bluuebunny/crossref_metadata_2025 huggingface dataset:
Impaired transactivation of the human CYP2J2 arachidonic acid epoxygenase gene in HepG2 cells subjected to nitrative stress
Authors: Cui Pei H , Lee Andy C , Zhou Fanfan , Murray Michael
Published: February 2010

Background and purpose:  Human cytochrome P450 2J2 (CYP2J2) generates epoxyfatty acids that modulate cellular apoptosis and proliferation. CYP2J2 regulation has not been intensively studied but induction of the activator protein‐1 (AP‐1) subunit c‐fos mediates CYP2J2 down‐regulation in hypoxia, a component of ischaemic injury. Decreased CYP2J2 expression may contribute to tissue injury.

Experimental approach:  HepG2 cells were treated with sodium nitroprusside (SNP) to induce nitrative stress, which has been associated with inflammation and infection in liver and other tissues. CYP2J2 protein and mRNA expression were evaluated by immunoblotting and real‐time PCR respectively. The role of mitogen‐activated protein (MAP) kinases in CYP2J2 dysregulation was assessed using specific inhibitors and dominant negative MAP kinase expression plasmids. CYP2J2‐luciferase reporter constructs and electromobility shift assays (EMSAs) were used to identify SNP‐regulated regions in the CYP2J2 gene.

Key results:  Cytochrome P450 2J2 was down‐regulated by SNP while the AP‐1 proteins c‐jun and c‐fos were up‐regulated; inhibition of p38 and ERK MAP kinases normalized their expression. The gene elements at −105/−95 and −56/−63 were required for the down‐regulation of CYP2J2 induced by nitrative stress.

Conclusions and implications:  p38 and ERK MAP kinases transduce stress stimuli that down‐regulate CYP2J2. Targeting these kinases may prevent the loss of CYP2J2 and epoxy‐fatty acids that protect cells against deleterious stresses.
The effect of lathyrism on dentin structure of the rat incisors: a morphometric and scanning electron microscopic investigation
Authors: El Rouby Dalia Hussein , Bashir Maha Hassan , Korany Nahed Sedky
Published: February 2010

J Oral Pathol Med (2010) 39: 424–430

Background:  The present study was designed to study the effect of β‐aminopropionitrile (β‐APN), present in Lathyrus sativus grass pea consumed in drought prone areas, on dentin of the continuously erupting rat incisors.

Methods:  Eighteen adult male rats were used. In the experimental group (18 rats), lathyrism was induced by a once daily subcutaneous administration of β‐APN for 40 days. The maxillary and mandibular incisors were examined ultrastructurally and morphometrically.

Results:  The mean number of patent tubules, the mean area, perimeter and the area percent of the tubules were analyzed. Ultrastructurally, the dentinal tubules of both coronal and radicular dentin in the lathyritic group were narrower or even obliterated compared with those in the control. The coronal and radicular dentin of the lathyritic group exhibited an irregular lattice of non‐mineralized small branching collagen fibrils obliterating the dentinal tubules. The mean number of patent tubules in the control and lathyritic groups revealed an insignificant difference. The mean area of the tubules showed a statistically significant difference in lathyritic radicular dentin (P = 0.0353). The percentage of the total surface area of the dentinal tubules significantly decreased in the radicular dentin of the lathyritic group (P = 0.024).

Conclusions:  These findings indicated a deleterious effect of lathyrism on dentin, with a possible negative impact on developing teeth integrity.
Anthropometric correlates of lipoprotein profile and blood pressure in high BMI African American children
Authors: Raman A , Sharma S , Fitch MD , Fleming SE
Published: February 2010

Objective:  To explore the association of anthropometric indices with lipoprotein profile and blood pressure as risk factors of cardiovascular disease, in African American (AA) children.

Methods:  A cross‐sectional analysis was carried out on children aged 9–13 years with BMI >85th percentile. Height, weight, waist and hip circumferences, % body fat and blood pressure [systolic (sBP) and diastolic (dBP)] were measured. Fasting plasma levels of triglycerides (TG), total cholesterol (TC), high‐density lipoprotein cholesterol (HDL‐C), low‐density lipoprotein cholesterol (LDL‐C), intermediate density lipoprotein cholesterol (IDL‐C) and very low‐density lipoprotein cholesterol (VLDL‐C) were analysed.

Results:  After accounting for age, gender and pubertal status of the child, multiple linear regression models showed that waist circumference and BMIz were strong predictors for lipoprotein variables. In independent analysis, waist circumference and BMI z‐scores were found to be interdependently associated with TG, LDL‐C:HDL‐C ratio, VLDL‐C and sBPz. However, for HDL‐C, TG:HDL‐C ratio and dBPz, waist circumference was independently and more strongly associated with these risk factors than BMI.

