bluuebunny/crossref_metadata_2025 huggingface dataset:
P–T–t evolution of garnet amphibolites in the Wutai–Hengshan area, North China Craton: insights from phase equilibria and geochronology
Authors: Qian J. H. , Wei C. J.
Published: February 2016

Garnet amphibolites can provide valuable insights into geological processes of orogenic belts, but their metamorphic evolution is still poorly constrained. Garnet amphibolites from the Wutai–Hengshan area of the North China Craton mainly consist of garnet, hornblende, plagioclase, quartz, rutile and ilmenite, with or without titanite and epidote. Four samples selected in a south–north profile were studied by the pseudosection approach in order to elucidate the characteristics of their metamorphic evolution, and to better reveal the northwards prograde change in P–T conditions as established previously. For the sample from the lower Wutai Subgroup, garnet exhibits obvious two‐substage growth zoning characteristic of pyrope (Xpy) increasing but grossular (Xgr) decreasing outwards in the core, and both Xpy and Xgr increasing outwards in the rim. Phase modelling using thermocalc suggests that the garnet cores were formed by chlorite breakdown over 7–9 kbar at 530–600 °C, and rims grew from hornblende and epidote breakdown over 9.5–11.5 kbar at 600–670 °C. The isopleths of the minimum An in plagioclase and maximum Xpy in garnet were used to constrain the peak P–T conditions of ~11.5 kbar/670 °C. The modelled peak assemblage garnet + hornblende + epidote+ plagioclase + rutile + quartz matches well the observed one. Plagioclase–hornblende coronae around garnet indicate post‐peak decompression and fluid ingress. For the samples from the south Hengshan Complex, the garnet zoning weaken gradually, reflecting modifications during decompression of the rocks. Using the same approach, the rocks are inferred to have suprasolidus peak conditions, increasing northwards from 11.5 kbar/745 °C, 12.5 kbar/780 °C to 13 kbar/800 °C. Their modelled peak assemblages involve diopside, garnet, hornblende, plagioclase, rutile and quartz, yet diopside is not observed petrographically. The post‐peak decompression is characterized by diopside + garnet + quartz + melt = hornblende + plagioclase, causing the diopside consumption and garnet compositions to be largely modified. Thus, the pesudosection approach is expected to provide better pressure results than conventional thermobarometry, because the later approach cannot be applied with confidence to rocks with multi‐generation assemblages. U–Pb dating of zircon in the Wutai sample records a protolith age of c. 2.50 Ga, and a metamorphic age of c. 1.95 Ga, while zircon in the Hengshan samples records metamorphic ages of c. 1.92 Ga. The c. 1.95 Ga is interpreted to represent the pre‐peak or peak metamorphic stages, and the ages of c. 1.92 Ga are assigned to represent the cooling stages. All rocks in the Wutai–Hengshan area share similar clockwise P–T morphologies. They may represent metamorphic products at different crustal depths in one orogenic event, which included a main thickening stage at c. 1.95 Ga followed by a prolonged uplift and cooling after 1.92 Ga.
Periodontal Conditions of Abutments and Non‐Abutments in Removable Partial Dentures over 7 Years of Use
Authors: da Fonte Porto Carreiro Adriana , de Carvalho Dias Kássia , Correia Lopes Ana Lílian , Bastos Machado Resende Camila Maria , Luz de Aquino Martins Ana Rafaela
Published: February 2016

Purpose

To evaluate the periodontal conditions and integrity of abutment and non‐abutment teeth of patients evaluated 7 years after insertion of the removable partial denture (RPD).

Materials and Methods

Twenty‐two patients (17 women, 5 men) were assessed at the moment of denture insertion and 7 years later. The following items were verified in each assessment: bleeding on probing (BP), probing depth (PD), gingival recession (GR), and mobility (M), comparing direct and indirect abutment teeth, and the teeth not involved in the denture design. Tooth integrity was also evaluated and classified as intact when no caries or fractures were observed. The Kruskal‐Wallis test was used to reveal statistical significance between the groups (p = 0.05) as well as the Bonferrroni‐corrected Mann‐Whitney test for post hoc comparison. The Wilcoxon test was used for evaluation within the group over time. Fisher's exact test was applied to cross data about abutment integrity.

Results

Statistically significant differences were found for GR (baseline, p < 0.001; 7 years, p < 0.001) and PD (baseline, p = 0.001; 7 years = 0.004) between the three groups at baseline and after 7 years of follow‐up. Mean BP and M values increased from initial assessment to after 7 years of RPD use in every group, but no statistically significant difference was found between the groups. For abutment integrity, a statistically significant difference (p = 0.028) was observed, and the direct abutment exhibited more (33.3%) caries and fractures.

