bluuebunny/crossref_metadata_2025 huggingface dataset:
Framing (implicitly) matters: The role of religion in attitudes toward immigrants and Muslims in Denmark
Authors: Anderson Joel , Antalíková Radka
Published: September 2014

Denmark is currently experiencing the highest immigration rate in its modern history. Population surveys indicate that negative public attitudes toward immigrants actually stem from attitudes toward their (perceived) Islamic affiliation. We used a framing paradigm to investigate the explicit and implicit attitudes of Christian and Atheist Danes toward targets framed as Muslims or as immigrants. The results showed that explicit and implicit attitudes were more negative when the target was framed as a Muslim, rather than as an immigrant. Interestingly, implicit attitudes were qualified by the participants’ religion. Specifically, analyses revealed that Christians demonstrated more negative implicit attitudes toward immigrants than Muslims. Conversely, Atheists demonstrated more negative implicit attitudes toward Muslims than Atheists. These results suggest a complex relationship between religion, and implicit and explicit prejudice. Both the religious affiliation of the perceiver and the perceived religious affiliation of the target are key factors in social perception.
High lipid order of Arabidopsis cell‐plate membranes mediated by sterol and DYNAMIN‐RELATED PROTEIN1A function
Authors: Frescatada‐Rosa Márcia , Stanislas Thomas , Backues Steven K. , Reichardt Ilka , Men Shuzhen , Boutté Yohann , Jürgens Gerd , Moritz Thomas , Bednarek Sebastian Y. , Grebe Markus
Published: September 2014

Membranes of eukaryotic cells contain high lipid‐order sterol‐rich domains that are thought to mediate temporal and spatial organization of cellular processes. Sterols are crucial for execution of cytokinesis, the last stage of cell division, in diverse eukaryotes. The cell plate of higher‐plant cells is the membrane structure that separates daughter cells during somatic cytokinesis. Cell‐plate formation in Arabidopsis relies on sterol‐ and DYNAMIN‐RELATED PROTEIN1A (DRP1A)‐dependent endocytosis. However, functional relationships between lipid membrane order or lipid packing and endocytic machinery components during eukaryotic cytokinesis have not been elucidated. Using ratiometric live imaging of lipid order‐sensitive fluorescent probes, we show that the cell plate of Arabidopsis thaliana represents a dynamic, high lipid‐order membrane domain. The cell‐plate lipid order was found to be sensitive to pharmacological and genetic alterations of sterol composition. Sterols co‐localize with DRP1A at the cell plate, and DRP1A accumulates in detergent‐resistant membrane fractions. Modifications of sterol concentration or composition reduce cell‐plate membrane order and affect DRP1A localization. Strikingly, DRP1A function itself is essential for high lipid order at the cell plate. Our findings provide evidence that the cell plate represents a high lipid‐order domain, and pave the way to explore potential feedback between lipid order and function of dynamin‐related proteins during cytokinesis.
Cytosine deaminase as a negative selectable marker for the microalgal chloroplast: a strategy for the isolation of nuclear mutations that affect chloroplast gene expression
Authors: Young Rosanna E. B. , Purton Saul
Published: September 2014

Negative selectable markers are useful tools for forward‐genetic screens aimed at identifying trans‐acting factors that are required for expression of specific genes. Transgenic lines harbouring the marker fused to a gene element, such as a promoter, may be mutagenized to isolate loss‐of‐function mutants able to survive under selection. Such a strategy allows the molecular dissection of factors that are essential for expression of the gene. Expression of individual chloroplast genes in plants and algae typically requires one or more nuclear‐encoded factors that act at the post‐transcriptional level, often through interaction with the 5′ UTR of the mRNA. To study such nuclear control further, we have developed the Escherichia coli cytosine deaminase gene codA as a conditional negative selectable marker for use in the model green alga Chlamydomonas reinhardtii. We show that a codon‐optimized variant of codA with three amino acid substitutions confers sensitivity to 5‐fluorocytosine (5‐FC) when expressed in the chloroplast under the control of endogenous promoter/5′ UTR elements from the photosynthetic genes psaA or petA. UV mutagenesis of the psaA transgenic line allowed recovery of 5‐FC‐resistant, photosynthetically deficient lines harbouring mutations in the nuclear gene for the factor TAA1 that is required for psaA translation. Similarly, the petA line was used to isolate mutants of the petA mRNA stability factor MCA1 and the translation factor TCA1. The codA marker may be used to identify critical residues in known nuclear factors and to aid the discovery of additional factors required for expression of chloroplast genes.
Large Scale Validation of a Flexible Multibody Wind Turbine Gearbox Model
Authors: Vanhollebeke Frederik , Peeters Pepijn , Helsen Jan , Di Lorenzo Emilio , Manzato Simone , Peeters Joris , Vandepitte Dirk , Desmet Wim
Published: September 2014

