bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphological and enzymatic correlates of aerobic and burst performance in different populations of Trinidadian guppiesPoecilia reticulata
Authors: Odell Jason P. , Chappell Mark A. , Dickson Kathryn A.
Published: September 2003

We examined the mechanistic basis for two whole-animal performance traits,aerobic capacity and burst speed, in six laboratory-reared Trinidadian guppy populations from different native drainages with contrasting levels of predation. Using within- and between-population variation, we tested whether variation in organs and organ systems (heart, gill and swimming motor mass)and the activities of several enzymes that support locomotion (citrate synthetase, lactate dehydrogenase and myofibrillar ATPase) are correlated with aerobic performance (maximum rates of oxygen consumption, V̇O2max) or burst performance (maximum swim speed during escape responses). We also tested for associations between physiological traits and habitat type (different drainages and predation levels).

Organ size and enzyme activities showed substantial size-independent variation, and both performance measures were strongly correlated to body size. After accounting for size effects, neither burst nor aerobic performance was strongly correlated to any organ size or enzymatic variable, or to each other. Two principal components (PCI, PC2) in both males and females accounted for most of the variance in the organ size and enzymatic variables. In both sexes, heart and gill mass tended to covary and were negatively associated with citrate synthetase and lactate dehydrogenase activity. In males (but not females), variation in aerobic performance was weakly but significantly correlated to variation in PC1, suggesting that heart and gill mass scale positively with V̇O2max. Neither of the component variables and no single morphological or enzymatic trait was correlated to burst speed in either sex.

Evolutionary changes in important life history traits occur rapidly in guppy populations subjected to different predation intensities (high mortality in downstream sites inhabited by large predatory fish; low mortality in upstream sites lacking large predators). We found significant differences between stream drainages in all morphological variables and most enzymatic variables, but only the mass of the swimming motor and LDH activity were significantly affected by predation regime. Overall, our data show that microevolution has occurred in the physiological foundations of locomotor performance in guppies, but evolutionary changes in physiology do not closely correspond to the predation-induced changes in life history parameters.
Time-course of the effect of dietaryl-tryptophan on plasma cortisol levels in rainbow troutOncorhynchus mykiss
Authors: Lepage Olivier , Vílchez Inmaculada Molina , Pottinger Tom G. , Winberg Svante
Published: September 2003

Isolated juvenile rainbow trout were fed a feed supplemented with l-tryptophan (TRP) for 3, 7 or 28 days, after which they were either sampled directly (undisturbed) or subjected to a standardised stressor prior to sampling. Controls (stressed and undisturbed) received the same feed but without any supplementary TRP. Stress resulted in a significant elevation of plasma [cortisol] in fish fed control feed and in fish fed TRP-supplemented feed for 3 and 28 days. However, fish fed TRP-supplemented feed for 7 days did not show any significant elevation of plasma [cortisol] in response to stress. Plasma levels of adrenocorticotropin followed the same general pattern as cortisol. Plasma and brain [TRP] were elevated in fish fed TRP-supplemented feed. The amino acid TRP is the precursor of the monoamine neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) and the brain 5-HT system is known to be involved in the control of the hypothalamic-pituitary-interrenal (HPI) axis. Fish fed TRP-supplemented feed showed elevated levels of 5-hydroxyindoleacetic acid (5-HIAA, a major 5-HT metabolite) in the hypothalamus and optic tectum. However, TRP treatment did not appear to result in any effects on brain dopaminergic activity and the effects on brain norepinephric activity do not support a role of norepinephrine in mediating the effects of TRP on HPI axis reactivity in rainbow trout.
Characterization of the passive component of force enhancement following active stretching of skeletal muscle
Authors: Herzog W. , Schachar R. , Leonard T. R.
Published: September 2003

The mechanisms causing the steady-state force enhancement following active skeletal muscle stretching are not well understood. Recently, we found direct evidence that part of the force enhancement is associated with the engagement of a passive component. In this study, we reproduced the conditions that give consistent passive force enhancement and evaluated the mechanical properties of this passive force enhancement so as to gain insight into its source. The three primary results were that (1) the passive force enhancement is long lasting (>25 s), (2) passive force enhancement was reduced in a dose-dependent manner by the amount of shortening preceding active muscle stretching, and (3) passive force enhancement could be abolished`instantaneously' by shortening-stretching the passive muscle by an amount equivalent to the active stretch magnitude. Together with the remaining results, we conclude that the source of the passive force enhancement must be arranged in parallel with the contractile force, it must consist of a viscoelastic molecular spring whose stiffness characteristic can be reset by shortening, and it must have a characteristic length that is governed by the length of the contractile components, possibly the sarcomeres. Based on these results, the molecular spring titin emerges as a possible candidate for the passive component of the steady-state force enhancement observed in this and previous studies.
The effect of side-restraint bearings on the performance of base-isolated buildings
Authors: Talbot J P , Hunt H E M
Published: September 2003

Base-isolation of buildings is a common solution to the problem of ground-borne vibration from urban road and rail networks. Conventional designs incorporate vibration isolation bearings between a building and its foundation, aligned in the vertical direction so as to isolate the building from vertical motion of its foundation. In some cases, in order to accommodate horizontal loads, additional side-restraint bearings aligned in the horizontal direction are required.

