Fluid Dynamics

A computer aided design (CAD) tool has been specifically developed for rapid and easy design of solid models for surfboard and sailboard fins. This tool simplifies the lofting of advanced fin cross-sectional foils, in this instance based upon the family of standard airfoil series set by the National Advisory Committee for Aeronautics (NACA), whilst retaining a basic parametric description at each cross-section.

The present study reports the effect of momentum injection at the inlet on the performance of an S-shaped rectangular diffuser having an aspect ratio of 6 at inlet. A cylinder of diameter 3 cm was placed at the inflexion plane across the width of the diffuser and rotated at different speeds to inject momentum to the decelerating flow as a result of boundary layer separation. It was found that pressure recovery and flow distribution improved significantly. Improvement in coefficient of pressure recovery was about 24% for duct having an area ratio of 2 and nearly 22% for duct with an area ratio of 3. Simultaneously the values of the coefficient of total pressure loss decreased by 32% and 51% for ducts with area ratio of 2 and 3 respectively.

Keywords: S-shaped rectangular diffuser; rotating cylinder; momentum injection; boundary layer; CFD; pressure recovery coefficient

In the present work, experimental and numerical studies for the hydrodynamics in a gassolid tapered fluidized bed have been carried out. The experimental results obtained by carrying out experiments in a tapered fluidized bed for glass bead (spherical) of 2.0 mm and dolomite (non-spherical particles) of 2.215 mm in diameter, were compared with the computational fluid dynamics (CFD) simulation results, using a commercial CFD software package, Fluent. The gas-solid flow was simulated using the Eulerian-Eulerian model and applying the kinetic theory of granular flow for solid particles. The Gidaspow drag model was used to calculate the gas-solid momentum exchange coefficients. Pressure drops predicted by the CFD simulations agreed reasonably well with experimental measurements for both types (spherical and non-spherical) of particles. Good agreement was also obtained between experimental and CFD predicted bed expansion ratios for both types of particles. Present study provides a useful basis for further works on the CFD of tapered fluidized bed.

Integrating geological concepts, such as relative positions and proportions of the different lithofacies, is of highest importance in order to render realistic geological patterns. The truncated plurigaussian simulation method provides a way of using both local and conceptual geological information to infer the distributions of the facies and then those of hydraulic parameters. The method (Le Loc'h and Galli 1994) is based on the idea of truncating at least two underlying multi-Gaussian simulations in order to create maps of categorical variable. In this manuscript we show how this technique can be used to assess contaminant migration in highly heterogeneous media. We illustrate its application on the biggest contaminated site of Switzerland. It consists of a contaminant plume located in the lower fresh water Molasse on the western Swiss Plateau. The highly heterogeneous character of this formation calls for efficient stochastic methods in order to characterize transport processes.

This project is modeled around reducing the overall drag and lift coefficient by modifying the geometry and comprehending the underlying rootphenomenon for the variation in these drag values. The designing of models used in this project is done through SOLIDWORKS, and CFD simulation in FLUENT (ANSYS) respectively. The purpose of this project is to reduce the inefficiency caused due to aerodynamic factors of drag, lift by presenting development, design and optimization of the geometry modifications of the base model. The improvement of aerodynamic behaviour around the periphery of the model is investigated through numerical simulation. The Ahmed Reference Body having 10 degree rear slant angle has been taken as benchmark model in this paper. Simulation of variants of multifarious modifications and examination of their results is performed to find the best suited variant form (dimension) to boost the aerodynamic efficiency of the model. CFD simulations on Ahmed Body were carried out in order to serve as a benchmark for validating all the simulation results. The steady-state simulations are based on the Reynolds averaged Navier-Stokes equations, with turbulence closure provided through two-equation k-epsilon realizable models.

Current aircraft engine designs tend towards higher bypass ratio, low-speed fan designs for improved fuel burn, reduced emissions and noise. Alternative propulsion concepts include counter-rotating propfans (CRPs) which have been investigated intensively in the 1970s and 1980s and demonstrated significant reductions in fuel burn. Currently, propfans are being studied again due to their inherent noise challenge and the potential for reduced environmental impact. A newly developed, integrated noise and performance assessment methodology for advanced propfan powered aircraft configurations is introduced. The approach is based on first principles and combines a coupled aircraft and propulsion system performance analysis with 3-D unsteady, full-wheel CRP CFD computations and aero-acoustic simulations. Special emphasis is put on computing CRP interaction tones. The method is capable of dealing with parametric studies and exploring noise reduction technologies.

