bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence and control of biases in student evaluations of teaching
Authors: Liaw Shu‐Hui , Goh Kim‐Leng
Published: January 2003

This paper shows that class size has inappropriately influenced students’ judgements on evaluations of lecturers in the Faculty of Economics and Administration, University of Malaya. A bias exists whereby courses with small enrolment receive good overall teaching ratings, whereas larger classes have produced poor evaluations. On the other hand, teaching ratings are not affected by instructor characteristics (instructional experience, rank and gender) or other course characteristics (type and level of subject, and time and day course is taught). To improve the construct validity of student ratings as a measure of teaching performance, this paper suggests using results from a regression model to estimate the bias factor associated with class size, and adjusting the overall teaching ratings based on this estimate in order to control for the bias.
Modelling of turbulent transport in arc welding pools
Authors: Chakraborty Nilanjan , Chakraborty Suman , Dutta Pradip
Published: January 2003

In this paper, we present a modified k‐ε model capable of addressing turbulent weld‐pool convection in the presence of a continuously evolving phase‐change interface during a gas tungsten arc welding (GTAW) process. The phase change aspects of the present problem are addressed using a modified enthalpy‐porosity technique. The k‐ε model is suitably modified to account for the morphology of the solid‐liquid interface. The two‐dimensional mathematical model is subsequently utilised to simulate a typical GTAW process with high power, where effects of turbulent transport can actually be realised. Finally, we compare the results from turbulence modelling with the corresponding results from a laminar model, keeping all processing parameters unaltered. The above comparison enables us to analyse the effects of turbulent transport during the arc welding process.
A second order finite volume technique for simulating transport in anisotropic media
Authors: Pasdunkorale A. Jayantha , Turner Ian W.
Published: January 2003

An existing two‐dimensional finite volume technique is modified by introducing a correction term to increase the accuracy of the method to second order. It is well known that the accuracy of the finite volume method strongly depends on the order of the approximation of the flux term at the control volume (CV) faces. For highly orthotropic and anisotropic media, first order approximations produce inaccurate simulation results, which motivates the need for better estimates of the flux expression. In this article, a new approach to approximate the flux term at the CV face is presented. The discretisation involves a decomposition of the flux and an improved least squares approximation technique to calculate the derivatives of the dependent function on the CV faces for estimating both the cross diffusion term and a correction for the primary flux term. The advantage of this method is that any arbitrary unstructured mesh can be used to implement the technique without considering the shapes of the mesh elements. It was found that the numerical results well matched the available exact solution for a representative transport equation in highly orthotropic media and the benchmark solutions obtained on a fine mesh for anisotropic media. Previously proposed CV techniques are compared with the new method to highlight its accuracy for different unstructured meshes.
Modelling natural and mixed convection in obstructed channels
Authors: Cruchaga Marcela , Celentano Diego
Published: January 2003

The modelling of steady‐state natural and mixed convection in obstructed channels is presented. The two‐dimensional numerical analysis is carried out with a finite element thermally coupled incompressible flow formulation written in terms of the primitive variables of the problem and solved via a generalized streamline operator technique. Natural convection is studied in several vertical channel configurations for a wide range of Rayleigh numbers while mixed convection is analysed in a horizontal channel with a built‐in rectangular cylinder for different Reynolds and Grashof numbers. The results obtained in this work are validated with available experiments and other existing numerical solutions.
Mixed convection boundary‐layer flow from a horizontal circular cylinder in micropolar fluids: case of constant wall temperature
Authors: Nazar Roslinda , Amin Norsarahaida , Pop Ioan
Published: January 2003

The laminar mixed convection boundary‐layer flow of a micropolar fluid past a horizontal circular cylinder in a stream flowing vertically upwards has been studied in both cases of a heated and cooled cylinder. The solutions for the flow and heat transfer characteristics are evaluated numerically for different parameters, such as the mixed convection parameter λ, the material parameter K (vortex viscosity parameter) and the Prandtl number Pr=1 and 6.8, respectively. It is found, as for the case of a Newtonian fluid considered for Pr=1, that heating the cylinder delays separation and can, if the cylinder is warm enough, suppress it completely. Cooling the cylinder, on the other side, brings the separation point nearer to the lower stagnation point and for sufficiently cold cylinder there will not be a boundary‐layer on the cylinder. This model problem may solve industrial problems with processing of polymeric liquids, lubricants and molten plastics.
Numerical simulation of heat transfer of turbulent impinging jets with two‐equation turbulence models
Authors: Merci Bart , Vierendeels Jan , De Langhe Chris , Dick Erik
Published: January 2003