This paper describes a theoretical investigation into the effect of side-restraint bearings on the performance of base-isolated buildings. Three generic models, based on a modern concrete-framed building, are used to demonstrate that a building's flexibility, the nature of the vibration input and the presence of a flexible foundation are all important in determining isolation performance. It is also illustrated how the concept of isolation frequency, commonly used to indirectly specify the stiffness of base bearings, may not be generally extended to side-restraint bearings. The models indicate that, for maximum performance, the stiffness of any side-restraint bearings should be minimized.
Workspace atlases for the computer aided design of the Delta robot
Authors: Liu X-J , Wang J , Zheng H
Published: September 2003

Parallel robots lead to complex kinematics equations, so determination of their workspaces is a challenging issue. The workspace of a robot is not fully characterized by its volume alone; the workspace shape is an important aspect as well. In this paper, the geometric determination of the workspace for Delta robots is presented. The workspace (workspace volume and workspace shape) for the robots is studied systematically in ‘the physical model of the solution space’, which is a useful tool to express relationships between the performance criteria and all link lengths of one type of robotic mechanism. Performance atlases of the workspace volume for the robots are plotted in the physical model of the solution space. The characteristics of the distribution of the workspace shapes in the physical model of the solution space are presented as well. The physical model of the solution space presents a new method for the computer aided design (CAD) of robotic mechanisms. The results are very useful for obtaining the optimum design of robotic mechanisms.
End-point position control of a single-link arm using shape memory alloy actuators
Authors: Han Y M , Park C J , Choi S B
Published: September 2003

This article presents a novel type of actuating mechanism for the end-point trajectory control of a single-link system. The actuating mechanism consists of two sets of shape memory alloy (SMA) springs to generate a desired link motion of the system. The governing equation of motion is derived using the Lagrangian equation and Jacobian matrix. The actuator dynamic of the SMA spring is then empirically identified and incorporated into the governing equation. A sliding mode controller that is robust to parameter variations such as the time constant of the SMA actuator is formulated to achieve desired end-point trajectories of the single-link system. The controller is experimentally realized and tracking control performances for various end-point position trajectories are presented. In addition, the simulated control results are compared with the measured ones in order to validate the proposed control model.
Componential coding in the condition monitoring of electrical machines Part 1: Principles and illustrations using simulated typical faults
Authors: Webber C J S , Payne B S , Gu F , Ball A D
Published: September 2003

This paper (Part 1) describes the principles of a novel unsupervised adaptive neural network anomaly detection technique, called componential coding, in the context of condition monitoring of electrical machines. Numerical examples are given to illustrate the technique's capabilities. The companion paper (Part 2), which follows, assesses componential coding in its application to real data recorded from a known machine and an entirely unseen machine (a conventional induction motor and a novel transverse flux motor respectively). Componential coding is particularly suited to applications in which no machine-specific tailored techniques have been developed or in which no previous monitoring experience is available. This is because componential coding is an unsupervised technique that derives the features of the data during training, and so requires neither labelling of known faults nor pre-processing to enhance known fault characteristics. Componential coding offers advantages over more familiar unsupervised data processing techniques such as principal component analysis. In addition, componential coding may be implemented in a computationally efficient manner by exploiting the periodic convolution theorem. Periodic convolution also gives the algorithm the advantage of time invariance; i.e. it will work equally well even if the input data signal is offset by arbitrary displacements in time. This means that there is no need to synchronize the input data signal with respect to reference points or to determine the absolute angular position of a rotating part.
Componential coding in the condition monitoring of electrical machines Part 2: Application to a conventional machine and a novel machine
Authors: Payne B S , Gu F , Webber C J S , Ball A D
Published: September 2003

This paper (Part 2) presents the practical application of componential coding, the principles of which were described in the accompanying Part 1 paper. Four major issues are addressed, including optimization of the neural network, assessment of the anomaly detection results, development of diagnostic approaches (based on the reconstruction error) and also benchmarking of componential coding with other techniques (including waveform measures, Fourier-based signal reconstruction and principal component analysis). This is achieved by applying componential coding to the data monitored from both a conventional induction motor and from a novel transverse flux motor. The results reveal that machine condition monitoring using componential coding is not only capable of detecting and then diagnosing anomalies but it also outperforms other conventional techniques in that it is able to separate very small and localized anomalies.
Dimensional analysis of leakage and mechanical power losses of kinematic Stirling engines
Authors: Prieto J I , Stefanovskiy A B
Published: September 2003

Dimensional analysis is applied to both leakage and mechanical power losses in order to obtain the set of parameters that influence power performance of the kinematic Stirling engine. An empircical model of mechanical power losses is proposed to complete the indicated power model previously introduced by Prieto and co-workers. That approach is mainly based on the characteristic Stirling number and allows the performance of known prototypes to be analysed from the viewpoint of indicated power, brake power and mechanical efficiency. After showing that similarity criteria can be extended to brake power performance, scaling factors have been derived for typical scaling cases. Some examples show that quasi-static simulation and scaling techniques may be combined to support preliminary design procedures.
Use of the inverse method to check the stress predictions in rough elastohydrodynamic lubrication contacts lubricated with a non-Newtonian fluid for a range of asperity geometries
Authors: Hooke C J , Li K Y
Published: September 2003