Conclusion

RPDs generated more periodontal damage to direct abutments, since higher gingival recession probing depth indexes, and presence of caries and fractures were observed in comparison to indirect abutments and non‐abutments.
Tests for Linearity in Star Models: Supwald and Lm‐Type Tests
Authors: Kılıç Rehim
Published: February 2016

This article investigates approximation and supremum approaches for testing linearity in smooth transition autoregressive (STAR) models. We show that since the approximation of STAR models by Taylor series expansions may not accurately describe the specific transition dynamic when the process is away from the null, LM‐type tests may fail to detect the form of nonlinearity for which they are designed for. Investigating a supremum approach, the article provides the asymptotic distribution of a SupWald test that is obtained by taking the supremum of a Wald statistic over the Cartesian product of the spaces for the transition and threshold parameters. Simulated asymptotic critical values for the resulting tests are provided for a wide range of autoregressive orders and shown to differ across exponential and logistic STAR (ESTAR and LSTAR) models. Monte Carlo experiments show that SupWald tests for ESTAR and LSTAR models outperform LM‐type tests, compares well relative to the recently developed score‐based tests and each SupWald statistic performs the best against the true alternative for which it is formed. SupWald tests also provide results that are consistent with the findings from (independently) estimating and diagnostic testing of STAR models in real exchange rate data.
Elevated interleukin‐8 in bile of patients with primary sclerosing cholangitis
Authors: Zweers Serge J. , Shiryaev Alexey , Komuta Mina , Vesterhus Mette , Hov Johannes R. , Perugorria María J. , de Waart D. Rudi , Chang Jung‐Chin , Tol Shanna , te Velde Anje A. , de Jonge Wouter J. , Banales Jesus M. , Roskams Tania , Beuers Ulrich , Karlsen Tom H. , Jansen Peter L. , Schaap Frank G.
Published: February 2016

Background & Aims

To better understand the pathogenesis of primary sclerosing cholangitis, anti‐ and pro‐inflammatory factors were studied in bile.

Methods

Ductal bile of PSC patients (n = 36) and controls (n = 20) was collected by endoscopic retrograde cholangiography. Gallbladder bile was collected at liver transplantation. Bile samples were analysed for cytokines, FGF19 and biliary lipids. Hepatobiliary tissues of PSC and non‐PSC patients (n = 8–11 per patient group) were collected at transplantation and were analysed for IL8 and FGF19 mRNA expression and IL8 localization. The effect of IL8 on proliferation of primary human cholangiocytes and expression of pro‐fibrotic genes was studied.

Results

In PSC patients, median IL8 in ductal bile was 6.6 ng/ml vs. 0.24 ng/ml in controls. Median IL8 in gallbladder bile was 7.6 ng/ml in PSC vs. 2.2 and 0.3 ng/ml in two control groups. IL8 mRNA in PSC gallbladder was increased and bile ducts stained positive for IL8. In vitro, IL8 induced proliferation of primary human cholangiocytes and increased the expression of pro‐fibrotic genes.

Conclusion

Elevation of IL8 in bile of PSC patients, collected at different stages of disease, indicates an ongoing inflammatory stimulus that drives IL8 production. This challenges the idea that advanced PSC is a burned‐out disease, and calls for reconsideration of anti‐inflammatory therapy in PSC.
Regulation of UVR8 photoreceptor dimer/monomer photo‐equilibrium in Arabidopsis plants grown under photoperiodic conditions
Authors: Findlay Kirsten M.W. , Jenkins Gareth I.
Published: February 2016

The UV RESISTANCE LOCUS 8 (UVR8) photoreceptor specifically mediates photomorphogenic responses to UV‐B. Photoreception induces dissociation of dimeric UVR8 into monomers to initiate responses. However, the regulation of dimer/monomer status in plants growing under photoperiodic conditions has not been examined. Here we show that UVR8 establishes a dimer/monomer photo‐equilibrium in plants growing in diurnal photoperiods in both controlled environments and natural daylight. The photo‐equilibrium is determined by the relative rates of photoreception and dark‐reversion to the dimer. Experiments with mutants in REPRESSOR OF UV‐B PHOTOMORPHOGENESIS 1 (RUP1) and RUP2 show that these proteins are crucial in regulating the photo‐equilibrium because they promote reversion to the dimer. In plants growing in daylight, the UVR8 photo‐equilibrium is most strongly correlated with low ambient fluence rates of UV‐B (up to 1.5 μmol m−2 s−1), rather than higher fluence rates or the amount of photosynthetically active radiation. In addition, the rate of reversion of monomer to dimer is reduced at lower temperatures, promoting an increase in the relative level of monomer at approximately 8–10 °C. Thus, UVR8 does not behave like a simple UV‐B switch under photoperiodic growth conditions but establishes a dimer/monomer photo‐equilibrium that is regulated by UV‐B and also influenced by temperature.
Functional and structural characterization of domain truncated violaxanthin de‐epoxidase
Authors: Hallin Erik Ingmar , Guo Kuo , Åkerlund Hans‐Erik
Published: February 2016

