Search

In this series of articles, the authors discuss various phenomena in fluid dynamics, which may be investigated via tabletop experiments using low-cost or home-made instruments. The thirteenth article in this series demonstrates some experiments with Hele-Shaw cells. [ABSTRACT FROM AUTHOR]

Fluids are high mobility environments that, under the action of external forces, are continuously and irreversibly deformed. The flow of fluid through a pipe is ensured by a pressure difference between its ends. The presented paper aims to experimentally determine the velocity profile of flowing a Newtonian fluid through a circular section pipe by measuring the local speed at five points on the pipe radius. [ABSTRACT FROM AUTHOR]

Unconventional fractured gas wells occasionally exhibit bilinear flow during early production. When this flow regime is observed, important fracture properties can be estimated such as conductivity and/or spacing. However, the application of present-day rate-transientanalysis (RTA) methods to bilinear flow results in up to 18% error. This error is rate-dependent, and occurs because of nonlinearities in the gas-diffusivity equation. This paper presents a new correction factor that handles the rate dependency of bilinear flow, and enables more-accurate reservoir characterization. The diffusivity equation of gas in porous media has some nonlinearities that cannot be addressed by only using the real-gas pseudopressure. Even though neglecting these nonlinearities results in a model that is sufficiently accurate for the radial-flow case, errors arise in the boundary-dominated-flow (BDF) (Fraim and Wattenbarger 1987), the linear-flow (Ibrahim and Wattenbarger 2006; Nobakht and Clarkson 2012), and, as shown in this article, the bilinear-flow cases. Currently, no research studies provide an accurate bilinear-flow analytical model for gas reservoirs. To bridge this gap and to provide rate-transient analysts with a practical tool, this work presents a correction factor that can be incorporated into the existing bilinear-flow models. The correction factor was developed following an approach similar to that of Ibrahim and Wattenbarger (2006). The first step was to simulate a number of reservoir and well conditions. Second, fracture properties were back calculated with the current bilinear-flow models. Finally, errors between the back calculated and the simulated properties were correlated to dimensionless drawdown. After these steps, a correction factor was obtained that applied to various bilinear-flow cases. The obtained numerical results indicate that errors in bilinear-flow models are correlated with rate, or more precisely, dimensionless drawdown [a similar behavior is observed in the analytical model of linear flow, as demonstrated by Ibrahim and Wattenbarger (2006)]. This correlation can be used to reduce error to less than ±3%. Because the simulated cases cover an extensive range of unconventionalreservoir conditions, the empirical correction is robust and applicable to a wide variety of reservoir conditions. Most importantly, the correction is practical and can be readily incorporated into existing bilinear-flow models. The application of the new correction is demonstrated in this article with synthetic and field examples. [ABSTRACT FROM AUTHOR]

Maximum flow problem is one of the most fundamental network optimization problems. Recently, experimental observations showed that an amoeboid organism, Physarum polycephalum, contains a tube network by means of nutrients and signals circulating through the body. The tube network can sense and adopt to local shear stress difference in its own body until the shortest tubes of connecting two food sources (placed at two exits of a maze) keep alive while longer tubes vanish eventually. Unlike to the global optimization algorithm Physarum solver, we develop a mathematical model of a dynamical system which capture the local control behavior of Physarum when searching for foods. With this new model, a novel adaptive amoeba algorithm for maximum flow problem is proposed, which can be used to solve shortest path problem as Physarum solver. Furthermore,we firsts apply this model to solve maximum flow problem, where its convergence is proved in this paper as well. Additionally, numerical results demonstrate the validity and efficiency of the proposed algorithm to solve maximum flow problem. [ABSTRACT FROM AUTHOR]

The broad family of κ-ε turbulence models is very often used in engineering computational fluid dynamics (CFD). All these models contain semi-empirical parameters that have been determined based on idealised flows. However, it is important to recall that the model parameters are not universal and not even necessarily constant. Consequently, a large span of model parameters can be found in the scientific literature. The objective of the present study is to determine optimised but generally applicable model parameters for the prediction of turbulent quantities for the realisable κ-ε model. Four canonic flow configurations are considered simultaneously in the optimisation: channel flow, flow over a backward-facing step, jet flow, and flow over a periodic hill. The optimisation problem thus involves several concurrent objectives that must be fulfilled simultaneously. The obtained optimised model parameters do not differ tremendously from the standard recommended values. Nevertheless, for all the configurations the optimised model delivers better, or at least equally good results compared with experimental measurements. Therefore, employing the model parameter values proposed in this work is recommended, since a slightly improved prediction is obtained at no additional numerical cost. [ABSTRACT FROM AUTHOR]

