V. V. N. K. , Guidotti Emanuele , Rubino Dante Tommaso , Tapinassi Libero , Prasad Sridhar
Published: November 2013

During the design of modern high efficiency, wide operating range centrifugal compressor stages, Computational Fluid Dynamics (CFD) plays an increasing role in the assessment of the performance prediction. Nevertheless experimental data are valuable and necessary to assess the performance of the stages and to better understand the flow features in detail.

A big effort is currently being made to increase the fidelity of the numerical models and the probe measurement accuracy during both the design and validation phases of centrifugal compressor stages. This study presents the flow analysis of centrifugal compressor stages using high fidelity computational fluid dynamics with a particular attention to the cavity flow modeling and comparison with experimental data, using an advanced fast response aerodynamic pressure probe.

Different flow coefficient centrifugal compressor stages were used for the validation of the numerical models with a particular attention to the effects of cavity flow on the flow phenomena.

The computational domain faithfully reproduced the geometry of the stages including secondary flow cavities. The availability of a new in-house automated tool for cavity meshing allowed to accurately resolve leakage flows with a reasonable increase in computational and user time.

Time averaged data from CFD analysis were compared with advanced experimental ones coming from the unsteady pressure probe, for both overall performance and detailed two-dimensional maps of the main flow quantities at design and off design conditions. It was found that the increase in computational accuracy with the complete geometry modeling including leakage flows was substantial and the results of the computational model were in good agreement with the experimental data. Moreover the combination of both advanced computational and experimental techniques enabled deeper insights in the flow field features.

The comparison showed that only with advanced high fidelity CFD including leakage flows modeling did the numerical predictions meet the requirements for efficiency, head and operating margin, otherwise not achievable with simplified models (CFD without cavities).
Time-Resolved Numerical Study of Axial Gap Effects on Labyrinth-Seal Leakage and Secondary Flow in a LP Turbine
Authors: Biester Marc H.-O. , Wiegmann Florian , Guendogdu Yavuz , Seume Joerg R.
Published: November 2013

One of the most promising ways to improve the efficiency of modern turbomachinery is the reduction of secondary flow-structures and associated losses. A widely spread approach is the usage of shrouded airfoils in combination with labyrinth-seals. The disadvantage of this arrangement is a small but inevitable labyrinth-leakage flow that tends to increase the secondary-flow structures. The present work investigates how the axial gap of the blade rows and the corresponding shift of the labyrinth’s inlet and outlet influences leakage related effects on the flow-field and loss-generation. In order to capture the inter-blade and leakage interaction properly, time-resolved RANS computations of a 1 1/2 stage low pressure turbine have been performed. Besides accounting for labyrinth seals, fillets have been modeled. The axial gap is varied from 20% to 80% axial chord length. Clocking-effects induced by the axial gap variation are compensated.

The leakage flow nearly retains the flow direction of the flow entering the blade row. In case of the largest axial gap, mixing causes the flow-angle of the leakage to tend towards that of the main-flow, thus reducing the incidence on the downstream blade row. Therefore, the turning of the low-momentum flow is increased compared to a small axial gap. This leads to a higher loading in the affected region and an increased passage vortex can be observed. By comparing the entropy generation of computations with and without labyrinth seals, the regions where leakage-related losses occur are identified and the relevant mechanisms are distinguished.
Aerodynamic Design and Analysis of a Flanged Diffuser Augmented Wind Turbine
Authors: Tourlidakis A. , Vafiadis K. , Andrianopoulos V. , Kalogeropoulos I.
Published: November 2013

