WSEAS CONFERENCES. WSEAS, Unifying the Science

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 Volume 3, 2008
Print ISSN: 1790-5087
E-ISSN: 2224-347X








Issue 1, Volume 3, January 2008

Title of the Paper: Effect of a Thin Floating Fluid Layer in Parametrically Forced Waves


Authors: Elena B. Martin, Jose M. Vega

Abstract: In order to describe correctly on-board experiments, where residual acceleration can have a significant impact in the fluid motion, we consider the effect of a thin immiscible fluid layer on top of a liquid substrate in incrementing the damping and promoting drift instabilities in spatially uniform standing Faraday waves. It is seen that the effective surface viscosity of the newtonian liquid film enhances drift instabilities that lead to various steadily travelling and standing and travelling oscillatory patterns, among others. In particular, travelling waves appear to be the primary instability of the basic standing wave for deep water problems.

Keywords: Faraday instability, weakly nonlinear analysis, oscillatory boundary layers, streaming flow, immiscible liquid film, surface viscosity, on-board experiments, vertically vibrated container.

Title of the Paper: Comparison of Surrogate Models for Turbomachinery Design


Authors: J. Peter, M. Marcelet

Abstract: This article addresses the issue of selecting surrogate models suitable for the global optimization of turbomachinery flows. As a first step towards this goal the analysis of a family of 2D flows on a two-parameter design space is presented. Four types of surrogate models are considered: least square polynomials, artificial neural networks (multi-layer perceptron and radial basis function) and Kriging. Discussed is the ability of these surrogate functions to give a satisfactory description of the exact function of interest on the design space, during a global optimization. The number of CFD evaluations for an adequate description of the exact function is presented

Keywords: Turbomachinery, global optimization, surrogate model

Title of the Paper: A Boundary Layer Inspection on a Wing Profile through High Resolution Thermography and Numerical Methods


Authors: M. Malerba, M. Argento, A. Salviuolo, G. L. Rossi

Abstract: In fluid-dynamic phenomena the boundary layer plays a fundamental role. It also affects the drag and lift force of a body immersed in a fluid. Reynolds analogy introduces the possibility to correlate fluidynamic to thermal field. By using high sensitivity thermographic systems, temperature pattern on the surface of solid bodies immersed into a fluid can be analysed. Temperature distribution depends on many combined effects, such as: conversion of kinetic energy of the flow into thermal energy, flow temperature variation in time and space, convection heat transfer phenomena between flow and body, conduction phenomena inside the body, and radiation heath exchange. A numerical approach is used to compare results of the proposed procedure. A transient simulation with increasing inlet fluid temperature is carried out to evaluate the thermal exchange between the airstream and the body. The effect of the different thermal exchange due to the local flow peculiarity is modelled.

Keywords: Boundary layer, Infrared thermography, Subsonic flow, Passive technique, Wing profile, CFD

Title of the Paper: Different Approaches for the Characterization of a Fractured Karst Aquifer


Authors: Claudia Cherubini, Nicola Pastore, Vincenzo Francani

Abstract: Karstic aquifers contain dissolution-generated cavities whose geometry is characterized by high variability; their cross-sections may range from uniform elliptical shapes, to high and narrow fissures, to irregular shapes partly filled with rock fragments and terra rossa deposits. In these conduits turbulent groundwater flow conditions may occur; in other cases no flow conditions may be due to the existence of lenses of terra rossa. In the examined site, located in the city of Bari, characterized by a fractured and karstic aquifer, an hydrogeological reconstruction of the heterogeneities is carried out, in order to simulate subterranean draining conditions that prove to be as near as possible to the real ones. Two different approaches are applied; the first one, aimed at only reconstructing the level of fracturation by means of geostatistical interpolation, and the second one, more complete, where multiple realizations are generated and conditioned to borehole data (RQD population), in order to obtain a three-dimensional distribution of fracture frequency, cavities and terra rossa lenses in the aquifer.

Keywords: heterogeneity, fractures, cavities, geostatistics, simulations

Title of the Paper: Analysis of Zero-Net-Mass-Flux Synthetic Jets using DNS


Authors: Declan Hayes-Mccoy, Xi Jiang, Duncan Lockerby

Abstract: Axisymmetric direct numerical simulations (DNS) are performed to study the formation criterion and evolution of zero-net-mass-flux synthetic jets. Jet formation is characterised by an oscillating streamwise jet centreline velocity, showing net momentum flux away from the orifice. This momentum flux away from the orifice takes the form of a series of vortical structures, often referred to as a vortex train. Simulation of the jet actuator consists of a modified oscillating velocity profile applied to a wall boundary. The jet issues into quiescent air, and the Reynolds numbers used vary from 85 < Re < 1000. Variations to the input simulation parameters are carried out in order to determine the overall effects on the flow field. From these results the conditions necessary for the formation of the synthetic jet along with the input parameters that provide an optimal jet output are deduced. Jet optimisation is defined by both the vortical strength and longevity of the vortex train as it travels downstream. This study examines the vortical structures, the jet centreline velocities along with other flow characteristics in order to deduce and visualise the effects of the input parameters on the jet performance. The results attained on altering the oscillation frequency of the jet actuator indicated that synthetic jets with zero mean velocity at the inflow behave significantly differently from jets with non-zero mean velocity at the inflow. An evolution study into the formation of the train of vortical structures associated with the formation of a synthetic jet is performed. This study is accompanied with a time history of the jet centreline velocity, showing the net momentum flux of the fluid away from the orifice of a fully developed synthetic jet. Further details on the jet centreline velocity for all cases are also presented; along with a study on the effect on the vortical structures of altering the Reynolds number of the flow.