Cities, due to the concentration of population, economic activities and built infrastructures, are high-risk and potential damage areas in global warming scenarios. Specific climate conditions, which occurs in urban areas, are expected to change with almost certainly disadvantageous effects on quality of life at outdoor spaces. This paper presents an evaluation of climate change impact on cities, by simulating the thermal performance of outdoor spaces, using different climate scenarios. The Plaza de Armas of Concepción (Chile) has been used as case study, and climate conditions at 2020, 2050 and 2080 have been produced for the acknowledged A2’medium-high’ emissions Greenhouse Gases GHG scenario, according to Intergovernmental Panel on Climate Change IPCC. To simulate the urban microclimate, the ENVI-met v4 software, a three-dimensional numerical model based primarily on fluid dynamic and thermodynamic models has been used to estimate interaction between surfaces, plant and atmosphere at the micro-scale. The comparison between different scenarios and discussion about results are presented as well. The results and discussion are a first step to advance on the knowledge of climate change impact for proposing adaptation strategies in the urban context. [ABSTRACT FROM AUTHOR]

Horizontal well is one of the most effective ways of developing unconventional oil and natural gas reservoirs. During horizontal well drilling, a stationary cuttings bed forms on the low-side of the wellbore. Formation of the bed is undesirable and has detrimental effect on wellbore hydraulic and drilling performance. Hydraulic optimization of the process strongly depends on accurate prediction of bed height and frictional pressure loss. Therefore, it is necessary to investigate hydraulic characteristics of horizontal wellbore with cuttings bed, which can be represented by partially blocked concentric annulus when centralizers are used with drillpipe. In this study, flow in a partially blocked concentric annulus is investigated using Computational Fluid Dynamics (CFD) approach. CFD simulation results are validated using established numerical solutions and experimental measurements obtained from concentric annulus. The analysis is performed for laminar flow of yield-power-law (YPL) fluid. Pressure loss and wall shear stress acting on the cuttings bed are obtained from CFD simulation. Results show significant variation in bed shear stress in the lateral direction. Hence, average bed shear stress ( τ ¯ bed ) is used to analyze the result. Unexpected τ ¯ bed trend is observed when bed height is increased at constant flow rate. As bed height increases, τ ¯ bed slightly decreases at low bed heights until it reaches the inner pipe. For bed height greater than annular clearance, τ ¯ bed trend is normal, it increases with bed height. Existing hole cleaning models require accurate prediction of τ ¯ bed and pressure loss in partially blocked concentric annuli. Therefore, combining existing non-circular duct modeling approach and simulation data, simplified models are developed to predict pressure loss and τ ¯ bed . Model predictions show reasonable agreement with simulation results. Maximum discrepancy of ±10% has been observed. [ABSTRACT FROM AUTHOR]

The paper provides numerical simulation of wind loads acting on industrial complex. The numerical modeling technique is given, as well as the results verification of the data obtained during the aerodynamic experiment in wind-tunnel. According to the verification the computation model was optimized. The resulting aerodynamic characteristics was obtained, the most unfavorable wind direction were revealed. [ABSTRACT FROM AUTHOR]

A simplified pore network model, which divided pore structure into cube lattices, was developed based on the digital core extracted from micro computerized tomography (µ-CT) in this study. It rolled the complex topology and connectivity of pore structure into adjacent cubes. The static property of each cube was determined by the statistic CT data. The connectivity of adjacent cubes and flow regime were determined by the capillary pressure difference which is a function of tunnel size, interfacial tension, wet contact angle, and external pressure gradient. In this simplified pore network model, the flow capacity properties are determined by number and size distribution, mobile tunnels, and fluid viscosity. The flow velocity and sweep efficiency are non-linear as mobile tunnels increase nonlinearly with increasing driving force before all tunnels start flowing. The critical pressure gradient that changed the non-linear flow to linear flow was performed as the threshold pressure gradient. The dynamic mobile performance of Oil In Place (OIP) is determined by the number of mobile tunnels and their diameter distribution for different pressure gradients. The relationship of microscopic sweep efficiency, water cut, and pressure gradient to oil recovery can be quantified by flow simulation in this pore network model. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to demonstrate the possibility to selectively tune the convective heat transfer coefficient in different sections of a heat sink by varying the density of microfeatures in order to minimize temperature gradients between discrete heat sources positioned along the flow path. Lifetime of power electronics is strongly correlated to the thermal management of the junction. Therefore, it is of interest to have constant junction temperatures across all devices in the array. Implementation of microfeature enhancement on the convective side improves the heat transfer due to an increase in surface area. Specific shapes such as micro-hydrofoils offer a reduced pressure drop allowing for combined improvement of heat transfer and flow performance. This study presents experimental results from an array of three discrete heat sources (20 x 15 mm) generating 100 W/cm² and positioned in line along the flow path with a spacing of 10 mm between each of the sources. The heat sink was machined out of aluminum 6061, and micro-hydrofoils with a characteristic length of 500 µm were embedded in the cold plate. The cooling medium used is water at a flow rate of 3.6-13.4 g/s corresponding to a Reynolds number of 420-1575. It is demonstrated that the baseplate temperature can be maintained below 90 °C, and the difference between the maximum temperatures of each heat source is less than 6.7 °C at a heat flux of 100 W/cm² and a water flow rate of 4.8 g/s. [ABSTRACT FROM AUTHOR]