Many researchers proposed methods for improving the efficiency of small Horizontal Axis Wind Turbines (HAWTs). One of the methods developed to increase the efficiency of HAWTs and to overcome the theoretical Betz limit is the introduction of a converging – diverging casing around the turbine. To further improve the performance of the diffuser a flange is placed at its outlet, which smoothes the flow along the diffuser interior, allowing larger diffusion angles to be utilized. The purpose of this research work is the aerodynamic design and computational analysis of such an arrangement with the use of Computational Fluid Dynamics (CFD). First, a HAWT rotor rotating at 600 RPM was designed with the use of the Blade Element Momentum (BEM) method. The three rotor blades are constructed using the NREL airfoil sections family S833, S834 and S835. The power coefficient of the rotor was optimised in a wind speed range of 5 – 10 m/s, with a maximum value of 0.45 for a wind speed of 7m/s. A full three-dimensional CFD analysis was carried out for the modeling of the flow around the rotor and through the flanged diffuser. The computational domain consisted of two regions with different frames of reference (a stationary and a rotating). The rotating frame rotates at 600 RPM and includes the rotor with the blades. All the simulations were performed using the commercial CFD software package ANSYS CFX. The Shear Stress Transport turbulence model was used for the simulations. Detailed flow analysis results are presented, dealing with the various investigated test cases, a) isolated turbine rotor, b) diffuser without the presence of the turbine, and c) the full turbine – diffuser arrangement for different flange heights and wind speeds. By varying the height of the flange and the wind speed, the effects of the above on the flow field and the power coefficient of the turbine were studied. The CFD resulting power coefficients are also compared and good agreement with existing in the literature experimental data was obtained. The results showed that there is a significant improvement in the performance of the wind turbine (by a factor from 2 to 5 on power coefficient at high blade tip speed ratio) and the proposed modification is particularly attractive for small wind turbines. The particular characteristics of the flow field, that are responsible for this improvement are identified and analysed in detail offering a better understanding of the physical processes involved.
Numerical and Experimental Comparison of a Tandem and Single Vane Deswirler Used in an Aero Engine Centrifugal Compressor
Authors: Wilkosz Benjamin , Schmidt Johannes , Guenther Christian , Schwarz Philipp , Jeschke Peter , Smythe Caitlin
Published: November 2013

The present work is part of the research project at the Institute of Jet Propulsion and Turbomachinery at the RWTH Aachen University in collaboration with GE Aviation. The subject is the numerical and experimental analysis of two blading strategies used in the diffusion system of an aero engine centrifugal compressor.

The transonic centrifugal compressor investigated contains a close-coupled impeller and passage diffuser [1], followed by a deswirler system. The deswirler redirects the flow towards the combustion chamber, while decreasing swirl and recovering pressure. It is characterized by a high aerodynamic loading, due to a moderate inlet Mach number of 0.35, in combination with a required flow redirection of 70° in circumferential and 135° in meridional direction. For this purpose, two different blading strategies are investigated, both retaining the same meridional flow path and integral chord length. The first design is a tandem configuration with 30 vanes in the first row and 60 vanes in the second row. In principal, this approach benefits from the small wetted surface, the short and thereby stable boundary layers as well as the positive blade interaction due to the close alignment [2]. The second design contains one row of 75 vanes. The higher solidity is needed to compensate for the longer boundary layers. The two deswirlers investigated are compared to a less compact baseline deswirler [3] with simple prismatic vanes.

Experimental and numerical data shows that both new configurations have very similar stage efficiency. The single row design shows a higher static pressure recovery, resulting in a +0.2%-points total-to-static isentropic efficiency increase compared to the tandem design. Detailed flow analysis in the deswirler system shows different characteristics in terms of losses, loss mechanisms and pressure build-up. Due to the required high turning, both designs suffer from flow separation. Nevertheless, the single row design shows its robustness under the impact of 3D flow, whereas the tandem suffers from end-wall induced losses. The results show that the classical mechanisms making a tandem favorable for high flow turning in 2D flow are counteracted by 3D flow mechanisms caused by the spanwise pressure gradient. The low aspect ratio even increases the effect of 3D end-wall mechanisms. These results, combined with a higher manufacturing effort, show that a tandem configuration is not necessarily the superior design for highly 3D flow conditions.
Unsteady Secondary Flow in a Low Pressure Turbine With Integrated 3D Design
Authors: Schrack D. , Schneider C. M. , Fraas M. , Rose M. G. , Staudacher S. , Engel K.
Published: November 2013