A numerical scheme that has already proved to be efficient and accurate for laminar heat transfer is extended for turbulent, axisymmetric heat transfer calculations. The extended scheme is applied to the steady‐state heat transfer of axisymmetric turbulent jets, impinging onto a flat plate. Firstly, the low‐Reynolds version of the standard k‐ε model is employed. As is well known, the classical k‐εturbulence model fails to predict the heat transfer of impinging jets adequately. A non‐linear k‐εmodel, with improvedε‐equation, yields much better results. The numerical treatment of the higher order terms in this model is described. The effect on the heat transfer predictions of a variable turbulent Prandtl number is shown to be small. It is also verified that the energy equation can be simplified, without affecting the results. Results are presented for the flow field and the local Nusselt number profiles on the plate for impinging jets with different distances between the pipe exit and the flat plate.
A linelet preconditioner for incompressible flow solvers
Authors: Soto Orlando , Löhner Rainald , Camelli Fernando
Published: January 2003

A parallel linelet preconditioner has been implemented to accelerate finite element (FE) solvers for incompressible flows when highly anisotropic meshes are used. The convergence of the standard preconditioned conjugate gradient (PCG) solver that is commonly used to solve the discrete pressure equations, greatly deteriorates due to the presence of highly distorted elements, which are of mandatory use for high Reynolds‐number flows. The linelet preconditioner notably accelerates the convergence rate of the PCG solver in such situations, saving an important amount of CPU time. Unlike other more sophisticated preconditioners, parallelization of the linelet preconditioner is almost straighforward. Numerical examples and some comparisons with other preconditioners are presented to demonstrate the performance of the proposed preconditioner.
The Delphi method and health research
Authors: de Meyrick Julian
Published: January 2003

The Delphi method is well suited to the research needed to inform health education and health promotion campaigns. This paper measures the current interest in the method by way of a literature review. It then describes how the method has evolved from its inception in the 1950s, to its current form. The focus is on a Delphi variant that is particularly relevant to health education – the Policy Delphi. The benefits of the method for the developer of health education and health promotion campaigns are then discussed. The main benefits relate to the gaining of expert opinions without the time and geographical restraints involved in alternative methods. The anonymity that is central to the Delphi method also has benefits for the researcher. The last section of the paper deals with potential pitfalls in the Delphi method that might undermine the successful application of the method, and recommends steps the practitioner can take to address these pitfalls.
A child‐to‐child approach to promoting healthier snacking in primary school children: a randomised trial in Northern Ireland
Authors: Freeman Ruth , Bunting Grace
Published: January 2003

Aims to assess the effectiveness of a child‐to‐child approach to promote healthier snacking in primary school children. A total of 55 schools in North and West Belfast were matched for socio‐economic status (SES). Ten schools were randomly selected and allocated into intervention and control groups. A total of 482 children took part. Older intervention children were given the “snacks facts” programme and became “teachers” in the child‐to‐child intervention. All children had baseline and final assessments made of their dental health knowledge (older children only), snacking knowledge and behaviours using questionnaires and rubbish bags. Older intervention children had greater increases in their mean knowledge scores compared with control children. Older intervention children had greater decreases in mean cariogenic snacking scores compared with control children. Younger children attending higher SES schools had significant decrease in mean cariogenic snacking score compared with children attending lower SES schools. Concludes that the child‐to‐child approach provided an avenue by which children improved their dental health knowledge and modified their snacking habits during break‐time at school.
Sex education and the young – some remaining dilemmas
Authors: Sieg Ellen
Published: January 2003

Discusses some of the continuing obstacles that prevent sex and relationship education (SRE) programmes in England from being more effective. The prevalence of teenage pregnancies and sexually transmitted infections that disproportionally affect the young indicate the urgency with which action needs to be taken. Discusses current sex education practices in England with reference to recent SRE guidelines and strategies, and in the light of the findings of a focus group of health care and education workers who deliver SRE to young people. The focus group uncovered several barriers to successful SRE. Suggests that apart from commissioning SRE guidelines the Department for Education and Skills needs to take a more overall and direct role in assuring that all young people are offered an adequate SRE. Concludes that any real and lasting changes can only be achieved if sex and relationship education goes beyond the individual to include a focus on social and cultural processes.
Exercise contemplators: unravelling the processes of change
Authors: McKenna Jim , Francis Caroline
Published: January 2003

Explores what people contemplating exercise (exercise contemplators) described, using the five processes of change that are considered by those who adhere to the Transtheoretical Model of Change, as most important for changing exercise behaviour. Also examines four delay tactics. Analysis of structured interviews with eight exercise contemplators identified three main findings, which show that the existing conceptualisations of the processes of change lack relevance to everyday accounts of trying to become more active. Further, in practice the processes were not readily differentiated by people, although process questionnaires require people to make these differentiations. Individuals reflected their optimism for change using two dimensions. How often an individual process was used seemed less important than the personal significance of experiences or events, especially the negative actions of significant others. The findings may help to explain why “process of change” questionnaires fail to predict change for exercise. The complex mix of the ways that processes and delay tactics are used, and how they are described, illustrates how challenging it may be for these people to change without help. These issues also affect counsellors who wish to develop stage‐matched counselling based on these elements of change.
Equipment assignment to multiple overhaul blocks in series systems
Authors: Talukder Shabbir , Knapp Gerald M.
Published: January 2003

