Computational 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

In the context of GEN-IV heavy liquid metal-cooled reactors safety studies, the flow blockage in a fuel sub-assembly is considered one of the main issues to be addressed and one of the most important accidents for Lead Fast Reactors (LFR). In order to model the temperature and velocity field inside a wrapped fuel assembly under unblocked and blocked conditions, a detailed experimental campaign as well as 3D thermal hydraulic analyses of the fuel assembly are required. The present paper is focused on the CFD modeling and preliminary computational analysis of the new experimental facility „Blocked‟ Fuel Pin bundle Simulator (BFPS) that will be inserted in the heavy liquid metal NACIE-UP (NAtural CIrculation Experiment-UPgrade) facility located at the ENEA Brasimone Research Center (Italy). The BFPS test section aims to carry out suitable experiments to fully investigate different flow blockage regimes in a 19-pin fuel bundle providing experimental data in support of the development of...

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.

Airinnova is a start-up company with a key competency in the automation of high fidelity computational fluid<br> dynamics (CFD) analysis. The goal of this SHAPE project, a collaboration with the PDC Center for High<br> Performance Computing at the KTH Royal Institute of Technology (KTH-PDC), was to develop automated<br> procedures for carrying out CFD analysis in the field of aerodynamic optimization and design. The project is a<br> significant step towards automation of the core processes that ordinarily would require specialist skills, such as<br> creation of the simulation mesh, thus assisting a broader sphere of engineers to design aircraft in more efficient<br> and simpler ways.

Public Universities in Southwestern Nigeria are densely populated student-resident campuses, so that provision of regular potable water and electricity are important, but power supply is not optimally available for all the necessary activities. This study assesses the hydropower potential of the water distribution networks in the Universities, with the view to augmenting the inadequate power supplies. The institutions with water distribution configuration capable of accommodating in-pipe turbine are identified; the hydropower parameters, such as the flow characteristics and the pipe geometry are determined to estimate the water power. Global positioning device is used in estimating the elevations of the distribution reservoirs and the nodal points. The hydropower potential of each location is computed incorporating Lucid ® Lift-based spherical turbine in the pipeline. From the analysis, the lean and the peak water power are between 1.92-3.30 kW and 3.95-7.24 kW, respectively, for re...

Phase change materials (PCMs) are classified according to their phase change process, temperature, and composition. The utilization of PCMs lies mainly in the field of solar energy and building applications as well as in industrial processes. The main advantage of such materials is the use of latent heat, which allows the storage of a large amount of thermal energy with small temperature variation, improving the energy efficiency of the system. The study of PCMs using computational fluid dynamics (CFD) is widespread and has been documented in several papers, following the tendency that CFD nowadays tends to become increasingly widespread. Numerical studies of solidification and melting processes use a combination of formulations to describe the physical phenomena related to such processes, these being mainly the latent heat and the velocity transition between the liquid and the solid phases. The methods used to describe the latent heat are divided into three main groups: source term...

Two-dimensional numerical simulations of compressible plane jet exhausting into parallel streams is performed using sixth-order compact scheme with third-order low storage Runge–Kutta method. Characteristic based boundary conditions are utilized in all simulations. Sixth-order tri-diagonal spatial filter is applied to suppress any high wave-number oscillation created at the boundaries and due to unresolved scales and mesh non-uniformities. The study focuses on the influence of velocity difference between the parallel streams on fully developed plane jet. The two dimensional simulation is found capable of capturing correct jet spreading and decay. Time-averages over stream-wise domain are used to capture the mean field and turbulence structures. It is found that the potential core length increases as the velocity ratio increases. The predicted mean velocity profiles show self-similar behavior and collapse well with previous experimental results. Turbulent intensity and Reynolds shear stress change with change in velocity ratio. However, the mean streamwise excess velocity profiles are unaffected by the change in velocity ratio.

The objective of this study is the development of an efficient high-order compact scheme for unsteady incompressible viscous flows. The scheme is constructed on a staggered Cartesian grid system in order to avoid spurious oscillations in the pressure field. Navier-Stokes equations are advanced in time with the second order Adams-Bashford method without considering the pressure terms in the predictor step, the velocity field is then corrected such that discrete mass continuity equations satisfied through pressure Poisson equation. Since the efficiency of the fractional step method depends on the Poisson solver, a V-cycle multigrid acceleration with compact Mehrstellen discretization based iterative method is implemented in the pressure Poisson equation to enhance the computational efficiency. The efficiency and accuracy of iterative Poisson solvers (pseudo-time, Jacobi, Gauss-Seidel) are also tested within the multigrid framework. The method is then validated by the simulations of the Taylor-Green vortex decaying problem. Results show that the fractional-step compact scheme with multigrid acceleration has high resolving efficiency that drastically reduces computational time and high-order accuracy making the method applicable for simulation of incompressible viscous flows.