Although wind turbine noise is mainly dominated by aero-acoustic noise, mechanical noise, coming from gearbox or generator, could—especially when it contains audible tonal components—result in nonconformity to local noise regulations. To reduce the mechanical noise from the gearbox, focus is put on first time right design. To achieve this, simulation models are being used earlier in the design process to predict possible issues. This paper starts with a short overview of the used model and gives additional insight in how forces from planetary gear stages should be introduced in the flexible housing. Main focus of this paper however is the approach that is being used to validate such a complex multibody model of a wind turbine gearbox. The validation approach consists of five levels: (1) individual components, (2) assembly of the empty gearbox housing, (3) the assembled gearbox, (4) the gearbox on the end-of-line (EOL) test rig, and (5) the gearbox in the wind turbine. This paper focuses on the experimental measurement results, the correlation approach for such complex models, and the results of this correlation for the first four levels showing the usability of these models to accurately predict the modal behavior.
A Numerical Study on the Influence of Hole Depth on the Static and Dynamic Performance of Hole-Pattern Seals
Authors: Migliorini Patrick J. , Untaroiu Alexandrina , Wood Houston G.
Published: September 2014

Annular seals serve an important role in the dynamics of turbomachinery by reducing leakage of a process fluid while also contributing potentially destabilizing forces to the rotor system. Hole-pattern seals have been the focus of many investigations, but recent experimental studies have shown that there are still many phenomena that require exploration. One such phenomenon is the influence of hole depth on the static and dynamic characteristics of the seal. In this paper, a hybrid computational fluid dynamics (CFD)/bulk-flow method is employed to investigate the nonmonotonic relationship between hole depth and leakage shown in experimental measurements of a hole-pattern seal by Childs et al. (2014, “The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals,” ASME J. Eng. Gas Turbines Power, 136(4), p. 042501). Three hole depths (1.905 mm, 3.302 mm, and 6.604 mm) and three running speeds (10,200 rpm, 15,350 rpm, and 20,200 rpm) are considered. For the steady-state flow, the 3D Reynolds-Averaged-Navier-Stokes (RANS) equations are solved with the k-ϵ turbulence model for a circumferentially periodic sector of the full seal geometry. The steady-state results are input into the first-order equations of a bulk-flow model to predict rotordynamic coefficients. Results of the hybrid method are compared to experimental data. CFD predicted leakage showed good agreement (within 5%) for the 3.302 mm and 6.604 mm hole depth configurations. For the 1.905 mm hole depth seal, agreement was within 17%. An additional set of calculations performed with the shear stress transport (SST) turbulence model produced worse agreement. Examination of streamlines along the seal show that the hole depth controls the shape of the vortex that forms in the hole, driving the resistance experienced by the jet flow in the clearance region. For the rotordynamic coefficients, good agreement is shown between predictions and experiment for most excitation frequencies.
Construction of Pump-Turbine Characteristics at Any Specific Speed by Domain-Partitioned Transformation
Authors: Zeng Wei , Yang Jiandong , Cheng Yongguang
Published: September 2014

Pump-turbine characteristics are important for designing pumped-storage plants and indispensable for simulating hydraulic transients, but are often not available in the preliminary design stage. Therefore, constructing a set of pump-turbine characteristics is necessary, when no suitable characteristics at the same specific speed can be used for substitution. In this paper, we propose a new method for pump-turbine characterization at any specific speed using a database of 25 available sets of pump-turbine characteristics. The intersecting curves, defined by the intersections of the characteristic curves with a coordinate axis, are formularized to prepare for the characterization primarily. Next is an introduction of a transformation method for characteristic curves base on domain partition, through which the curves are transformed into eight characteristic surface meshes in eight separate domains. Then, we present the construction procedures in each domain, which include merging the transformed surface meshes for all the sets of collected characteristic curves into a cube mesh, constructing a super surface by interpolation to construct the regular characteristic surface meshes for an arbitrary specific speed, and transforming the constructed meshes reversely to get the conventional characteristic curves. This method is verified by comparing them to measured characteristic curves with reasonable accuracies.
Computational Flow Analysis of Wind Farms Using a Simplified Rotor Disc Model With Radially Varying Thrust Coefficient
Authors: Vafiadis K. , Stergiannis N. , Tourlidakis A.
Published: September 2014

Large scale horizontal axis wind turbines are one of the most promising renewable energy technologies. When they are installed in wind farms (onshore and offshore) they can exploit the most of the available wind energy of a site. The accurate calculation of their aerodynamic interaction due to the wake development is crucial for the design of the layout and the operation of a wind farm. Simulating a wind farm with more than one fully detailed wind turbines and possibly complex terrain geometry requires significant computational power and time. Therefore, the turbine rotors are approximated as discs which behave as momentum sinks. This approach has been adopted in the present study which focuses on the development of a simplified rotor disc model. However, in the present contribution, in order to approximate the axial thrust across the disc in a more accurate manner, a novel model that involves a radially varying thrust coefficient is utilized which is extracted from the CFD full rotor transient analysis results. The analysis is carried out with the use of two commercial CFD codes, ANSYS CFX and ANSYS Fluent for the full rotor and the simplified model, respectively. For the development of the radial distribution of thrust along the blades, both steady and transient computations are carried out and the results are compared against available experimental data. For the full rotor simulation the time-averaged transient results are compared against the steady ones and with the results of the actuator disc approach. Two different turbulence models, k-epsilon and Shear Stress Transport, were used along with the three dimensional RANS equations. The detailed assessment of the differences in the flow field as it is obtained from the steady and transient analysis of both full rotor and actuator disc approximations indicated that a good agreement exists between the two distributions and the existing differences are identified and quantified.
Steady State Detection in Industrial Gas Turbines for Condition Monitoring and Diagnostics Applications
Authors: Celis Cesar , Xavier Érica , Teixeira Tairo , Pinto Gustavo R. S.
Published: September 2014