Keywords: Synthetic jet, DNS, axisymmetric, vortical structures

Title of the Paper: Film Cooling and Hub Disk Leakage Flow Experiments in a Fully Rotating HP Turbine Stage


Authors: M. Pau, A. De La Loma, G. Paniagua, D. Delhaye

Abstract: This paper describes the experimental methodology, test conditions, and uncertainty analysis concerning a novel rim seal film cooling experiments on a fully rotating HP transonic turbine stage under engine representative conditions. A complex secondary air system has been designed in order to feed the cooled turbine. The rotor blade has been heavily instrumented at the platform, 7% and 15% of the blade height with fast response pressure sensors and double-layer thin film gauges, allowing a complete aero-thermal characterization of the flow field. The hub disk leakage and platform cooling blowing ratios have been varied independently in order to assess their impact individually. Furthermore, tests have been performed at two different rotational speeds. The presented study should help designers improve the protection of the rotor platform and minimize the amount of coolant used.

Keywords: Gas turbine, leakage flows, film cooling.

Title of the Paper: Analysis of Nonlinear Isentropic Sound Wave-Propagation in a Cylindrical Tube Filled with Fluid-Saturated Porous Media


Authors: Hazim M. Dwairi

Abstract: A theory of sound waves propagation in porous media that includes the nonlinear effects of Forchheimer type with nonzero radial velocity effects is laid out utilizing variational solutions technique. It is shown that the main parameters governing the propagation of sound waves are shear wave number, reduced frequency number, porosity, Darcy number, and Forchheimer number. The manner in which the flow influences the attenuation and the phase velocities of forward and backward propagating isentropic acoustic waves is deduced. It is found that increasing Darcy number and Forchheimer number increased wave’s attenuation and phase velocity for both forward and backward sound waves, whereas increasing the porosity decreased attenuation and phase velocity for both waves. The effect of increasing the reduced frequency is found to increase attenuation of the forward waves and decrease attenuation and phase velocity of the backward sound waves. Moreover, the effect of the steady flow is found to decrease the attenuation and phase velocities for forward sound waves and enhance them for the backward sound waves.

Keywords: sound waves, porous medium, fluid flow, noise isolator.

Issue 2, Volume 3, April 2008

Title of the Paper: Modelling the Zero-Inertia, Horizontal Viscous Dam-Break Problem


Authors: B. Nsom, W. Ndong, B. Ravelo

Abstract: This paper considers the dam-break problem in a horizontal smooth 1D channel, for hydrogeological hazards purpose. The fluid is muddy and it can be described by a Newtonian model, provided that the inertial effects be neglected versus the viscous ones in the momentum balance. Assuming the shallow water approximation, a non dimensional equation is built from the continuity and the Navier-Stokes equations in the limit of zero-inertia and solved analytically in two limits: short time and long time. These solutions are then combined into a single, universal model. Limitations of the model are examined by comparison to a converged finite difference numerical solution of the flow equation.

Keywords: Dam failure, Finite difference method, Flow regimes, Numerical models, One dimensional flow, Shallow water approximation, Similar solution

Title of the Paper: Wall Shear Stress and Atherosclerosis: Numerical Blood Flow Simulations in the Mouse Aortic Arch


Authors: P. Ruengsakulrach, A. K. Joshi, S. Fremes, S. Foster, J. Butany, B. Wiwatanapataphee, Y. Lenbury

Abstract: The aims of this study were (1) to demonstrate the feasibility of computational fluid dynamic (CFD) modelling of realistic blood flow in the mouse aortic arch, and (2) to determine the relation of wall shear stress and atherosclerosis in the mouse aortic arch. ApoE knockout mice were chosen for this study. The blood flow fraction in the major branches of the mouse aortic arch was measured by ultrasound biomicroscopy. The geometry of the aortic arch was captured by plastic casting and micro CT imaging. Mouse blood viscosities were measured by rheometry. A pathological examination was performed. A well-validated in-house finite element code, which solves the three dimensional Navier-Stokes equations, was used to compute the wall shear stress and velocity patterns in the ascending aorta and the aortic arch. The distribution of the wall shear stress was correlated with the distribution of the atherosclerosis from the pathological examination in order to investigate the effect of wall shear stress on atherosclerosis. It is concluded that CFD modeling of hemodynamics in the mouse aortic arch is feasible. Qualitative impressions show that atherosclerosis was related with the region of low wall shear stress in mouse aortic arch.

Keywords: Blood Flow, Mouse, Aortic Arch, Wall Shear Stress, Atherosclerosis

Title of the Paper: Dynamic Behaviour of Plates Subjected to a Flowing Fluid


Authors: Y. Kerboua, A. A. Lakis

Abstract: Elastic structures subjected to a flowing fluid undergo a considerable change in their dynamic behaviour and can lose their stability. In this article we describe the development of a fluid-solid finite element to model plates subjected to flowing fluid under various boundary conditions. The mathematical model for the structure is developed using a combination of a hybrid finite element method and Sanders’ shell theory. The membrane displacement field is approximated by bilinear polynomials and the transversal displacement by an exponential function. Fluid pressure is expressed by inertial, Coriolis and centrifugal fluid forces, written respectively as function of acceleration, velocity and transversal displacement. Bernoulli’s equation for the fluid-solid interface and a partial differential equation of potential flow are applied to calculate the fluid pressure. The impermeability condition ensures contact between the system of plates and the fluid. Mass and rigidity matrices for each element are calculated by exact integration. Calculated results are in reasonable agreement with other analytical theories.

