In the present paper, simulation for shell and tube heat exchanger investigated using CFD techniques. Numerical simulations of the turbulent, three-dimensional fluid flow and heat transfer are performed using Ansys Fluent 6.3. The effect of friction characteristics on the model of heat exchanger is discussed. A RNG κ-ε turbulence model with non-equilibrium wall function and 2 nd order upwind is used. The present model is validated with the experimental literature and show a good agreement. The numerical results of the present study predict reasonably agree well with available correlations. Finally the present study model can be used to model a shell and tube heat exchanger with a satisfactory accuracy level in predictions.

The work represents a systematic numerical optimization methodology using artificial neural network and hybrid genetic algorithm for a bi-directional axial impulse turbine used in wave energy harvesting system. Reynolds-averaged Navier-Stokes equations with k-ε turbulence model were discretized and solved for unstructured tetrahedral grid elements for flow analyses. Efficiency enhancement of the turbine was chosen as an objective. The design variables chosen were numbers of stator and rotor blades. The responses obtained from CFD analysis were used to train the neural network. The optimal point search from the network by hybrid genetic algorithm produced 13% increase in turbine efficiency. Detailed description of the methodology and analysis of the results has been presented in this paper.

CFD (Computational Fluid Dynamics) algorithms are nowadays a necessary tool in the aerospace science, as their application allows for the prediction of the aerodynamic characteristics of complete aircraft configurations in a relatively short period of time. A brief presentation and evaluation of such a recently developed academic code, named Galatea, is the main goal of this study. Galatea employs the Reynolds Averaged Navier-Stokes (RANS) equations, discretized with a node-centered finite-volume scheme on three-dimensional unstructured hybrid grids for the simulation of inviscid and viscous compressible fluid flows. For the turbulence prediction appropriate turbulence models (k-ε, k-ω and SST) have been incorporated, while for the acceleration of the solution an agglomeration multigrid scheme along with a suitable parallelization strategy are employed. For the assessment of this algorithm runs over the wing-body and the wing-body-horizontal tail NASA Common Research Model (CRM) configurations were performed, allowing for a comparison in terms of accuracy of the obtained results with the experimental wind tunnel data, as well as with the computational results of corresponding reference solvers.

Solar chimney is a new method to produce electrical power. It employs solar radiation to raise the temperature of the air and the buoyancy of warm air to accelerate the air stream flowing through the system. By converting thermal energy into the kinetic energy of air movement, solar chimneys have a number of different applications such as ventilation, passive solar heating and cooling of buildings, solar-energy drying, and power generation. Moreover, it can be employed as an energy conversion system from solar to mechanical. A component, such as a turbine or piezoelectric component, set in the path of the air current, converts the kinetic energy of the flowing air into electricity. In this paper, a numerical investigation on a prototypal solar chimney system integrated in a south facade of a building is presented. The chimney is 4.0 m high, 1.5 m wide whereas the thickness is 0.20 m for the vertical parallel walls configuration and at the inlet 0.34 m and at the outlet 0.20 m for convergent configuration. The chimney consists of a converging channel with one vertical wall and one inclined of 2°. The analysis is carried out on a three-dimensional model in airflow and the governing equations are given in terms of k-ε turbulence model. The problem is solved by means of the commercial code Ansys-Fluent. The numerical analysis was intended to examine the effect of the solar chimney’s height and spacing. Further, comparison between radiative and non-radiative model is examined and discussed. Results are given in terms of wall temperature distributions, air velocity and temperature fields and transversal profiles for a uniform wall heat flux on the vertical wall equal to 300 W/m 2 . Thermal and fluid dynamics behaviors are evaluated in order to have some indications to improve the energy efficiency of the system.

This paper illustrates a numerical investigation on a prototypal ventilated roof for residential use. The analysis is carried out on a two-dimensional model in air flow and the governing equations are given in terms of k-ε turbulence model. Due the symmetry geometric and thermal has been studied a single flap of the roof. The analysis is performed in order to evaluate the thermofluidodynamic behavior of the roof as a function of geometric parameters such as the inclination, the layer of ventilation gap and the hipped roof height. The problem is solved by means of the commercial code Ansys-Fluent and the results are performed for assigned wall heat flux on the top wall. Results are given in terms of wall temperature distributions, air velocity, temperature profiles along the cross sections of the roof to estimate the differences among the various configurations. Further, the ventilated roof is compared with other types of roof.