Conclusion:  Waist circumference was a stronger predictor for lipoprotein variables and blood pressure in high BMI AA children than other anthropometric indices, and may be adequate as a screening test to identify children who are at increased risk for cardiovascular disease.
Mechanism for the hydrolysis of hyaluronan oligosaccharides by bovine testicular hyaluronidase
Authors: Kakizaki Ikuko , Ibori Nobuyuki , Kojima Kaoru , Yamaguchi Masanori , Endo Masahiko
Published: February 2010

Synthetic hyaluronan oligosaccharides with defined structures and their pyridylaminated derivatives were used to investigate the mechanism of hydrolysis of hyaluronan by bovine testicular hyaluronidase. The products of the hydrolysis were analyzed by HPLC and ion‐spray mass spectroscopy (MS). It was confirmed that the minimum substrate for bovine testicular hyaluronidase is the hyaluronan hexasaccharide, even though it is a poor substrate that is barely cleaved, even on prolonged incubation. When hyaluronan octasaccharide was the substrate, increasing amounts of tetrasaccharide and hexasaccharide were produced with increasing time of incubation. Whereas disaccharide was not detectable in the reaction mixture by HPLC, MS analysis revealed trace amounts. The data suggest that the enzyme generates a disaccharide intermediate from hyaluronan oligosaccharide, the majority of which is transferred to the nonreducing ends of other oligosaccharides, only traces being released as free disaccharide. When hyaluronan octasaccharide, with an unsaturated glucuronic acid at the nonreducing end, was used as a substrate, only a tetrasaccharide was detected by HPLC. However, MS showed that the product was a mixture of equal amounts of two tetrasaccharides, one with and the other without the unsaturated glucuronic acid. This suggests that, in the case of substrates with a double bond at the nonreducing end, a tetrasaccharide is cleaved off instead of a disaccharide. The results of the experiments with pyridylaminated oligosaccharides were entirely consistent with these conclusions, and in addition showed the importance of the reducing end of the substrate for the enzyme to recognize the length of the saccharide.
The role of mast cells in wound healing
Authors: Ng Michael FY
Published: February 2010

Mast cells are predominantly found in the vicinity of connective tissue vessels of skin and mucosa. The main immunological functions of mast cells are in IgE‐mediated reactions and in helminth infestations. Mast cells respond to tissue injury by releasing inflammatory mediators and have been implicated in diseases of excessive fibrosis of the dermis such as scleroderma. Current evidence suggests that mast cells exert its role during inflammation and cellular proliferation. Animal models have shown that by stabilising mast cells at the early stages of wound healing, wound contraction is reduced. Mast cells are an ideal candidate to play a pivotal role in wound healing due to its location, substances released and clinical associations.
Representation of ecosystem services by tiered conservation strategies
Authors: Eigenbrod Felix , Anderson Barbara J. , Armsworth Paul R. , Heinemeyer Andreas , Gillings Simon , Roy David B , Thomas Chris D , Gaston Kevin J.
Published: February 2010

In human‐dominated regions, protected areas are complemented by other conservation strategies (e.g., restrictive zoning, incentive payments) to maintain biodiversity and other ecosystem services. These strategies are often not mutually exclusive, with many areas covered by multiple (tiered) management strategies. However, it is not known whether tiering increases (or decreases) representation of ecosystem services. Here, we compare the representation of four ecosystem services by areas protected by both tiered and single conservation strategies (protected areas, restrictive zoning, and incentive payments to landowners) in a human‐dominated region (England). Tiering always coincided with the highest levels of stored carbon, sometimes coincided with high biodiversity and agricultural production, but never coincided with high recreational value. We also show that tiering is common in England and biased towards upland areas. Future evaluations of the effectiveness of conservation strategies should consider the degree of overlap of the different strategies fully to understand which are most effective.
On the Mechanical Behavior of Boron Nitride Nanotubes
Authors: Ghassemi H. M. , Yassar R. S.
Published: February 2010

Boron nitride (BN) nanotubes have structural and mechanical properties similar to carbon nanotubes and are known to be the strongest insulators. Great interest has been focused on understanding the mechanical properties of BN nanotubes as a function of their structural and physical properties. Yet, the published data have not been reviewed and systematically compared. In this paper, we critically review the mechanical properties of BN nanotubes from both experimental and simulation perspectives. The experimental reports include thermal vibrations, electric induced resonance method, and in situ force measurements inside transmission electron microscopy. The modeling and simulation efforts encompass tight bonding methods and molecular dynamics. Replacing the covalent sp2 bond (C–C) by ionic bond (B–N) results in differences in the mechanical properties of BN nanotubes in comparison to carbon nanotubes. The experimental and computational simulations indicate that BN nanotubes are highly flexible. High necking angles in BN nanotubes are assumed to be correlated with unfavorable bonding in B–B and N–N atoms.
The Method of Accounting for Loading Cycle Asymmetry in Cyclic Durability Analysis
Authors: Muratov R. H. , Kornilova M. A.
Published: February 2010