Keywords: Vibration, Finite element, Plates, Potential flow, Fluid structure interaction, Critical velocity.

Title of the Paper: Preparation of Flood Reduction Plan for Surat City and Surrounding Region (India)


Authors: Prasit G. Agnihotri, Jayantilal N. Patel

Abstract: Floods affect Suart city situated on river Tapi in India many times, which creates damage to the people and properties. In this paper the study of floods at Surat city in general and the study of flood occurred at Surat during 2006 in particular has been made. Certain preventive and curative measures are suggested for reducing the effects of flood in the study area. Flood reduction plan for the study area has been also prepared and presented in this paper.

Keywords: Surat, River Tapi, Flood, Submergence, Flood Level, Desilting, Diversion, Protection Wall, Flood Reduction Plan

Title of the Paper: Rainfall – Runoff Modeling: Comparison and Combination of Simple Time-Series, Linear Autoregressive and Artificial Neural Network Models


Authors: A. Jagan Mohan Reddy, Ch. Suresh Babu, P. Mallikarjuna

Abstract: Runoff simulation and forecasting is essential for planning, designing and operation of water resources projects. In the present study, the rainfall – runoff process is modeled using empirical methods such as simple time - series (STS) and linear autoregressive (ARX) models and compared with Artificial Neural Networks (ANNs). It also explores the improvement in the performance of neural networks by combing them with empirical methods. The study uses the monthly data at Sriramsagar, Mancherial and Polavaram gauging sites of Godavari basin of India. The ANN models, because of their nonlinear modeling capability, outperformed the empirical approaches. The study also reveals that the performance of ANN models in the simulation and forecasting of monthly runoff during monsoon period can be improved considerably by including the residuals derived from STS and ARX models as additional inputs together with rainfall.

Keywords: Simple time-series model, Linear autoregressive model, Artificial neural network, Comparison and combination, Performance evaluation

Title of the Paper: Heat and Water Management in a PEM Fuel Cell


Authors: Ebrahim Afshari, Seyed Ali Jazayeri

Abstract: Proton exchange membrane (PEM) fuel cells are promising power-generation sources for mobile and stationary applications. In this paper a non-isothermal, single-domain and two-dimensional computational fluid dynamics model is presented to investigate heat and water transfer in a PEM fuel cell. A set of governing equations, conservation of mass, momentum, species, energy and charge for gas channels, gas diffusion layers, catalyst layers and the membrane regions are considered. These equations are solved numerically in a single domain, using finite-volume-based computational fluid dynamics technique. This model accounts for the major transport phenomena in a PEM fuel cell: convective and diffusive heat and mass transfer, electrode kinetics, and potential fields. The results are shown to be in good agreement with previous work and it is validated with recent experimental data available

Keywords: PEM Fuel cell; Heat; Non-isothermal, Single-Domain; CFD

Title of the Paper: On Coherent Structures in a Separated/Reattached Flow


Authors: Zhiyin Yang, Ibrahim E. Abdalla

Abstract: It is well known that large-scale organised motions, usually called coherent structures, exist in many transitional and turbulent flows. The topology and range of scales of coherent structures change widely in different flows. However, it is not well established what kind of large-scale coherent structures exists in separated/reattached transitional flows. Large Eddy Simulation (LES) with a dynamic subgrid-scale model is employed to investigate a separated boundary layer transition under 2% free stream turbulence level and without free stream turbulence on a flat plate with a blunt leading edge. Flow visualization is employed to show the entire transition process leading to breakdown to turbulence and large-scale coherent structures have been identified at various stages of the transition process. However, there are some noticeable difference between the flow case with and without free stream turbulence. The Kelvin-Helmholtz rolls, which are clearly visible under no free stream turbulence (NFST), are not so clearly visible under 2% free steam turbulence (FST) case. The Lambda-shaped vortical structures which can be clearly seen in the NFST case can hardly be identified in the FST case. Generally speaking, the effects of free-stream turbulence have led to an early breakdown of the separated boundary layer and hence increased the randomisation in the vortical structures, degraded the spanwise coherence of those large-scale structures.

Keywords: Large-eddy simulation; large-scale coherent structures; free stream turbulence; transition

Title of the Paper: Flow Analysis of Annular Jets by Proper Orthogonal Decomposition. Active Control on in the Initial Zone of Large Diameter Ratio Annular Instabilities with Acoustic Excitations