These design guideline are believed to be as accurate as possible, but are very general and not for specific design cases. They were designed for engineers to do preliminary designs and process specification sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document is entrusted to the recipient personally, but the copyright remains with us. It must not be copied, reproduced or in any way communicated or made accessible to third parties without our written consent.

This paper describes the summary of a three-year development program for the first-stage stationary vane and rotating blade for the next generation, 1500°C class, high-efficiency gas turbine. In such a high-temperature gas turbine, the first turbine vane and blade are the most important hot parts. Full-coverage film cooling (FCFC) is adopted for the cooling scheme, and directionally solidified (DS) nickel base superalloy and thermal barrier coating (TBC) will be used to prolong the creep and thermal fatigue life. The concept of the cooling configuration, fundamental cascade test results, and material test results will be presented.

... School of Engineering Springfield, Massachussetts Drag Reduction and Wake Minimization on Marine Vehicles ,,P. ,3 1991 By: , Craig A. Hunter Pasquale Delore Walter M. Presz, Jr. Final Report Office of Naval Research Grant N0014-89-J-1883 00 July 1991 I I Page 2. Abstract ...

We present a laterally emitting, coupled cavity micro fluidic dye ring laser, suitable for integration into lab-on-a-chip micro systems. The micro-fluidic laser has been successfully designed, fabricated, characterized and modelled. The resonator is formed by a micro-fluidic channel bounded by two isosceles triangle mirrors. The micro-fluidic laser structure is defined using photo lithography in 10 microns thick SU-8 polymer on a glass substrate. The micro fluidic channel is sealed by a glass lid, using PMMA adhesive bonding. The laser is characterized using the laser dye Rhodamine 6G dissolved in ethanol or ethylene glycol as the active gain medium, which is pumped through the micro-fluidic channel and laser resonator. The dye laser is optically pumped normal to the chip plane at 532 nm by a pulsed, frequency doubled Nd:YAG laser and lasing is observed with a threshold pump pulse energy flux of around 55 micro-Joule/square-milimeter. The lasing is multi-mode, and the laser has switchable output coupling into an integrated polymer planar waveguide. Tuning of the lasing wavelength is feasible by changing the dye/solvent properties.

This paper presents the general purpose framework Peano for the solution of partial differential equations (PDE) on adaptive Cartesian grids. The strict structuredness and inherent multilevel property of these grids allows for very low memory requirements, efficient (in terms of hardware performance) implementations of parallel multigrid solvers on dynamically adaptive grids, and arbitrary spatial dimensions. This combination of advantages distinguishes Peano from other PDE frameworks. We describe shortly the underlying octree-like grid type and its most important properties. The main part of the paper shows the framework concept of Peano and the implementation of a Navier-Stokes solver as one of the main currently implemented application examples. Various results ranging from hardware and numerical performance to concrete application scenarios close the contribution.

A new general cell-centered solution procedure based upon the conventional control or finite volume (CV or FV) approach has been developed for numerical heat transfer and fluid flow which encompasses both structured and unstructured meshes for any kind of mixed polygon cell. Unlike conventional FV methods for structured and block structured meshes and both FV and FE methods for unstructured meshes, tile irregular control volume (ICV) method does not require the shape of the element or cell to be predefined because it simply exploits the concept of fluxes across cell faces. That is, the ICV method enables meshes employing mixtures of triangular, quadrilateral, and any other higher order polygonal cells to be exploited using a single solution procedure. The ICV approach otherwise preserves all the desirable features of conventional FV procedures for a structured mesh; in the current implementation, collocation of variables at cell centers is used with a Rhie and Chow interpolation (to suppress pressure oscillation in the flow field) in the context of the SIMPLE pressure correction solution procedure. In fact all other FV structured mesh-based methods may be perceived as a subset of the ICV formulation. The new ICV formulation is benchmarked using two standard computational fluid dynamics (CFD) problems, i.e., the moving lid cavity and the natural convection driven cavity. Both cases were solved with a variety of structured and unstructured meshes, the latter exploiting mixed polygonal cell meshes. The polygonal mesh experiments show a higher degree of accuracy for equivalent meshes (in nodal density terms) using triangular or quadrilateral cells; these results may be interpreted in a manner similar to the CUPID scheme used in structured meshes for reducing numerical diffusion for flows with changing direction.