Photosynthetic organisms need protection against excessive light. By using non‐photochemical quenching, where the excess light is converted into heat, the organism can survive at higher light intensities. This process is partly initiated by the formation of zeaxanthin, which is achieved by the de‐epoxidation of violaxanthin and antheraxanthin to zeaxanthin. This reaction is catalyzed by violaxanthin de‐epoxidase (VDE). VDE consists of three domains of which the central lipocalin‐like domain has been the most characterized. By truncating the domains surrounding the lipocalin‐like domain, we show that VDE activity is possible without the C‐terminal domain but not without the N‐terminal domain. The N‐terminal domain shows no VDE activity by itself but when separately expressed domains are mixed, VDE activity is possible. This shows that these domains can be folded separately and could therefore be studied separately. An increase of the hydrodynamic radius of wild‐type VDE was observed when pH was lowered toward the pH required for activity, consistent with a pH‐dependent oligomerization. The C‐terminally truncated VDE did not show such an oligomerization, was relatively more active at higher pH but did not alter the KM for ascorbate. Circular dichroism measurements revealed the presence of α‐helical structure in both the N‐ and C‐terminal domains. By measuring the initial formation of the product, VDE was found to convert a large number of violaxanthin molecules to antheraxanthin before producing any zeaxanthin, favoring a model where violaxanthin is bound non‐symmetrically in VDE.
Unobserved Heterogeneity, Exit Rates, and Re‐Employment Wages
Authors: Fernández‐Blanco Javier , Gomes Pedro
Published: February 2016

Exit rates from unemployment and re‐employment wages decline over a period of unemployment, after controlling for worker observable characteristics. We study the role of unobserved heterogeneity in an economy with asymmetric information and directed search. We show that the unique equilibrium is separating and that skilled workers have more job opportunities and higher wages. The composition of the unemployed varies with the duration of unemployment, so average exit rates and wages fall with time. The separating equilibrium relies on performance‐related pay schemes and the ability of firms to commit to renting an input that is complementary to worker skills.
Cyclic movement frequency is associated with muscle typology in athletes
Authors: Bex T. , Baguet A. , Achten E. , Aerts P. , De Clercq D. , Derave W.
Published: February 2016

There is a continuing research interest in the muscle fiber type composition (MFTC) of athletes. Recently, muscle carnosine quantification by proton magnetic resonance spectroscopy (1H‐MRS) was developed as a new non‐invasive method to estimate MFTC. This cross‐sectional study aims to better understand estimated MFTC in relation to (a) different disciplines within one sport; (b) cyclic sport exercise characteristics; (c) within‐athlete variability; and (d) athlete level. A total of 111 elite athletes (74 runners, 7 triathletes, 11 swimmers, 14 cyclists and 5 kayakers) and 188 controls were recruited to measure muscle carnosine in gastrocnemius and deltoid muscle by 1H‐MRS. Within sport disciplines, athletes were divided into subgroups (sprint‐, intermediate‐, and endurance‐type). The controls were used as reference population to allow expression of the athletes’ data as Z‐scores. Within different sports, endurance‐type athletes systematically showed the lowest Z‐score compared to sprint‐type athletes, with intermediate‐type athletes always situated in between. Across the different sports disciplines, carnosine content showed the strongest significant correlation with cyclic movement frequency (R = 0.86, P = 0.001). Both within and between different cyclic sports, estimated MFTC was divergent between sprint‐ and endurance‐type athletes. Cyclic movement frequency, rather than exercise duration came out as the most determining factor for the optimal estimated MFTC in elite athletes.
A Systematic Cell‐Based Analysis of Localization of Predicted Drosophila Peroxisomal Proteins
Authors: Baron Matthew N. , Klinger Christen M. , Rachubinski Richard A. , Simmonds Andrew J.
Published: February 2016

Peroxisomes are membrane‐bound organelles found in almost all eukaryotic cells. They perform specialized biochemical functions that vary with organism, tissue or cell type. Mutations in human genes required for the assembly of peroxisomes result in a spectrum of diseases called the peroxisome biogenesis disorders. A previous sequence‐based comparison of the predicted proteome of Drosophila melanogaster (the fruit fly) to human proteins identified 82 potential homologues of proteins involved in peroxisomal biogenesis, homeostasis or metabolism. However, the subcellular localization of these proteins relative to the peroxisome was not determined. Accordingly, we tested systematically the localization and selected functions of epitope‐tagged proteins in Drosophila Schneider 2 cells to determine the subcellular localization of 82 potential Drosophila peroxisomal protein homologues. Excluding the Pex proteins, 34 proteins localized primarily to the peroxisome, 8 showed dual localization to the peroxisome and other structures, and 26 localized exclusively to organelles other than the peroxisome. Drosophila is a well‐developed laboratory animal often used for discovery of gene pathways, including those linked to human disease. Our work establishes a basic understanding of peroxisome protein localization in Drosophila. This will facilitate use of Drosophila as a genetically tractable, multicellular model system for studying key aspects of human peroxisome disease.
Electrical synapses and the development of inhibitory circuits in the thalamus
Authors: Zolnik Timothy A. , Connors Barry W.
Published: February 2016

Key points

The thalamus is a structure critical for information processing and transfer to the cortex.

Thalamic reticular neurons are inhibitory cells interconnected by electrical synapses, most of which require the gap junction protein connexin36 (Cx36).

We investigated whether electrical synapses play a role in the maturation of thalamic networks by studying neurons in mice with and without Cx36.