Authors: A. Danlos, E. Rouland, B. Patte-Rouland

Abstract: Proper Orthogonal Decomposition (P.O.D.) is a technique used for analysis of vortex structures in a turbulent flow. In this study, complex shear flows are observed by P.I.V. measurements (Particle Image Velocimetry) of a large diameter ratio annular jet. The annular jet is an example of complex shear flow situations. Two axisymmetric shear layers, originating at the jet exit, one at the nozzle lip and the other at the centre body, eventually meet downstream or interact with each other. The main aim of this study is to observe and analyze the effects of active control using acoustic waves on an annular jet with a great diameter ratio (r= 0.91), in order to find a new way to reduce jet instabilities. This contribution discusses the application of Proper Orthogonal Decomposition to the P.I.V. (Particle Image Velocimetry) velocity fields of an annular jet and on a statistic of time resolved tomographic images of the initial zone of the annular jet. Acoustic waves are then applied on the annular jet with different frequencies (fundamental, first harmonic…). Measurements are conducted with a Reynolds number ReDo=107800. The fluctuation frequency of the stagnation point is known for this Reynolds number. The Strouhal number corresponding to this frequency is StDo = 0.27. The P.O.D. analysis applied on a natural annular jet and an excited annular jet enables us to see the importance of the triggering of the acoustic wave with the stagnation point motion. An active control is therefore necessary to use acoustic excitation to reduce instabilities in the initial zone of these turbulent jets. Active control has already been used with round jets and has given promising results, but only a few studies have been conducted on annular jets in this field. This work will permit us essentially to have a better knowledge of annular jets and to meet manufacturers' needs.

Keywords: Particle Image Velocimetry, Proper Orthogonal Decomposition, annular jet, control, acoustics excitations

Title of the Paper: Flow Field and Oscillation Frequency of a Rotating Liquid Droplet


Authors: Tadashi Watanabe

Abstract: Oscillations and rotations of a liquid droplet are simulated numerically using the level set method, and the combined effects of oscillation amplitude and rotation rate on the drop-shape oscillation is studied. The oscillation frequency is shown to decrease as the amplitude of oscillation increases. The oscillation frequency increases, in contrast to the effect of amplitude, as the rotation rate increases. The pressure distribution in the droplet corresponds to the frequency shift, and it is shown that the oscillations without frequency shift are possible. It is found that the relation between the amplitude and the rotation rate is linear both for the frequency shift of zero and for the pressure difference of zero even though the fluid properties are different. The flow fields in and around the droplet are visualized, and it is shown that the vortices formed by the oscillation are not affected by the rotation. Parallel computations are performed with satisfactory high efficiency for the calculations of the pressure field, and the importance of the communication rate is demonstrated.

Keywords: Droplet, Oscillation, Amplitude, Rotation, Frequency, Level Set Method, Parallel Computation

Title of the Paper: Optimal Design of Hydraulic Turbine Distributor


Authors: Ahmed Alnaga, Jean-Louis Kueny

Abstract: This work concerns the development of an automatic iterative procedure for optimal design of hydraulic turbine distributors. This procedure based on the geometry parameterization of the distributor to facilitate the fully automatic generation of the design by modifying the geometry parameters, and Evolutionary Algorithms to define the best design parameters using optimal functions (regrouped fixed objectives) evaluated from CFD results to decide the design quality. This procedure is successfully applied in two examples of Francis turbine distributors, the first with a specific speed equal to 81 and the second with a specific speed equal to 48. We obtained two new geometries with better efficiency and performance compared to the initial designs.

Keywords: Hydraulic turbines, geometry parameterization, flow simulation, evolutionary algorithms.

Title of the Paper: Comparing Various Methods for Topology and Shape Optimization of Floating Breakwaters


Authors: Ghassan Elchahal, Pascal Lafon, Rafic Younes

Abstract: In this paper, structural optimization of a floating breakwater is addressed through several methods concerning its topology and shape, which constitutes a new application. Three methods are introduced to handle the optimization problem. The first one discusses the shape optimization of a simple predefined geometrical form. The second, studies the topological optimization based on bit array representation of a triangular mesh using genetic algorithms. An attempt to overcome the limitations of bit-array was developed through several steps (new partition element, mesh distinguishing between the representation type and finite element analysis, varying finite element problem size, creating a density vector to control the presence or absence of the boundaries, generating initial population representing void domains instead of void elements). The third method concerns shape optimization, based on a variable number of points creating a structural domain. In contrary to traditional methods where the variable points are indicated by the user, it searches for the optimum number of points to create the optimum shape. Finally, a comparison between these methods for the case of the floating breakwater is discussed.

Keywords: Wave modelling; Floating breakwaters; Shape and topology optimization.

Issue 3, Volume 3, July 2008

Special Issue: Sustainable Energy and Environmental Fluid mechanics

Guest Editor: Dr. Mohammad Rasul

Title of the Paper: The Influence of Freshwater Biofilms on Drag in Hydroelectric Power Schemes


Authors: J. M. Andrewartha, J. E. Sargison, K. J. Perkins

Abstract: Freshwater biofilms are currently being studied to determine their effect on the capacity of hydroelectric power scheme canals and the structure of their turbulent wall layers. Mean velocity boundary layer profiles and total drag measurements have been conducted in a purpose built recirculating water tunnel on freshwater biofilms grown in a hydroelectric canal. Two different fouled surfaces were compared with a smooth painted surface to determine the effects of the physical characteristics of a biofilm on skin friction drag. A 310% increase in local skin friction coefficient was measured for a biofilm dominated by long filamentous algae streamers, and a 50% increase was measured for a biofilm dominated by a low-form gelatinous diatom.