This work describes the development and implementation of a signal analysis module which allows the reliable detection of operating regimes in industrial gas turbines. Its use is intended for steady state-based condition monitoring and diagnostics systems. This type of systems requires the determination of the operating regime of the equipment, in this particular case, of the industrial gas turbine. After a brief introduction the context in which the signal analysis module is developed is highlighted. Next the state of the art of the different methodologies used for steady state detection in equipment is summarized. A detailed description of the signal analysis module developed, including its different sub systems and the main hypotheses considered during its development, is shown to follow. Finally the main results obtained through the use of the module developed are presented and discussed. The results obtained emphasize the adequacy of this type of procedures for the determination of operating regimes in industrial gas turbines.
Transient Operation in Pipeline Compressor Stations
Authors: Kurz Rainer , White Robert C. , Brun Klaus
Published: September 2014

Many pipelines are not operated under steady state conditions. This is in particular true for pipelines that are highly integrated with other pipelines, or have many different feed or gas take-off points. In many cases, the demand changes frequently, and cannot always be planned with a long time horizon.

In this study, a simplified transient pipeline model, together with a high fidelity model of a compressor installation and its control system are used to evaluate control strategies that can optimize the fuel consumption and reaction time in these transient situations. The model for the compressor installation contains an accurate representation of the compressor and driver performance, together with the capability to simulate different, but realistic control strategies.

This allows specific and general recommendations on the use of control algorithms.
Influence of Alloy Behavior on Multiaxial Fatigue Lifing Criteria for Turbine Disk Bores
Authors: Greving D. J. , Kantzos P. T. , Menon M. N.
Published: September 2014

In a previous paper, a criterion for multiaxial lifing of turbine disk bores made from a nickel base super alloy, DP-718, was substantiated using results from spin pit testing of mini disks. In this paper, another turbine and compressor disk alloy, Alloy 10, exhibiting a different material behavior than DP-718 is examined from multiaxial point of view. This new alloy manufactured by powder metallurgy processing, has a coarser grain size, lower tensile yield strength, contains a much finer distribution of brittle carbides in its microstructure and shows a significant difference in failure initiation behavior under low cycle fatigue when compared to DP-718. Under the multiaxiality conditions experienced by disk bores, Alloy-10 lives seem to correlate well using an effective stress based criterion, whereas DP-718 was found to follow principal stress based criterion. Interesting differences between DP-718 and Alloy-10 in alloy and fractographic behavior under uniaxial and multiaxial conditions are discussed.
The Effect of an Eroded Leading Edge on the Aerodynamic Performance of a Transonic Fan Blade Cascade
Authors: Hergt A. , Klinner J. , Steinert W. , Grund S. , Beversdorff M. , Giebmanns A. , Schnell R.
Published: September 2014

Especially at transonic flow conditions the leading edge shape influences the performance of a fan profile. At the same time the leading edge of a fan profile is highly affected by erosion during operation. This erosion leads to a deformation of the leading edge shape and a reduction of the chord length. In the present experimental and numerical study, the aerodynamic perfomance of an original fan profile geometry is compared to an eroded fan profile with a blunt leading edge and a chord length reduced by about 1 percent. The experiments are performed at a linear fan blade cascade in the Transonic Cascade Wind Tunnel of DLR in Cologne. The inflow Mach number during the tests is 1.25 and the Reynolds number 1.5 × 106. All tests are carried out at a low inflow turbulence level of 0.8 percent. The results of the investigation show that losses are increased over the whole operating range of the cascade. At the aerodynamic design point the losses raise by 25 percent. This significant loss increase can be traced back to the increase of the shock losses at the leading edge. The change in shock structure is investigated and described in detail by means of PIV measurements and Schlieren imaging. Additionally, the unsteady fluctuation of the shock position is measured by a high speed shadowgraphy. Then the frequency range of the fluctuation is obtained by a Fourier analysis of the time resolved shock position. Furthermore, liquid crystal measurements are performed in order to analyze the influence of the leading edge shape on the development of the suction side boundary layer. The results show that for the original fan blade the transition occurs at the shock position on the blade suction side by a separation bubble whereas the transition onset is shifted upstream for the fan blade with the blunt leading edge.
Film Cooling and Shock Interaction: An Uncertainty Quantification Analysis With Transonic Flows
Authors: Carnevale Mauro , D’Ammaro Antonio , Montomoli Francesco , Salvadori Simone
Published: September 2014

This work shows an Uncertainty Quantification (UQ) study of film cooling with shock impingement. A numerical method is proposed to use high order polynomials for the reconstruction of the stochastic output, without the instabilities characteristic of UQ with shock dominated flows. At the same time it is shown that the region with highest uncertainty is driven by a complex flow physics involving shock–boundary layer interaction and the generation of tornado vortices that merge with kidney ones.