Drawing of the hollow all-polymer Bragg fibers based on PMMA/PS and PVDF/PC materials combinations are demonstrated. Hole collapse during drawing effects the uniformity of a photonic crystal reflector in the resultant fiber. We first investigate how the core collapse effects fiber transmission properties. We then present modelling of fluid dynamics of hollow multilayer polymer fiber drawing. Particularly, hole collapse during

A 2-D mathematical model (SED-2) was developed simulating the sediment transport in alluvial shallow-wide streams in order to solve practical problems in the Nile River. The Finite Difference technique was used to solve the convectiondiffusion equation of the suspended sediment in open channels. A 2-D hydrodynamic model (HYD-2) was used to describe the flow field solving the Reynolds form of the Navier-Stokes momentum equations in two dimensions in addition to the continuity equation. The developed 2-D mathematical model was verified using actually measured field data. The field data were collected from one of the main canals of irrigation network in Egypt called El-Naser main canal. Good agreement was observed between the model results and the field observations. The model could be applied for solving local hydraulic and navigation problems where some reaches of the Nile River suffering. Various proposals could be investigated and the optimal solution in each case could be reached.

Analytical expressions correlating the volumetric flow rate to the inlet and outlet pressures are derived for the time-independent flow of Newtonian fluids in cylindrically-shaped elastic tubes using a one-dimensional Navier-Stokes flow model with two pressure-area constitutive relations. These expressions for elastic tubes are the equivalent of Poiseuille and Poiseuille-type expressions for rigid tubes which were previously derived for the flow of Newtonian and non-Newtonian fluids under various flow conditions. Formulae and procedures for identifying the pressure field and tube geometric profile are also presented. The results are validated by a finite element method implementation. Sensible trends in the analytical and numerical results are observed and documented.

A conceptual framework for analysing the energetics of density-stratified Boussinesq fluid flows is discussed. The concept of gravitational available potential energy is used to formulate an energy budget in which the evolution of the background potential energy, i.e. the minimum potential energy attainable through adiabatic motions, can be explicitly examined. For closed systems, the background potential energy can change only due to diabatic processes. The rate of change of background potential energy is proportional to the molecular diffusivity. Changes in the background potential energy provide a direct measure of the potential energy changes due to irreversible diapycnal mixing. For open systems, background potential energy can also change due to boundary fluxes, which can be explicitly measured. The analysis is particularly appropriate for evaluation of diabatic mixing rates in numerical simulations of turbulent flows. The energetics of a shear driven mixing layer is used to i...

This report summarizes research advances pursued with award funding issued by the DOE to Drexel University through the Presidential Early Career Award (PECASE) program. Professor Rich Cairncross was the recipient of this award in 1997. With it he pursued two related research topics under Sandia's guidance that address the outstanding issue of fluid-structural interactions of liquids with deformable solid materials, focusing mainly on the ubiquitous dynamic wetting problem.

Numerically challenging, comprehensive benchmark cases are of great importance for researchers in the field of CFD. Numerical benchmark cases offer researchers frameworks to quantitatively explore limits of the computational tools and to validate them. Therefore, we focus on simulation of numerically challenging benchmark tests, laminar and transient 3D flows around a cylinder, and aim to establish a new comprehensive benchmark case by doing direct numerical simulations with three distinct CFD software packages. Although the underlying benchmark problems have been defined firstly in 1996, the first case which was a steady simulation of flow around a cylinder at Re = 20 could be accurately solved first in 2002 by John. Moreover, there is no precisely determined results for non-stationary case, the simulation of transient flow with time varying Reynolds number. The benchmark problems are studied with three CFD software packages, OpenFOAM, Ansys-CFX and FeatFlow which employ different numerical approaches to the discretization of the incompressible Navier-Stokes equations, namely finite volume method, element based finite volume method and finite element method respectively. The first benchmark test is considered as the "necessary condition" for the software tools, then they are compared according to their accuracy and performance in the second benchmark test. All the software tools successfully pass the first test and show well agreeing results for the second case such that the benchmark result was precisely determined. As a main result, the CFD software package with high order finite element approximation has been found to be computationally more efficient and accurate than the ones adopting low order space discretization methods.

The decay of vortices in flows of an electrically conducting fluid in the presence of a magnetic field is studied. Two flow configurations are considered: 1) flow in a double array of vortices; 2) flow behind a two-dimensional grid. It is found that in the presence of a uniform transverse magnetic field, the vortices decay much faster than those in a viscous fluid in the absence of magnetic field. It is observed that in the steady flow behind a two-dimensional grid in the presence of a uniform transverse magnetic field, a pair of bound eddies appear behind the single elements of the grid. The scale of these eddies depends on the strength of the magnetic field. It is also found that the distance from the stagnation point over which the vortices decay to zero decreases with increase in the magnetic field. At large distance, however, the streamlines become parallel as in the case of a viscous fluid.