Keywords: biofilm, biofouling, boundary layer, drag, hydroelectric, skin friction, water tunnel

Title of the Paper: Experimental and Computational Investigation of Flow Around a 3-1 Prolate Spheroid


Authors: D. B. Clarke, P. A. Brandner, G. J. Walker

Abstract: The flow around a 3-1 prolate spheroid near the critical Reynolds number is investigated experimentally and numerically. This work was conducted as part of a larger project to examine the flow around Unmanned Underwater Vehicles. The experimental investigation has been performed in a water tunnel at the Australian Maritime College. Fast response pressure probes and a 3-D automated traverse have been developed to investigate the state of the boundary layer. A commercial CFD code has been modified to allow the experimentally determined boundary layer state to be included in the computation. Qualitative and quantitative comparisons between the measured and calculated results are discussed. The tests on the spheroid were conducted within a Reynolds numbers range of 0.6 × 106 to 4 × 106. The results presented here are for an incidence of 10o.

Keywords: spheroid, boundary layer, transition, computational, experimental, pressure, flow visualisation

Title of the Paper: A Numerical Prediction of the Hydrodynamic Torque acting on a Safety Butterfly Valve in a Hydro-Electric Power Scheme


Authors: A. D. Henderson, J. E. Sargison, G. J. Walker, J. Haynes

Abstract: A numerical study of the flow through a safety butterfly valve used in a hydro-electric power scheme to stop water supply to a downstream penstock is reported. Computational fluid dynamics applied in a quasi-steady manner is used to predict the variation in hydrodynamic torque coefficient with opening angle during a constant head test. Factors influencing these results, such as Reynolds number and unsteady flow effects, are found to be significant. The predicted results are compared with field measurements of the full-size valve. Issues associated with applying the numerical results to predict valve characteristics at higher Reynolds numbers are discussed. Further computational and experimental studies are recommended.

Keywords: Numerical, Safety, Butterfly valve, Torque, Hydro-electric power

Title of the Paper: A Scalar Concentration (Komori) Probe for Measuring Fluctuating Dye Concentration in Water


Authors: J. T. Madhani, R. J. Brown

Abstract: The scalar (dye) concentration probe of Komori has been used at QUT to measure the mixing and dispersion of pollutants in rivers from outboard motors and in a gross pollutant trap (GPT). Although usages have been documented in literature, little is known of the Komori (dye) probe’s frequency response characteristics and the quality of data sampled. In this work, the frequency response characteristic of the Komori probe is determined by injecting methylene blue dye over a range of water flow velocities. Despite some noise and drift, the data collected from the probe is useful because of its high frequency response in comparison to regular commercial concentration probes. The rise and fall times are reported and the theoretical response time is also determined. It is found that the frequency response is a strong function of flow velocity and a maximum of 100 Hz is noted under typical operating conditions. Comparison between rise and fall data show that the rise time is generally shorter than half the fall time.

Keywords: Concentration probe, dye measurement, frequency response, Komori probe, tracer, rise time and fall time

Title of the Paper: Flow Field Phenomena about Lift and Downforce Generating Cambered Aerofoils in Ground Effect


Authors: J. W. Vogt, T. J. Barber, E. Leonardi

Abstract: A Computational Fluid Dynamics investigation was conducted to ascertain and highlight the different ways in which ground effect phenomena are present around both an upright (lift generating) and inverted (downforce generating) cambered aerofoil when in close proximity to the ground. The trends in force and flow field behaviour were observed at various ground clearances, while the angle of attack was held constant at 6 degrees. The different mechanisms by which ground effect influences the two different configurations were highlighted through observation of the pressure coefficient plots, contour maps of velocity and turbulence intensity and their effect on the normal and drag forces. The primary contributing factor to the increase in normal force for the lifting aerofoil, as the ground was approached, was a constriction and rise in pressure of the flow. For the downforce aerofoil, a significantly sped up flow increased suction and enhanced downforce. Also discussed is the observation of a reduction in lift for the upright aerofoil as its ground clearance is reduced through high and medium clearances.

Keywords: Aerodynamics, Ground Effect, Computational Fluid Dynamics, Aerofoil

Title of the Paper: Evaluation of a Proposed and an Existing Dust Ventilation/Collection System in an Underground Mine Crushing Plant


Authors: J. Naser, F. Alam, M. Khan

Abstract: Computational Fluid Dynamics (CFD) modeling of two alternative dust collection systems in an underground mine-crushing plant was carried out. In the proposed system, dust was collected/absorbed through the holes along the top edge of the Run of Mine (ROM) bin. In the existing conventional approach, the outgoing dust laden air is collected through an exit in the ceiling. The dust collection performances of both systems were summarized. Detail results are presented in the form of velocity vectors and dust concentration iso-surface contours. Dust was found to be well contained within the crusher bin for the proposed system and stands out as a viable option. However, the velocity magnitudes were found to be high in and around the hole exits, which has the potential to lead to undesirable pressure drop and generation of noise.

Keywords: Dust, modeling, CFD, multiphase, ventilation.

Title of the Paper: Numerical Modelling of Reverse Flow Phenomena in a Channel with Obstruction Geometry at the Entry


Authors: M. A. Kabir, M. M. K. Khan, M. G. Rasul

Abstract: Numerical modelling and simulation of the reverse flow phenomenon in a channel with obstruction geometry at the entry were performed using CFD-ACE+ simulation solver. Obstruction geometries used for simulation were triangle, circle, semicircle and flat plate. Simulations were performed for different gap to width ratio, for different gap between the test channel and obstruction geometry, and for different Reynolds number. The simulated results are discussed and compared with flow visualization images. Simulations results predicted the occurrence of reverse flow and existence of other flow features such as vortex shedding at both ends. The numerically predicted results of the flow phenomena are generally in good agreement with the experimentally observed flow visualization images.