High-pressure turbine stages are characterized by transonic conditions with the suction side of the nozzle affected by the shock shed by the trailing edge of the adjacent aerofoil. Due to manufacturing deviations and in service degradation the geometrical parameters, such as trailing edge thickness and hole diameter, are subjected to random variations, changing the shock location and the heat transfer loading on the stator nozzle. For these reasons an UQ methodology has been used in this study to model the interaction between the impinging shock and film cooling. The variability of the geometrical parameters has been represented with uniform probability distributions and the stochastic output is obtained using Probabilistic Collocation Method with Padè’s polynomials. Transonic flows are challenging in Uncertainty Quantification because a better reconstruction of the stochastic output can be achieved increasing the order of polynomials but higher order polynomials become unstable for the Runge’s phenomenon. This work proposes a method that allows the application of high order Padè’s polynomial without having instabilities in the stochastic output. The proposed methodology can be applied to other transonic configurations in gas turbines, requiring only a limited number of simulations to reconstruct the stochastic output. The results show that the maximum level of uncertainty is located downstream the region of interaction between shock and boundary layer. In particular the shock generates complex flow structures that develop into tornado vortices, highly dependent on the uncertainty input.
Effects of Wet Compression on the Flow Behavior of a Centrifugal Compressor: A CFD Analysis
Authors: Surendran Anish , Kim Heuy Dong
Published: September 2014

Wet compression has been emerging as a prominent method for augmenting net power output from land based gas turbine engine. It is proven more effective than the conventional inlet cooling methods. In this method, fine water droplets are injected just upstream of the compressor impeller. These water droplets absorb the latent heat of evaporation during the compression process of gas-water droplet two-phase flow, consequently reducing the temperature rise. Many gas turbine engineers have performed the feasibility and usefulness studies on this wet compression, but physical understanding on the wet compression process is highly lacking, and related compression flow mechanism remains ambiguous. In the present study, a computational fluid dynamics method has been applied to investigate the wet compression effects on a low speed centrifugal compressor. A Langrangian particle tracking method was employed to simulate the air-water droplet two-phase flow. The power saving achieved with different injection ratio of water droplets has been calculated and it is found that significant saving can be obtained with a water droplet injection ratio of above 3%. The vapor mass fraction varies linearly along the streamwise direction, making the assumption for a constant evaporation rate is valid. With the increase in the injection ratio the polytropic index for compression is coming down. The diffuser pressure recovery has been improved significantly with the wet compression; while the total pressure ratio across the impeller does not improve much. Contrary to the expectation, the evaporation rate is found to be coming down with the increase in the compressor mass flow rate. It is observed that the operating point, at which the peak pressure ratio occurs, shift towards higher mass flow rate during wet compression due to the local recirculation region within the vaneless space between the impeller and diffuser.
Tip Gap Variation on a Transonic Rotor in the Presence of Tip Blowing
Authors: Guinet Cyril , Streit J. Anton , Kau Hans-Peter , Gümmer Volker
Published: September 2014

High stability and efficiency are the main two objectives in the design of an axial-flow compressor. Stability usually reduces at higher stage loading, and the stability margin critically drops in transient operation and through the life cycle of an engine. A major reason for this to happen is the growing tip gap. A recirculating tip blowing casing treatment has shown the ability to enhance stability. To be able to use it as a stability control system at varying tip clearances in aircraft engines, the behavior of this casing treatment at different tip clearances was considered important and investigated in this paper.

The present study investigates in depth the ability of a tip blowing casing treatment to postpone stall at three different tip clearances. The results prove a substantial beneficial effect for design and increased tip gaps and show some negative impact of the casing treatment for a small tip gap. The study is carried out on a 1.5 stage research compressor. The investigated rotor was already investigated with an axial-slot casing treatment for different tip gap heights at the Institute for Flight Propulsion. The design of a recirculating tip blowing casing treatment is simulated with an equivalent numerical setup. A tip blowing casing treatment consists of a bleed port connected to a tip blowing upstream of the rotor. The streamwise pressure gradient drives the tip blowing with a high injection velocity.