In this study, a combined experimental and computational study for the design of a low water consumption cooling tower is performed. The purpose of the study is to reduce the water consumption without decreasing the efficiency of a typical cooling tower. To achieve this aim, it is necessary to enhance the homogeneity of mist/air mixture. For this purpose, firstly, an experimental set-up including a small scale wind tunnel is installed which provides opportunity to examine different inlet and outlet configurations easily. Computational Fluid Dynamics (CFD) is used extensively to examine the effects of different configurations before experimental studies. Simulations of different inlet and outlet configurations are performed using only air. Several turbulators are designed and simulated to increase the turbulence levels. A three dimensional multi-phase CFD model is utilized to design a nozzle-turbulator system for the cooling tower. As results of the computational and experimental studies, the most efficient inlet and outlet configurations are specified and turbulators are selected from the alternative designs.

This paper presents a method to evaluate ejector efficiency in function of local flow parameters. The paper is divided into two parts. In the first part, a Computational Fluid-Dynamics (CFD) approach for convergent nozzle ejectors is presented and computational results are validated using experimental velocity and temperature profiles at different sections. The validation process includes the evaluation of seven Reynolds-Averaged Navier–Stokes (RANS) turbulence models: the Spalart-Allmaras and the k–omega SST models show better performance in terms of convergence capability and flow and thermal field prediction. In the second part, local flow phenomena and their influence on ejector component efficiencies are investigated. The validated CFD approach is used to determine the efficiencies of the ejector primary nozzle, suction chamber, and mixing zone. Efficiency maps, regressing equation linking efficiencies, and local flow quantities are proposed and discussed. Finally, global ejector performance is mapped and considerations are outlined.

In many industrial applications, some measurement instruments must be placed in a pipe in which fluid flows. Two phase cross flows around a body have seldom been studied until now and considering these flows can play a significant role in long-term reliability and safety of industrial systems. In this paper drag coefficient, pressure coefficient and void fraction around triangular bodies with different leading edge angles were considered. Also effect of Reynolds number and inlet void fraction on drag coefficient and pressure coefficient has been investigated and flow treatment behind the triangular obstacle has been examined. To achieve this aim, main equations of flow have been developed for investigation of drag coefficient in air-water two phase. Our numerical analyses were performed by a designed and written CFD package which is based on Eulerian-Eulerian approach. Geometries, which have been studied in this article, are triangle, with different leading edge angle. Other parameters such as two phase Reynolds number, free stream void fraction and bubble size were considered, too. Drag coefficient is closely relates to the turbulence and the bubble motion. Since these mechanisms vary over time, we used final value of drag coefficient after convergence. The results showed that drag coefficient is strongly depended of Reynolds number. In this simulation it can be seen that both the drag coefficient and pressure drag coefficient decrease whit increase in two phase Reynolds number and increase with decrease in inlet void fraction.

Even after many years of the application of numerical CFD techniques to flow through porous fences, still there is disagreement between researchers regarding the best turbulence model to be implemented in this field. Moreover, different sources claim to have achieved good agreement between numerical results and experimental data; however, it is not always possible to compare numerical and experimental results due to the lack of information or variations in test conditions. In this paper, five different turbulence models namely; K-ε models (standard, RNG and Realizable) and K-ω models (Standard and SST), have been applied through a 3D CFD model to investigate air flow behind a porous panel, under the same conditions (boundary conditions and numerical schemes). Results are compared with wind tunnel experiments. Comparison is based on the vertical velocity profile at a location 925 mm downstream of the fence along its center line. All models were capable of reproducing the velocity profile, however, some turbulence models over-predicted the reduction of velocity while it was under-predicted by other models, however, discrepancy between CFD modelling and experimental results was kept around 20%. Comprehensive description of the turbulence structure and the streamlines highlight the fact that the criterion for selecting the best turbulence model cannot rely only on the velocity comparison at one location, it must also include other variables.