This article addresses the peristaltic transport of Eyring-Prandtl fluid in an inclined asymmetric channel. Heat and mass transfer phenomena along with Soret and Dufour effects is analyzed. Effects of inclined magnetic field and Joule heating are also discussed. Long wavelength approximation is adopted. Numerical computations for flow quantities of interest are analyzed. It is found that the parabolic velocity profile tends to shift from center of the channel towards the channel walls in the case of opposing flow. Velocity and temperature decrease whereas concentration increases by increasing the non-Newtonian parameter. Further the dependence of magnetic field on the angle is quite significant. [ABSTRACT FROM AUTHOR]

A two-fluid model of Herschel–Bulkley fluid flow through tubes of small diameters and slip at the wall is studied. It is assumed that the core region consists of Herschel–Bulkley fluid and Newtonian fluid in the peripheral region. Following the analysis of Chaturani and Upadhya, the equations of motion have been linearized and analytical solution for velocity, flow flux, effective viscosity, core hematocrit and mean hematocrit has been obtained. The expressions for all these flow relevant quantities have been numerically computed by using Mathematica software and the effects of various relevant parameters on these flow variables have been studied. It is found that effective viscosity, core hematocrit and mean hematocrit of Newtonian fluid are less than those for Bingham fluid, power-law fluid and Herschel–Bulkley fluid. Effective viscosity increases with the yield stress, power-law index, slip and tube hematocrit but decreases with Darcy number. It is observed that the effective viscosity and mean hematocrit increase with tube radius but the core hematocrit decreases with tube radius. Further, it is noticed that the flow exhibits the anomalous Fahraeus–Lindqvist effect. [ABSTRACT FROM AUTHOR]

3D stacked technology has emerged as an effective mechanism to overcome physical limits and communication delays found in 2D integration. However, 3D technology also presents several drawbacks that prevent its smooth application. Two of the major concerns are heat reduction and power density distribution. In our work, we propose a novel 3D thermal-aware floorplanner that includes: (1) an effective thermal-aware process with three different evolutionary algorithms that aim to solve the soft computing problem of optimizing the placement of functional units and through silicon vias, as well as the smooth inclusion of active cooling systems and new design strategies, (2) an approximated thermal model inside the optimization loop, (3) an optimizer for active cooling (liquid channels), and (4) a novel technique based on air channel placement designed to isolate thermal domains have been also proposed. The experimental work is conducted for a realistic many-core single-chip architecture based on the Niagara design. Results show promising improvements of the thermal and reliability metrics, and also show optimal scaling capabilities to target future-trend many-core systems. [ABSTRACT FROM AUTHOR]

Copyright of DYNA - Ingeniería e Industria is the property of Publicaciones Dyna SL and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article focuses on the research "Simultaneous Multifracture Treatments: Fully Coupled Fluid Flow and Fracture Mechanics for Horizontal Wells." Topics include simulate multiple-hydraulic-fracture propagation from a horizontal wellbore using novel fracture-propagation model (FPM), showing fracture deformation with fluid flow in the fractures and the horizontal wellbore by displacement discontinuity method (DDM), and frictional pressure drop in the wellbore and perforation zones.

Elastic inverse-scattering theory has been extended for fluid discrimination using the time-lapse seismic data. The fluid factor, shear modulus, and density are used to parameterize the reference medium and the monitoring medium, and the fluid factor works as the hydrocarbon indicator. The baseline medium is, in the conception of elastic scattering theory, the reference medium, and the monitoring medium is corresponding to the perturbed medium. The difference in the earth properties between the monitoring medium and the baseline medium is taken as the variation in the properties between the reference medium and perturbed medium. The baseline and monitoring data correspond to the background wavefields and measured full fields, respectively. And the variation between the baseline data and monitoring data is taken as the scattered wavefields. Under the above hypothesis, we derived a linearized and qualitative approximation of the reflectivity variation in terms of the changes of fluid factor, shear modulus, and density with the perturbation theory. Incorporating the effect of the wavelet into the reflectivity approximation as the forward solver, we determined a practical prestack inversion approach in a Bayesian scheme to estimate the fluid factor, shear modulus, and density changes directly with the time-lapse seismic data. We evaluated the examples revealing that the proposed approach rendered the estimation of the fluid factor, shear modulus, and density changes stably, even with moderate noise. [ABSTRACT FROM AUTHOR]