A design speed line is simulated for three tip clearance values with and without the tip blowing casing treatment. The impact of the interaction between the tip blowing and the tip gap vortex is analyzed. A detailed analysis of the passage flow is conducted. A comparison of the stall margin is made. The study is carried out using URANS simulations.
Modeling and Simulation of the Start-Up Operation of a Heavy-Duty Gas Turbine by Using NARX Models
Authors: Asgari Hamid , Chen XiaoQi , Sainudiin Raazesh , Morini Mirko , Pinelli Michele , Spina Pier Ruggero , Venturini Mauro
Published: September 2014

In this study, nonlinear autoregressive exogenous (NARX) models of a heavy-duty single-shaft gas turbine (GT) are developed and validated. The GT is a power plant gas turbine (General Electric PG 9351FA) located in Italy.

The data used for model development are three time series data sets of two different maneuvers taken experimentally during the start-up procedure. The resulting NARX models are applied to three other experimental data sets and comparisons are made among four significant outputs of the models and the corresponding measured data.

The results show that NARX models are capable of satisfactory prediction of the GT behavior and can capture system dynamics during start-up operation.
Combustion and Oxidation Kinetics of Alternative Gas Turbines Fuels
Authors: Glaude Pierre-Alexandre , Sirjean Baptiste , Fournet René , Bounaceur Roda , Vierling Matthieu , Montagne Pierre , Molière Michel
Published: September 2014

Heavy duty gas turbines are very flexible combustion tools that accommodate a wide variety of gaseous and liquid fuels ranging from natural gas to heavy oils, including syngas, LPG, petrochemical streams (propene, butane…), hydrogen-rich refinery by-products; naphtha; ethanol, biodiesel, aromatic gasoline and gasoil, etc. The contemporaneous quest for an increasing panel of primary energies leads manufacturers and operators to explore an ever larger segment of unconventional power generation fuels. In this moving context, there is a need to fully characterize the combustion features of these novel fuels in the specific pressure, temperature and equivalence ratio conditions of gas turbine combustors using e.g. methane as reference molecule and to cover the safety aspects of their utilization.

A numerical investigation of the combustion of a representative cluster of alternative fuels has been performed in the gas phase, namely two natural gas fuels of different compositions, including some ethane, a process gas with a high content of butene, oxygenated compounds including methanol, ethanol, and DME (dimethyl ether). Sub-mechanisms have specifically been developed to include the reactions of C4 species. Major combustion parameters, such as auto-ignition temperature (AIT), ignition delay times (AID), laminar burning velocities of premixed flames, adiabatic flame temperatures, and CO and NOx emissions have then been investigated. Finally, the data have been compared with those calculated for methane flames.

These simulations show that the behaviors of alternative fuels markedly differ from that of conventional ones. Especially, DME and the process gases appear to be highly reactive with significant impacts on the auto-ignition temperature and flame speed data, which justifies burner design studies within premixed combustion schemes and proper safety considerations. The behaviors of alcohols (especially methanol) display some commonalities with those of conventional fuels. In contrast, DME and process gas fuels develop substantially different flame temperature and NOx generation rates than methane. Resorting to lean premix conditions is likely to achieve lower NOx emission performances. This review of gas turbine fuels shows for instance that the use of methanol as a gas turbine fuel is possible with very limited combustor modifications.
Dry-Cooled Supercritical CO2 Power for Advanced Nuclear Reactors
Authors: Conboy T. M. , Carlson M. D. , Rochau G. E.
Published: September 2014

Currently, waste heat rejection from electrical power systems accounts for the largest fraction of water withdrawals from the US fresh water table. Siting of nuclear power plants is limited to areas with access to a large natural supply of fresh or sea water. Due to a rise in energy needs and increased concern over environmental impact, dry air cooling systems are poised to play a large role in the future energy economy. In practice, the implementation of dry air-cooled condensing systems at steam plants has proven to be capital-intensive and requires the power cycle to take a significant efficiency penalty. These shortcomings are fundamental to dry-air steam condensation, which must occur at a fixed temperature. Closed-cycle gas turbines are an alternative to the conventional steam Rankine plant that allow for much improved dry heat rejection compatibility. Recent research into advanced nuclear energy systems has identified the supercritical CO2 (s-CO2) Brayton cycle in particular as a viable candidate for many proposed reactor types. The s-CO2 Brayton cycle can maintain superior thermal efficiency over a wide range of ambient temperatures, making these power systems ideally suited for dry air cooling, even in warm climates. For an SFR operating at 550°C, thermal efficiency is calculated to be 43% with a 50°C compressor inlet temperature. This is achieved by raising CO2 compressor inlet pressure in response to rising ambient temperatures. Preliminary design studies have shown that s-CO2 power cycle hardware will be compact and therefore well-matched to near-term and advanced integral SMR designs. These advantages also extend to the cooling plant, where it is estimated that dry cooling towers for an SFR-coupled s-CO2 power cycle will be similar in cost and scale to the evaporative cooling tower for an LWR. The projected benefits of the s-CO2 power cycle coupled to dry air heat rejection may enable the long-awaited rise of next-generation nuclear energy systems, while re-drawing the map for siting of small and large nuclear energy systems.
Efficient Uncertainty Quantification of Centrifugal Compressor Performance Using Polynomial Chaos
Authors: Panizza Andrea , Rubino Dante Tommaso , Tapinassi Libero
Published: September 2014