When Cx36 was deleted, inhibitory synapses were more numerous, although both divergent inhibitory connectivity and dendritic complexity were reduced. Surprisingly, we observed non‐Cx36‐dependent electrical synapses with unusual biophysical properties interconnecting some reticular neurons in mice lacking Cx36.

The results of the present study suggest an important role for Cx36‐dependent electrical synapses in the development of thalamic circuits.

Neurons within the mature thalamic reticular nucleus (TRN) powerfully inhibit ventrobasal (VB) thalamic relay neurons via GABAergic synapses. TRN neurons are also coupled to one another by electrical synapses that depend strongly on the gap junction protein connexin36 (Cx36). Electrical synapses in the TRN precede the postnatal development of TRN‐to‐VB inhibition. We investigated how the deletion of Cx36 affects the maturation of TRN and VB neurons, electrical coupling and GABAergic synapses by studying wild‐type (WT) and Cx36 knockout (KO) mice. The incidence and strength of electrical coupling in TRN was sharply reduced, but not abolished, in KO mice. Surprisingly, electrical synapses between Cx36‐KO neurons had faster voltage‐dependent decay kinetics and conductance asymmetry (rectification) than did electrical synapses between WT neurons. The properties of TRN‐mediated inhibition in VB also depended on the Cx36 genotype. Deletion of Cx36 increased the frequency and shifted the amplitude distributions of miniature IPSCs, whereas the paired‐pulse ratio of evoked IPSCs was unaffected, suggesting that the absence of Cx36 led to an increase in GABAergic synaptic contacts. VB neurons from Cx36‐KO mice also tended to have simpler dendritic trees and fewer divergent inputs from the TRN compared to WT cells. The findings obtained in the present study suggest that proper development of thalamic inhibitory circuitry, neuronal morphology, TRN cell function and electrical coupling requires Cx36. In the absence of Cx36, some TRN neurons express asymmetric electrical coupling mediated by other unidentified connexin subtypes.
Setting Material Function Design Targets for Linear Viscoelastic Materials and Structures
Authors: Corman R. E. , Rao Lakshmi , Ashwin Bharadwaj N. , Allison James T. , Ewoldt Randy H.
Published: February 2016

Rheologically complex materials are described by function-valued properties with dependence on a timescale (linear viscoelasticity), input amplitude (nonlinear material behavior), or more generally both (nonlinear viscoelasticity). This complexity presents a difficulty when trying to utilize these material systems in engineering designs. Here, we focus on linear viscoelasticity and a methodology to identify the desired viscoelastic behavior. This is an early-stage design step to optimize target (function-valued) properties before choosing or synthesizing a real material. In linear viscoelasticity, it is not obvious which properties can be treated as independent design variables. Thus, it is nontrivial to select the most design-appropriate constitutive model, to be as general as possible, but not violate fundamental restrictions. We use the Kramers–Kronig constraint to show that frequency-dependent moduli (e.g., shear moduli G′(ω) and G″(ω)) cannot be treated as two independent design variables. Rather, a single function such as the relaxation modulus (e.g., K(t) for force-relaxation or G(t) for stress relaxation) is an appropriate function-valued design variable. A simple case study is used to demonstrate the framework in which we identify target properties for a vibration isolation system. Viscoelasticity improves performance. Different parameterizations of the kernel function are optimized and compared for performance. While parameterization may limit the generality of the kernel function, we do include a nonobvious representation (power law) that is found in real viscoelastic material systems and in the spring-dashpot paradigm would require an infinite number of components. Our methodology provides a means to answer the question, “What viscoelastic properties are desirable?” This ability to identify targeted behavior will be useful for subsequent stages of the design process including the selection or synthesis of real materials.
Study of Heat Transfer and Fluid Flow in Heat Exchanger and Improve Their Energy Efficiency
Authors: Koosha Nasir
Published: February 2016

In this study, two rows of fins from a fin-tube plate recuperator heat exchanger with two different materials, ceramic and steel, have been simulated by cfx software. First, by using experimental data that are in access, the independency from network and the confirmation of pattern authenticity have been checked. Equations from the equations of steady-state (SST) model k–ω have been used for applying turbulence terms in dominant. After network stabilization in greatest Reynolds number, the flow in the recuperator heat exchanger has been studied for two other Reynolds numbers. From the simulations, it is concluded that by increasing Reynolds number the temperature of fins' surfaces, outlet fluid temperature, and the temperature of tubes' surfaces will be increased, but totally the amount of overall heat transfer in time unit will be increased by the increase in Reynolds number. Also, it is observed that changing the material from steel to ceramic does not have that much difference for heat transfer in flow in low temperatures but the temperature of fins' surfaces for different materials and similar boundary status is different.
Numerical Study of Multistage Serial and Parallel Configurations of Thermoacoustic Engines
Authors: Badi Adnan Poshtkouhian , Beheshti Hamid
Published: February 2016