In present article, we have studied the blood flow through tapered artery with stenosis. The non-Newtonian nature of blood in small arteries is analyzed mathematically by considering the blood as Carreau fluid. Carreau fluid is a type of generalized Newtonian fluid. At low shear rate Carreau fluids behaves as a Newtonian fluid n = 1 and at high shear rate as power law fluid. For n < 1 Carreau fluid gives pseudoplastic(non-Newtonian), or shear-thinning fluids have a lower apparent viscosity at higher shear rates and for n > 1 Carreau fluid behaves as Dilatant(non-Newtonian), or shear-thickening fluids increase in apparent viscosity at higher shear rates. All three cases are appropriate for blood flow in arteries because the assumption of Newtonian behavior of blood is acceptable for high shear rate flow, i.e. the case of flow through larger arteries. It is not, however, valid when the shear rate is low as is the flow in smaller arteries and in the downstream of the stenosis. It has been pointed out that in some diseased conditions, blood exhibits remarkable non-Newtonian properties. The representation for the blood flow is through an axially non-symmetrical but radially symmetric stenosis. Symmetry of the distribution of the wall shear stress and resistive impedance and their growth with the developing stenosis is another important feature of our analysis. Analytical solutions has been evaluated for velocity, resistance impedance, wall shear stress and shear stress at the stenosis throat. The graphical results of different types of tapered arteries (i.e converging tapering, diverging tapering, non-tapered artery) have been examined for different parameters of interest. [ABSTRACT FROM AUTHOR]

Withering is the first processing step in the tea processing factory. For efficient tea processing, withering should be as uniform as possible. Uniformity in the trough withering greatly depends on the uniformity of the drying air temperature and velocity distribution along the trough. In literature no study is reported on thermal and velocity profiles of drying air during withering in a trough which would bring about uniformity in the degree of wither. In this backdrop, in the present work a 3D model has been developed using Fluent 6.2 computational fluid dynamics (CFD) package to predict the temperature and velocity distributions of drying air in a withering trough. The results of the model show wide variation in temperature and velocity distributions along the trough length, which contributes non-uniformity in tea leaves withering. The model has been validated within the acceptable limit (within ±1.43%) using the data that were collected from an open tea withering trough installed at Rosekandi tea estate factory, Assam, India. Thus, there is a good agreement between experimental and computational values. Therefore, the present numerical model can be extended incorporating the necessary changes in the trough design so as to obtain a uniform withering of tea leaves. [ABSTRACT FROM AUTHOR]

FORGE (Fate of Repository Gases) is an international research project supported by funding under the European Commission FP7 Euratom program and lasting four years from 2009 to 2013. The project is dedicated to understanding gas generation and migration as part of the quantitative assessment of a geological repository for radioactive waste. Within the FORGE project, Work Package 1 is dedicated to numerical modeling of a two-phase flow system (hydrogen gas due to corrosion and groundwater) in a geological repository for radioactive waste. Several benchmark exercises were proposed that cover the modeling of a deep geological repository from the disposal cell scale to the repository scale with different codes. During the definition of the exercises, special emphasis was given to the roles of the excavation-disturbed zone and of the inter faces between materials, which could act as a conduit for preferential flow. Some changes were made in the TOUGH2 code to enable the implementation of the prescribed conditions, models, and parameters of the benchmark. The results of the calculations performed with different codes show that TOUGH2 gives comparable results under the numerically challenging conditions defined in the exercise. Some differences were observed resulting from the use of different codes and also from some simplifications in the parameters and models adopted by the participating teams. In this paper, the cell-scale benchmark exercise and the results obtained by the Swiss Federal Nuclear Safety Inspectorate {ENSI) with TOUGH2 will be described, together with some difficulties encountered during the simulation, e.g., convergence problems. The results of other teams participating in the benchmark are in good agreement with the ENSI results. [ABSTRACT FROM AUTHOR]

The performance of automotive turbocharger turbines has long been realized to be quite different under pulsating flow conditions compared to that under the equivalent steady and quasi-steady conditions on which the conventional design concept is based. However, the mechanisms of this phenomenon are still intensively investigated nowadays. This paper presents an investigation of the response of a stand-alone rotor to inlet pulsating flow conditions by using a validated unsteady Reynolds-averaged Navier-Stokes solver (URANS). The effects of the frequency, the amplitude, and the temporal gradient of pulse waves on the instantaneous and cycle integrated performance of a radial turbine rotor in isolation were studied, decoupled from the upstream turbine volute. A numerical method was used to help gain the physical understanding of these effects. A validation of the numerical method against the experiments on a full configuration of the turbine was performed prior to the numerical tool being used in the investigation. The rotor was then taken out to be studied in isolation. The results show that the turbine rotor alone can be treated as a quasi-steady device only in terms of cycle integrated performance; however, instantaneously, the rotor behaves unsteadily, which increasingly deviates from the quasi-steady performance as the local reduced frequency of the pulsating wave is increased. This deviation is dominated by the effect of quasi-steady time lag; at higher local reduced frequency, the transient effects also become significant. Based on this study, an interpretation and a model of estimating the quasi-steady time lag have been proposed; a criterion for unsteadiness based on the temporal local reduced frequency concept is developed, which reduces to the A criterion proposed in the published literature when cycle averaged. This in turn emphasizes the importance of the pressure wave gradient in time. [ABSTRACT FROM AUTHOR]