Keywords: Reverse Flow, Test Channel, Obstruction, Flow Visualization and Simulation

Title of the Paper: A Study of Bubble Trajectory and Drag Co-efficient in Water and Non-Newtonian Fluids


Authors: N. M. S. Hassan, M. M. K. Khan, M. G. Rasul

Abstract: A new experimental set-up was used to analyze the characteristics of the bubbles rising in water and three different concentrations of xanthan gum solutions for higher Reynolds number. The bubble size, bubble rise velocity, and bubble trajectory were measured using a combination of non-intrusive-high speed photographic method and digital image processing. The results of bubble trajectory for various bubbles in water and different xanthan gum solutions are presented and discussed. In trajectory analysis, it is seen that the smaller bubbles show helical or zigzag motion and larger bubbles follow spiral motion for water. In xanthan gum solutions, small bubbles experience less horizontal motion than that in water. Larger bubbles produce more spiral motion with the increase in xanthan gum concentration. Drag coefficients for air bubbles at higher Reynolds number are reported. It is seen that the experimental drag coefficient increases with the increase in xanthan gum concentration corresponding to the same bubble volume.

Keywords: Bubble trajectory, bubble volume, drag co-efficient, Reynolds number, polymer solution, non-intrusive method

Title of the Paper: A Study of Spin Effects on Tennis Ball Aerodynamics


Authors: Firoz Alam, Aleksandar Subic, Jamal Naser, M. G. Rasul, M. M. K. Khan

Abstract: Due to complex surface structure, the aerodynamic behaviour of a tennis ball is significantly different compared to other sports balls. This difference is more obvious when spin is involved. Although several studies have been conducted on drag and lift in steady state condition (no spin involved) by the authors and others, little or no studies have been conducted on spin effect. It is known that the spinning can affect aerodynamic drag and lift of a tennis ball thus the motion and flight of the ball. The primary objective of this work was to study the effect of spin using experimental and computational methods. Several new tennis balls were used in experimental study as function of wind speed, seam orientation and spins. A simplified model of a tennis ball was used in computational study using commercial software ‘FLUENT’. The simulation results were compared with the experimental findings. The study shows that the spin has significant effects on the drag and lift of a new tennis ball, and the averaged drag coefficient is relatively higher compared to the non- spin condition. The study has also found a significant variation between CFD and EFD results as the complex tennis ball with fuzz elements was difficult to model in CFD.

Keywords: Drag coefficient, lift coefficient, spin, wind tunnel, EFD, CFD

Title of the Paper: An Experimental and Computational Study of Aerodynamic Properties of Rugby Balls


Authors: Firoz Alam, Aleksandar Subic, Simon Watkins, Jamal Naser, M. G. Rasul

Abstract: The aerodynamic properties of rugby balls as a function of wind speeds and yaw angles were measured using experimental and computational methods. The average drag and side forces coefficients for all speeds and yaw angles were computed and compared. The flow pattern around the rugby ball was visualized using wool tuft and smoke. No significant variation in Reynolds numbers was found in CFD results, however, some variations were noted in experimental findings. The average drag coefficient of a rugby ball at zero yaw was 0.18 and 0.14 in experimental and computational studies and this rose to about 0.60 and 0.50 when yawed at 90 degrees respectively.

Keywords: Drag coefficient, side force, wind tunnel, EFD, CFD

Title of the Paper: Sustainability in Building Environment: A Review and Analysis on Mould Growth in a Subtropical Climate


Authors: M. M. Rahman, M. G. Rasul, M. M. K. Khan

Abstract: A review on mould growth in buildings in a subtropical climate and the characteristics of moulds in a subtropical Central Queensland University (CQU), Rockhampton campus, Australia, buildings are presented and analysed. The mould (fungal spore) concentrations indoors and outdoors are compared and correlations between mould concentrations and environmental parameters such as temperature and humidity are developed. Specific genera of moulds and total spores were identified and recovered colonies were counted from the airborne samples. The SPSS (Statistical Product and Service Solutions) software was used for nonparametric data analysis. Total airborne mould concentrations were found highest in the dry season and lowest in the wet season and were positively correlated with relative humidity and temperature. Further studies are recommended for controlling mould growth in buildings in a subtropical climate.

Keywords: Airborne fungal spores, a subtropical climate, total fungal spores, Burkard spore trap, Spearman correlation coefficient.

Title of the Paper: Modelling of Flow and Tracer Dispersion over Complex Urban Terrain in the Atmospheric Boundary Layer


Authors: A. T. Skvortsov, P. D. Dawson, M. D. Roberts, R. M. Gailis

Abstract: A new mathematical model of polutant plume dispersion in an urban environment is presented. The model uses parameters that explicitly take into account turbulent flow close to the ground and the urban canopy parameters enabling an analytic calculation of the plume concentration profiles and concentration fluctuations. Model predictions are compared with some recent experimental data, showing a close match. The model developed can be used as an analytical tool for predicting CBR plume behaviour in complex urban environments, or as a prototype and performance check for a new generation of dispersion models.

Keywords: Plume, Pollutant, Dispersion, Tracer, Urban Canopy, Concentration Fluctuations, Intermittency, Model.

