An Impact Of Various Shroud Bleed Slot Configurations And Cavity Vanes On Compressor Map Width And The Inducer Flow Field

This paper describes an investigation of map width enhancement and a detailed analysis of the inducer flow field due to various bleed slot configurations and vanes in the annular cavity of a turbocharger centrifugal compressor. The compressor under investigation is used in a turbocharger application for a heavy duty diesel engine of approximately 400 hp. This investigation has been undertaken using a computational fluid dynamics (CFD) model of the full compressor stage, which includes a manual multiblock-structured grid generation method. The influence of the bleed slot flow on the inducer flow field at a range of operating conditions has been analyzed, highlighting the improvement in surge and choked flow capability. The impact of the bleed slot geometry variations and the inclusion of cavity vanes on the inlet incidence angle have been studied in detail by considering the swirl component introduced at the leading edge by the recirculating flow through the slot. Further, the overall stage efficiency and the nonuniform flow field at the inducer inlet have been also analyzed. The analysis revealed that increasing the slot width has increased the map width by about 17%. However, it has a small impact on the efficiency, due to the frictional and mixing losses. Moreover, adding vanes in the cavity improved the pressure ratio and compressor performance noticeably. A detail analysis of the compressor with cavity vanes has also been presented.

Map Width Enhancement Technique for a Turbocharger Compressor

This paper presents an investigation of map width enhancement and the performance improvement of a turbocharger compressor using a series of static vanes in the annular cavity of a classical bleed slot system. The investigation has been carried out using both experimental and numerical analysis. The compressor stage used for this study is from a turbocharger unit used in heavy duty diesel engines of approximately 300 kW. Two types of vanes were designed and added to the annular cavity of the baseline classical bleed slot system. The purpose of the annular cavity vane technique is to remove some of the swirl that can be carried through the bleed slot system, which would influence the pressure
ratio. In addition to this, the series of cavity vanes provides a better guidance to the slot recirculating flow before it mixes with the impeller main inlet flow. Better guidance of the flow improves the mixing at the inducer inlet in the circumferential direction. As a consequence, the stability of the compressor is improved at lower flow rates and a wider map can be achieved. The impact of two cavity vane designs on the map width and performance of the compressor was highlighted through a detailed analysis of the impeller flow field. The numerical and experimental study revealed that an effective vane design can improve the map width and pressure ratio characteristic without an efficiency penalty compared to the classical bleed slot system without vanes. The comparison study between the cavity vane and noncavity vane configurations presented in this paper showed that the map width was improved by 14.3% due to a significant reduction in surge flow and the peak pressure ratio was improved by 2.25% with the addition of a series of cavity vanes in the annular cavity of the bleed slot system.

Determining trophic niche width: An experimental test of the stable isotope approach

Determining the trophic niche width of an animal population and the relative degree to which a generalist population consists of dietary specialists are long-standing problems of ecology. It has been proposed that the variance of stable isotope values in consumer tissues could be used to quantify trophic niche width of consumer populations. However, this promising idea has not yet been rigorously tested. By conducting controlled laboratory experiments using model consumer populations (Daphnia sp., Crustacea) with controlled diets, we investigated the effect of individual- and population-level specialisation and generalism on consumer d C mean and variance values. While our experimental data follow general expectations, we extend current qualitative models to quantitative predictions of the dependence of isotopic variance on dietary correlation time, a measure for the typical time over which a consumer changes its diet. This quantitative approach allows us to pinpoint possible procedural pitfalls and critical sources of measurement uncertainty. Our results show that the stable isotope approach represents a powerful method for estimating trophic niche widths, especially when taking the quantitative concept of dietary correlation time into account. © 2012 The Authors.

A LEED STRUCTURAL STUDY OF THE CO INDUCED RECONSTRUCTION OF PD(110) - EVIDENCE FOR A MISSING ROW STRUCTURE

Molecularly adsorbed CO on Pd{110} has been shown (R. Raval et al., Chem. Phys. Lett. 167 (1990) 391, ref. [1]) to induce a substantial reconstruction of the surface in the coverage range 0.3 <theta less-than-or-equal-to 0.75. Throughout this coverage range, the adsorbate-covered reconstructed surface exhibits a (4 x 2) LEED pattern. However, the exact nature of the reconstruction remains uncertain. We have conducted a LEED I(E) "fingerprinting" analysis of the CO/Pd{110}-(4 x 2) structure in order to establish the type of reconstruction induced in the metal surface. This study shows that the LEED I(E) profiles of the integral order and appropriate half-order beams of the CO/Pd{110}-(4 x 2) pattern closely resemble the I(E) profiles theoretically calculated for a Pd{110}-(1 x 2) missing-row structure. Additionally, there is a strong resemblance to the experimental LEED I(E) profiles for the Cs/Pd{110}-(1 x 2) structure which has also been shown to exhibit the missing-row structure. On the basis of this evidence we conclude that the CO/Pd{110}-(4 x 2) LEED pattern arises from a missing-row reconstruction of the Pd{110} surface which gives rise to a strong underlying (1 x 2) pattern plus a poorly ordered CO overlayer which produces weak, diffuse fourth-order spots in the LEED pattern.