: The purpose of the testing reported herein was to obtain data describing fluid and structural behavior (interaction of fluid on structure and of structure on fluid) in a controlled experiment in a systematic manner. These data are to be used for (a) validation of fluid/structure interaction (FSI) modeling codes and (b) to demonstrate a process for archiving and accessing the data. The approach, which uses two types of models (wing and tethered mass), was to obtain ambient upstream, wall, and downstream static and dynamic fluid pressures for the models in various dynamic conditions.

The statistics of isotropic homogeneous decaying at moderately large Reynolds number are studied in detail using a Fourier-space band-filtering method on flow fields obtained by direct numerical simulation. Two distinct aspects of the non-Gaussianity of the turbulent field are ...

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

Cerebral vasospasm after aneurysmal subarachnoid hemorrhage is a potentially severe sequel. The induction of hypertension, hypervolemia, and hemodilution is advocated for vasospasm, but it is unclear whether hemodilution confers any benefit. A finite element model of oxygen transport in the proximal middle cerebral artery (MCA) was used to evaluate the complex relationship among hematocrit, viscosity, oxygen content, and blood flow in the setting of vasospasm. A single-phase non-Newtonian finite element model based on three-dimensional incompressible Navier–Stokes equations was constructed of the M1 segment. The model was solved at vessel stenoses ranging from 0% to 90% and hematocrit from 0.2 to 0.6. A small area of poststenotic recirculation was seen with mild (30%) stenosis. Poststenotic eddy formation was noted with more severe (60% to 90%) stenosis. Volumetric flow was inversely related to hematocrit at mild stenosis (0% to 30%). With near-complete stenosis (90%), a paradoxical increase in flow was seen with increasing hematocrit. Oxygen transport across the segment was related to hematocrit at all levels of stenosis with increasing oxygen transport despite a reduction in blood flow, suggesting that with clinically significant vasospasm in the MCA, hemodilution does not improve oxygen transport, but to the contrary, that ischemia may be worsened.

Laminar steady state natural convection in a two-dimensional symmetrical trapezoidal enclosure has been studied using a finite element method. In this investigation, the top wall is considered adiabatic, both inclined sidewalls are maintained at a constant cold temperature and an isoflux heat source is provided at the bottom surface. The pressure-velocity form of the Navier-Stokes equations and energy equation are used to represent the mass, momentum and energy conservations of the fluid medium in the enclosure. Galerkin weighted residual method of finite element formulation with triangular mesh elements is employed. The fluid investigated here is air of Prandtl number fixed at 0.7. The Rayleigh number is varied from 10^3 to 10^6 while the sidewall inclination angle is varied from -15° to 45°. The results are presented in terms of streamline and isotherm plots as well as the variation of average Nusselt number with Rayleigh number for different base wall tilt angles of 0°, 15°, and 30°. The results show that the average Nusselt number increases with the increase of Rayleigh number and the effect of the sidewall inclination angle on heat transfer is significantly reduced at higher Rayleigh number. Effects of sidewall inclination angle on convection heat transfer characteristics decrease with the increase of base wall tilt angle at higher Rayleigh number and Rayleigh number equal to 10^5 can be considered as a critical limit for the present.

Earth pipe cooling technology is a building design approach for cooling a room in a passive process without using any customary units. It can reduce energy consumption of the buildings for hot and humid subtropical zones. This chapter investigates the performance of horizontal earth pipe cooling (HEPC) in combination with a green roof system. To measure the performance, a thermal model was developed using Fluent in ANSYS 15.0. Data were collected from three air-conditioning modeled rooms installed at Central Queensland University, Rockhampton, Australia. One of the rooms was connected to a HEPC system, the second to a green roof system, and the third standard room had no cooling system. The effect of air temperature, air velocity, and relative humidity of the hybrid earth pipe cooling performance were assessed. A temperature reduction of 4.26°C is predicted for a combined HEPC and green roof system compared to the standard room, which will assist the inhabitants to achieve thermal comfort and save energy in the buildings.