The inverse method enables a check to be made on the pressures and stresses calculated in rough elastohydrodynamic lubrication (EHL) contacts. Essentially, a rough, soft surface is run against a smooth, hard counterface in a twin disc machine for a limited time. This tends to deform the asperities on the soft disc and, at the end of the run, the profile is measured and used as input to an EHL solver to determine the hydrodynamic pressures. From these the stresses are calculated. If the material has deformed and deformation has ceased, the maximum stress should be equal to the yield strength of the soft disc. This comparison provides a quantitative check on the accuracy of the EHL analysis and on the assumptions made about the fluid rheology. Allowance has, of course, to be made for the build-up of residual stress in the disc material.

The method is applied here to surfaces in which defects with a range of sizes have been manufactured. A non-Newtonian fluid with reasonably well-established characteristics was used under conditions of moderate slip. Good agreement is found between the predicted stresses and the material strength for all defect geometries, suggesting that the fluid properties are sufficiently well defined for accurate predictions to be made of the pressures and stresses in EHL conjunctions.
Influence of layers on flexural motion of a multilayer assembly due to the laser ablation process
Authors: Yilbas B S , Hyder J
Published: September 2003

Laser-induced evaporation results in recoil pressure at the vapour-liquid interface, which in turn gives rise to flexural wave generation in the substrate material due to impact pressure loading at the interface. In the present study, recoil pressure due to laser non-conduction limited heating is formulated and because of pressure loading at the vapour-liquid interface the flexural motion of the substrate material is modelled. A multilayer cantilever arrangement of the workpiece, consisting of layers of steel and Inconel alloy, is considered. In order to investigate the influence of the number of layers on the resulting flexural motion and stress fields, four cases and three layer arrangements are taken into account. It is found that the maximum displacement in the order of 10-4m occurs while the maximum equivalent stress is about 20 MPa. The maximum magnitude of shear stress is higher than that of equivalent stress.
An investigation into the non-linear dynamics of an unbalanced flexible rotor running in an unsupported squeeze-film damper bearing
Authors: Bonello P , Brennan M J , Holmes R
Published: September 2003

The non-linear dynamics of a multimodal flexible rotor running in an unsupported squeeze-film damper (SFD) bearing are investigated analytically and experimentally. The main aim is to assess the ability to predict and explain the non-linear performance using an integrated analytical technique and a standard model for the SFD. A fast harmonic balance method that uses receptance functions is used to determine periodic solutions. A modal-based approach is used for the analysis of the stability and bifurcation of these solutions, as well as the analysis of aperiodic motion. Non-synchronous motion with combination frequencies and subharmonic motions are correctly predicted. It is also shown that such an SFD introduces subcritical superharmonic resonance when it is apparently inactive. It is concluded that, despite the economy in design, the benefits of using an unsupported SFD in a flexible rotor-rigid bearing housing system are dubious.
Experimental investigation of unsteady flow phenomena in a three-stage axial compressor
Authors: Niehuis R , Bohne A , Hoynacki A
Published: September 2003

In the past years, a three-stage axial compressor equipped with a modern controlled diffusion airfoil (CDA) blading has been investigated in much detail, applying state-of-the-art steady and unsteady measurement techniques, at RWTH Aachen University. The compressor under investigation exhibits design features of real industrial compressors. By performing high-resolution measurements both in space and time, a thorough insight into various flow phenomena in the compressor has been achieved, leading to a better understanding of various flow phenomena such as rotor—stator interaction, tip clearance flow and viscous flow effects in a multistage compressor environment. After a short summary of some performance characteristics at design and off-design, this paper focuses on the analysis of interaction phenomena present in the three-stage axial compressor. The interaction phenomena are described on a more global scale. In order to quantify the upstream and downstream influence of the three rotor blades, a suitable parameter is presented.
Boundary layer investigations on a highly loaded transonic compressor cascade with shock/laminar boundary layer interactions
Authors: Hilgenfeld L , Cardamone P , Fottner L
Published: September 2003

Detailed experimental and numerical investigations of the flowfield and boundary layer on a highly loaded transonic compressor cascade were performed at various Mach and Reynolds numbers representative of real turbomachinery conditions. The emerging shock system interacts with the laminar boundary layer, causing shock-induced separation with turbulent reattachment. Steady two-dimensional calculations have been performed using the Navier—Stokes solver TRACE-U. The flow solver employs a modified version of the one-equation Spalart—Allmaras turbulence model coupled with a transition correlation by Abu-Ghannam/Shaw in the formulation by Drela. The computations reproduce well the experimental results with respect to the profile pressure distribution and the location of the shock system. The transitional behaviour of the boundary layer and the profile losses in the wake are properly predicted as well, except for the highest Mach number tested, where large separated regions appear on the suction side.
Effect of forward sweep in a transonic compressor rotor
Authors: Passrucker H , Engber M , Kablitz S , Hennecke D. K.
Published: September 2003