An Investigation of Compressor Map Width Enhancement and the Inducer Flow Field Using Various Configurations of Shroud Bleed Slot

This paper describes an investigation of various shroud bleed slot configurations of a centrifugal compressor using CFD with a manual multi-block structured grid generation method. The compressor under investigation is used in a turbocharger application for a heavy duty diesel engine of approximately 400hp. The baseline numerical model has been developed and validated against experimental performance measurements. The influence of the bleed slot flow field on a range of operating conditions between surge and choke has been analysed in detail. The impact of the returning bleed flow on the incidence at the impeller blade leading edge due to its mixing with the main through-flow has also been studied. From the baseline geometry, a number of modifications to the bleed slot width have been proposed, and a detailed comparison of the flow characteristics performed. The impact of slot variations on the inlet incidence angle has been investigated, highlighting the improvement in surge and choked flow capability. Along with this, the influence of the bleed slot on stabilizing the blade passage flow by the suction of the tip and over-tip vortex flow by the slot has been considered near surge.

Community engagement in Belfast: Queen's University and the Sandy Row community

This chapter examines a case study of a university-community civic engagement project involving a homework club in an area of significant educational and social disadvantage. The chapter gives voice to community leaders who talk about the role of the initiative and their relationship with the university.

Learning Bounded Tree-Width Bayesian Networks via Sampling

Learning Bayesian networks with bounded tree-width has attracted much attention recently, because low tree-width allows exact inference to be performed efficiently. Some existing methods [12, 14] tackle the problem by using k-trees to learn the optimal Bayesian network with tree-width up to k. In this paper, we propose a sampling method to efficiently find representative k-trees by introducing an Informative score function to characterize the quality of a k-tree. The proposed algorithm can efficiently learn a Bayesian network with tree-width at most k. Experiment results indicate that our approach is comparable with exact methods, but is much more computationally efficient.

Determinants and two-year change in anterior chamber angle width in a Chinese population

Objective: To study the population distribution and longitudinal changes in anterior chamber angle width and its determinants among Chinese adults. Design: Prospective cohort, population-based study. Participants: Persons aged 35 years or more residing in Guangzhou, China, who had not previously undergone incisional or laser eye surgery. Methods: In December 2008 and December 2010, all subjects underwent automated keratometry, and a random 50% sample had anterior segment optical coherence tomography with measurement of angle-opening distance at 500 μm (AOD500), angle recess area (ARA), iris thickness at 750 μm (IT750), iris curvature, pupil diameter, corneal thickness, anterior chamber width (ACW), lens vault (LV), and lens thickness (LT) and measurement of axial length (AL) and anterior chamber depth (ACD) by partial coherence laser interferometry. Main Outcome Measures: Baseline and 2-year change in AOD500 and ARA in the right eye. Results: A total of 745 subjects were present for full biometric testing in both 2008 and 2010 (mean age at baseline, 52.2 years; standard deviation [SD], 11.5 years; 53.7% were female). Test completion rates in 2010 varied from 77.3% (AOD500: 576/745) to 100% (AL). Mean AOD500 decreased from 0.25 mm (SD, 0.13 mm) in 2008 to 0.21 mm (SD, 13 mm) in 2010 (difference, -0.04; 95% confidence interval [CI], -0.05 to -0.03). The ARA decreased from 21.5±3.73 10^-2 mm² to 21.0±3.64 10 ^-2 mm² (difference, -0.46; 95% CI, -0.52 to -0.41). The decrease in both was most pronounced among younger subjects and those with baseline AOD500 in the widest quartile at baseline. The following baseline variables were significantly associated with a greater 2-year decrease in both AOD500 and ARA: deeper ACD, steeper iris curvature, smaller LV, greater ARA, and greater AOD500. By using simple regression models, we could explain 52% to 58% and 93% of variation in baseline AOD500 and ARA, respectively, but only 27% and 16% of variation in 2-year change in AOD500 and ARA, respectively. Conclusions: Younger persons and those with the least crowded anterior chambers at baseline have the largest 2-year decreases in AOD500 and ARA. The ability to predict change in angle width based on demographic and biometric factors is relatively poor, which may have implications for screening. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article. © 2012 American Academy of Ophthalmology.