Issue 4, Volume 3, October 2008

Title of the Paper: Using GIS Buffer Technique to Improve Rainfall-Radar Reflectivity Relationship Estimation


Authors: Sarintip Tantanee, Saman Prakarnrat

Abstract: In Past decade, Thailand has regularly faced the problem of flash flood and landslides, especially over the lower Northern part of the country. This area is mountainous area where there is the problem of raingage scarcity and absence. In order to construct the effective warning system, the appropriate rainfall estimation should be first developed. Thus, this research was implemented based on the concept of using information from radar to detect rainfall in order to solve the problem of information lacking over ungaged area. This research was setup under the collaboration among Naresuan University, Thai Meteorological Department and Royal Irrigation Department. The objective of the research is to estimate the rainfall (R) from Z-R relationship by using the measured reflectivity (Z) from radar station located at the middle of flash flood risky area in Lower Northern Thailand. Coupling GIS technique with probability matching, the Spatial Probability Technique (SPT) and Buffer Probability Technique (BPT) were developed to evaluate the appropriate Z-R pair for Z-R relationship analysis. From both techniques, the obtained Z-R relationship can be expressed in form of, where are Function Parameters, as the previous studies. Comparing between these two techniques on rainfall detecting from reflectivity, the obtained R Z=aRb a,b2 from both processes are slightly difference, whereas, BPT provided less standard error of estimation. However, this study emphasized only on the Z-R relationship, the further study should be done with the other parameters to support the disaster warning system in the future.

Keywords: Rainfall, Radar, Reflectivity, Z-R Relationship, Buffer, Spatial, Ungauged area


Title of the Paper: Modelling Muddy Flash Floods and Debris Flows


Authors: B. Nsom, B. Ravelo, W. Ndong, N. Latrache, K. Bouchlaghem, S. Elouragini

Abstract: After long and intense rains in a mountainous region, large quantities of water flow in the torrents. For some reason, this flow can be obstructed by cross-linked branches and debris (natural dam). When the hydrostatic pressure exerted by the fluid exceeds a given yield value, the dam collapses and the fluid is released inside and outside the torrent bed, as well. Such scenario which is known as a dam-break flow can describe the initiation of certain geological flows, (debris flows, mudflows, etc.). As for any gravity current, the flow description depends on the time scale. Immediately after the dam collapse, the inertial forces are the dominant ones and this configuration can model a flah flood. Flash floods develop at time and space scales that conventional observation systems are not able to monitor, so reliable modelling remains a crucial step. At larger time scale, a viscous regime takes place where the viscous forces become the dominant ones and this configuration can model a classical debris flow. Debris floods develop in a long domain, i.e. a domain of space that is much longer than it is wide. They generally erode their bed and transport much energy and can move rocks and boulders upon very long distances. Both, the flash flows and the debris floods constitute dangerous phenomena for public safety and quality of life. The originality of the present approach is to consider these two flood waves as special cases of a single global model of a dam-break flow of a muddy fluid, depending on the time scale. The study was experimental, analytical and numerical, as well. The experimental study performed in previous work consisted in designing model fluids to be used in the laboratory experiments, characterizing these synthetic muds and monitoring the corresponding dam-break flows in the laboratory. The corresponding results agreed with the theoretical study presented here and which consists in stating the equations of motion governing the different flows studied, and solving them in their non dimensional form, both analytically and numerically.

Keywords: Dam failure, Finite difference method, Herschel-Bulkley fluid, Inertial regime, Numerical models, One dimensional flow, Shallow water approximation, Similar solution, Viscous regime.

Title of the Paper: Calculus of Indicated Power by Mathematical Modeling Method of Compression Process and Study of  Exegetic Efficiency of the Helical Screw Compressor with Oil Injection


Authors: Petrilean Dan Codrut, Dosa Ion

Abstract: The first part of the article studies the problem of establishing a mathematical model that ensures the calculus of the output power for the helical screw compressor with oil injection. In the second part the problem of establishing the equation of exegetic efficiency for helical screw compressors with oil injection is further explored. The obtained results are checked by carrying out case studies on real compressors.

Key words: indicated power, exergy, helical screw compressor, mathematical modeling method, exegetic efficiency, modeling of working conditions.

Title of the Paper: Von Karman Vortices Formation at the Trailing Edge of a Turbine Blade


Authors:  Daniele Simoni, Marina Ubaldi, Pietro Zunino

Abstract: - The paper presents the results of an experimental investigation of the von Karman vortices formation at the blade trailing edge of a large scale turbine cascade. The mean and time varying characteristics of the flow in the trailing edge region were measured by means of a two-component fiber-optic laser Doppler velocimeter over an experimental grid very close to the blade trailing edge. A phase locked ensemble averaging technique has been applied to separate coherent and incoherent contributions in the instantaneous LDV data. The trailing edge of the central blade of the cascade has been instrumented with a multisensor surface mounted hot-film probe. The probe outputs proportional to the instantaneous wall shear stress were sampled simultaneously with a filtered reference signal from a hot-wire probe located in the wake and sensitive to the vortex periodicity. Organised periodic structures have been clearly identified in the flow and their evolution in time has been documented through a sequence of instantaneous pictures of the periodic flow field during a cycle of the vortex shedding. Time-averaged and time-resolved ensemble averaged wall shear stresses on the blade trailing edge help to identify the positions where the boundary layers separate and to analyze the effects of the vortex shedding on the wall shear stress along the trailing edge.