This paper presents the design and testing of a transonic compressor rotor with forward sweep. The rotor was used to investigate the influence of forward sweep on the performance and stability of a single-stage transonic compressor compared with a baseline design with radially stacked blade sections. The comparison was done numerically with the three-dimensional Navier—Stokes code TRACE-S and experimentally in the Darmstadt transonic compressor test rig. It was found that the new rotor with forward sweep has an increased efficiency and also a much better stall margin (much more in the rig test than predicted by the three-dimensional Navier—Stokes calculation). Particularly close to stall, the forward sweep diverts the flow towards the blade tip region which helps to stabilise this region. For that reason it is possible to throttle the forward-swept rotor much further than the radially stacked rotor, although the forward-swept rotor does already suffer from separated flow in the hub.
Transonic radial compressor inlet design
Authors: Lohmberg A , Casey M , Ammann S
Published: September 2003

The design of radial compressor inlets for transonic flow is examined. A theoretical model [1] quantifies the losses in the tip sections caused by the choke margin (incidence) and the blockage of the blades. It identifies clear design rules for the tip sections: to achieve the highest efficiency, these require minimum blockage (low blade thickness and splitter vanes) and low choke margin (close to the unique-incidence condition). Simulations of the NASA rotor 37 transonic axial compressor (with CFX-TASCflow) are used to validate the use of three-dimensional viscous computational fluid dynamics (CFD) for transonic compressor inlets and to demonstrate that the key performance features suggested by the simple model are also modelled in three-dimensional viscous flow simulations. The simple model together with CFD simulations has been used for the design of tip sections at the inlet of a transonic radial compressor. CFD simulations were used to select the position of the shock to give a low choke margin, to reduce the preshock Mach number and also to optimize the shape and position of the leading edge of the splitter vanes.
Active control of the aerodynamic performance and tonal noise of axial turbomachines
Authors: Neuhaus L , Schulz J , Neise W , Möser M
Published: September 2003

Two projects on axial fans are presented in this paper. The first aims at improving the aerodynamic performance and reducing the tip clearance noise caused by the rotating instability. This is achieved by injecting air into the radial gap between the impeller blade tips and the fan casing. Steady air injection with small mass flows results in remarkable reductions in the noise level along with improved aerodynamic performance. Larger injected mass flows give significant improvements in the aerodynamic performance at the expense of an increased overall noise level. The second project uses flow control actively to reduce the blade passage frequency (BPF) level. Experimental results are presented for steady jets injected into the main flow and cylindrical rods at axial positions downstream of the impeller blades. The method is successful for higher-order mode sound fields where the BPF level is reduced by up to 20.5 dB.
Influence of blade passing on the stator wake in a transonic turbine stage investigated by particle image velocimetry and laser vibrometry
Authors: Woisetschläger J , Lang H , Hampel B , Göttlich E , Heitmeir F
Published: September 2003

The aerodynamic behaviour of stator and rotor interaction in axial flow turbines is complex and highly unsteady. Particle image velocimetry (PIV) and laser vibrometry (LV) were used to investigate the phenomena observed in a transonic turbine stage operated continuously in a cold-flow test rig. While LV gave basic information on the frequency behaviour of the density fluctuations in the stator wake, stereoscopic PIV was used for investigations of the flowfield vorticity during rotor blade passing. Phase locking of the vortex shedding to the seventh and eighth harmonics of the blade passing frequency was observed.
Experimental and numerical investigation of trailing edge film cooling downstream of a slot with internal rib arrays
Authors: Martini P , Schulz A , Whitney C. F. , Lutum E
Published: September 2003

To enhance turbine efficiency, the trailing edge thickness of stators and blades needs to be as thin as possible. One limitation on the trailing edge thickness is the requirement to cool this life-limiting region of the blade. One technique used to achieve a thin cooled trailing edge is that of a pressure side cutback with film cooling slots. There is a paucity of fluid and heat transfer data regarding this type of geometry which is currently being addressed by the EC-funded Framework V project AITEB. This paper reports on experimental work being undertaken by the University of Karlsruhe and accompanying computational fluid dynamics (CFD) calculations being performed by MTU Aero Engines and ALSTOM Power. Experimental and numerical data presented include cutback surface film cooling effectiveness together with slot discharge coefficient values.
Direct numerical simulation, large eddy simulation and unsteady Reynolds-averaged Navier—Stokes simulations of periodic unsteady flow in a low-pressure turbine cascade: A comparison
Authors: Michelassi V , Wissink J. G. , Rodi W
Published: September 2003

The unsteady periodic flow in a low-pressure (LP) prismatic turbine vane with incoming wakes is computed by direct numerical simulation (DNS), large eddy simulation (LES) and unsteady Reynolds-averaged Navier—Stokes simulations (URANSs). The results are compared with existing measurements at a Reynolds number Re = 5.18 × 104 which reveal the presence of a large unsteady stalled region on the suction side. Both DNS and LES suggest that the boundary layer separates while being still laminar, with subsequent turbulent reattachment. Several URANSs with and without a transition model and a constraint on the turbulence time-scale designed to prevent excessive production in the stagnation region are analysed and compared with the DNS and LES. The useful information provided by DNS and LES has made it possible to improve the results of the URANSs, which ensure a fair reproduction of the flow, especially in terms of blade load and losses, although they partly fail to detail the complex wake—boundary layer interaction in the separated flow region.
Unsteady dissipation measurements on a flat plate subject to wake passing
Authors: Stieger R. D. , Hodson H. P.
Published: September 2003