This paper presents a fully automated procedure to estimate the uncertainty of compressor stage performance, due to impeller manufacturing variability. The methodology was originally developed for 2D stages, i.e., stages for which the impeller blade angle and thickness distribution are only defined at the hub end-wall. Here, we extend the procedure to general 3D stages, for which blade angle and thickness distributions can be prescribed independently at the shroud and hub endwalls. Starting from the probability distribution of the impeller geometrical parameters, 3D sample geometries are generated and 1D/2D aerodynamic models are created, which are used to predict the performance of each sample geometry. The original procedure used the Monte Carlo method to propagate uncertainty. However, this requires a large number of samples to compute accurate performance statistics. Here we compare the results from Monte Carlo, with those obtained using Sparse Grid Polynomial Chaos Expansion (PCE) and a Multidimensional Cubature Rule for uncertainty propagation. PCE has exponential convergence in the stochastic space for smooth functions, and the use of sparse grids mitigates the increase of sample points due to the increase in the number of uncertain parameters. The cubature rule has accuracy limitations, but sample points increase only linearly with the number of parameters. For a 3D stage, the probability distributions of the performance characteristics are computed, as well as the sensitivity to the design parameters. The results show that PCE and Multidimensional Cubature give similar results to MC computations, with a much lower computational effort.
Faults Diagnosis in Rotating Machines Using Higher Order Spectra
Authors: Yunusa-Kaltungo Akilu , Sinha Jyoti K.
Published: September 2014

Higher order spectra (HOS) and higher order coherences (HOC) are two classes of higher order signal processing tools that have gained recent attention in the area of rotating machines’ condition monitoring (CM). Hence, the current study compares and presents the results of the performances of both HOS and HOC in the diagnosis of rotating machines’ faults, through the numerically simulated vibration signals and the experimentally measured vibration response on a rotating rig with healthy condition and the rotor with a transverse crack.
An Experimental Study of Heat Transfer on an Outlet Guide Vane
Authors: Wang Chenglong , Wang Lei , Sundén Bengt , Chernoray Valery , Abrahamsson Hans
Published: September 2014

In the present study, the heat transfer characteristics on the suction and pressure sides of an outlet guide vane (OGV) are investigated by using liquid crystal thermography (LCT) method in a linear cascade. Because the OGV has a complex curved surface, it is necessary to calibrate the LCT by taking into account the effect of viewing angles of the camera. Based on the calibration results, heat transfer measurements of the OGV were conducted. Both on- and off-design conditions were tested, where the incidence angles of the OGV were 25 degrees and −25 degrees, respectively. The Reynolds numbers, based on the axial flow velocity and the chord length, were 300,000 and 450,000. In addition, heat transfer on suction side of the OGV with +40 degrees incidence angle was measured. The results indicate that the Reynolds number and incidence angle have considerable influences upon the heat transfer on both pressure and suction surfaces. For on-design conditions, laminar-turbulent boundary layer transitions are on both sides, but no flow separation occurs; on the contrary, for off-design conditions, the position of laminar-turbulent boundary layer transition is significantly displaced downstream on the suction surface, and a separation occurs from the leading edge on the pressure surface. As expected, larger Reynolds number gives higher heat transfer coefficients on both sides of the OGV.
Performance Investigation Into Supersonic Diffuser for a High Pressure Centrifugal Compressor
Authors: Sugimoto Takao , Kawanishi Tsukinami , Kumamaru Hiroshige , Tohbe Yasumasa
Published: September 2014

In high pressure centrifugal compressors, the overall stage performance is greatly influenced by its diffuser performance. Extremely complicated non-uniform and unsteady flow exists in the region between the impeller exit and the diffuser inlet. Furthermore, in the case of supersonic diffuser, shock waves can be observed near the diffuser inlet. These can cause aerodynamic losses. Therefore, it is essential to recognize such complicated flow to realize an appropriate diffuser design.

An investigation into the performance of supersonic diffuser was carried out using a high pressure compressor test rig for a small industrial gas turbine with a high back swept impeller and a quasi pipe-shaped channel diffuser.

In addition, 3D quasi-unsteady flow analyses of the entire compressor by a RANS code with Non Linear Harmonic method at several operating conditions between surge and choke were conducted to investigate the details of unsteady flow between the impeller exit and the diffuser exit.

The results of the performance test and that of the 3D unsteady flow analyses have shown good agreement in the pressure rise and the isentropic efficiency at several operating conditions. These support high accuracy of the flow analyses and the performance measurements.
Secondary Flows, Endwall Effects and Stall Detection in Axial Compressor Design
Authors: Banjac Milan , Petrovic Milan V. , Wiedermann Alexander
Published: September 2014

This paper describes a methodology and a fully tested and calibrated mathematical model for the treatment of endwall effects in axial compressor aerodynamic calculations. Additional losses and deviations caused by the clearance and secondary flows are analyzed. These effects are coupled with endwall boundary layer losses and blockage development. Stall/surge detection is included and mutual interaction of different loss mechanisms is considered.