This paper covers the development of a heuristic method for grouping equipment into blocks for application of preventive maintenance overhauls within a series system, so as to minimize total maintenance‐related costs for the system. Previously, group technology (GT) concepts have not been applied to this problem, and this research investigated the applicability of such concepts to the block overhaul problem (specifically, the SLCA method was applied). Performance of the heuristic is analyzed with respect to runtime and solution quality.
Incorporating overall probability of system failure into a preventive maintenance model for a serial system
Authors: Kardon Bruce , Fredendall Lawrence D.
Published: January 2003

This paper develops a model that allows consideration of not only the total maintenance costs but also the overall probability of a system breakdown when determining the time intervals between preventive maintenance activities. Using the model, which assumes that component failures follow a Weibull distribution, managers can determine the required preventive maintenance interval to achieve a desired probability of system failure, and they can calculate the total expected costs of both breakdowns and maintenance actions. The model’s application is illustrated using the impact of four different maintenance policies. The model assures top management that the unavailable system time due to equipment breakdown will be within a specified limit.
Maintenance practices in Hong Kong and the use of the intelligent scheduler
Authors: Tse Peter W.
Published: January 2003

With the shift of manufacture to mainland China, the utility and building services industries in Hong Kong have become dominant. To ensure adherence to proper routine operations and the provision of quality services, the equipment of these sectors must be maintained in good condition. The results of a recently conducted survey indicate that equipment failure‐driven and time‐based maintenance are most commonly used in Hong Kong. Only a few companies use condition‐based preventive maintenance. This paper presents an overview of maintenance practice in Hong Kong, and introduces the novel concept of intelligent predictive maintenance. In this maintenance system, the seriousness of the damage that is caused by faults in equipment can be determined, and the remnant life of the defective equipment can be predicted. Moreover, the system can automatically schedule maintenance activities in an efficient manner. With such abilities in equipment prognosis and automatic maintenance scheduling, the “fire‐fighting” situations that often occur in failure‐driven and time‐based maintenance can be avoided. Hence, any waste of resources and loss of production that are due to the mismanagement of maintenance can be substantially reduced.
An effectiveness‐centred approach to maintenance management
Authors: Pun Kit‐Fai , Chin Kwai‐Sang , Chow Man‐Fai , Lau Henry C.W.
Published: January 2003

This paper reviews the basic concepts of several maintenance approaches and discusses the increasing needs of effectiveness‐centred maintenance (ECM). It discusses the principles and relates them to the measurement of ECM performance. The development and implementation of the ECM approach is elaborated based on a pilot program in the radio unit of an electricity company in Hong Kong. Two ECM performance indices (i.e. individual system effectiveness (ISE) and overall system effectiveness (OSE)) were introduced to monitor the ECM process in the company. Being an integrated maintenance approach, ECM focuses on system functions and customer service, and may contribute to the continuous improvement of maintenance management practices in organizations irrespective of their business nature and size.
Object/objective‐oriented maintenance management
Authors: Zhu Guojun , Gelders Ludo , Pintelon Liliane
Published: January 2003

Approaches maintenance management in a systematic way so as to achieve its business objectives. From a managerial point of view, this so‐called object/objective‐oriented maintenance management (OOMM) is an integral process of asset (equipment) management with behavior‐based maintenance (BBM) as a major element. Within the OOMM concept, the objective‐approach focuses on the managing of the maintenance processes so as to achieve the business objectives, and the object‐approach emphasizes the object (asset or equipment) and the behavioral failures. Furthermore, combined together, the two approaches reflect the basic characteristics of the maintenance process. Also, both sides affect and influence each other, and are inseparable within OOMM. BBM addresses the monitoring and controlling of the technical and economic behavior of a piece of equipment in two ways.
Corporate communication and strategy in the field of projects
Authors: Goczol J. , Scoubeau C.
Published: January 2003

The communication concerning situations of project marketing (space industry, train construction, engineering, building construction, …) does not lead to a lot of researches and publications. An attempt will be made in this article, to establish the link between project and corporate communication considering the various steps in the development of a particular project strategy. This induces the development of the identity of the firm, the definition of the main targets (sociogram approach) and the development of particular tools at both an internal and an external level. It appeared in this study that the traditional communication mix arrives late after the management communication and the organizational communication. Concerning the tools, the relational network seems to be the best adapted to the particular situation and the targeting allows a good despatching of the resources at this level. The firms have in fact to develop both a functional and a relational positioning.
Systematic performance improvement – refining the space between learning and results
Authors: Burrow Jim , Berardinelli Paula
Published: January 2003