Axisymmetric solution of radial, axial and tangential components of velocity of flow through a cylindrical chamber with an inflow containing swirl and outflow is investigated numerically using Finite Volume Method. An in-house developed computer code for solving the three components of velocity and pressure is developed and validated using experimental data available from literature on the problem of axial vortex breakdown of confined flow in a cylinder due to rotation of one of the end walls. The code uses a staggered approach and fractional step projection method for decoupling the velocity and pressure. The convection and diffusion terms are approximated using a second-order accurate central difference scheme. This paper discusses the characteristics features of flow such as mixing streams, streams of fluid flowing close to the solid walls(cooling streams), swirl motion and  development of flow structures.

ABSTRACT One of the most efficient ways to reduce the pollution and fuel consumption of an automotive engine is to downsize the engine, whilst maintaining a high level of power and torque. This is achieved by using turbochargers. In urban, and often in suburban, traffic conditions the engine power demand is weak in relation to the maximum power available, so the turbocharger runs at low speed. To appreciate and improve engine performance, it is necessary to know the characteristics of the turbomachinery in this functioning area, characteristics which are not given by turbocharger manufacturer. The reason for this lack of information will be explained and the experiments we are currently conducting at low turbocharger speed are presented. Experimentally, it has been demonstrated that the measured performances of the compressor are dependent on heat exchange (convection and conduction) and are also linked to the pressure and temperature of the lubricating oil. At the CNAM laboratory, the turbocharger test rig has been equipped with a special torquemeter, allowing rotation speeds of up to 120000 rpm, set up between the turbine and the compressor. The turbine is thus separated from the compressor and could be considered as a drive which provides mechanical power to the turbocharger (torquemeter + compressor + bearing unit). Temperature and pressure of the lubricating oil can be adjusted to an experiment’s requirements. The test bench lay out is described. To achieve accurate measurements and evaluate the influence of heat exchanges, tests have been carried out with the whole compressor thermally isolated and with preheated inlet air. The compressor can be assumed to be adiabatic, and the power given to the air flow can be calculated using the first law of thermodynamics. Mechanical bearing losses can be deduced from this calculation and torquemeter power, but also from measurements of lubricating oil flow, and oil temperature at inlet and outlet. The results of experiments for different lubricating oil temperatures and pressures and turbocharger speeds are presented. Real compressor characteristics curves are set up and a comparison of experimental mechanical power losses with a journal bearing CFD model is presented.

This thesis investigates the technical problems associated with large-scale stand-alone wind powered desalination employing a short-term energy store, particularly the complexities associated with the intermittent operation of the desalination plant. To achieve this, a non-linear, time domain system model of an existing wind powered desalination plant has been developed using the propriety code Simulink. Two desalination techniques have been considered: reverse osmosis and electrodialysis, due firstly to their relatively low specific energy consumption, and secondly, their efficient coupling to a wind turbine generator. As a way of reducing power mismatch, optimising water production, and above all reducing the switching rates of the desalination units, operation of the reverse osmosis and electrodialysis units under variable power conditions is suggested. Little information is available on plant performance under such conditions. A mathematical model has therefore been developed to...

A computational fluid dynamics (CFD) modelling study is undertaken integrating the air-fired and oxy-fuel combustion cases for chemical reactions, radiative heat transfer, and gas compositions into a 3-D hybrid unstructured grid CFD code. A swirl injection system is used to achieve the flame stability of the turbulent non-premixed combustible gases. An Eddy Breakup (EBU) combustion model with appropriate empirical coefficients is employed for this study. Validation and comparison of both combustion cases with the experimental data, which conducted on a 100 kW facility unit, were made by comparing the temperature distribution levels and species concentration levels. The oxy-fuel combustion case showed that the flame is obviously concentrated in the central region, and it is not spread inside the furnace compared to the air-fired flame. The swirl effect is certainly used to enhance the turbulent mixing and to achieve the internal recirculation of flames. By switching to oxy-fuel fired...

Title: Sampling inhomogeneous turbulent fields. Authors: Adrian, RJ; Moin, P.; Moser, RD. Affiliation: AA(National Aeronautics and Space Administration. Ames Research Center, Moffett Field, CA.), AB(National Aeronautics and Space Administration. ...

In this paper we present the design problem of helical tubular PhotoBioReactors (PBR) based on energy consumption minimization, using the radius of curvature for the cultivation of microalgae. Computational Fluid Dynamics (CFD) is used to design a configuration of the helical pipeline with minimum energy consumption. We determined how flow direction changes affect energy consumption. Additionally, it was found that the radius of curvature affects the pressure drop in the PBR’s pipe, so a cost function has been developed to solve an optimization problem seeking to obtain the optimum radius of curvature and a helical tubular PBR design with low pumping rates.