The LP turbine research rig “ATRD” allows the study of detailed aerodynamics at low Reynolds numbers. The two-stage LP turbines are designed by MTU Aero Engines GmbH and tested in cooperation with the Institute of Aircraft Propulsion Systems (ILA) at Stuttgart University. This paper focuses on the development of the unsteady secondary flow field in two turbine geometries. The flow structures and vortex behaviour of a turbine with integrated 3D design (I3D) is compared to those of a datum case with axisymmetric endwalls. The unsteady flow and its effect on the time mean flow is analysed with five hole probe area traverse data and multistage URANS CFD calculations. The improvement through design optimisation is assessed by analysing secondary flow features as well as loss generation in the first rotor and the second vane. The RANS and URANS predicted improvements in turbine efficiency agree well with the measurement within wide uncertainty bounds. The structure of the secondary flow field is substantially unaltered by the I3D design, but loss coefficients show row loss reductions. The secondary flow structure of the first rotor is dominated by the first NGV which was not redesigned. Therefore an opportunity exists for further performance improvement with its redesign.
Performance Analysis of a Rotating Labyrinth Seal With Radial Growth
Authors: Subramanian Sivakumar , Sekhar A. S. , Prasad B. V. S. S. S.
Published: November 2013

A computational methodology is proposed to predict the running clearance of a six-tooth straight-through rotating labyrinth seal numerically by taking into account both the centrifugal and thermal growths. Four different angular velocities ranging from 0 to 3000 rad/s are chosen to study the influence of rotation on the leakage flow rate. The detailed leakage flow fields and the structural deformations are presented. Further, different pressure ratios in the range of 1.1 to 2.5 have been investigated for a wide range of initial clearances. The methodology is validated against the available data in the literature. It is found out that there is a significant reduction in leakage flow rate by incorporating the radial growth for a particular operating condition. However, for a given initial clearance, the rotation has negligible effect on the reduction in the leakage flow rate, except at pressure ratios lower than 1.7. Further; the rotation has more prominent effect for smaller clearance values.
Mild Hybridization via Electrification of the Air System: Electrically Assisted and Variable Geometry Turbocharging Impact on an Off-Road Diesel Engine
Authors: Terdich Nicola , Martinez-Botas Ricardo F. , Romagnoli Alessandro , Pesiridis Apostolos
Published: November 2013

Electric turbocharger assistance consists in incorporating an electric motor/generator within the turbocharger bearing housing to form a mild-hybrid system, without altering other mechanical parts of the engine. This makes it an ideal and economical short to medium term solution for the reduction of CO2 emissions.

The scope of the paper is to assess the improvements in engine energy efficiency and transient response correlated to the hybridization of the air system. To achieve this, an electrically assisted turbocharger with a variable geometry turbine has been compared to a similar, not hybridized, system over step changes of engine load. The variable geometry turbine has been controlled to provide different levels of initial boost, including one optimized for efficiency, and to change its flow capacity during the transient. The engine modeled is a 7-litre, 6-cylindres diesel engine with a power output of over 200 kW and a sub-10 kW turbocharger electric assistance power. To improve the accuracy of the model, the turbocharger turbine has been experimentally characterized by means of a unique testing facility available at Imperial College and the data has been extrapolated by means of a turbine meanline model.

Optimization of the engine boost to minimize pumping losses has shown a reduction in brake specific fuel consumption up to 4.2%. By applying electric turbocharger assistance, it has been possible to recover the loss in engine transient response of the efficiency optimized system, as it causes a reduction in engine speed drop of 71% to 86% and of 79% to 94% in engine speed recovery time. When electric assistance is present in the turbocharger, actuating the turbine vanes to assist transient response has not produced the desired result but only a decrement in energy efficiency. If the variable geometry turbine is opened during transients, an improvement in specific energy efficiency with negligible decrement in engine transient performances has been achieved.
Rotating Instability in an Annular Cascade: Detailed Analysis of the Instationary Flow Phenomena
Authors: Pardowitz Benjamin , Tapken Ulf , Sorge Robert , Thamsen Paul Uwe , Enghardt Lars
Published: November 2013