Planned learning can be applied to a range of education and training interventions and events in an organization. Its value can be directly measured through observable performance improvement of trainees in job contexts following the planned learning highlighting transfer of learning. More specific and directly connected organizational metrics need to be identified. The connections should be both to the trainee performance and learning and to the broader organizational performance. Reports a redefinition of training evaluation resulting from the authors work with members of a global manufacturing training department. The effort was undertaken to create a process for the department to demonstrate the impact of planned learning on key organizational performance measures. The value‐added from training was established when the direct relationships between training (planned learning) and systematic job performance improvements were observed that were drawn from and directly linked to broader organizational productivity and performance metrics. From those successful field experiences and the training evaluation literature, proposes a refinement within the traditional four‐level evaluation process akin to a new level 3.5 – performance impact, to fit between Kirkpatrick’s model of level 3 (behavior) and level 4 (results).
Workplace learning by action learning: a practical example
Authors: Miller Peter
Published: January 2003

Leaders of organisations are seeking new ways of developing capacities in their organisations to learn and re‐learn. Describes an action learning approach to facilitating the implementation of a workplace learning strategy to assist a group of managers enhance their capacity to learn and respond to organisational issues more effectively. Outlines the methodology used and the attempt to measure behavioural and organisational performance improvements as a result of the intervention. Lessons learnt that may be useful to others responsible for implementing workplace learning are detailed.
Web based continuing professional development – a learning architecture approach
Authors: Brosnan Kevin , Burgess Robin C.
Published: January 2003

Uses Wenger’s learning architecture as a conceptual framework for analysing the design and support of a Web‐based continuing professional development (CPD) course. Describes the key elements of the learning architecture and discusses their relevance to Web‐based CPD. In particular notes the importance of a design paradigm that focuses on social networks and the support necessary for their development. Using empirical data from a Web‐based course for professionals in health and social care to illustrate aspects of Wenger’s learning architecture, evaluates successful CPD learning against this theoretical framework. The course drew heavily on the participants’ ongoing workplace practice and was significant in shaping that practice. Concludes, on the basis of experience gained through the course, that Wenger’s concepts provide a useful evaluation framework and design paradigm for Web‐based CPD.
Creating new learning communities: towards effective e‐learning production
Authors: Russell David , Calvey David , Banks Mark
Published: January 2003

This paper examines how small firms that produce “e‐learning” materials collaborate and communicate with their clients, external agencies and end users. Our premise is this: given increased demands for more sophisticated and “learning‐led” products, it is becoming increasingly crucial for e‐learning firms to source and exploit content, education, knowledge and expertise that is extrinsic to the traditional boundaries of the “firm”. These shifts raise a set of problems related to how firms can effectively interact and collaborate with others in order to create, distribute and evolve effective e‐learning tools and products. Based on our own case study research and building on the existing literature on “communities of practice”, we argue that the formation of new “learning communities” is a strategy now being undertaken by leading firms in order to meet demands for “learning‐led” products.
Strategic management of technological innovations in the small to medium enterprise
Authors: Pratali Paolo
Published: January 2003

This paper addresses the problems inherent in identifying technological innovations that can improve company competitiveness with the ultimate aim of increasing the value of a specific enterprise. A model is proposed that, starting with the competitive weight of a technological innovation to processes or products, yields a strategic weight that enables decision makers to evaluate the increase in business value consequent on application of such innovation. The proposed model is composed of four sub‐models: the first is an analysis of process/product competitiveness aimed at identifying competitive priorities and therefore appropriate technologies; the second sub‐model identifies the priorities of technological intervention from amongst the competitive technologies selected; the third sub‐model correlates the two previous sub‐models and thereby expresses a “strategic weight” of the technological projects with respect to the competitive priorities of the processes or products; the fourth and last sub‐model applies scenario simulation and sustainable growth verification to estimate the impact of strategic project innovations in terms of increased business value.
A hierarchical framework of new products development: an example from biotechnology
Authors: Tereza Alexandre Maria , Furrer Olivier , Sudharshan D.
Published: January 2003