Transport through phloem is of significant interest in engineering applications, including self-powered microfluidic pumps. In this paper we present a phloem model, combining protein level mechanics with cellular level fluid transport. Fluid flow and sucrose transport through a petiole sieve tube are simulated using the Nernst-Planck, Navier-Stokes, and continuity equations. The governing equations are solved, using the finite volume method with collocated storage, for dynamically calculated boundary conditions. A sieve tube cell structure consisting of sieve plates is included in a two dimensional model by computational cell blocking. Sucrose transport is incorporated as a boundary condition through a six-state model, bringing in active loading mechanisms, taking into consideration their physical plant properties. The effects of reaction rates and leaf sucrose concentration are investigated to understand the transport mechanism in petiole sieve tubes. The numerical results show that increasing forward reactions of the proton sucrose transporter significantly promotes the pumping ability. A lower leaf sieve sucrose concentration results in a lower wall inflow velocity, but yields a higher inflow of water due to the active loading mechanism. The overall effect is a higher outflow velocity for the lower leaf sieve sucrose concentration because the increase in inflow velocity outweighs the wall velocity. This new phloem model provides new insights on mechanisms which are potentially useful for fluidic pumping in self-powered microfluidic pumps. [ABSTRACT FROM AUTHOR]

Flows in the urban boundary layer (UBL) are strongly affected by the inhomogeneous roughness elements at the bottom surface. In particular, in the near-ground region (roughness sublayer), the effect of the surface roughness dominates that complicates the behaviours of mean flow and turbulence and subsequently the near-wall transport processes. To safeguard the health of urban inhabitants, it is crucial to develop an in-depth understanding of the correlation among near-wall fluid motions, UBL turbulence and city ventilation. However, rather limited information is available. In this study, physical modelling in a laboratory wind tunnel is employed to measure the profiles of both stream-wise and vertical velocities over an array consisting of idealised two-dimensional (2D) roughness elements. Various arrangements are adopted in attempt to cover different flow regimes to examine city ventilation problems. The ventilation performance is measured by the air exchange rate (ACH). Consistent with our previous large-eddy simulation (LES) results, the current wind tunnel measurements suggest that city ventilation is dominated by the ACH turbulent component, i.e., air masses are mainly driven by atmospheric turbulence (at least 80% of the total ACH). [ABSTRACT FROM AUTHOR]

Considered herein is a generalized two-component Camassa-Holm system modeling the shallow water waves moving over a linear shear flow. The existence of the global weak solutions to the generalized two-component Camassa-Holm system is established and the solution is obtained as a limit of approximate global strong solutions. [ABSTRACT FROM AUTHOR]

Computation of flow past high speed vehicles requires the use of a reliable turbulence model. Unfortunately, most of the turbulence models are developed for incompressible flows. Application of these models directly to high speed boundary layers with large density gradients can lead to significant errors in prediction of skin friction. Several compressibility corrections have been suggested in literature to predict these turbulent flows at high Mach numbers. In the present work, we have used two such corrections for the Spalart-Allmaras turbulence model and studied their performance at high angles-of-attack. Flow past an ogive cylinder is considered for the study. [ABSTRACT FROM AUTHOR]

The article offers information on a research paper which shows the research work in the numerical simulation of proppant transport in hydraulically simulated fractures for oil and gas production. It informs that a three dimensional (3D) computational-of the fracturing process (CFD) model with Lagrangian solid-particle transport is applied to examine the propagation of sand in a simulated fracture. It also informs that the model provides better understanding of the fracturing process.

The article offers information on a study which shows the use of lattice Boltzmann method (LBM) in simple pore geometries overcoming the weaknesses of lattice gas cellular automata. It informs that LBM takes into account molecular-level interactions by use of adsorptive/cohesive forces among the fluid particles and defining a Langmuir-slip boundary condition at the organic pore walls. It mentions that LBM can be used for development of new-generation shale-gas-reservoir flow simulators.

The article focuses on a study showing the effect of geometry on the flow transition and the beta factor of non-darcy flow using lattice Boltzmann simulations and stochastically constructed two dimensional porous media models. It informs that it is necessary to include two distinctive characteristic lengths to account for the effect of pore-scale heterogeneity. It reports that the inspection of flow patterns revealed steady vortices and onset of unsteady motions in the Forchheimer regime.