The proposed method has been demonstrated on the universal slopes equation (Manson 1965) and the modified universal slopes equation (Muralidharan & Manson 1998). New equations take into account independence of the transient strain range from the cycle average stress, define more precisely the impact of the cycle average stress upon the durability, take into account the impact of cycle average strain plastic constituent upon the durability. The resulted equations have been validated with finite element analyses of non-notched samples and full-scale parts, for which the results of cyclic tests in the conditions of asymmetric loading are available. The analyses have been performed employing an elastic-plastic approach using cyclic strain curves taken from original durability equations. The use of new equations ensured a good match between design and experimental durability values. Also, the new equations were used to plot Smith, Hay and Wo¨hler diagrams for low, mean and high durability. The resulted analytical diagrams represent a high quality illustration of the experimental diagrams found in the publications. The presented approach to the accounting for cycle average stress and strain will also apply when using experimental cyclic durability curves specific for the material.
Identification in Rotordynamics: Model-Based vs. Direct Measurements
Authors: Wang Qingyu , Pettinato Brian , Maslen Eric
Published: February 2010

In a rotor-bearing system, there are usually some under- or unmodeled components, such as foundations and seals. Identifying the dynamic characteristics of these components often requires both an analytical model and test data due to the working conditions, such as running speed above the first bending mode and non-collocation measurements. The existing methods always identify the dynamic characteristics by solving the equations of motion at discrete frequencies of the measured frequency response functions (FRFs). They have two problems: first, the physical background of the identification is buried in the equation solving process, and second, there is no quality estimation of the identified result. This paper discusses the first problem which is the equation solving process. The second problem, quality estimation, is discussed in a subsequent paper [1]. This paper reveals that model-based identification is the interconnection of certain transfer functions. These transfer functions are either generated from an analytical model (the common model-based method), or directly measured (direct measurement method). The process of both these methods is then illustrated by use of experimental data. A novel seal test design is proposed based on the idea of the direct measurement method. Identification under complex situations is also considered as complementary to the main content, such as different input/output locations. The conditions for identifiability are given.
A Discussion on Volute Design Method for Radial Inflow Turbines
Authors: Chen Hua
Published: February 2010

This paper discusses the external volute design methods for radial inflow turbines. First the existing 1-D methods are reviewed and the difficulty for such methods to completely define the volute geometry is highlighted. A method to partially overcome this difficulty is presented. To fully solve the problem, multi-dimensional methods are required. An improvement is given to the extended 2-D method proposed first by the author thirteen years ago. By solving the conservative form of the continuity equation, rather than the non-conservative formation of the potential flow, smoothness of the volute geometry is improved. Finally a new 3-D method is described. In this method, the flow inside the volute is treated as irrotational and tangentially uniform, this allows the 3-D flow be mapped to a 2-D flow in the z-r plane. This 2-D potential flow is then solved together with the stream surface equations through iterations, and the volute geometry is generated in the process.
Non-Axisymmetric End Wall Profiling in Transonic Compressors—Part I: Improving the Static Pressure Recovery at Off-Design Conditions by Sequential Hub and Shroud End Wall Profiling
Authors: Reising Steffen , Schiffer Heinz-Peter
Published: February 2010

Secondary flows involving cross flow and three-dimensional separation phenomena in modern axial compressors at high stage loading contribute significantly to a reduction in overall efficiency. This two-part paper presents a numerical study on the potential aerodynamic benefits of using non-axisymmetric end walls in an axial compressor, involving both the rotor and the stator row. This first paper describes the sequential profiling of stator end walls in a transonic compressor at several operating points to suppress separation. An automated multi-objective optimizer connected to a 3-D RANS flow solver was used to find the optimal end wall geometries. As a design exercise, the stator hub end wall of Configuration I of the Darmstadt Transonic Compressor was first optimized at design conditions, keeping the shroud end wall constant. This led to an increase in efficiency of 1.8% due to the suppression of the hub-corner stall. However, this was accompanied by an increased area of reverse flow at the casing, which was even more distinct at off-design conditions near stall. The numerical surge limit of the datum axisymmetric design could no longer be reached and was then determined by the new separation close to the stator casing. A subsequent optimization of the shroud end wall was carried out using the improved profiled hub as the initial design. An operating point near stall with a strongly developed separation was chosen for this purpose. The second optimization resulted in a further improvement in the characteristic speed line over the entire off-design region. Although the shroud contour was designed at off-design conditions, the optimization gained an additional 0.03% in efficiency for the design point. The lower surge limit of the datum design could also be reached again, even at higher efficiency and pressure ratios. The investigations showed that end wall profiling in high loaded compressor stators can be considered as a good supplement to 3-D blading to control separation areas and improve the entire component’s characteristics.
Blade Excitation in Pulse-Charged Mixed-Flow Turbocharger Turbines
Authors: Senn Stephan M. , Seiler Martin , Schaefer Ottmar
Published: February 2010