A multi-fidelity global metamodel is presented for uncertainty quantification of computationally expensive simulations. The multi-fidelity approximation is built as the sum of a low-fidelity-trained metamodel and the metamodel of the difference (error) between high-and low-fidelity simulations. The metamodel is based on dynamic stochastic radial basis functions, which provide the prediction along with the associated uncertainty. New training points are added where the prediction uncertainty is largest, according to an adaptive sampling procedure. The prediction uncertainty of both the low-fidelity and the error metamodel are considered for the adaptive training of the low-and high-fidelity metamodels, respectively. The method is applied to a steady fluid-structure interaction (FSI) problem of a 3D NACA 0009 stainless steel hydrofoil. Two functions are considered simultaneously, namely lift and drag coefficients, versus angle of attack and Reynolds number. Two problems are presented: in the first problem the high-fidelity evaluations are obtained through steady FSI computer simulations, whereas in the second problem they are given by available experimental data from literature. Low-fidelity evaluations are provided in both cases by steady hydrodynamic simulations. The overall uncertainty of the multi-fidelity metamodel is used as a convergence criterion.

We carry out an analytical study of laminar circular hydraulic jumps, in generalized-Newtonian fluids obeying the two-parametric power-law model of Ostwald-de Waele. Under the boundary-layer approximation we obtained exact expressions determining the flow, an implicit relation for the jump radius is derived. Corresponding results for Newtonian fluids can be retrieved as a limiting case for the flow behavior index n=1, predictions are made for fluids deviating from Newtonian behavior.

The primary aim of this pilot study was to study uterine artery (UtA) blood flow volume in uneventful human pregnancies delivered at term, at mid and late gestation by means of 3D and bi-dimensional ultrasound imaging with angio-Doppler combined with fluid-dynamic modeling. Secondary aims were to correlate flow volume to placental site and to UtA Pulsatility Index (PI).

Liquid sloshing is an oscillatory motion of a free liquid surface that occurs inside partially filled containers. This phenomenon generates forces that can have a significant influence on a vehicle's safety and stability. Several studies report methodologies for predicting the liquid slosh in various containers or to the analysis of vehicle stability based upon simplified and linear models of liquid motion without sufficient consideration of the dynamic interactions between the liquid motion and vehicle stability. This work highlights the various parameters attributed to sloshing and gives a review of some selected investigations considering linear and also nonlinear dynamics.

As características dos escoamentos que aparecem com frequência na natureza são influenciadas direta-mente pela viscosidade dinâmica do fluido. Tal influência pode ser notada, por exemplo, na distribuição de velocidades na seção de um conduto circular sob pressão ou na força de arrasto imposta a uma esfera submetida a um campo de velocidade constante. Nos dois casos citados, a viscosidade do fluido escoante modifica os campos de velocidades e de forças. Ademais, escoamentos de fluidos newtonianos em que a força viscosa é dominante sobre a inércia são regidos pela equação de Navier-Stokes. Nestes casos, para geometrias simples e condições de contorno bem definidas, soluções analíticas existem, tanto no regime permanente quanto no transiente. No entanto, para a maioria dos problemas de Engenharia, não existem soluções analíticas. Sendo assim, utilizam-se métodos numéricos para simular escoamentos laminares, regidos pela equação de Navier-Stokes. Neste cenário, métodos de partícula são vantajosos por não necessitarem de malhas na discretização do domínio (meshless ou meshfree), podendo assim representar fronteiras com formas geométricas variadas. Além disso, métodos particulados dispensam a discretização dos termos não li-neares da equação de Navier-Stokes associados à aceleração convectiva, uma vez que as partículas são acompanhadas ao longo da a simulação (abordagem Lagrangiana). O método de partícula SPH (Smo-othed Particle Hydrodynamics) vem sendo utilizado, como sucesso, tanto em escoamentos turbulentos como problemas envolvendo propagação de ondas solitárias [5], sloshing [1], ressalto hidráulico [2] e ruptura de barragens [4], quanto em escoamentos laminares [6, 7]. Isto posto, a comunicação científica em tela tem por finalidade avaliar a aplicabilidade do método SPH a escoamentos laminares em regime transiente. Avalia-se, como estudo de caso, o escoamento de Cou-ette transiente com gradiente de pressão. O escoamento de Couette nada mais é do que o escoamento entre placas planas, horizontais e paralelas, considerando a largura da seção e comprimento do domínio infinitos. Impõe-se uma velocidade constante à placa superior (v x (t, x, d) = V , onde d é a distância entre as placas), enquanto que a velocidade da placa inferior é nula (v x (t, x, 0) = 0). Aplica-se também um gradiente de pressão constante, na direção do escoamento. Avaliando a solução analítica do escoamento de Couette transiente com gradiente de pressão, o perfil de velocidades pode ser obtido com a aplicação do método de separação de variáveis (análise de Fourier), sendo dada por: v x (y,t) = ∂p ∂x y 2ν (y − d) + V y d + ∞ ∑ n=1 2V nπ (−1) n − ∂p ∂x 2d 2 νn 3 π 3 ((−1) n − 1) sin nπy d exp − νn 2 π 2 d 2 t. (1) Já a solução numérica do escoamento de Couette transiente com gradiente de pressão, obtida com o método SPH, considera um domínio retangular (1,0 × 0,6 m), com condição de contorno periódica nas fronteiras laterais (x = 0 m e x = 0, 6 m). A condição de contorno periódica e de aderência são represen-tada por partículas fantasma [8]. O núcleo de suavização utilizado nas simulações é o spline cúbico 2D, com suporte compacto e comprimento de suavização igual a h = 1, 2 ∆x. O espaçamento médio entre 1 295