The open sump is a typical inlet passage for small to middle-sized pumping station. It is important for the efficiency and safe operation of pumps that the open sump has an optimum design. The flow through the sump and into the pump is calculated using CFD. The incompressible N-S equations are solved by the finite volume method. The RNG k-ε turbulence model and the SIMPLEC algorithm for pressure-velocity coupling are used. Many different designs for the open sump are considered, the results of which are compared based on common criteria to evaluate the sump performance. Design values for the width, the depth of submergence and the bellmouth shape are derived.

Air flow management in a Data-center is a critical problem when designing HVAC (Heating, Ventilation and Air-Conditioning) system. Providing a sufficient cooling air volume at a designed temperature to all the informatics equipments, avoiding recirculation phenomenon, optimizing the installations in order to minimize the temperature difference between air exiting the CRAC (Computer Room Air Conditioning) and the air at the intake of the servers are parts of the multiples target that have to be reached in order to have the most efficient ventilation system. In most of today’s data center, the IT (Information Technology) equipment dissipates between 12kW of heat for regular material, to up to 32kW for the recent high density server’s rack. Such a power release has to be cooled by efficient cooling system. During this process the airflow temperature can increase by over 10K, and the air velocity can vary from 0.09m/s to more than 5m/s. Considering these large gradient of temperature and air speed several phenomenon must be taken into account, including turbulent natural convection. To achieve these goals, we will use a CFD software to predict the airflow behaviour inside the Data-center. Therefore, the code must be able to accurately model turbulent airflow and heat transfers. We used the software (http/www.thetis.enscbp.fr) to simulate a 2D turbulent natural convection in a square cavity. The k-ε equations were solved to predict turbulent effects. The obtained results were compared to an experimental benchmark and are presented in the document. In the last part of the paper we present the results of a 2D simulation representing a working server in a computer room cooled by a CRAC (Computer Room Air Conditioning) unit. The airflow characteristics in the whole domain were determined using various dimensionless numbers in order to select the right physical and mathematical objects. Finally the results of a 3D simulation are presented and the cooling system performances are estimated.

Based on FLUENT software, the standard k–ε turbulence model is adopted to simulate 3D-flow field in the forebay of a combined sluice-pump station. Flow field of the diffusion channel and suction passage is obtained after numerical simulation. Results show that flow in the fore-bay appears side-direction and vortexes exist in it and inlet of the suction passage. According to the results, optimum measures such as changing the wing wall form, extending the sluice pier, adding tri-prisms are conducted on the basis of original design. The vortexes are eliminated finally. Flow in diffusion channel appears front inflow and is improved effectively.

Large eddy simulation is used to study the flow over a backward-facing step interacting with a periodic array of streamwise microjets emenating from the step at a 45° angle to the step face. Averaged streamwise velocity profiles are in good agreement with experimental data. A well defined turbulent inlet profile for the microjet is found to be important to obtain correct streamwise normal fluctuations near the step. To simulate cases as per the experimental setup a microjet inlet pipe section is necessary for the simulations. The studies with passive scalars need to be conducted to quantify scalar mixing. The monotonicity problem of simulating passive scalar can be overcome by simply clipping the unbounded values. This technique works because the volume occupied by overshoot values of passive scalar are small compared to the total volume of the backward-facing step geometry.

Squeeze film dynamical effects are relevant in many industrial components, bearings and seals being the most conspicuous applications. But they also arise in other industrial contexts, for instance when dealing with the seismic excitation of spent fuel racks. The significant nonlinearity of the squeeze-film forces prevents the use of linearised flow models, therefore a fully nonlinear formulation must be used for adequate computational predictions. Because it can accommodate laminar and turbulence flow effects, a simplified bulk-flow model — based on gap-averaged Navier-Stokes equations and incorporating all relevant inertial and dissipative terms — was previously developed by the authors (Antunes & Piteau, 2010), assuming a constant skin-friction coefficient. In this paper we introduce an improved theoretical formulation, fully developed elsewhere (Piteau & Antunes, 2010), such that the dependence of the friction coefficient on the local flow velocity is explicitly accounted for, so that it can be applied to laminar, turbulent and mixed flows. The main part of the paper is then devoted to the presentation and discussion of the results from an extensive series of experiments performed at CEA/Saclay. The test rig consisted on a long gravity-driven instrumented plate of rectangular shape colliding with a planar surface. Theoretical results stemming from both analytical flow models are compared with the experimental measurements, in order to assert the strengths and drawbacks of the simpler original model, as well as the improvements brought by the new but more involved flow formulation.