The focus of this study is on serial and parallel configurations of a multistage thermoacoustic engines (TAE). Thermoacoustics integrates fluid dynamics, thermodynamics, and acoustics to explain the interactions existing between heat and sound. Considerable amounts of waste heat are released to the environment in everyday industrial processes. This waste heat cannot be reused due to its low temperature. One way for reusing some of this waste heat is to employ a thermoacoustic heat pump. TAEs can be driven by waste heat and are capable of supplying the power to drive the thermoacoustic heat pumps. However, due to the low temperature of this waste heat, single-stage TAEs cannot provide the required temperature lifts. Multistage TAEs are advantageous because they can provide sufficient temperature lifts. In this study, a computational fluid dynamics (CFD) simulation is carried out to understand the conversion process of heat to sound and study the nonlinear conjugation of unsteady heat release and acoustic disturbances. The two main parameters evaluated in this simulation are the initial pressure disturbance and the stack's temperature gradient. Their effects on actuating limit cycle oscillations are examined in a 2D numerical model. The numerical simulation results indicate that the pressure amplitude varies through alteration made in these mentioned parameters. The present numerical results are validated by previously published data.
Universal Modeling Method: The Instrument for Centrifugal Compressor Gas Dynamic Design
Authors: Galerkin Y. , Rekstin A. , Soldatova K. , Drozdov A.
Published: February 2016

Similarity theory principles are widely applied in gas dynamic design. But completely new solutions must be realized on a base of engineering approaches to predict performances. The heart of the Universal modeling engineering method is the physical model that is based on flow visualization and measurements inside rotating impellers. The math model is a sum of algebraic equations for calculation of head losses. Normalized velocity gradients along and normal to blade surfaces are arguments. Empirical coefficients values are established in a course of the identification — calculated performances are compared with the measured ones for several dozens of model stages tests with wide range of design parameters. The 4th version of the TU SPb modeling method (the set of the several computer programs) was applied in design practice in 1993–2010. Some Russian and foreign manufacturers realized several dozens of designed compressors with power up to 25 MW. The level of design point parameters prediction was so satisfactory that the manufacturers do not prove designs by model tests anymore. The whole performance prediction was not so good. The other difficulty — to predict design point efficiency with accuracy about 0.5% the very careful choice of empirical coefficients is necessary. The difficulties have been overcome in the new 5th and 6th versions. Most effective multistage compressors plant test performances were modeled successfully by 5th version program with the single set of empirical coefficients. Calculated performances and geometry of several dozens of stages of these compressors can be are applied in designs as usual model stages. The current designs are executed by the 5th and 6th version computer programs. The single stage 32 MW pipe line compressor was recently designed for the Ukrainian partner who offered high-RPM drive and favorable single-stage scheme. The test of the model at the 1:2 scale validated project parameters. Design pressure ratio and efficiency curves have matched completely. The predicted maximum efficiency 90% was proven.
Numerical Investigation on Effect of Aspect Ratio of Axisymmetric Circumferential Groove Casing Treatment Coupled to a Transonic Axial Flow Compressor Stage
Authors: Mehta Nishit J. , Alone Dilipkumar Bhanudasji , Choksi Harish S.
Published: February 2016

While the effects of axisymmetric casing treatment on performance of an axial compressor stage have been extensively studied numerically as well as experimentally, the major geometrical parameters which govern these effects have been identified. Studies are now focused on understanding how each of these parameters individually impacts the performance of a casing treatment.

The present work aims to study the impact on performance of casing treatment geometry when aspect ratio of the grooves is varied in a circumferential groove casing treatment. The compressor geometry chosen for this study has design characteristics of a transonic compressor stage. Flow field solutions were derived for baseline model by solving steady state 3-D Reynolds-Averaged Navier-Stokes (RANS) equations for three grid densities and the grid independence was proved. The basic casing treatment geometry has 10 circumferential grooves of width 4mm and axial spacing of 2mm between each groove. The aspect ratio was varied by changing the depth of the grooves in each case. These casing treatment geometries were superimposed over the rotor domain with the grooves extending over the entire blade tip chord and flow field solutions were again obtained for various aspect ratios of grooves.

These results depict improvement in the range of operation in terms of mass flow rate. Results also show that the aspect ratio of the grooves significantly influences the overall effectiveness of casing treatment on the performance of compressor stage. Improvement in overall compressor efficiency is noted with lower aspect ratio casing treatments when compared to those with higher aspect ratios, however, the range improvement is higher with higher aspect ratios. It is also observed that, after a certain depth of grooves is reached, there is no significant improvement in performance on further increasing the depth and hence the aspect ratio.

Post processing results of the flow solutions are presented which confirm the trends and show that the flow behavior near rotor tip governs this effect.
Numerically Understand the Combined Effect of Tip Clearance and Circumferential Grooves Casing Treatment on the Performance of Single Stage Transonic Axial Flow Compressor
Authors: Goswami Mitesh , Alone Dilipkumar Bhanudasji , Choksi Harish S.
Published: February 2016