In this article, a fully three-dimensional computational modeling approach in the time and frequency domain is presented which allows to accurately predicting fluid-structure interactions (FSI) in pulse-charged mixed-flow turbocharger turbines. As part of the approach, a transient computational fluid mechanics analysis is performed based on the compressible inviscid Euler equations covering an entire engine cycle. The resulting harmonic orders of aerodynamic excitation are imposed in a forced response analysis of the respective eigenvector to determine effective stress amplitudes. The modeling approach is validated with experimental results based on various mixed-flow turbine designs. It is shown that the numerical results accurately predict the measured stress levels. The numerical approach can be used in the turbine design and optimization process. Aerodynamic excitation forces are the main reason for high cycle fatigue in turbocharger turbines and therefore, a fundamental understanding is of key importance.
Aerodynamic Design to Increase Pressure Ratio of Centrifugal Compressors for Turbochargers
Authors: Tamaki Hideaki , Unno Masaru , Kawakubo Tomoki , Hirata Yutaka
Published: February 2010

This paper describes the ways to increase pressure ratio of centrifugal compressors on condition of fixed impeller diameter. The compressors discussed in the paper were designed for turbochargers applied to 500kW class Diesel engines and their impeller diameters were about 140mm. Pressure ratio was increased from 3.6 to 4.8 at first and then increased from 4.8 to 5.7. The pressure was raised by means of increase in rotational speed together with additional increase in pressure coefficient. The pressure coefficient was increased by means of increase in work coefficient. The increases in rotational speed and work coefficient lead to increase in relative Mach number at inducer. However, the relative Mach number at inducer of the compressor with a pressure ratio of 3.6 already exceeded 1.3. Therefore, it was expected that complicated flow features related to the occurrence of shock wave would deteriorate the new compressors’ efficiency and operating range. In order to avoid this problem, following new measures were taken with conventional design methods. (1) Reduction of a blade loading — an increase in number of blade by means of double splitter (two adjoining splitters). (2) Introduction of technologies to enhance an operating range — recirculation device. (3) Selection of a proper diffuser to convert kinetic energy at an impeller exit to static pressure — vaned diffuser with elliptic leading edge. Newly designed compressors realized expected performance, stage pressure ratio and efficiency. Suitability of these measures was confirmed.
The Application of Non-Axisymmetric Endwall Contouring in a Single Stage, Rotating Turbine
Authors: Snedden Glen , Dunn Dwain , Ingram Grant , Gregory-Smith David
Published: February 2010

As turbine manufacturers strive to develop machines that are more efficient, one area of focus has been the control of secondary flows. To a large extent these methods have been developed through the use of computational fluid dynamics and detailed measurements in linear and annular cascades and proven in full scale engine tests. This study utilises 5-hole probe measurements in a low speed, model turbine in conjunction with computational fluid dynamics to gain a more detailed understanding of the influence of a generic endwall design on the structure of secondary flows within the rotor. This work is aimed at understanding the influence of such endwalls on the structure of secondary flows in the presence of inlet skew, unsteadiness and rotational forces. Results indicate a 0.4% improvement in rotor efficiency as a result of the application of the generic non-axisymmetric endwall contouring. CFD results indicate a clear weakening of the cross passage pressure gradient, but there are also indications that custom endwalls could further improve the gains. Evidence of the influence of endwall contouring on tip clearance flows is also presented.
CFD Optimization of Liquid Annular Seals for Leakage and Rotordynamics Improvement
Authors: Pugachev Alexander O.
Published: February 2010

The study deals with optimization of leakage and rotordynamic characteristics of liquid annular seals. A nonlinear constrained multi-objective optimization problem is considered. An objective function is a weighted sum of leakage and whirl-frequency ratio of the seal. Side constraints are imposed on design variables. The seal consists of two rings which shape can be either cylinder or converging taper or diverging taper. There are four design variables — seal length and diameters of the rings. A non-gradient-based method is used for solving the optimization problem. Analysis of the seal performance is based on computational fluid dynamics (CFD). A full 3D eccentric CFD model of the seal including upstream and downstream regions is constructed in ANSYS CFX. The solution procedures for prediction of rotordynamic coefficients are discussed and compared. The whirling rotor method under the assumption of centered circular orbit is used in optimization runs. The CFD model of the seal is validated against experimental data taken from the literature. A mesh independence study is carried out. An optimization environment includes automatic grid generation, parallel CFD calculations of the seal, and optimization algorithm. Two optimization runs corresponding to low-speed and high-speed cases are performed. Seals with improved characteristics include near-cylindrical and divergent-tapered rings. Performance of three seals from the Pareto set is calculated for different rotational speeds and inlet pressures. Generally, the rotordynamic performance degrades at other operating conditions. Additional study for the seals with enlarged clearance is carried out to model effect of wear.
Calculation Methods for the Determination of Blade Excitation Due to Suction Elbows in Centrifugal Compressors
Authors: Reichl Armin , Dickmann Hans-Peter , Ku¨hnel Janpeter
Published: February 2010