Many new products are based on new technologies, which may in turn be based on new scientific discoveries. The extant literature on new product development has focused on how a firm may successfully commercialize new products. There is a corporate cost associated with new product failure, which extends beyond the final product‐manufacturing corporation to all the parties involved in the supply chain for the failed product. The new product development community has developed frameworks for managing the new product development process to minimize new product failure, notably by incorporating customer preferences into a cross‐functional approach to new product design and by creating a set of decision points or stage gates. The focus of these has been on the latter stages of the new product development process. Besides corporate decisions, society and its various institutions play a role in the shaping of new products from knowledge discoveries. Identifies how other participants may indeed influence the development of new products. Permits a more deliberate understanding of the possible impact of aiding or preventing a movement up the development hierarchy and so a clearer understanding of the potential benefits and opportunity costs may arise.
Building organisational culture that stimulates creativity and innovation
Authors: Martins E.C. , Terblanche F.
Published: January 2003

The purpose of this article is to present, by means of a model, the determinants of organisational culture which influence creativity and innovation. A literature study showed that a model, based on the open systems theory and the work of Schein, can offer a holistic approach in describing organisational culture. The relationship between creativity, innovation and culture is discussed in this context. Against the background of this model, the determinants of organisational culture were identified. The determinants are strategy, structure, support mechanisms, behaviour that encourages innovation, and open communication. The influence of each determinant on creativity and innovation is discussed. Values, norms and beliefs that play a role in creativity and innovation can either support or inhibit creativity and innovation depending on how they influence individual and group behaviour. This is also explained in the article.
Determinants of innovation in small food firms
Authors: Avermaete Tessa , Viaene Jacques , Morgan Eleanor J. , Crawford Nick
Published: January 2003

This paper focuses on innovation in small food‐ and drink‐manufacturing enterprises in two Belgian regions. The aim of the research was to identify patterns of innovative activities. Based on both literature and empirical analyses, a framework was developed to help in understanding some aspects of the determinants of innovation in small food firms. Two conclusions can be drawn from the research. On the one hand, it is clear that innovation was regarded as essential by most small food firms. Such firms tended to continuously introduce new products, develop new processes, make changes in the organisational structure and explore new markets. On the other hand, the research demonstrated that some aspects of innovation depend on the age of the company, company size and regional economic performance.
General Solution for Mechanical and Thermal Stresses in a Functionally Graded Hollow Cylinder due to Nonaxisymmetric Steady-State Loads
Authors: Jabbari M. , Sohrabpour S. , Eslami M. R.
Published: January 2003

In this paper, the general theoretical analysis of two-dimensional steady-state thermal stresses for a hollow thick cylinder made of functionally graded material is developed. The temperature distribution is assumed to be a function of radial and circumferential directions with general thermal and mechanical boundary conditions on the inside and outside surfaces. The material properties, except Poisson’s ratio, are assumed to depend on the variable r and they are expressed as power functions of r. The separation of variables and complex Fourier series are used to solve the heat conduction and Navier equations.
Direct Design of Ducts
Authors: Ashrafizadeh A. , Raithby G. D. , Stubley G. D.
Published: January 2003

This paper describes a method for calculating the shape of duct that leads to a prescribed pressure distribution on the duct walls. The proposed design method is computationally inexpensive, robust, and a simple extension of existing computational fluid dynamics methods; it permits the duct shape to be directly calculated by including the coordinates that define the shape of the duct wall as dependent variables in the formulation. This “direct design method” is presented by application to two-dimensional ideal flow in ducts. The same method applies to many problems in thermofluids, including the design of boundary shapes for three-dimensional internal and external viscous flows.
Performance Analysis of a Two-Stage Electrohydraulic Servovalve in Centrifugal Force Field
Authors: He Y. B. , Chua P. S. K. , Lim G. H.
Published: January 2003

Electrohydraulic servosystems are commonly used in various engineering applications due to their high power-to-weight ratio, good performance, and ease of control. Electrohydraulic servovalves are affected by centrifugal forces when they are used in the fields of spaceflight, earthquake simulation, and geotechnique. Based on theories of fluid dynamics and performance of an electrohydraulic servovalve, the fluid flow and structure of a two-stage electrohydraulic servovalve are analyzed when the valve is affected by centrifugal forces in operation. From calculation and experimental data it is found that centrifugal acceleration is directly proportional to null shift and the scale factor is formulated. Relevant methods to reduce the influence of the centrifugal force are provided.
Experimental Characterization of Compact Heat Exchangers With Short Flow Lengths at Simulated Elevated Altitudes
Authors: Mathias J. A. , Cao J. , Ewing M. E. , Christensen R. N.
Published: January 2003

This paper presents experimental pressure drop and heat transfer results of compact heat exchangers made with plain rectangular fins of short flowlengths tested with air at very low Reynolds numbers. Experiments were performed at sea level and at simulated elevated altitudes up to 25,298 m (83,000 ft). From the experimental results, the additional pressure drop of the air caused by the developing boundary layers and the hydrodynamic entrance length were determined. An equation was produced that predicted the average Nusselt number of the air, which significantly decreased with nondimensional length. The experimental results varied with respect to the aspect ratio of the rectangular duct and nondimensional length, which is inversely related to the Reynolds number.
Aerodynamic Design and Performance of Aspirated Airfoils
Authors: Merchant Ali
Published: January 2003