This paper deals with the numerical studies on the combined effect of tip clearance and axisymmetric circumferential grooves casing treatment (CGCT) on the overall performance and stall margin of a single stage transonic axial flow compressor. Steady state numerical analysis was carried out by solving three dimensional Reynolds-averaged-Navier-Stokes (RANS) Equations using the Shear Stress Transport (SST) k-ω Turbulence Model. The numerical stall inception point was identified from the last converged point by the convergence criteria, and the stall margin was numerically predicted. Additionally, the stall margin and the isentropic peak stage efficiencies of the circumferential casing grooves with various tip clearances were compared and evaluated in order to explore the influence of the tip clearance. Results obtained were compared with those obtained on the baseline compressor with the smooth casing (SC). Further computational studies were conducted to study the role of the tip leakage flow in axial compressor in triggering the stall. The relationship between the tip clearance flow, flow field and surge margin extension from circumferential groove casing treatment with various rotor tip clearances were studied numerically. The application of the circumferential groove casing treatment with varying clearance leads to significant improvement in the operating stability of compressor with slight reduction in the isentropic peak stage efficiency for small tip clearances, whereas there was slight increment in the isentropic peak stage efficiency at higher tip clearance of 2.5 mm.
Gas Dynamic Designs of Centrifugal Compressors for Gas Industry
Authors: Galerkin Y. , Rekstin A. , Soldatova K. , Drozdov A.
Published: February 2016

Centrifugal compressors for gas industry consume huge amount of energy. As a rule, they are single-shaft, with two or more stages and with comparatively low pressure ratio. Compressors operate at low Mach numbers and high Reynolds numbers. Two design parameters influence mostly stage performances. Stage flow coefficient optimal values lie in range 0.060–0.11. Chosen number of stages establishes value of this coefficient if speed of a rotor rotation is fixed. Design loading factor optimal values are 0.42–0.52. It corresponds to high efficiency, shifts a surge limit far from a design point and makes power maximal in a design point. Some considerations about impeller and diffuser types are presented. Design procedure consists on application of the Universal modeling programs for main dimensions optimization and performance calculations. Q3D non-viscid velocity diagrams are analyzed for optimization of blade configuration. Samples of design are presented, 32 MW single-stage pipeline compressor stage with record efficiency included.
Influence of Compound Lean on an Industrial Steam Turbine Stage
Authors: Deshpande Srikanth , Thern Marcus , Genrup Magnus
Published: February 2016

Compound lean implemented on stator of an industrial steam turbine stage in order to reduce secondary losses are discussed. Baseline stator is a prismatic vane with aspect ratio of unity. Compound lean stator blade is designed by shearing the airfoil sections in tangential direction. Modifications are analyzed numerically using commercial code CFX. Three blade rows i.e. one complete stage with a downstream stator are analyzed. Steady state Reynolds averaged Navier Stokes equations are solved. Total pressure loss (TPL) is used as objective function to monitor reduction in secondary losses. Rotor is retained the same for baseline as well as compound leaned stator. Results show reduction in total pressure loss of stator in excess of 5 %. Also, computations of co-efficient of secondary kinetic energy shows significant reduction in secondary losses in excess of 30 % in stator. Efficiency gained by implementation of compound lean are discussed.
Validation of a 1D Transient Simulation Model of a Multistage Axial Compressor
Authors: Kundu Reema , Prasad J. V. R. , Neumeier Yedidia
Published: February 2016

An unsteady one-dimensional dynamic model has been developed at Georgia Tech to investigate the impact of stage characteristics as well as load distribution on the compression and expansion waves that develop prior to a surge event in a multistage axial compressor. In the developed model, each of the blade rows is replaced by a duct of varying cross-sectional area with force and work source terms. The source terms model the force and energy imparted by a blade row to the working fluid. The modeling assumes the flow to be inviscid, unsteady, compressible and axisymmetric. While rotating stall cannot be explicitly modeled in a 1D mean-line method, the effect of rotating stall can be captured by a judicious choice of source terms that reflects the loss of pumping capability of a stage. Conservation of mass, momentum and energy are applied to an elemental control volume resulting in one-dimensional quasi-linear Euler system of equations. A non-uniform grid and the second-order central difference Kurganov-Tadmor (KT) scheme are used to discretize the one-dimensional computational domain. The resulting ODEs are solved with an explicit second order Runge-Kutta solver. A throttle schedule is used to introduce perturbations at a selected operating condition in order to study flow oscillations that can lead to a stall event. The current study is aimed at validation of the developed flow solver using an industrial compressor database. Further, the current study is aimed at understanding the interaction between the stages with regards to pressure oscillations leading to stall.
Health Assessment of Gas Turbine Compressor Using Process History Based Modelling Approach
Authors: Raghavan Shaiju M. , Palatel Arun , Simon Jayaraj
Published: February 2016