Dual number automatic differentiation was applied to two computational fluid dynamics codes, one written specifically for this purpose and one "legacy" Fortran code. Results for the simple case of a fully developed laminar flow in a channel validated the approach in computing derivatives with respect to both a fluid property and a geometric dimension. DNAD was also implemented into the JET Fortran program which is available with a popular turbulence modeling textbook. Mean centerline velocity derivatives for a self-similar round jet with respect to all applicable turbulence model closure coefficients for k-ω and k-ε models were obtained. [ABSTRACT FROM AUTHOR]

Abstract: The problem of free convection heat with mass transfer for MHD non-Newtonian Eyring–Powell flow through a porous medium, over an infinite vertical plate is studied. Taking into account the effects of both viscous dissipation and heat source. The temperature and concentration are of periodic variation. The governing non-linear partial differential equations of this phenomenon are transformed into non-linear algebraic system utilizing finite difference method. Numerical results for the velocity, temperature and concentration distributions as well as the skin friction, heat and mass transfer are obtained and reported in tabular form and graphically for different values of physical parameters of the problem. Also, the stability condition is studied. [Copyright &y& Elsevier]

We describe a nonlocal linear partial differential equation arising in the analysis of dynamics of a nematic liquid crystal. We confirm that it accounts for the kick-back phenomenon by decoupling the director dynamics from the flow. We also analyse some of the mathematical properties of the decoupled director equation. [ABSTRACT FROM AUTHOR]

We evaluate by direct calculation the Lopatinski determinant for ZND detonations in Majda's model for reacting flow and show that on the nonstable (nonnegative real part) complex half-plane it has a single zero at the origin of multiplicity one, implying stability. Together with results of Zumbrun on the inviscid limit, this recovers the result of Roquejoffre-Vila that viscous detonations of Majda's model also are stable for sufficiently small viscosity, for any fixed detonation strength, heat release, and rate of reaction. [ABSTRACT FROM AUTHOR]

We discuss numerical methods to solve the Cauchy problem for hyperbolic equations, paying attention to equations which describe physical phenomena in fluid dynamics. We concentrate on Godunov-type methods which adopt Riemann solvers. These methods constitute a formidable task due to complexity of hyperbolic equations. Despite this complexity we show that the Godunov-type methods can be successfully applied to simulate complex systems such as described by equations of magnetohydrodynamics. In particular, we simulate thermal mode in a two-dimensional x-point magnetic field topology that is embedded in a gravitationally stratified solar atmosphere. [ABSTRACT FROM AUTHOR]

Copyright of Brodogradnja is the property of Brodarski Institut and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: We present a novel method to simulate fibers in flows transporting droplets. We discuss how to model the collisions of droplets and fibers. Since droplet-fiber collision is computationally expensive we use a new stochastic approach modeling the collision probability of droplets and fibers. From a continuous spatial distribution of the particle masses we can calculate the impact on a specific fiber at any arbitrary point. This gives an average mass and momentum of the droplets which is transferred to the fiber. We integrate our model in a fiber dynamics simulation tool (FIDYST) used to simulate industrial manufacturing processes. [Copyright &y& Elsevier]

Abstract: A solution code of the Stokes flow system in three dimensions under a self-gravitating field was developed with a free surface in order to simulate the long-time scale evolution of the solid earth system on the massively parallel-vector super computer Earth Simulator 2 (ES2). The largely deformable surface of a planetary body is represented by a sharp boundary of scalar color function, which is advected by the CIP-CLSR method. The self-gravitating field is calculated by the Poisson equation of the gravity potential. A low viscous material (sticky air) surrounding the planet mimics its free surface motion. In order to solve the ill conditioned Stokes problem of the finite difference discretization on a staggered grid, I employ the iterative Stokes flow solver, robust to large viscosity jumps, using a strong Schur complement preconditioner and mixed precision arithmetic utilizing the double-double method. In this paper, I present an overview of the numerical algorithms and the current parallel programming strategy for the efficient performance on ES2. In addition, preliminary results of the core formation simulation are demonstrated in three dimensions as an example of the target Stokes flow system of this simulation code. [Copyright &y& Elsevier]

A new vegetation modeling concept for Building and Environmental Aerodynamics wind tunnel investigations was developed. The modeling concept is based on fluid dynamical similarity aspects and allows the small-scale modeling of various kinds of vegetation, e.g. field crops, shrubs, hedges, single trees and forest stands. The applicability of the modeling concept was validated in wind tunnel pollutant dispersion studies. Avenue trees in urban street canyons were modeled and their implications on traffic pollutant dispersion were investigated. The dispersion experiments proved the modeling concept to be practicable for wind tunnel studies and suggested to provide reliable concentration results. Unfavorable effects of trees on pollutant dispersion and natural ventilation in street canyons were revealed. Increased traffic pollutant concentrations were found in comparison to the tree-free reference case. [Copyright &y& Elsevier]

The article discusses analytical models that depict the wellbore-temperature-distribution. It says that the analysis of pressure-transient test data is achieved through proper fluid flow and heat transfer modeling and simulation. One solution uses transient temperature-flow model in the dimensionless perspective which assumes the constant mass density and steady velocity. Another model is the exclusion of heat conduction which does not require differential equation approximations.