Boundary layer measurements were performed on a flat plate with an imposed pressure gradient typical of a high-lift low-pressure (LP) turbine blade and subject to incoming turbulent wakes shed from a moving bar wake generator. A multiple-orientation one-dimensional laser doppler anemometry (LDA) technique was used to measure the ensemble-average mean flow and Reynolds stresses. These ensembleaverage measurements were used to calculate the boundary layer dissipation, thereby providing unprecedented experimental evidence of the loss-reducing mechanisms associated with wake-induced transition. The benign character of the calmed zone was confirmed and the early stages of boundary layer separation were found to have laminar levels of dissipation. A deterministic natural transition phenomenon was identified between wake passing events, highlighting the existence of natural transition phenomena in LP turbine style pressure distributions.
Heat transfer measurements on an intermediate-pressure nozzle guide vane tested in a rotating annular turbine facility, and the modifying effects of a non-uniform inlet temperature profile
Authors: Povey T , Chana K. S. , Jones T. V.
Published: September 2003

In modern gas turbine engines there exist significant temperature gradients in the combustor exit flow. These gradients arise because both fuel and dilution air are introduced within the combustor as discrete jets. The effects of this non-uniform temperature field on the aerodynamics and heat transfer rate distributions of nozzle guide vanes and turbine blades is difficult to predict, although an increased understanding of the effects of temperature gradients would enhance the accuracy of estimates of turbine component life and efficiency. Low-frequency measurements of heat transfer rate have been conducted on an annular transonic intermediate-pressure (IP) nozzle guide vane operating downstream of a high-pressure (HP) rotating turbine stage. Measurements were conducted with both uniform and non-uniform inlet temperature profiles. The non-uniform temperature profile included both radial and circumferential gradients of temperature. Experiments were conducted in the isentropic light piston facility at QinetiQ Pyestock, a short-duration engine-size turbine facility with 1.5 turbine stages, in which Mach number, Reynolds number and gas—wall temperature ratios are correctly modelled. Experimental heat transfer results are compared with predictions performed using boundary layer methods.
Influence of the state of the inlet endwall boundary layer on the interaction between pressure surface separation and endwall flows
Authors: de la Blanco E. Rosa , Hodson H. P. , Vazquez R , Torre D
Published: September 2003

This paper describes the effect of the state of the inlet boundary layer (laminar or turbulent) on the structure of the endwall flow on two different profiles of low-pressure (LP) turbine blades (solid thin and hollow thick). At present the state of the endwall boundary layer at the inlet of a real LP turbine is not known. The intention of this paper is to show that, for different designs of LP turbine, the state of the inlet boundary layer affects the performance of the blade in very different ways. The testing was completed at low speed in a linear cascade using area traversing, flow visualization and static pressure measurements. The paper shows that, for a laminar inlet boundary layer the two profiles have a similar loss distribution and structure of endwall flow. However, for a turbulent inlet boundary layer the two profiles are shown to differ significantly in both the total loss and endwall flow structure. The pressure side separation bubble on the solid thin profile is shown to interact with the passage vortex, causing a higher endwall loss than that measured on the hollow thick profile.
Optimization of blade—diffuser interaction for improved turbine performance
Authors: Kreitmeier F , Greim R
Published: September 2003

Flowfields within turbines are generally three-dimensional and unsteady. Typically, the flow-fields in the interaction zone between the last stage and the diffuser are strongly inhomogeneous. This non-uniformity strongly limits the downstream diffusion process, so that significant improvement can be achieved by making the total pressure field in this zone more uniform. One way to achieve this is by using kinks in the endwall contours and, if necessary, one or two splitters. The use of balance-based space averaging and modelling procedures can help to characterize these flows, and to develop an optimum interaction zone and diffuser geometry. In the study described here, as an example the interaction zone of high-pressure/intermediate-pressure (HP/IP) and low-pressure (LP) diffusers of steam turbines were numerically and partly experimentally optimized for a fixed blading and exhaust. The operating conditions were also kept constant except that for low pressures the flowfield was studied for a range of back pressures (i.e. exhaust velocities). The optimization process starts with an initial flowfield in the interaction zone generated numerically or experimentally. Using these data a design procedure is applied that creates both a much more uniform total pressure field at the last stage exit and a diffuser geometry possibly with one or two splitters and proven for an earlier LP design experimentally. It was demonstrated that, depending on the inhomogeneity of the flow from the upstream stage, a performance improvement of several percentage points could be achieved.
Nucleation phenomena in a multi-stage low pressure steam turbine
Authors: Bohn D. E. , Sürken N , Kreitmeier F
Published: September 2003

During the expansion of steam in the low pressure (LP) stages of steam turbines, the originating two-phase wet-steam mixture causes considerable thermodynamic losses as well as aerodynamic losses. The reduction of these loss mechanisms is the subject of research project at the Institute of Steam and Gas Turbines, Aachen University.