The impact of boundary layer aspiration, or suction, on the aerodynamic design and performance of turbomachinery airfoils is discussed in this paper. Aspiration is studied first in the context of a controlled diffusion cascade, where the effect of discrete aspiration on loading levels and profile loss is computationally investigated. Blade design features which are essential in achieving high loading and minimizing the aspiration requirement are described. Design studies of two aspirated compressor stages and an aspirated turbine exit guide vane using three dimensional Navier-Stokes calculations are presented. The calculations show that high loading can be achieved over most of the blade span with a relatively small amount of aspiration. Three dimensional effects close to the endwalls are shown to degrade the performance to varying degrees depending on the loading level.
Euler Number Based Orifice Discharge Coefficient Relationship
Authors: Morrison Gerald L.
Published: January 2003

A new relationship for orifice flow meter discharge coefficients has been developed which replaces the Reynolds number dependence with the Euler number. Both relationships have the same accuracy for the calculation of the discharge coefficient but the new relationship eliminates the need to know fluid viscosity.
Scaling Effect on Prediction of Cavitation Inception in a Line Vortex Flow
Authors: Hsiao Chao-Tsung , Chahine Georges L. , Liu Han-Lieh
Published: January 2003

The current study considers the prediction of tip vortex cavitation inception at a fundamental physics based level. Starting form the observation that cavitation inception detection is based on the “monitoring” of the interaction between bubble nuclei and the flow field, the bubble dynamics is investigated in detail. A spherical model coupled with a bubble motion equation is used to study numerically the dynamics of a nucleus in an imposed flow field. The code provides bubble size and position versus time as well as the resulting pressure at any selected monitoring position. This model is used to conduct a parametric study. Bubble size and emitted sound versus time are presented for various nuclei sizes and flow field scales in the case of an ideal Rankine vortex to which a longitudinal viscous core size diffusion model is imposed. Based on the results, one can deduce cavitation inception with the help of either an “optical inception criterion” (maximum bubble size larger than a given value) or an “acoustical inception criterion” (maximum detected noise higher than a given background value). We use here such criteria and conclude that scaling effects can be inherent to the way in which these criteria are exercised if the bubble dynamics knowledge is not taken into account.
Conditional Sampling in a Transitional Boundary Layer Under High Freestream Turbulence Conditions
Authors: Volino Ralph J. , Schultz Michael P. , Pratt Christopher M.
Published: January 2003

Conditional sampling has been performed on data from a transitional boundary layer subject to high (initially 9%) freestream turbulence and strong (K=ν/U∞2dU∞/dx as high as 9×10−6) acceleration. Methods for separating the turbulent and nonturbulent zone data based on the instantaneous streamwise velocity and the turbulent shear stress were tested and found to agree. Mean velocity profiles were clearly different in the turbulent and nonturbulent zones, and skin friction coefficients were as much as 70% higher in the turbulent zone. The streamwise fluctuating velocity, in contrast, was only about 10% higher in the turbulent zone. Turbulent shear stress differed by an order of magnitude, and eddy viscosity was three to four times higher in the turbulent zone. Eddy transport in the nonturbulent zone was still significant, however, and the nonturbulent zone did not behave like a laminar boundary layer. Within each of the two zones there was considerable self-similarity from the beginning to the end of transition. This may prove useful for future modeling efforts.
Effects of Concave Curvature on Boundary Layer Transition Under High Freestream Turbulence Conditions
Authors: Schultz Michael P. , Volino Ralph J.
Published: January 2003

An experimental investigation has been carried out on a transitional boundary layer subject to high (initially 9%) freestream turbulence, strong acceleration (K=ν/Uw2dUw/dx as high as 9×10−6), and strong concave curvature (boundary layer thickness between 2% and 5% of the wall radius of curvature). Mean and fluctuating velocity as well as turbulent shear stress are documented and compared to results from equivalent cases on a flat wall and a wall with milder concave curvature. The data show that curvature does have a significant effect, moving the transition location upstream, increasing turbulent transport, and causing skin friction to rise by as much as 40%. Conditional sampling results are presented which show that the curvature effect is present in both the turbulent and nonturbulent zones of the transitional flow.
Eulerian/Lagrangian Analysis for the Prediction of Cavitation Inception
Authors: Farrell Kevin J.
Published: January 2003