Experimental investigations on a single stage centrifugal compressor showed that asymmetric suction elbows can cause unacceptable blade vibrations. For turbocharger applications it is important to assess this issue in an early design phase. Although computational methods are known to estimate the influence of the asymmetric flow structure on referring blade vibration resonance by means of unsteady CFD and FE vibration analysis, those are not suitable for the design process, as they are too time and CPU consuming. Thus, the focus of this project is to define a procedure which determines the blade excitation by simplified models that can easily be integrated into the compressor design loop. For the evaluation of blade excitation due to asymmetric incoming flow, the flow fields at the inlet of the impeller using calculation methods of varying accuracy are compared. The potential energy of the harmonic blade excitations at the inlet of the impeller at different axial and radial positions is determined and evaluated by Fast Fourier Transform analysis over the circumference. The flow field of the unsteady calculation acts as a reference, since it was used to reproduce the measured blade vibrations in an accurate way in [1]. The blade excitation potential due to asymmetric incoming flow is examined by means of several steady CFD calculations, each differing in the model resolution. It is shown that the potential blade vibration excitation due to suction elbows or asymmetric aspiration ports is accurately determined by a standard steady-state calculation and therefore the computational effort can be minimized.
Experimental Investigation of Mistuning Effects on High Pressure Compressor Stators
Authors: Zhang Chao , Abate Aldo , Crockett John , Ho Eric
Published: February 2010

High pressure compressor (HPC) stator vanes of small gas turbine engines frequently have high circumferential variation of vibratory stress. This is very important for vibratory stress measurement by strain gauge tests and structural high cyclic fatigue characterization. The current paper presents experimental results of studying the effects of HPC stator angular positions in gas turbine engines on the circumferential distribution pattern of vibratory stress. Strain gauge tests were done on a stator with cantilevered vanes. Each vane had a strain gauge deployed at the same location. The stator was installed in gas turbine engines at two different angular positions during strain gauge tests. The experimental results show that more than one resonant peak occurred for a given vibratory mode and engine order resonance. The frequencies of resonant peaks were close to one another. The circumferential distribution of maximum vibratory stress (i.e., the maximum magnitude of these resonant peaks) with respect to the stator itself has a similar pattern at the two different angular positions. This clearly indicates the distribution pattern does not follow the gas-path aerodynamic pressure, but follows the stator angular positions. The frequency of the maximum vibratory stress was found to vary from sector to sector instead of from vane to vane; the vanes in each sector have a same frequency. Mistuning analysis was performed on the HPC stator to illustrate a number of resonant peaks and the sector-to-sector frequency variation of the maximum vibratory stress. The approach of “subset of nominal system modes” (SNM) [1, 2] was employed for mistuning analysis and the frequency distributions of stator vanes obtained by bench frequency response tests were used as input data. At the end, one might conclude that the high circumferential variation of vibratory stress be related to mistuning effects due to small variations in vane properties.
Investigation of CFD Prediction Capabilities for Low Reynolds Turbine Aerodynamics
Authors: Muth Bastian , Schwarze Marco , Niehuis Reinhard , Franke Matthias
Published: February 2010

The objective of this work is to study the performance of low pressure turbines operating at low Reynolds numbers by extensive experiments and to validate numerical simulation results with the experimental data. Particular attention is payed to the prediction capabilities of current numerical turbulence and transition models in order to be able to benchmark the performance of future turbine airfoil profiles and to optimise their aero design. The LPT-Cascade under consideration has been investigated at the High Speed Cascade Wind Tunnel of the Institute of Jet Propulsion to gather information about the performance of turbine airfoils under low Reynolds operating conditions. The experiments were executed in the range of Re = 40′000 to 400′000 with steady state inflow conditions at different Mach number levels. The main focus of the investigation thereby was on the range of Re = 40′000 to 70′000. The high speed cascade wind tunnel of the University of Federal Armed Forces Munich allows for an independent Reynolds and Mach number variation such that an extensive database can be generated for realistic engine operation conditions. One major test objective was related to flow separation phenomena on the suction surface and its influence on the performance of the turbine profile. For this purpose both the loss behaviour and the pressure distribution on suction and pressure surface of the blade were measured and analysed. In addition to the experiments numerical flow simulations were conducted for the same turbine profile. In order to achieve more information on the influence of different turbulence and transition models on the flow separation, transition, and reattachment behaviour, two different CFD codes were used for comparison purposes. On the one hand the CFD code TRACE, which is developed by the German Aerospace Center (DLR) and MTU Aero Engines and on the other hand the general purpose code ANSYS CFX were applied. The aim is to assess the prediction capabilities of the different codes especially in the low Reynolds number range.
A Numerical and Experimental Performance Comparison of an 86 MM Radial and Back Swept Turbine
Authors: Barr Liam , Spence Stephen , Thornhill David , Eynon Paul
Published: February 2010