Gas turbine based combined cycle power plants are found to play vital role in electric power generation in recent years. Modern gas turbines are integral elements in these plants operating at very high temperature with high efficiency. Improvements in plant reliability, availability and maintainability (RAM) have been major areas of concern for power producers to ensure competitive positions. In gas turbine based power generation systems, the performance of the turbine drops due to several reasons like compressor fouling and inlet filter clogging. For improving plant RAM, advanced methods of health monitoring are vital for gas turbine plant components such as inlet air filter, compressor, combustion chamber and turbine. This paper focuses on health monitoring of gas turbine compressor considering major fault condition of compressor fouling. The health monitoring is achieved by developing a compressor model, to predict the performance of the compressor at design and off-design operational conditions. A thermodynamic model of the gas turbine system has limited applicability for health monitoring applications. The modelling framework has to incorporate the complex assembly of various components that make up the overall system and the real time off-design operations of the system. With the recent developments in computational methods and availability of vast computing power, process history data models are found to be convenient options for the system modelling. Among the process history data based methods, Artificial Neural Networks (ANN) have proved to be effective for modelling non-linear and complex processes. Hence, ANN is used as the modelling platform for this study and the model is developed from process data of a GE frame 9E machine. Residuals generated from the model are used for analysing the health of the system. The prediction of future events achieved through the model is found to provide vital information for the decision making and planning of maintenance actions. Principal Component Analysis (PCA) is a suitable method that is efficient in accounting the variability of the data. It derives the loading vectors and is suitable for improving the effectiveness of the ANN model. Different fault conditions relevant to the gas turbine compressor are demonstrated with actual plant data using the ANN based health monitoring system. Effect of compressor fouling and recouping of fouling effect with off line compressor water wash are also analysed in this paper.
Shape Optimization of Flexible Supports for Aero Engines
Authors: Gnanasundaram Govindaraji , Setty Srinath , Kasina Lakshman , Kotur Raghavan
Published: February 2016

Flexible supports are used in many aero and automobile industrial applications. They transmit loads, accommodate misalignment, allow axial displacement, ensure no loss of lubricants, absorb shock and dampen vibration, withstand high temperatures, allow easy installation and disassembling. Flexible supports react on connected equipment components when subjected to misalignment and torque. The reaction forces and moments on components due to flexible supports should be within the allowable limits or otherwise it can cause failure of gears, shafts, bearings, and other equipment components.

These flexible supports used in aero engine applications expected to meet design and manufacturing criteria. Flexible supports should have required stiffness values in different directions to meet rotor dynamic stability criteria. Flexible supports also required to meet strength and durability criteria for the given material at the required maximum operating temperature. The designed component should be producible and meet manufacturing limitations.

The main objective of this paper is to optimize single and multiple convolutes types of flexible supports with in the manufacturing limits and in the given design space. A methodology is developed to optimize the components to meet required stiffness, strength and durability criteria. Parametric models of flexible support are developed in UNIGRAPHICS NX9. Design parameters such as overall length, convolute height, convolute radius and angle are considered for the optimization study. ANSYS Workbench is used for the analysis and optimization of flexible support.
Experimental Analysis of a Dual-Fuel Engine Fueled by Producer Gas Derived From Pine Leaves and Cattle Dung Briquettes
Authors: Dabi Maryom , Saha Ujjwal K.
Published: February 2016

In the recent times, there has been a much concerned about the efficient utilization and conservation of energy across the globe. The fossil fuels supply most of the energy requirements, however, it is a non-renewable energy source having a limited reserve across the globe. In view of this, there has been a continuous drive to explore the renewable, easily available and environment friendly energy sources to partially or fully replace the fossil fuel. With this background, this paper investigates the viability of utilizing producer gas, derived from the biomass briquettes, as the primary fuel to run a diesel engine in dual fuel mode. Biomass used was sun-dried pine leaves and cow dung. Briquettes were prepared at the proportion of 75 % cow dung and 25 % pine leaves, by mass, using water as the binder. The producer gas, generated from a downdraft gasifier, was fed to single cylinder, four-stroke, water-cooled, 5.2 kW compression ignition engine to run on dual fuel mode. A minor modification of engine was carried out to suit the dual fuel mode operation. The performance and emission characteristics of the engine were studied at various loads. The system sustains well in a dual fuel mode although there is a drop in brake thermal efficiency in the range of 7 to 22%. There is a significant reduction, up to 93%, in NOX emission in the exhaust but CO and CO2 emission increases, more than 40% and 8% respectively, in the dual fuel mode.
Performance Prediction of Darrieus Turbine Through Numerical Analysis
Authors: Mukherjee Prasenjit , Saha Ujjwal K.
Published: February 2016

With the rising fossil-fuel prices, energy scarcity and climate-change, renewable energy plays an important role in producing local, clean and inexhaustible energy source to supply world rising demand for electricity. The selection of suitable wind turbine plays a vital role for urban power generation where wind is characterised by unsteadiness and turbulence. Thus, blade aerodynamics of wind turbine has a significant effect on turbine efficiency.

In this study, the aerodynamic aspect of a straight bladed Darrieus turbine is numerically analyzed. Two dimensional numerical modelling and simulation of unsteady flow through the rotor blades (NACA 0018) of the turbine is performed using ANSYS FLUENT 14.5. The unsteady Reynolds averaged Navier-Stokes (RANS) equation is used to demonstrate the effects on the performance of two dimensional Darrieus turbine blade. The Shear Stress Transport (SST) k-ω model has been adopted for the turbulence closure. For the proposed analysis, the flow field characteristics are investigated at different azimuthal angle and tip speed ratio. Further, the parametric quantities such as solidity, number of blades and blade thickness have being investigated for a uniform free stream velocity of 6 m/s. The effect of laminar boundary layer separation on performance of the Darrieus turbine has also been taken into account during the study of flow physics around the blade. The results obtained are compared with the reported experimental and computational data.
Assessment of Different Turbulence Models for Predicting Laminar Separation Bubble Over Thick Airfoils
Authors: Kumar Lakshmanan Saravana , Mishra Alok , De Ashoke
Published: February 2016