Individual mathematical correlations for different effects have been created or adopted from earlier papers with the aim of forming one integral model that is completely described in this paper. Separate mathematical correlations and calibration measures are discussed in detail in the first part of the paper.

The developed overall model is suitable for application in two-dimensional or mean-line compressor flow calculations. During the development, it was tested, calibrated and validated using throughflow calculations comparing numerical results with experimental data for a large number of test cases. These test cases include compressors with very different configurations and operating ranges. The data on the compressors were taken from the open literature or obtained from industrial partners.
Corrosion and Erosion Behavior in Supercritical CO2 Power Cycles
Authors: Fleming Darryn , Kruizenga Alan , Pasch James , Conboy Tom , Carlson Matt
Published: September 2014

Supercritical Carbon Dioxide (S-CO2) is emerging as a potential working fluid in power-production Brayton cycles. As a result, concerns have been raised regarding fluid purity within the power cycle loops. Additionally, investigations into the longevity of the S-CO2 power cycle materials are being conducted to quantify the advantages of using S-CO2 versus other fluids, since S-CO2 promises substantially higher efficiencies. One potential issue with S-CO2 systems is intergranular corrosion [1]. At this time, Sandia National Laboratories (SNL) is establishing a materials baseline through the analysis of 1) “as received” stainless steel piping, and 2) piping exposed to S-CO2 under typical operating conditions with SNL’s Brayton systems. Results from ongoing investigations are presented.

A second issue that SNL has discovered involves substantial erosion in the turbine blade and inlet nozzle. It is believed that this is caused by small particulates that originate from different materials around the loop that are entrained by the S-CO2 to the nozzle, where they impact the inlet nozzle vanes, causing erosion. We believe that, in some way, this is linked to the purity of the S-CO2, the corrosion contaminants, and the metal particulates that are present in the loop and its components.
A Design Strategy for Supercritical CO2 Compressors
Authors: Monje B. , Sánchez D. , Savill M. , Pilidis P. , Sánchez T.
Published: September 2014

The international scientific community researching the supercritical carbon dioxide power cycle has already developed the first turbomachinery designs, which are currently operating in reference laboratories worldwide. Nevertheless, the performance of this equipment is still quite far from the target values yielding fairly disappointing system efficiencies (65% vs. 80% total to total efficiency for radial compressors). In the light of these past results, the thermal Power Group (GMTS) at the University of Seville, Spain, has been researching the SCO2 cycle during the last few years. Hence, after researching elementary diffusion processes and some basic features of the system, the authors are now in the process of developing guidelines for compressor design based on one-dimensional codes developed in-house and CFD analysis. The results stemming from both approaches are presented in this paper showing that the rather simple 1D model is able to produce a fairly good model which can then be tuned with a more complex and computationally expensive 3D CFD code. The entire approach is presented in this paper, from the initial reference value for the key design parameters through the 1D code and to the multi-dimensional tool. The results of the two latter approaches are compared in detail in this paper.
Performance Improvement of Multistage Centrifugal Compressor With Low Flow-Rate Stages Based on Factory Acceptance Test Data
Authors: Tamaki Hideaki , Kawakubo Tomoki , Unno Masaru , Abe Shinji , Majima Kanji
Published: September 2014

This study reports on the process of performance improvement in a six-stage compressor which encountered rotor vibration near its design flow rate during a factory acceptance test. This multistage compressor comprised three blocks, each of which also included a two-stage compressor. Flow instability in the 2nd or 3rd block, i.e. any of the 3rd to 6th stages, was suspected as the cause of the rotor vibration. This paper shows the process used to determine a modification plan to enhance the stable operating range; based on data obtained by a factory acceptance test.

The performance of each block was measured in that test, but not that of each stage. Improving the compressor performance therefore requires a new database, which represents the stage characteristics as operated during the factory acceptance test. A new database was thus constructed using a 1-D performance prediction method, the loss models of which were tuned to reproduce each block performance obtained by the factory acceptance test. Subsequently, stage-stacking calculations were conducted based on this database and modification plans devised, while single-stage tests for the 3rd and 6th stages were also conducted in a test stand to make a final decision on modification. This paper reports on both these results and data-reduction procedures.
Numerical Investigation of the Impact of Part-Span Connectors on Aero-Thermodynamics in a Low Pressure Industrial Steam Turbine
Authors: Häfele M. , Starzmann J. , Grübel M. , Schatz M. , Vogt D. M. , Drozdowski R. , Völker L.
Published: September 2014