This report details the numerical and experimental investigation of the performance characteristics of a conventional radial turbine compared with a new back swept design for the same application. The blade geometry of an existing turbine from a turbocharger was used as a baseline. A new back swept blade was subsequently designed for the rotor, which departed from the conventional radial inlet blade angle to incorporate a 25° inlet blade angle. A comparative numerical analysis between the two geometries is presented. Results show that the 25° back swept blade offers significant increases in efficiency while operating at lower than optimum velocity ratios (U/C). Improvements in efficiency at off-design conditions could significantly improve turbocharger performance since the turbine typically experiences lower than optimum velocity ratios while accelerating during engine transients. A commercial CFD code was used to construct single passage steady state numerical models. The numerical predictions show off-design performance gains of 2% can be achieved, while maintaining design point efficiency. A finite element stress analysis was conducted to show that the nonradial inlet blade angle could be implemented without exceeding the acceptable stress levels for the rotor. A modal analysis was also carried out in order to identify the natural blade frequencies, showing that these were not significantly changed by the implementation of backswept blading. A prototype backswept rotor was produced and tested in a direct comparison with the baseline rotor geometry. Experimental performance results showed strong correlations with those obtained numerically, and verified the predicted performance gains at off-deign velocity ratios. This numerical and experimental study has shown that it is feasible from both an aerodynamic and structural point of view to improve the performance characteristic of a radial turbine at lower than optimum velocity ratios through the implementation of back swept blading.
Advanced Non-Axisymmetric Endwall Contouring for Axial Compressors by Generating an Aerodynamic Separator—Part I: Principal Cascade Design and Compressor Application
Authors: Dorfner Christian , Hergt Alexander , Nicke Eberhard , Moenig Reinhard
Published: February 2010

Modern methods for axial compressor design are capable of shaping the blade surfaces in a three dimensional way. Linking these methods with automated optimization techniques provides a major benefit to the design process. The application of non-axisymmetric contoured endwalls is considered to be very successful in turbine rotors and vanes. Concerning axial compressors non-axisymmetric endwalls are still a field of research. This two-part paper presents the recent development of a novel endwall design. An aerodynamic separator, generated by a non-axisymmetric endwall groove, interacts with the passage vortex. This major impact on the secondary flow results in a significant loss reduction because of load redistribution, reduction of recirculation areas and suppressed corner separation. The first paper deals with the development of the initial endwall design using a linear compressor cascade application. A brief introduction of the design methods is provided, including the automated optimization, the 3D process chain with a focus on the endwall contouring tool. Hereafter the resulting flow phenomena and physics due to the modified endwall surface are described and analyzed in detail. Additionally, the endwall design principal is transferred to an axial compressor stage. The endwall groove is applied to the hub and casing endwalls of the stator and the initial numerical investigation is presented. For highly loaded operating points the flow behaviour at the hub region can be improved in accord with the cascade results. Obviously, the casing region is dominated by the incoming tip vortex generated by the rotor and still remains an area for further investigations concerning non-axisymmetric endwall contouring.
Rotordynamic Comparison of Built-Up Versus Solid Rotor Construction
Authors: Moore J. Jeffrey , Lerche Andrew H.
Published: February 2010

Most manufacturers of multi-stage centrifugal compressors for the oil and gas industry utilize a solid shaft rotor construction. The impellers use a shrink fit onto the shaft with spacers in between the impellers. With the introduction of the guidelines in the 7th edition of API 617, built-up rotors for centrifugal compressors using a tie-bolt are recognized by API. This study compares the rotordynamic performance of the identical compressor using both a tie-bolt design and a more conventional solid rotor for a two-stage pipeline application. A full API 617 lateral analysis is performed on the two designs, assuming identical impeller flow path, stage spacing, and hub diameter. The critical speed and unbalance response are computed, and a full Level 2 stability analysis is performed for each case. The results show the tie-bolt construction to be slightly lighter and stiffer, resulting in a higher critical speed and improved rotordynamic stability.
Pulse Performance Modeling of a Twin Entry Turbocharger Turbine Under Full and Unequal Admission
Authors: Costall Aaron W. , McDavid Robert M. , Martinez-Botas Ricardo F. , Baines Nicholas C.
Published: February 2010