The propagation of internal electromagnetic waves in an inviscid chiral fluid in the presence of the external constraint of transverse magnetic field is investigated. These waves are shown to be generated due to the stabilizing nature of the distribution of charge density. It is shown that the effect of the external constraint of magnetic field in a chiral fluid is analogous to the effect of viscosity in ordinary fluids. The wave equation, derived from the conservation of mass and momentum together with Maxwell's equations and suitable auxiliary equations for chiral materials, reveals the existence of a critical level (i.e., resonance level) at which the Doppler shifted frequency Ωd = 0, i.e., at the point where the basic fluid velocity matches with the phase velocity of the wave. The solution of this wave equation is obtained near and away from the critical levels from which the attenuation of waves is predicted using momentum flux. This is verified using group velocity approach. [ABSTRACT FROM AUTHOR]

Thermal radiation effects on MHD flow past an impulsively started vertical plate in the presence of heat source/sink is investigated, by taking into account the heat due to viscous dissipation. The governing boundary layer equations of the flow field are solved by an implicit finite difference method of Crank-Nicholson type. A parametric study is performed to illustrate the influence of radiation parameter, magnetic parameter, Grashof number, Prandtl number, Eckert number on the velocity, temperature and concentration profiles. Also, the local and average skin-friction, Nusselt number and Sherwood number are presented graphically. The numerical results reveal that the radiation induces a rise in both the velocity and temperature, and a decrease in the concentration. Also with an increase in the heat absorption/generation parameter the velocity increases whereas the temperature decreases. The model finds applications in solar energy collection systems, geophysics and astrophysics, aero space and also in the design of high temperature chemical process systems. [ABSTRACT FROM AUTHOR]

In this paper is reported an analytical and numerical study on double-diffusive natural convection in a non-Newtonian power-law fluid confined in a shallow horizontal rectangular enclosure submitted to uniform heat and mass fluxes along its short vertical sides, while the horizontal ones are insulated and impermeable. Here, the cases of aiding and opposing thermal and solutal buoyancy forces of equal intensities are considered. In the first part of the work the full governing equations are solved and the effects of the power-law behavior index, n, and the generalized thermal Rayleigh number, RaT, are examined and analyzed. In the second part, an analytical solution, based on the parallel flow approximation valid in the case of a shallow cavity, is proposed and an excellent agreement of results between the two approaches is observed, which validates them mutually. [ABSTRACT FROM AUTHOR]

The present paper reports numerical results of mixed convection and surface radiation within a horizontal ventilated cavity heated from below and provided with an adiabatic thin partition on the heated surface. Air, a radiatively transparent medium, is considered to be the cooling fluid. The effect of the governing parameters, which are the Reynolds number, 200 ≤ Re ≤ 5000, the relative height of the baffle, 0 ≤ Hb ≤ 0.75, and the emissivity of the walls, 0 ≤ ϵ ≤ 1, on the fluid flow and heat transfer characteristics is studied in detail. The maximum and mean temperatures, the ratio, QE/QL, of the heat quantities leaving the cavity through the exit, QE, and through the left vertical cold side, QL, are also presented versus the above controlling parameters. [ABSTRACT FROM AUTHOR]

Blade failure in turbomachinery is frequently caused by an excessive resonant response. Forced response of the blades originates from unsteady fluid structure interactions as conditioned in the inlet section by duct bends, struts, or inlet guide vanes. This paper presents the computational part of a research effort that focuses on the blade forced response in a centrefugal compressor Unsteady fluid flow simulations are used to quantify the forcing function acting on the compressor blades due to inlet flow distortion. The measured inlet flow distribution is applied as inlet boundary conditions in the computation. The unsteady investigation provided the temporal evolution of the distorted flow through the compressor The time-resolved blade pressure distribution showed the temporal evolution of the dynamic load on the blade surface caused by the inlet distortion. The results suggest that the forcing function is most sensitive in the leading edge region due to inlet angle variations. Toward the impeller stability line the increase in incidence caused separation on the suction side of the main blade and therefore considerably altered the amplitude and the phase angle of the unsteadiness. The investigation of the effect of idealizing the inlet flow distribution on the forcing function showed an increase in the peak amplitude of approximately 30% compared with the actual inlet flow distribution. [ABSTRACT FROM AUTHOR]