Accurate laminar-turbulent prediction is very much important to understand the complete performance characteristics of any airfoil which operates at low and medium Reynolds number. In this article, a numerical study has been performed over two different thick airfoils operating at low Reynolds number using k-ω SST, k-kl-ω and Spalart-Allmaras (SA) RANS models. The unsteady two dimensional (2D) simulations are performed over NACA 0021 and NACA 65-021 at Re 120,000 for a range of angle of attacks. The performances of these models are assessed through aerodynamic lift, drag and pressure coefficients. To obtain better comparison, the simulated results are compared with the experimental measurements and XFOIL results as well. In this present study, it is found that the k-kl-ω transition model is capable of predicting correct lift, drag coefficient and separation bubble as reported in experiments. At high angles of attack, this model fails to predict performance variables accurately. The SA and SST models are fail to predict laminar separation bubble. However, At high angle of attack, SA model shows better predictions compared to k-kl-ω and k-ω SST models.
Study of the Effect of Multi-Stage Cyclic Symmetric Modeling on the Natural Frequencies of Bladed Disks of an Aero Engine Rotor System
Authors: Srinivas Siva , Roy Hardik , Shanmugam Esakki Muthu
Published: February 2016

Majority of the failures in Gas turbine Blades are caused by High Cycle Fatigue induced by the vibratory stresses in the rotor blades. The first step in blade design is the prevention of coincidence of natural frequencies of the blades with the frequencies of the fluctuating Gas loads.

The forcing frequency is a function of number of upstream and downstream stator blades, and rotational speed. In gas turbines with multiple stages, modal analysis of bladed-disks is individually performed i.e. stage by stage. As the structure is rotationally periodic, cyclic symmetric boundary conditions can be utilized, over 360 degree modeling. The advantage of cyclic symmetry over full model lies in reduced degrees of freedom and hence reduced computational time. In most of the available tools, cyclic symmetry for modal analysis is limited to single stage. As such there is no provision to model and analyze multiple stages at the same time. This leads to inaccurate values of natural frequencies as the flexibility introduced by the adjacent stages is not being taken into consideration. An alternative to this is full 3D modeling and analysis of all the combined stages.

Bladh et al. (2003) [1] have shown that interstage coupling can significantly affect the dynamics of the multi-stage assembly and in some cases lead to an underestimation of vibratory levels. Sokolowski et al [2] studied the influence of inclusion of shaft in the model on the natural frequencies and mode shapes of the shrouded bladed discs up to four nodal diameters for first two frequency series (mode shapes). Rzadkowski and Drewczynski (2006) [3] have used full 360 degrees models to study the free and forced dynamics of multi-stage systems. However this method is avoided as the computational cost is prohibitive.

Multi stage cyclic symmetry overcomes this obstacle in which each stage is cyclically modeled and an inter-stage coupling is introduced between adjacent stages. The advantage of multi stage cyclic symmetry lies in the significant reduction in the number of elements and therefore computational time. Laxalde et al. (2007) [4] were the first to come up with the method of dynamic analysis of turbo machinery rotors with multi stage cyclic symmetry using interstage coupling. They considered an example of two-stage High Pressure compressor. The results were validated against a complete 360 degrees reference model. Forced response analysis of rotor stages to fluctuating gas loads with and without interstage coupling definition was also presented and compared. In the present work a complete Gas Turbine rotor system with multiple stages of Compressor, Shaft and Turbine were analyzed together.
CFD Analysis to Investigate the Effect of Vortex Generators on a Transonic Axial Flow Compressor Stage
Authors: Kumar Rajendran Avinash , Shobhavathy M. T. , Ajith Kumar R.
Published: February 2016

The performance of the compressor blade is considerably influenced by secondary flow effects, like the cross flow on the end wall as well as corner flow separation between the wall and the blade. Computational Fluid Dynamics (CFD) has been extensively used to analyze the flow through rotating machineries, in general and through axial compressors, in particular. The present work is focused on the studying the effects of Vortex Generator (VG) on test compressor at CSIR National Aerospace Laboratories, Bangalore, India using CFD. The compressor consists of NACA transonic rotor with 21 blades and subsonic stator with 18 vanes. The design pressure ratio is 1.35 at 12930 RPM with a mass flow rate of 22 kg/s. Three configurations of counter rotating VGs were selected for the analysis with 0.25δ, 0.5δ and δ height, where δ was equal to the physical thickness of boundary layer (8mm) at inlet to the compressor rotor [11]. The vortex generators were placed inside the casing at 18 percent of the chord ahead to the leading edge of the rotor. A total of 63 pairs of VGs were incorporated, with three pairs in one blade passage. Among the three configurations, the first configuration has greater impact on the end wall cross flow and flow deflection which resulted in enhanced numerical stall margin of 3.5% from baseline at design speed. The reasons for this numerical stall margin improvement are discussed in detail.