The pulsating nature of the gas flow within the exhaust manifold of an internal combustion engine is not well captured by the quasi-steady techniques typically employed by cycle simulation programs for turbocharger modeling. This problem is compounded by the unequal admission conditions imposed on the turbine by the use of multiple entry housings, installed as standard on pulse turbocharged diesel engines. This unsteady behavior presents the simulation engineer with a unique set of difficulties when modeling turbocharger turbines. It is common for experienced analysts to accommodate multiple entries by splitting the flow across duplicate components and by tuning the level of interference between volute entries, but this necessarily bespoke approach is limited to upstream modifications that cannot capture true turbine unsteady operation. This paper describes recent simulation code development work undertaken at Caterpillar to improve machine sub-model accuracy essential for virtual product development meeting US nonroad Tier 4 emission standards. The resulting turbine performance model has been validated against experimental data for a twin entry turbocharger suitable for heavy duty nonroad applications, obtained using a permanent magnet eddy-current dynamometer and pulse flow test facility. Comparison between experiment and prediction demonstrates good agreement under full admission in terms of both instantaneous flow capacity and turbine actual power, though unequal admission results indicate the need for further model development.
Water Droplets Dispersion and Optimization of Water Removal Suction Slot Locations on Stationary Blades in Last-Stage of a 600 MW Steam Turbine
Authors: Wang Xinjun , Su Pengfei , Chou Luke , Guan Panlong , Li Chunguo , Zhou Hongyu
Published: February 2010

Water droplets dispersion through a stationary cascade channel and their deposition on the blade surface in the last-stage of a 600MW steam turbine have been simulated with CFD software FLUENT. So the deposition on stationary blades along the axial and radial direction was determined. In the experiment, the performance of water removal by suction slots on stationary blades surface was investigated. The results showed that: 12.2% of water at the inlet still existed as droplets, depositing on the concave side of the airfoils in contrast with only 1.6% on the convex side. The volume of the water removed by the suction slots on the concave side was bigger than that on the convex side. The closer the slot position was to the trailing edge, the bigger the volume was. The volume became smaller and then larger with the increase in slot width; the minimum value occurred when slots were about 3.0 mm in width. The bigger suction pressure difference would initiate a bigger volume of water removed by suction slots, but the increase in main flow rate would quickly initiate a smaller volume.
An Energy-Based Method for Uni-Axial Fatigue Life Calculation
Authors: Ozaltun Hakan , Seidt Jeremy , Shen M.-H. Herman , George Tommy , Cross Charles
Published: February 2010

An energy based fatigue life prediction framework has been developed for calculation of remaining fatigue life of in-service gas turbine materials. The purpose of the life prediction framework is to account for the material aging effect on fatigue strength of gas turbine engines structural components which are usually designed for infinite life. Previous studies [1–7] indicate the total strain energy dissipated during a monotonic fracture process and a cyclic process is a material property that can be determined by measuring the area underneath the monotonic true stress-strain curve and the sum of the area within each hysteresis loop in the cyclic process, respectively. The energy-based fatigue life prediction framework consists of the following entities: (1) development of a testing procedure to achieve plastic energy dissipation per life cycle and (2) incorporation of an energy-based fatigue life calculation scheme to determine the remaining fatigue life of in-service gas turbine materials. The accuracy of the remaining fatigue life prediction method was verified by comparison between model approximation and experimental results of Aluminum 6061-T6 (Al 6061-T6). The comparison shows promising agreement, thus validating the capability of the framework to produce accurate fatigue life prediction.
Numerical Investigation of the Effect of Tip Leakage Flow on an Aggressive S-Shaped Intermediate Turbine Duct
Authors: Sanz W. , Kelterer M. , Pecnik R. , Marn A. , Go¨ttlich E.
Published: February 2010

The demand of a further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters which rotate at lower speed. Therefore, it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at a larger diameter without any loss generating separation or flow disturbances. Due to costs and weight this intermediate turbine duct has to be as short as possible. This leads to an aggressive (high diffusion) S-shaped duct geometry. In order to investigate the influence of the blade tip gap height of a preceding rotor on such a high-diffusion duct flow a detailed measurement campaign in the Transonic Test Turbine Facility at Graz University of Technology has been performed. A high diffusion intermediate duct is arranged downstream a high-pressure turbine stage providing an exit Mach number of about 0.6 and a swirl angle of −15 degrees (counter swirl). A low-pressure vane row is located at the end of the duct and represents the counter rotating low pressure turbine at larger diameter. At the ASME 2007, results of these investigations were presented for two different tip gap heights of 1.5% span (0.8 mm) and 2.4% span (1.3 mm). In order to better understand the flow phenomena observed in the intermediate duct a detailed numerical study is conducted. The unsteady flow through the whole configuration is simulated for both gap heights as well as for a rotor with zero gap height. The unsteady data are compared at the stage exit and inside the duct to study the flow physics. The calculation of the zero gap height configuration allows to determine the influence of the tip leakage flow of the preceding rotor on the intermediate turbine duct. It turns out that for this aggressive duct the tip leakage flow has a very positive effect on the pressure recovery.
Numerical Study on End-Wall Flow in Highly Loaded Supercritical Compressor Cascades
Authors: Jiang Bin , Wang Songtao , Feng Guotai , Wang Zhongqi
Published: February 2010