Abstract: Fast indoor airflow simulations are necessary for building emergency management, preliminary design of sustainable buildings, and real-time indoor environment control. The simulation should also be informative since the airflow motion, temperature distribution, and contaminant concentration are important. Unfortunately, none of the current indoor airflow simulation techniques can satisfy both requirements at the same time. Our previous study proposed a Fast Fluid Dynamics (FFD) model for indoor flow simulation. The FFD is an intermediate method between the Computational Fluid Dynamics (CFD) and multizone/zonal models. It can efficiently solve Navier–Stokes equations and other transportation equations for energy and species at a speed of 50 times faster than the CFD. However, this speed is still not fast enough to do real-time simulation for a whole building. This paper reports our efforts on further accelerating FFD simulation by running it in parallel on a Graphics Processing Unit (GPU). This study validated the FFD on the GPU by simulating the flow in a lid-driven cavity, channel flow, forced convective flow, and natural convective flow. The results show that the FFD on the GPU can produce reasonable results for those indoor flows. In addition, the FFD on the GPU is 10–30 times faster than that on a Central Processing Unit (CPU). As a whole, the FFD on a GPU can be 500–1500 times faster than the CFD on a CPU. By applying the FFD to the GPU, it is possible to do real-time informative airflow simulation for a small building. [Copyright &y& Elsevier]

Abstract: In the past, different calculation models for wind-driven rain (WDR) have been developed and progressively improved. Today, the models that are most advanced and most frequently used are the semi-empirical model in the ISO Standard for WDR (ISO), the semi-empirical model by Straube and Burnett (SB) and the CFD model by Choi, extended by Blocken and Carmeliet. Each of these models is quite different, and to the knowledge of the authors, no comparison of these models has yet been performed. This paper first presents a detailed overview of the three models, including new insights in similarities between these models and relations with recent research results. Based on this overview, it provides a comparison focused on the extent to which the different influencing parameters of WDR are implemented in the models. It shows that the implementation of the influencing parameters is most pronounced for the CFD model, less pronounced for the ISO model and least pronounced for the SB model. It is also shown that in the two semi-empirical models, the values of the wall factor W (for ISO) and the rain admittance function RAF (for SB), which have the same definition in both models, can differ more than a factor 2 from each other. The two models can therefore provide very different results. They also require differently defined reference wind speed values as input. The overview and the comparison in this paper provide the basis for future comparison studies and future improvements of the semi-empirical models. [Copyright &y& Elsevier]

Abstract: In this work the comfort level, namely the thermal comfort, local thermal discomfort and air quality levels, in a classroom with desks equipped with two personalized ventilation systems, in slightly warm environments, is evaluated. A manikin, a ventilated classroom desk, two indoor climate analyzers, a multi-nodal human thermal comfort numerical model and a computational fluid dynamic numerical model, are used. The classroom desk, with double occupation capacity, is used by a student, located in the right side seat. Each personalized ventilation system is equipped with one air terminal device located above the desk writing area, in front to the trunk area, and an other located below the desk writing area, in front to the legs area. The thermal comfort level is evaluated by the developed multi-nodal human thermal comfort numerical model, using a PMV value, the local thermal discomfort level, namely the draught risk and the air velocity fluctuation equivalent frequencies, is evaluated by empirical models, while the air quality level and the detailed airflow around the manikin are evaluated by the computational fluid dynamic numerical model. In the experimental tests the mean air velocity and the turbulence intensity in the upper air terminal device are 3.5m/s and 9.7%, while in the lower air terminal device are 2.6m/s and 15.2%. The mean air temperature in the air terminal devices is around 28°C, while the mean radiant temperature in the occupation area, the mean air temperature far from the occupation area and the internal mean air relative humidity were, respectively, 28°C, 28°C and 50%. The air velocity and temperature around the occupant are measured around 15 human body sections. The actual personalized ventilation system, which promotes an ascendant airflow around the occupant with highest air renovation rate in the respiration area, promotes acceptable thermal comfort conditions and air quality in the respiration area in accord to the present standards. The draught risk is verified in the head and left leg and the uncomfortable air velocity equivalent frequency is verified in the left arm. The left human body sections present higher local thermal discomfort levels than the right human body sections, because they are also influenced by the left air terminal device. In accord to the obtained results, the classroom desk design, equipped with two personalized ventilation systems, guarantees acceptable thermal comfort conditions and promotes good air quality conditions, with acceptable local thermal discomfort conditions and with low energy consumption level. [Copyright &y& Elsevier]

A model for oil-in-water emulsion has been developed in this paper A group of viscosity coefficients transiting smoothly and incessantly from the thick film region to the thin film region is defined. The contributions from disperse and continuous phases to the total lubricant pressure and pressure gradient are functions of the oil concentration and the film thickness. The parameters used in these functions are determined by a series of computational fluid dynamics simulations. The onset of inversion and the viscosity after inversion are also investigated. It is found that the critical volume fraction of oil in the inception of inversion is dependent on the oil viscosity and a factor regarding the combined effects from the emulsifier, pH value, droplet size, and the shear rate. A series of simulations using the proposed model has been carried out and compared with the experimental results, such as the film thickness and the extension of oil pool for various rolling speeds and supply oil concentrations. The numerical outputs are basically in agreement with the experiments. [ABSTRACT FROM AUTHOR]