An Eulerian/Lagrangian computational procedure was developed for the prediction of cavitation inception by event rate. The carrier-phase flow field was computed using an Eulerian Reynolds-averaged Navier-Stokes (RANS) solver. The Lagrangian analysis was one-way coupled to the RANS solution, since at inception, the contributions of mass, momentum, and energy of the microbubbles to the carrier flow are negligible. The trajectories were computed using Newton’s second law with models for various forces acting on the bubble. The growth was modeled using the Rayleigh-Plesset equation. The important effect of turbulence was included by adding a random velocity component to the mean flow velocity and by reducing the local static pressure. Simulation results for the Schiebe body indicate agreement with experimentally observed trends and a significant event rate at cavitation indices above visual inception.
Laminar, Gravitationally Driven Flow of a Thin Film on a Curved Wall
Authors: Ruschak Kenneth J. , Weinstein Steven J.
Published: January 2003

Gravitationally driven flow of a thin film down an arbitrarily curved wall is analyzed for moderate Reynolds number by generalizing equations previously developed for flow on a planar wall. In the analysis, the ratio of the characteristic film thickness to the characteristic dimension of the wall is presumed small, and terms estimated to be first order in this parameter are retained. Partial differential equations are reduced to ordinary differential equations by the method of von Ka´rma´n and Pohlhausen; namely, an expression for the velocity profile is assumed, and the equation for conservation of linear momentum is averaged across the film. The assumed velocity profile changes shape in the flow direction because a self-similar profile, one of fixed shape but variable magnitude, leads to an equation that typically fails under critical conditions. The resulting equations for film thickness routinely accommodate subcritical-to-supercritical transitions and supercritical-to-subcritical transitions as classified by the underlying wave propagation. The more severe supercritical-to-subcritical transition is manifested by a standing wave where the film noticeably thickens; this standing wave is a simple analogue of a hydraulic jump. Predictions of the film-thickness profile and variations in the velocity profile compare favorably with those from the Navier-Stokes equation obtained by the finite element method.
Rotating Effect on Fluid Flow in Two Smooth Ducts Connected by a 180-Degree Bend
Authors: Liou Tong-Miin , Chen Chung-Chu , Chen Meng-Yu
Published: January 2003

Laser Doppler velocimetry (LDV) measurements are presented of turbulent flow in a two-pass square-sectioned smooth duct simulating the coolant passages employed in gas turbine blades under rotating and nonrotating conditions. For all cases studied, the Reynolds number characterized by duct hydraulic diameter and bulk mean velocity was fixed at 1×104. The rotation number Ro was varied from 0 to 0.2. It is found that as Ro is increased, both the skewness (SK) of streamwise mean velocity and magnitude of secondary-flow velocity increase linearly, SK=2.3 Ro and U2+V2¯/Uh=2.3 Ro+0.4, and the magnitude of turbulence intensity level increases exponentially. As Ro is increased, the curvature induced symmetric Dean vortices in the turn for Ro=0 is gradually dominated by a single vortex most of which impinges directly on the outer part of leading wall. The high turbulent kinetic energy is closely related to the dominant vortex prevailing inside the 180-deg sharp turn. The size of separation bubble immediately after the turn is found to diminish to null as Ro is increased from 0 to 0.2. A simple correlation is developed between the bubble size and Ro. A critical range of Ro responsible for the switch of faster moving flow from near the outer wall to the inner wall is identified. For both rotating and nonrotating cases, the direction and strength of the secondary flow with respect to the wall are the most important fluid dynamic factors affecting local the heat transfer distributions inside a 180-deg sharp turn. The role of the turbulent kinetic energy in the overall enhancement of heat transfer is well addressed.
A Nonlinear k-ε-kp Two-Phase Turbulence Model
Authors: Zhou L. X. , Gu H. X.
Published: January 2003

Nonlinear relationships of two-phase Reynolds stresses with the strain rates together with the transport equations of gas and particle turbulent kinetic energy and the two-phase correlation turbulent kinetic energy are proposed as the nonlinear k-ε-kp turbulence model. The proposed model is applied to simulate swirling gas-particle flows. The predicted two-phase time-averaged velocities and Reynolds stresses are compared with the PDPA measurements and those predicted using the second-order moment model. The results indicate that the nonlinear k-ε-kp model has the modeling capability near to that of the second-order moment model, but the former can save much computation time than the latter.
A Finite Element Model and Electronic Analogue of Pipeline Pressure Transients With Frequency-Dependent Friction
Authors: Shu Jian-Jun
Published: January 2003

A finite element model and its equivalent electronic analogue circuit has been developed for fluid transients in hydraulic transmission lines with laminar frequency-dependent friction. Basic equations are approximated to be a set of ordinary differential equations that can be represented in state-space form. The accuracy of the model is demonstrated by comparison with the method of characteristics.
Prediction of Centrifugal Slurry Pump Head Reduction: An Artificial Neural Networks Approach
Authors: Engin Tahsin , Kurt Akif
Published: January 2003