This paper presents a numerical study on three-dimensional flow phenomena near the endwall of a linear high-turning compressor cascade at supercritical flow conditions. The compressor cascade with 60° camber angle was designed at a higher supercritical speed (M1>0.9) by optimum method based on the baseline which aimed at improving the flow near the stator hub of small transonic fans. The camber line and thickness distribution curves of the baseline are formed by quadratic polynomials and double cubic curves respectively. The stack line and the thickness distribution near the end-wall were chosen as optimization variables to approach the objective function of total pressure loss coefficient, since they are the two main geometry parameters which can influence end-wall flow obviously. The analysis in current paper focuses on comparing the flow phenomena near the end-wall of baseline cascade with that of optimized one. Numerical simulation results are presented to show the loss reduction from the baseline to the optimized cascade near end-wall. The boundary-layer development on the suction surface, flow separation structure, shockwave and local supersonic area on the suction surface near the end-wall are analyzed in detail. The optimized cascade has a stronger shockwave near the leading edge. It was found that the radial flow of the boundary-layer caused by the optimization of stack line is the key factor influencing the aerodynamics loss near the end-wall at supercritical condition which also plays an important part in second-flow and flow separation in the corner. An understanding of the low-loss pattern of the end-wall flow and the flow filed structure for high-turning compressor at higher supercritical flow conditions then is summarized at the end of this paper.
LP Turbine Laminar Separation With Actuated Transition: DNS, Experiment and Fluidic Oscillator CFD
Authors: Ries Tobias , Mohr Frederick , Baumann Jenny , Rose Martin , Rist Ulrich , Raab Irene , Staudacher Stephan
Published: February 2010

Laminar separation bubbles form on the back surfaces of aero-engine LP turbine blades. In recent years significant weight and cost reductions and performance improvements have been achieved through a better understanding of the behavior of such separation bubbles. A project is underway at the Universita¨t Stuttgart to study a possible technique to suppress laminar separation bubbles using actuated transition. This paper reports on DNS results with and without actuation for different frequencies, amplitudes and Reynolds numbers, revealing the nature of the transitional process. Early results from an experimental simulation are included. In addition numerical simulations of fluidic oscillators which are capable to provide the required frequencies at a size which would fit into an LP turbine are presented.
Energy Cost Assessment of the Active Control of a Rotating Machine by Using an Electromagnetic Actuator and a Piezoelectric Actuator
Authors: Skladanek Yan , Der Hagopian Johan , Mahfoud Jarir
Published: February 2010

The performances for controlling a rotating machine by using either an Electromagnetic Actuator or a Piezoelectric Actuator are compared in this work. The aim is to establish selection criteria based on environmental impact. Life Cycle Analysis shows that the operating stage has a considerable impact. In this study, only the operating stage is considered. The energy consumed by the actuators seems to be the appropriate indicator for the same “mechanical” performances. Numerical studies are carried out in order to quantify the energy consumed in each case. Modal control strategy with a fuzzy controller is used. The controller inputs are displacements and velocities. The system studied is modeled by using finite element method and the electrical circuit of each actuator is modeled by using basic electricity and electromagnetism theories. Several configurations are assessed and defined by using the chosen Functional Unit. The results obtained show that both controllers are efficient and enable recommendations for optimal control procedures design for the energy consumed.
Buckling Analysis of Afterburner Liner of an Aero Gas Turbine Engine
Authors: Potluri Sri Shanti , Patel Surendra Kumar
Published: February 2010

The afterburner in an aero-engine is employed for augmentation of the basic thrust of the engine to improve the fighter aircraft take-off, climb and combat performance. The liner forms one of the main components of the afterburner system. Buckling is a dominant mode of failure for the afterburner structure due to its inherent slender geometry and external pressure loading system in addition to low stiffness due to high temperature. This paper deals with design aspects involved in the afterburner structure — the augmenter liner where combustion takes place during reheat. The liner therefore experiences high thermal loads, variable differential pressure and severe loads as encountered during an engine flameout condition. This paper describes the approach adopted for the design of an afterburner liner for buckling strength which assures safety and producibility by fulfillment of design and fabrication constraints. The design methodology is validated through flame out test on full-scale component. Further in pursuit of weight efficient design, the liner configuration with corrugations is attempted.
A Method for Forced Response Analysis of Mistuned Bladed Discs With Aerodynamic Effects Included
Authors: Petrov E. P.
Published: February 2010

A method has been developed for high-accuracy analysis of forced response levels for mistuned bladed discs vibrating in gas flow. Aerodynamic damping, the interaction of vibrating blades through gas flow and the effects of structural and aerodynamic mistuning are included in the bladed disc model. The method is applicable to cases of high mechanical coupling of blade vibration through a flexible disc and, possibly shrouds, and to cases with stiff discs and low mechanical coupling. The interaction of different families of bladed disc modes is included in the analysis providing the capability of analysing bladed discs with pronounced frequency veering effects. The method allows the use of industrial-size sector models of bladed discs for analysis of forced response of a mistuned structure. The frequency response function matrix of a structurally mistuned bladed disc is derived with aerodynamic forces included. A new phenomenon of reducing bladed disc forced response by mistuning to levels that are several times lower than those of their tuned counterparts is revealed and explained.