Rotating instability (RI) occurs at off-design conditions in compressors, predominantly in configurations with large tip or hub clearance ratios of s* ≥ 3% [1]. RI is the source of the blade tip vortex noise and a potential indicator for critical operating conditions like rotating stall and surge. The objective of this paper is to give more physical insight into the RI phenomenon using the analysis results of combined near-field measurements with High-Speed PIV and unsteady pressure sensors. The investigation was pursued on an annular cascade with hub clearance. Both the unsteady flow field next to the leading edge as well as the associated rotating pressure waves were captured. A special analysis method illustrates the characteristic pressure wave amplitude distribution, denoted as ‘Modal Events’ of the RI. Moreover, the slightly adapted method reveals the unsteady flow structures corresponding to the RI. Correlations between the flow profile, the dominant vortex structures and the rotating pressure waves were found. Results provide evidence to a new hypothesis, implying that shear layer instabilities constitute the basic mechanism of the RI.
Bacteriophages as Pathogens and Immune Modulators?
Authors: Lengeling A. , Mahajan A. , Gally D. L.
Published: November 2013

While Shiga toxins (Stx) are key determinants of enterohemorrhagic
Escherichia coli
(EHEC) pathophysiology in humans, their dissemination to target organs following gastrointestinal EHEC infection is still poorly understood. Most types of Stx target cells with globotriaosylceramide (Gb3) receptors, which are expressed on endothelial cells. According to current theory, Stx is trafficked on the surface of peripheral blood cells, and transfer of toxin from these trafficking cells to endothelial cells results in microvascular damage to target organs, including the kidneys and brain. Inside the cell, Stx inhibits protein synthesis, resulting in cell death. Host “repair” responses can lead to microthrombus formation, erythrocyte damage, and reduced oxygen supply, potentially resulting in organ failure. A recent study [L. V. Bentancor et al., mBio 4(5):e00501-13, 2013, doi:10.1128/mBio.00501-13] indicates that another mechanism for Stx “dissemination” needs to be considered. Bentancor et al. demonstrated that high-pressure injection of a plasmid encoding the “prokaryotic” Stx2 sequence into mice can lead to mortality, with pathology indicative of Stx activity and antibody responses to Stx. While the plasmid levels and injection methodology were extreme, the study indicates that these sequences are potentially taken up into eukaryotic cells, transcribed, and translated, producing active Stx. Stx genes are present on integrated bacteriophage genomes in EHEC, and Stx-encoding phages are released following bacterial lysis in the gastrointestinal tract. We therefore need to consider whether bacteriophage sequences can be expressed in eukaryotic cells, what the wider implications are for our understanding of many “bacterial” diseases, and the possibility of developing novel interventions that target bacteriophages.
Durable recovery of the macular architecture and functionality of a diagnosed age-related macular degeneration 1 year after a single intravitreal injection of dobesilate
Authors: Cuevas P , Outeiriño L A , Azanza C , Giménez-Gallego G
Published: November 2013

Among the age-related diseases that affect vision, age-related macular degeneration is the most frequent cause of blindness in patients older than 60 years. In this communication, we report the full anatomical and functional recovery of a patient diagnosed with wet age-related macular degeneration 1 year after a single intravitreal injection of dobesilate.
A NOTE ON ACOUSTIC BLACK HOLES IN NEO-NEWTONIAN THEORY
Authors: FABRIS J. C. , PIATTELLA O. F. , VELTEN H. E. S. , SALAKO I. G. , TOSSA J.
Published: November 2013

Newtonian fluid dynamics allows the construction of acoustic metrics from which black hole configurations can be studied. However, relativistic pressure effects are neglected within Newtonian theory. We study acoustic black holes in the framework of neo-Newtonian hydrodynamics, which is designed to take into account relativistic inertial effects of the pressure p. Within this new hydrodynamical context we show how p can influence the formation of the acoustic horizons.