A three-dimensional nucleating wet steam flow with homogeneous/heterogeneous nucleation in the three front stages of an industrial LP-steam turbine is investigated numerically. The steady, viscous, and compressible metastable steam flow calculations are performed with a Navier—Stokes flow solver incorporating the IAPWS-IF97 steam tables. A union numerical approach for both the homo- and heterogeneous nucleation occurring on soluble nuclei is employed to capture the effects related to the nucleation phenomenon. The model links the interfacial surface tension, the size of nuclei, the chemical characteristics of the substances forming the droplets, and the expansion rate with the nucleation rate. In order to take into account the additional viscous effects due to shrouded bladings, the open shroud cavities are modeled in detail. Droplet density spectra, radial droplet number, droplet diameter, and wetness fraction distributions at the exit of the third stage are calculated.

It is shown that impurities can cause nucleation to appear at lower supersaturations with higher nucleation rates compared to homogeneous nucleation of pure steam. In this way, thermodynamic and kinematic relaxation losses are reduced. Owing to the dissipative viscous effects near the endwalls, the nucleation fronts exhibit convex shapes. They are locally bound within the region of high expansion rates in the second stage's nozzle guide vane. For both heterogeneous and homogenous nucleating flows the wetness is highly dispersed with narrow droplet density spectra behind the three front stages.
Demonstration of balance-based space averaging and modelling in view of blading—diffuser interaction
Authors: Kreitmeier F , Lücking P
Published: September 2003

Advanced experimental and numerical methods in the field of fluid dynamics and turbomachinery are increasingly successful in describing real flowfields, i.e. fields that are generally three-dimensional and unsteady. For many purposes, e.g. flow characterization, it is necessary to reduce these flowfields step by step to three-, two- or one-dimensional large-scale unsteady flowfields. This procedure permits a lower-level simulation of the flowfields. However, many averaging approaches are arbitrary or succeed in balancing the flowfields in only a few physical aspects. The first author has already shown the steps of a balance-based procedure that avoids this limitation. Small-scale time averaging of (probabilistically) turbulent inhomogeneities by means of irreversible and reversible small-scale time averaging processes on a threefold infinitesimal control volume element has already been demonstrated. The present paper demonstrates the balance-based procedure of space averaging. It is carried out by averaging generally three-dimensional small-scale time-averaged (deterministic) inhomogeneities using irreversible and reversible space averaging processes on onefold infinitesimal and finite control surfaces. The procedure is, similarly to small-scale time averaging, based on conservative and independent non-conservative small-scale time-averaged integral balance equations. The general concept is to represent all the relevant fluxes through the control surface by appropriate average quantities or numbers. The full use of the vector equations for the linear and angular momentum is important. One of the consequences in space averaging is the introduction of a wrench (parallel linear and angular momentum vectors), which is generally used only in mechanics for the reduction of force systems in space. The flowfield inhomogeneity is described on all dimensional levels via the diffusion intensity of the irreversible averaging process, and, only for space averaging, via the distance vector and the parameter of the wrench. A numerical example on different dimensional levels is presented in detail. The procedure also illustrates the basis of a new and more complete two-and one-dimensional large-scale unsteady theory generally in fluid dynamics and especially in turbomachinery.
Stall inception phenomena in a single-stage axial-flow pump
Authors: Goltz I , Kosyna G , Stark U , Saathoff H , Bross S
Published: September 2003

The paper describes an experimental investigation on stall inception phenomena in a single-stage axial-flow pump, utilizing an oil flow technique and two different photo techniques. Moreover, the unsteady casing wall pressure was measured. Representative results are shown and discussed: the pump characteristic for two different NPSH values, selected oil flow pictures of the casing wall and the rotor blades, the wall pressure distribution at design, selected pictures of the cavitating core of the tip clearance vortex at stable and unstable operating conditions and the visualization of a cross-passage vortex as a deep stall phenomenon. These results allow a number of key features of the stall inception process to be identified and to be followed along the unstable part of the pump characteristic.
Hydrolysis of Diribonucleoside Monophosphate Diesters Assisted by a Manganese(II) Complex
Authors: Yashiro Morio , Higuchi Maiko , Komiyama Makoto , Ishii Youichi
Published: September 2003

An Mn2+ complex with 2,2′:6′,2″-terpyridine (terpy) was found to promote the hydrolysis of NpN (NpN = diribonucleoside monophosphate diester) efficiently at pH 7.0 and 50 °C under ambient conditions. The structure of the Mn2+ complex involving a phosphodiester molecule, [(terpy)(dpp)MnII(μ-dpp)2MnII(dpp)(terpy)], dpp = diphenyl phosphate anion, was established by X-ray crystallography, and the coordination mode of Mn2+ to a phosphodiester molecule was considered.
Convergent Total Syntheses of Oligosaccharides by One-Pot Sequential Stereoselective Glycosylations
Authors: Hashihayata Takashi , Ikegai Kazuhiro , Takeuchi Kazuya , Jona Hideki , Mukaiyama Teruaki
Published: September 2003

