Fluid Dynamics

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

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.

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.

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

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...

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.

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

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.