Low-level light signals that are highly dependent on temperature are very common in measurement applications that employ sensors coupled to optical fibres. In order to amplify and condition the signal, photomultipliers are traditionally used together with climatic chambers in which the ambient temperature of the chamber is controlled. The present paper proposes the use of an avalanche photodiode (due to its lower price and size) to amplify the signal. However, this change implies more careful temperature control. This is why we propose to control the temperature in the photodiode itself and to use a thermoelectric cooler. This system design suggests the convenience of the development of a thermal study that is presented here. The electrical intensity of the thermoelectric cooler, the influence of the surrounding temperature and the use of isolating material or air in the space between the photodiode and the walls of the chamber are analysed. Computational fluid dynamic (CFD) techniques were applied to model the system and the model was satisfactorily validated. The feasibility of carrying out the temperature control in the cold junction of the thermoelectric cooler instead of in the photodiode itself was tested and was found to improve control. (M. Manuela Prieto Gonz alez), manuelap@correo.uniovi.es (E. Braña Arg€ uelles), campo@ate.uniovi.es (J. Carlos Campo Rodr ıguez), miguel@ate.uniovi.es (M.

title: The Fluid Dynamical Forces Involved in Grass Fire Propagation. We know from previous numerical modeling studies that it is possible, using a combination of a simplified set of fluid dynamical equations, observations, and full-scale time-dependent three-dimensional numerical analyzes, to examine many essential mechanisms involved in cumulus cloud dynamics. Much of our understanding of the relationship between convective storms and their environments have been obtained from numerical modeling studies in which the characteristics of the environment can be controlled. The conditions of the simulated environments were highly idealized, horizontally homogeneous, and time invariant. This research, which began in the early 1940's and continues today, is mainly concerned with the dynamical mechanisms by which a thunderstorm updraft evolves, propagates, and changes shape as it moves. In this study we are concerned with the dynamical mechanisms by which a fire plume evolves, propaga...

Pulsed beams, originating from a high pressure, fast acting valve equipped with a shaped nozzle, can now be generated at high repetition rates and with moderate vacuum pumping speeds. The generated high intensity beams properties are discussed, together with their propagation in the vacuum system requirement of skimmed beams systems.

In an effort to corroborate theoretical and experimental techniques used for cold spray particle velocity analysis, two theoretical and one experimental methods were used to analyze the operation of a nozzle accelerating aluminum particles in nitrogen gas. Two-dimensional (2D) axi-symmetric computations of the flow through the nozzle were performed using the Reynolds averaged Navier-Stokes code in a computational fluid dynamics platform. 1D, isentropic, gas-dynamic equations were solved for the same nozzle geometry and initial conditions. Finally, the velocities of particles exiting a nozzle of the same geometry and operated at the same initial conditions were measured by a dual-slit velocimeter. Exit plume particle velocities as determined by the three methods compared reasonably well, and differences could be attributed to frictional and particle distribution effects.