A numerical study on the flow in a three stage low pressure industrial steam turbine with conical friction bolts in the last stage and lacing wires in the penultimate stage is presented and analyzed. Structured high-resolution hexahedral meshes are used for all three stages and the meshing methodology is shown for the rotor with friction bolts and blade reinforcements. Modern three-dimensional CFD with a non-equilibrium wet steam model is used to examine the aero-thermodynamic effects of the part-span connectors. A performance assessment of the coupled blades at part load, design and overload condition is presented and compared with measurement data from an industrial steam turbine test rig. Detailed flow field analyses and a comparison of blade loading between configurations with and without part-span connectors are presented in this paper. The results show significant interaction of the cross flow vortex along the part-span connector with the blade passage flow causing aerodynamic losses. This is the first time that part-span connectors are being analyzed using a non-equilibrium wet steam model. It is shown that additional wetness losses are induced by these elements.
On the Potential of a Multi-Fidelity G-POD Based Approach for Optimization and Uncertainty Quantification
Authors: Toal David J. J.
Published: September 2014

Traditional multi-fidelity surrogate models require that the output of the low fidelity model be reasonably well correlated with the high fidelity model and will only predict scalar responses. The following paper explores the potential of a novel multi-fidelity surrogate modelling scheme employing Gappy Proper Orthogonal Decomposition (G-POD) which is demonstrated to accurately predict the response of the entire computational domain thus improving optimization and uncertainty quantification performance over both traditional single and multi-fidelity surrogate modelling schemes.
Experimental Investigation on Lean Blow Out of a Piloted Aero-Engine Burner
Authors: Bhagwan R. , Wollgarten J. C. , Habisreuther P. , Zarzalis N.
Published: September 2014

One of the preferred ways to reduce NOX formation in an aero-engine is to operate lean throughout the whole operational range; however the lean combustion suffers from poor stability. To avoid the problem associated with stability, often a rich pilot flame is used along with a main flame to act as a source of heat and radicals to the main flame. The focus of the paper is to discuss the influence of the liquid fuel spray characteristics and effect of flow parameters on the lean blow out (LBO) limits of a piloted burner. In order to understand the observed remarkable LBO limits of the pilot flame with Jet A-1 (LBO = 145 kg-air to kg-fuel at 0.1 MPa of combustor pressure), velocity field measurements by laser Doppler Anemometry (LDA) technique have been performed. Furthermore, the flame structure has been analyzed with OH* chemiluminescence imaging. Experimental results show that the LBO limits of the burner running with liquid fuel further improves with an increase in combustor pressure. Such improvement in LBO limits is attributed to the change in the liquid fuel distribution caused by the change in the combustor pressure. For gaseous fuel measurements, results indicate that the equivalence ratio and the momentum ratio of the pilot jet to the co-annular flow are the dominating parameters that control the mixing process in the combustor and the ensuing effect on the flame structure and location of flame stabilization is substantial. The flame stabilizes either along the centreline or along the shear layer between two jets. Such information is useful in designing a lean partially premixed combustion system where a pilot flame is required to stabilize a main lean flame.
S2 Surface Quasi-3D Aerodynamic Design Using the Continuous Adjoint Method for Multi-Stage Turbine
Authors: Chen Lei , Chen Jiang
Published: September 2014

The adjoint method eliminates the dependence of the gradient of the objective function with respect to design variables on the flow field making the obtainment of the gradient both accurate and fast. For this reason, the adjoint method has become the focus of attention in recent years. This paper develops a continuous adjoint formulation for through-flow aerodynamic shape design in a multi-stage gas turbine environment based on a S2 surface quasi-3D problem governed by the Euler equations with source terms. Given the general expression of the objective function calculated via a boundary integral, the adjoint equations and their boundary conditions are derived in detail by introducing adjoint variable vectors. As a result, the final expression of the objective function gradient only includes the terms pertinent to those physical shape variations that are calculated by metric variations. The adjoint system is solved numerically by a finite-difference method with explicit Euler time-marching scheme and a Jameson spatial scheme which employs first and third order dissipative flux. Integrating the blade stagger angles and passage perturbation parameterization with the simple steepest decent method, a gradient-based aerodynamic shape design system is constructed. Finally, the application of the adjoint method is validated through a 5-stage turbine blade and passage optimization with an objective function of entropy generation. The result demonstrates that the gradient-based system can be used for turbine aerodynamic design.
Improvement of Efficiency by Design Optimization of a Centrifugal Pump Impeller
Authors: Bellary Sayed Ahmed Imran , Samad Abdus
Published: September 2014

Shape optimization of centrifugal impeller blades has been performed through numerical analysis and implementation of multiple surrogate based optimization methodology. Design variables which are used to define blade angles at leading and trailing edges were introduced to increase the hydraulic efficiency of the impeller. The efficiency was selected as an object function and the optimization was performed using a surrogate base optimization methods. A three-dimensional simulation using Reynolds-averaged Navier Stokes equations for the performance analysis was carried out after designing the geometries of the impellers at the design points selected from the design space which was defined by the lower and upper limits of the variables. Throughout the shape optimization, the hydraulic efficiency was increased by decreasing losses near the blade surfaces and impeller passage. Among different surrogates, a weighted average model produced better results. The application of the multiple surrogate methods not only improved quality of single objective optimization but also gives the feedback of the fidelity of the optimization models.