The present study is concerned with the effect of fuel droplet size, air inlet preheating and air swirl number on complex soot process in a turbulent liquid-fuelled combustor. A hybrid Eulerian-Lagrangian method is employed to model the reactive flow-field inside the combustor. Equations governing the gas phase are solved by a control volume based semi-implicit iterative procedure while the time-dependent differential equations for each sizes of the fuel droplets are integrated by a semi-analytic method. The processes leading to soot consist of both formation and combustion. Soot formation is simulated using a two-step model while a finite rate combustion model with eddy dissipation concept is implemented for soot combustion. Also, mathematical models for turbulence, combustion, and radiation are used to take account the effects of these processes. Results reveal the significant influence of liquid fuel droplet size, air inlet temperatures and swirl numbers on soot emission from turbulent spray flames. The predictions show that reduction of spray droplet size and increases of air inlet temperature and swirl numbers considerably, increases soot emission from spray flames.

In this study we will examine the applicability of flow induced by a rotating disk in evaluating the performance of polymeric and surfactant additives in reducing skin friction drag. It is shown that these additives can dramatically reduce friction drag provided that the flow is occurring under turbulent conditions while they have no effect on Taylor instabilities. Based on the experimental data, a drag reduction in the range of 10% can be achieved with the effect becoming more pronounced with an increase in the Reynolds numbers.

This work presents a computational fluid dynamics simulation to investigate the effects of inlet geometry on the pressure drop and particle collection efficiency of a tangential inlet cyclone. Three-dimensional, steady governing equations for the incompressible, turbulent flow inside a tangential inlet cyclone are solved numerically under certain boundary conditions. The continuous gas flow is predicted by solving Navier-Stokes equations using the differential RSM turbulence model. The second phase is modeled based on a Lagrangian approach. The commercial CFD code Fluent was used for numerical analysis. Computational results compared experimental data available in the literature for validation. Various cyclones, each has different geometrical ratio of inlet section, studied in this paper. Detail analyses of the effects of inlet geometry on the flow behavior, pressure drop and collection efficiency were given.

An experimental study of turbulence behind a fractal orifice plate, a variant of classical circular orifice plate, was conducted in a circular wind tunnel. Four fractal orifice plates with iteration levels from zero to three in combination with a classical circular orifice plate, each with equal flow area, were used in the study. Of the two main objectives, the first one was to test the superiority of the proposed fractal orifice plate against the classical one and the second one was to investigate the fractal orifice effect on the flow properties. Across the fractal orifice plate, a decrease in the pressure drop and an increase in the flow mixing is observed making it much more efficient than the classical orifice plate. It was suggested that at each fractal iteration, the added edge sharpness generated finer flow structures and these flow structures were eventually responsible for the improved efficiency.

In this research, centrifugal compressor of a gas turbine is investigated experimentally and numerically. Operation line of the compressor as a component of the gas turbine is obtained experimentally by measurements of impeller rotational speed, and flow parameters at the compressor inlet and outlet during the gas turbine operation. The flow field inside the impeller and diffusers are analyzed numerically using a full 3D Navier-Stokes program with SST turbulence model. Boundary conditions for the numerical simulation are specified from the experimental measurements. The operation line of the compressor is obtained numerically, which is compared with that of the experimental results, and shows good agreement. Having validated the numerical results, the performance characteristic curves of the compressor are obtained numerically in a wide range.

In the present study, a numerical simulation is carried out in order to optimize the length of the mixing part of a T-junction to obtain a homogenous temperature distribution at the outlet. Different RANS turbulence models are tested: the Realizable k-ε the k-ω standard and the k-ω SST. The behavior of turbulent mixing flow in the mixing part of the pipe has helped in understanding the causes of discrepancy between the models used. The test case analysed in this paper is an unsteady state three-dimensional turbulent flow. The numerical results obtained show that there is a difference in the prediction of the thermal field when different models are used. The results obtained for both k-ω standard and SST models are closer compared with those given by the Realizable k-ε model. The numerical results show that a distance of x/L = 0.625 from the branch is enough to supply devices with a constant temperature.