A convergent total synthesis of F1α antigen, a member of the tumor-associated O-linked mucin glycosyl amino acid, was tried by one-pot sequential glycosylation. Highly α-selective glycosylation of amino acid 7 with thioglycoside 6 was successfully carried out by combining trityl trifluoromethanesulfonate (TrOTf) and N-iodosuccimide (NIS) which gave glycosyl amino acid 21 in high yield (97%, α/β = 83⁄17). Next, the glycosylation of thioglycoside 4 with galactosyl phenyl carbonate 2 or fluoride 3 was tried by the promotion of trityl tetrakis(pentafluorophenyl)borate [TrB(C6F5)4] or trifluoromethanesulfonic acid (TfOH); protected F1α 25 was afforded in 80 or 89% overall yield, respectively, by the further addition of glycosyl amino acid 5 and NIS. The desired trisaccharide was obtained in high yield after removal of the protecting groups. Next, a convergent total synthesis of branched hepta-β-glucoside 30 having phytoalexin-elicitor activity was efficiently performed by way of two one-pot sequential glycosylation reactions: that is, trisaccharide 34 was synthesized in high yield by TfOH-catalyzed one-pot glycosylation using three given monosaccharides (31, 35, and 36) as shown in Scheme 12 and by subsequent selective deprotection of 6′-O-TBDPS group. The second one-pot glycosylation of trisaccharide 34 with three monosaccharides (31, 32, and 33d) also proceeded smoothly to afford heptaglucoside 43 stereoselectively in 48% total yield based on monosaccharide 32. Phytoalexin-elicitor active branched hepta-β-glucoside 30 was afforded by the sequential deprotection.
Efficient Synthesis of Heterocyclic 2-Deoxysteptamine Derivatives as RNA Binding Ligands
Authors: Ding Yili , Hofstadler Steven A , Swayze Eric E , Griffey Richard H
Published: September 2003

An efficient strategy for the synthesis of heterocyclic 2-deoxystreptamine derivatives is described. The resulting compounds showed good RNA binding affinities from ESI-MS RNA binding assay.
Synthesis and Properties of Carbazole–Terephthalate Cyclophane
Authors: Tani Keita , Matsumura Koh , Togo Eiichi , Hori Kazushige , Tohda Yasuo , Takemura Hiroyuki , Ohkita Hideo , Ito Shinzaburo , Yamamoto Masahide
Published: September 2003

As a first example of carbazole–acceptor cyclophane, carbazole–terephthalate cyclophane 1a was prepared. The structure of 1a was characterized by 1H NMR and X-ray analysis. Absorption spectrum of 1a showed the existence of transannular π–π electronic interaction and little charge transfer interaction. Fluorescence spectrum of 1a in THF exhibited intramolecular exciplex emission around 525 nm.
Synthesis of Stannole Anion by Alkylation of Stannole Dianion
Authors: Saito Masaichi , Haga Ryuta , Yoshioka Michikazu
Published: September 2003

Reaction of tert-butylchloride with the stannole dianion first and simply prepared by the reduction of 1,1,2,3,4,5-hexaphenylstannole with lithium in ether gave 1-tert-butylstannole anion which was characterized by 1H, 13C, 119Sn, and 7Li NMR spectra and whose reactivities were investigated.
Biphenylene Bridged Bifunctional Hybrid Mesoporous Silsesquioxanes with Sulfonic Acid Functionalities and Crystalline Pore Walls
Authors: Kapoor Mahendra P , Yang Qihua , Goto Yasutomo , Inagaki Shinji
Published: September 2003

The first synthesis of highly hydrophobic bifunctional biphenylene bridged hybrid mesoporous silsesquioxane with sulfonic acid functionalities and crystalline pore walls is reported.
Water-soluble Fluorescent Nanospheres as Fluorosensor for Detection of Cu2+
Authors: Xu Shiyi , Tu Guoli , Han Xiaozu
Published: September 2003

A novel water-soluble fluorescent nanosphere as fluorosensor was prepared by emulsifier-free emulsion copolymerization of styrene with naphthalimide derivative (A). The fluorosensor was high sensitive for detection of Cu2+. Comparied with other fluorosensors based on organic fluorophore, it has two advantages. First, there is no pollution to environment in the use of it. Second, it can be used repeatedly.
A Facile Method for Synthesis of Alkyl Phenyl Selenides. The Reaction of Diphenyl Diselenide with Oxygen-containing Compounds Using La/Me3SiCl/cat.I2/cat.CuI System
Authors: Nishino Toshiki , Nishiyama Yutaka , Sonoda Noboru
Published: September 2003

Alcohols, ethers, and esters were directly converted to the corresponding alkyl phenyl selenides by the reaction of diphenyl diselenide and the La/Me3SiCl/cat.I2/cat.CuI. It was suggested that alkyl phenyl selenides were formed by the SH2 type reaction of diphenyl diselenide with alkyl radicals generated from alcohols, ethers or esters.
Tungstophosphoric Acid-catalyzed Oxidative Desulfurization of Light Oil with Hydrogen Peroxide in a Light Oil/Acetic Acid Biphasic System
Authors: Yazu Kazumasa , Furuya Takeshi , Miki Keiji , Ukegawa Koji
Published: September 2003