Key-Words: - Turbine blade boundary layers, Turbine blade wakes, Von Karman vortices, Wall shear stress, Hot-film measurements.

Title of the Paper: Experimental and Computational Aerodynamic Investigations of a Car


Authors: Manan Desai, S. A. Channiwala, H. J. Nagarsheth

Abstract:- In the recent times, CFD simulations [1], with the advent of computer architectures with superfast processing capabilities are rapidly emerging as an attractive alternative to conventional wind tunnel tests which are either too restrictive or expensive, for aerodynamic styling of a car. The paper describes comparative assessment of two distinct experimental strategies of aerodynamic predictions by conventional wind tunnel approach and its subsequent validation with advanced computational procedures, carried out as a part of design process of a small hybrid car proposed to be named as ADRENe. The experimental investigations were performed on an open circuit suction type wind tunnel having a 30cm x 30cm x 100cm test section, on a geometrically similar, reduced scale (1:15) clay model, while the three dimensional computational analysis was carried out using Gambit as the preprocessing software and Fluent as the solver and post processor. A good agreement between performance values obtained independently by two experimental methods, suggests their reliability and suitability for further experimentation purposes. The comparison with computational approach shows that the computed drag forces and pressure distributions agree well with the experimental values over the entire range of air velocities, however, the agreement with the data for drag coefficient varies, which appears to suggest a higher degree of dependency on the grid quality and elements selection.

Key-Words: - Car design, Aerodynamics, Wind tunnels, CFD.

Title of the Paper: Void Fraction Fluctuations in Two Phase Flow: Theoretical Models


Authors: G. B. Roston, M. E. Ascheri, M. C. Martin, R. Pizarro

Abstract: The knowledge on the structure and dynamical behavior of the two phase flow is important for a great number of processes, including the coolant behavior in a nuclear power reactor. Previous studies performed on gas liquid phase or in experimental devices specially designed for that purpose, have introduced theoretical models that describe the void fraction fluctuations in a two phase flow. Nevertheless, they only partially explained the measured effects or have a doubtful applicability. In this work, from data obtained from a BWR nuclear power plant, we apply different mathematical models in order to study the change of the intensity of the void fraction fluctuations along the channel. By comparing these models, we conclude that the bimodal twophase flow model is a more realistic one for void fraction estimation. This model can be applied for high void fraction rate and converges to the Poisson model for low void fraction rate. The expected contribution of this work is, by means of a proper use of neutron signal analysis, to obtain a better understanding of the dynamics and structure of the two phase flow in a nuclear power reactor.

Key-Words: Two phase flow, Bimodal model, Neutron noise, Coolant, Nuclear reactor.

Title of the Paper: Simulation of Viscous Flows with a Gridless Particle Method


Authors: Fotios G. Stamatelos, John S. Anagnostopoulos

Abstract: The aim of this paper is to present the numerical simulation of the evolution of the viscous, low Reynolds flows in two-dimensional cases with the use of the Smoothed Particle Hydrodynamics (SPH) method. This work is considered as the first step towards the simulation of complex three-dimensional flows, which occur in impulse water turbines. The method was originally developed for solving problems of astrophysical nature and belongs to the mesh less methods, as it does not require any computational grid. A set of discrete fluid particles is used to represent the continuous fluid, and their trajectories are being calculated in a Lagrangian sense through time. The 2-D test cases examined in this paper are the Couette and the Poiseuille Flow, and the basic problem of the liquid column collapse (Dam Break). For the first two test cases the numerical results were tested against analytical solutions from the literature, while for the third test case experimental measurements were used for the validation of the calculations. The agreement of the numerical results with the corresponding analytical and experimental data is quite good and encouraging towards the use of the SPH method in modelling of more complex, unsteady and multiphase flow fields, while the performance of the algorithm referring to the speed of the calculations and the qualitative results is remarkable.

Key-Words: - Smoothed Particle Hydrodynamics (SPH), Dam Break, Couette and Poiseuille Flow, Numerical Modelling

Title of the Paper: Nonlinear Behavior of Pile-Soil Subjected to Torsion due to

Environmental Loads on Jacket Type Platforms.


Authors: M. R. Emami Azadi, S. Nordal, M. Sadein

Abstract: - In the present study, the torque-twist behavior of non-linear pile-soil system related to the wavecurrent loading on Jacket type offshore platform is investigated. The non-linearities of pile-soil with respect to both depth and the twist angle of pile are considered. The basic differential equilibrium equations of the pilesoil system are derived based on hyper- elasticity theory of soil. A numerical central finite difference method is applied based on simplification of stress field around the pile elements which takes into account changes in the s e co nd a r y shear stress components and also non-linearities due to non-homogeneous soil condition. This method uses a one-dimensional mesh along pile-soil interface. It also takes into account the changes in G of soil with respect to the twist angle of pile. In a separate work, the simulated torque-twist behavior of pile-soil system based on this analysis approach is compared with the results of more refined finite element analysis by using continuum mechanics theory and also full scale pile-soil test results (Emami,2002). The torque-twist results by using the proposed approach have been used to study the behavior of two jacket-pile-soil systems under sea environmental and accidental loading.

Key-Words: - Pile-Soil interaction, Jacket-Pile-Soil system, Pile-Soil Non-linearities, Disk Model of Soil, Torque-Twist (t-t) transfer curves



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