Slot width augmentation in a slotted-wall transonic linear cascade wind tunnel

Transonic tests in linear cascade wind tunnels can suffer
from significant test section boundary interference effects in pitch. A slotted tailboard has been designed and optimised with an in-house Euler numerical method to reduce such ef- fects. Wind tunnel measurements on an overspeed Mach 1.27 discharge from a Rolls-Royce T2 cascade, featuring strong end-wall shock-induced interference, showed a 77% reduction in the flow pitchwise periodicity error with the optimised tail- board, with respect to the baseline open-jet cascade flow. Two-dimensional Euler predictions were also cross-validated against a three-dimensional Reynolds averaged computation, to explore the three-dimensionality of the discharge

Learning Bayesian Networks with Bounded Tree-Width via Guided Search

Bounding the tree-width of a Bayesian network can reduce the chance of overfitting, and allows exact inference to be performed efficiently. Several existing algorithms tackle the problem of learning bounded tree-width Bayesian networks by learning from k-trees as super-structures, but they do not scale to large domains and/or large tree-width. We propose a guided search algorithm to find k-trees with maximum Informative scores, which is a measure of quality for the k-tree in yielding good Bayesian networks. The algorithm achieves close to optimal performance compared to exact solutions in small domains, and can discover better networks than existing approximate methods can in large domains. It also provides an optimal elimination order of variables that guarantees small complexity for later runs of exact inference. Comparisons with well-known approaches in terms of learning and inference accuracy illustrate its capabilities.

Variational Monte Carlo study of core-valence separation schemes for first-row atoms and positive ions /

All-electron partitioning of wave functions into products ^core^vai of core and valence parts in orbital space results in the loss of core-valence antisymmetry, uncorrelation of motion of core and valence electrons, and core-valence overlap. These effects are studied with the variational Monte Carlo method using appropriately designed wave functions for the first-row atoms and positive ions. It is shown that the loss of antisymmetry with respect to interchange of core and valence electrons is a dominant effect which increases rapidly through the row, while the effect of core-valence uncorrelation is generally smaller. Orthogonality of the core and valence parts partially substitutes the exclusion principle and is absolutely necessary for meaningful calculations with partitioned wave functions. Core-valence overlap may lead to nonsensical values of the total energy. It has been found that even relatively crude core-valence partitioned wave functions generally can estimate ionization potentials with better accuracy than that of the traditional, non-partitioned ones, provided that they achieve maximum separation (independence) of core and valence shells accompanied by high internal flexibility of ^core and Wvai- Our best core-valence partitioned wave function of that kind estimates the IP's with an accuracy comparable to the most accurate theoretical determinations in the literature.

The effects of the menstrual cycle and hormonal contraceptives on the central thermoeffector threshold temperatures and width of the interthreshold zone

Basal body temperature (BBT) and thermoeffector thresholds increase following ovulation in many women. This study investigated if solely central thermoregulatory alterations are responsible. Seven females in a non-contraceptive group (NCG) were compared with 5 monophasic contraceptive users (HCG) on separate accounts: pre-ovulation (Trial I; d 2-5) and post-ovulation (Trial 2; 4-8 d post-positive ovulation) for NCG, and active phase for HCG (d 2-5, d 18-21). During immersion in 28°C water to the axilla, participants exercised for 20-30 min on an underwater ergometer. After steadily sweating, immersion continued until metabolism increased two-fold due to shivering. Rectal (Tre) BBT was not different between trials for neither NCG (1: 37.34±0.16°C; 2: 37.35±0.27°C) nor HCG. At exercise termination, Tre forehead sweating cessation increased (P<0.05) in trial 2 irrespective of group (1: 37.55±0.39°C; 2: 37.90±0,46°C). Tre shivering onset did not increase (P>0.05) in trial 2 (1: 36.91±0.50°C; 2: 37.07±0,45°C). The widths of the interthreshold zone increased (P<0.05) in trial 2 (1: 0.64±0.22°C; 2: 0.82±0.37°C) due to the increased sweating threshold only. HCG cooled quicker (1: -l.15±0,43°C; 2: -1.00±0.50°C) than NCG participants (1: - 0.58±0.22°C; 2: -0.52±O.29°C), and tympanic (Tty) sweat thresholds were significantly (P<0.05) decreased (1: 34.76±0.54°C; 2: 35.39±0.61°C) versus NCG (l: 35.57±0.77°C; 2: 35.89±1.04°C). Lastly, Tre and Tty thresholds were significantly different (P

Investigations on the Multiferroic and Thermoelectric properties of Low and Intermediate band width Manganites

This thesis lays importance in the investigation on the multiferroic and thermooelectric properties of selected representatives of low bandwidth and intermediate band width manganites. The first candidate, Strontium doped Gd manganite, is prepared by wet solid state reaction method and the second candidate, Na doped La manganite, by citrate gel method. In addition to the above mentioned properties, magneto resistance and dielectric properties are investigated. Using dielectric spectroscopic the dispersion parameters are correlated to the relaxation mechanisms and an attempt is made to obtain the grain and grain boundary contribution to the impedance of the sample through impedance spectroscopy studies.