Dibenzothiophenes were oxidized effectively with H2O2 in the presence of 12-tungstophosphoric acid in the tetradecane/AcOH biphasic system to give their corresponding sulfones as the major products. The oxidation proceeded in the AcOH phase and most of the sulfones distributed there, resulting in the successive removal of the sulfur compounds from the tetradecane phase. This biphasic oxidation system can effectively reduce the sulfur content in light oil.
Structure Analysis of Photo-induced Triplet Phenylnitrene Using Synchrotron Radiation
Authors: Kawano Masaki , Takayama Terufumi , Uekusa Hidehiro , Ohashi Yuji , Ozawa Yoshiki , Matsubara Koudatsu , Imabayashi Hidekazu , Mitsumi Minoru , Toriumi Koshiro
Published: September 2003

The crystal structures of [(PhCH2)2NH2]+[m-C6H4(N3)(COO)]− before and after UV-irradiation were analyzed at 25 K by using an X-ray vacuum camera set up at the synchrotron laboratory (SPring-8). The C–N (nitrene) bond distance in the triplet state of the photo-induced m-carboxyphenylnitrene is determined to be 1.34(4) Å.
Preparation of CO2 Absorbent by Spray Pyrolysis
Authors: Choi Ki-Hyouk , Korai Yozo , Mochida Isao
Published: September 2003

Li2ZrO3 particles were prepared by spray pyrolysis and solid state reaction to compare their CO2 absorption capacity and rate. The former method provided much higher CO2 absorption capacity and rate than those by the latter. Spherical particles of rather small and uniform size allow the faster diffusion of Li to the surface for higher CO2 absorption capacity and regeneration of absorption through CO2 recovery.
Crystal Structures of 9,10-Bis[bis(2-pyridylmethy)aminomethyl]anthracene and Its ZnCl2 Complex. Intramolecular π–π Interaction between Anthracene and ZnCl2-complexed Pyridine
Authors: Kubo Kanji , Mori Akira
Published: September 2003

Anthracene derivatives having dipicolylaminomethyl group exhibited an emission-intensity enhancement in the presence of Zn2+. On the basis of an X-ray crystallographic analysis, the binding of Zn2+ to the dipicolylaminomethyl unit inhibits the photoinduced electron transfer process. Intramolecular π–π interactions between the anthracene and the ZnCl2-complexed pyridine were observed.
Porous Phosphor Thin Films of Oxyfluoride SiO2–BaMgF4: Eu2+ Glass–Ceramics Prepared by Sol–Gel Method
Authors: Fujihara Shinobu , Kitta Seiki , Kimura Toshio
Published: September 2003

Eu2+ ions were incorporated into SiO2–BaMgF4 glass–ceramic thin films using a sol–gel method. The addition of N,N-dimethylformamide to a starting solution resulted in a porous microstructure of the film prepared. The films exhibited blue emission peaking at 420 nm by excitation at 290 nm. The emission was effectively enhanced in the porous film owing to scattering absorption of the excitation light.
Photocatalytic Degradation of 2-Propanol Diluted in Water with TiO2 Photocatalyst Loaded on Si3N4
Authors: Yamashita Hiromi , Maekawa Kazuhiro , Nakatani Yoshihiro , Park Jin-Joo , Anpo Masakazu
Published: September 2003

TiO2 photocatalysts loaded on Si3N4 (TiO2/Si3N4) prepared by an impregnation method showed higher photocatalytic activity for the degradation of 2-propanol diluted in water than TiO2 loaded on SiO2 (TiO2/SiO2). The formation of well-crystallized TiO2 on Si3N4 and the hydrophobic property of Si3N4 were found to be related to the efficient photocatalytic activity of TiO2/Si3N4.
Halogenation of Aromatic Compounds by N-chloro-, N-bromo-, and N-iodosuccinimide
Authors: Tanemura Kiyoshi , Suzuki Tsuneo , Nishida Yoko , Satsumabayashi Koko , Horaguchi Takaaki
Published: September 2003

An efficient and mild method for the halogenation of aromatic compounds using N-chloro-, N-bromo-, and N-iodosuccinimide in the presence of NH4NO3 or FeCl3 in acetonitrile was developed.
Crystal Structure of Bis(dimethyldioctadecylammonium) Hexamolybdate: a Molecular Model of Langmuir–Blodgett Films
Authors: Ito Takeru , Sawada Keiju , Yamase Toshihiro
Published: September 2003

Dimethyldioctadecylammonium salts of reduced polyoxomolybdates in the organic solvent are gradually oxidized to provide bis(dimethyldioctadecylammonium) hexamolybdate, the crystal structure of which affords a molecular model for Langmuir–Blodgett films.
Polymer and “Trimer-of-Dimers” Complexes Derived from [Rh2(form)4] (form− = N,N′-Di-p-tolylformamidinate anion) and 1,4-Diisocyanobenzene
Authors: Handa Makoto , Yasuda Motoi , Muraki Yasuhiro , Yoshioka Daisuke , Mikuriya Masahiro , Kasuga Kuninobu
Published: September 2003

A polymer complex ([Rh2(form)4(1,4-dib)]n; form− = N,N′-di-p-tolylformamidinate anion, 1,4-dib = 1,4-diisocyanobenzene) and a “trimer-of-dimers” complex ([{Rh2(form)4}3(1,4-dib)2]) were prepared. They were characterized based on the elemental analyses, X-ray structure analyses, and diffuse reflectance spectra.