The feasibility of using artificial neural networks (ANN) in the prediction of head reduction of centrifugal pumps handling slurries is examined. An ANN model is proposed and compared with the empirical correlation given by the present authors earlier. The comparison showed that the ANN could successfully be used for the prediction of head reductions of centrifugal slurry pumps. The mean deviation between predicted and experimental values is 5.86% which is reasonable for slurry handling processes.
An Improved Neural-Network-Based Calibration Method for Aerodynamic Pressure Probes
Authors: Fan Hui-Yuan , Lu Wei-zhen , Xi Guang , Wang Shang-jin
Published: January 2003

Calibration of multihole aerodynamic pressure probe is a compulsory and important step in applying this kind of probe. This paper presents a new neural-network-based method for the calibration of such probe. A new type of evolutionary algorithm, i.e., differential evolution (DE), which is known as one of the most promising novel evolutionary algorithms, is proposed and applied to the training of the neural networks, which is then used to calibrate a multihole probe in the study. Based on the measured probe’s calibration data, a set of multilayered feed-forward neural networks is trained with those data by a modified differential evolution algorithm. The aim of the training is to establish the mapping relations between the port pressures of the probe being calibrated and the properties of the measured flow field. The proposed DE method is illustrated and tested by a real case of calibrating a five-hole probe. The results of numerical simulations show that the new method is feasible and effective.
Modeling Film Dynamics in Spray Impingement
Authors: Trujillo Mario F. , Lee Chia-fon F.
Published: January 2003

A numerical and analytic study of film formation and evolution during spray impingement is presented. For the part of the film which excludes drop impact locations, the governing equations reduce to a convenient form that can be exploited using a Lagrangian particle method. At impingement points the source terms for mass and energy are calculated based on conservation principles and phenomenological results. It is shown that during the period where most of the film evolution takes place, the effect of gas shear and surface tension are negligible. Numerical testing is performed to ensure convergence. Comparisons to spray impingement experiments consisting of film extension and thickness measurements yield reasonable agreement with the exception of the shallow angle impingement case where it is suspected that the total mass deposited is overpredicted.
Comparative Evaluation of Some Existing Correlations to Predict Head Degradation of Centrifugal Slurry Pumps
Authors: Engin Tahsin , Gur Mesut
Published: January 2003

In order to optimally design a slurry transportation system, it is necessary to know how the presence of solids will change the performance of the slurry pump to be installed. This paper makes the comparison of some existing correlations available in the literature to predict the head reduction factors of such centrifugal pumps handling slurries. For this purpose, a large number of published data for various centrifugal slurry pump tests in the literature have been used to develop a new correlation and then this correlation and all others have been tested against the data. For the proposed correlation, the mean and average deviations between the calculated and measured head reduction factor is 8.378 and 0.620%, respectively, for all data of mostly handling commercial slurries. It also produces 12.441% mean deviation in the prediction of efficiency ratio for 216 data points. Overall, the new correlation that can be applied to both metal and rubber lined pumps with impeller diameter up to 850 mm, gives remarkably closer fit to the published data of both head and efficiency ratios than all existing correlations.
Shear-Driven Flow in a Toroid of Square Cross Section
Authors: Humphrey J. A. C. , Cushner J. , Al-Shannag M. , Herrero J. , Giralt F.
Published: January 2003

The two-dimensional wall-driven flow in a plane rectangular enclosure and the three-dimensional wall-driven flow in a parallelepiped of infinite length are limiting cases of the more general shear-driven flow that can be realized experimentally and modeled numerically in a toroid of rectangular cross section. Present visualization observations and numerical calculations of the shear-driven flow in a toroid of square cross section of characteristic side length D and radius of curvature Rc reveal many of the features displayed by sheared fluids in plane enclosures and in parallelepipeds of infinite as well as finite length. These include: the recirculating core flow and its associated counterrotating corner eddies; above a critical value of the Reynolds (or corresponding Goertler) number, the appearance of Goertler vortices aligned with the recirculating core flow; at higher values of the Reynolds number, flow unsteadiness, and vortex meandering as precursors to more disorganized forms of motion and eventual transition to turbulence. Present calculations also show that, for any fixed location in a toroid, the Goertler vortex passing through that location can alternate its sense of rotation periodically as a function of time, and that this alternation in sign of rotation occurs simultaneously for all the vortices in a toroid. This phenomenon has not been previously reported and, apparently, has not been observed for the wall-driven flow in a finite-length parallelepiped where the sense of rotation of the Goertler vortices is determined and stabilized by the end wall vortices. Unlike the wall-driven flow in a finite-length parallelepiped, the shear-driven flow in a toroid is devoid of contaminating end wall effects. For this reason, and because the toroid geometry allows a continuous variation of the curvature parameter, δ=D/Rc, this flow configuration represents a more general paradigm for fluid mechanics research.