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This paper presents a new model of 2D performance calculation applied to VAWT. The idea consist in considering only one blade to which a rotational oscillation motion is gave. Hence, the effect of the machine rotation and the influence of the rest of the machine on the focused blade are modelled. The study is purely numerical based upon the use of ANSYS-Fluent code to solve unsteady RANS equations, which follow from the new model. Several 2D geometry configurations of Darrieus machine were tested using the new approach and the results are compared to ones applied to the whole 2D rotor. A quasi concordance of the results is noticed for the overall predictions done from the two CFD methods. Although computational time is lower for the new model, tests reveal inadequate prediction of the peak's power coefficient and its Tip Speed Ratio value.

The objective of the current paper is to study the flow around Seiun Maru Highly Skewed (HSP) marine propeller by assessment of blade forces and moments under non-cavitating case. The calculations are performed in open water (steady case) and non-uniform ship wake (Unsteady case). The governing equations based on Reynolds Averaged Navier-Stokes Equation (RANSE) are solved using Finite Volume Method. Ansys Fluent 14.0 is used to implement the simulation. For the steady case, Moving Reference Frame (MRF) is selected while sliding mesh technique is adopted for the unsteady case. Calculated open water performances in terms of thrust and torque coefficients fit very well with experimental data for a wide range of advance ratio. In the unsteady calculations, axial velocities, deduced from the nominal wake, are introduced in the Ansys fluent code. To locate suitably the non-uniform wake in the propeller front plane, three positions of inlet wake have been taken into account to determine their effects on the accuracy of the results. Obtained results show that computed performances are improved compared to panel method when the inlet is close to the propeller.

The present work concerns a numerical study of a three-dimensional laminar flow in forced convection crossing a rectangular channel provided with a baffle attached on its lower wall. The conservati...

This paper presents and discusses the results of the transient numerical simulation carried out for an isolated main rotor model and a helicopter in vertical descent autorotation by developing the 6-degree of freedom, rigid-body equations of helicopter motion. The Unsteady Reynolds Averaged Navier-Stokes model is used to simulate the unsteady flow field surrounding four-bladed BO-105 isolated main rotor and complete helicopter which includes the fuselage and the tail rotor. The principal autorotation characteristics for the helicopter such as induced velocity, rate of descent, main rotor angular speed, thrust and torque have been calculated. The simulation results show the creation of a spanwise flow on the upper surface of the blade, and moving fluid in the direction of the blade tip in a region downstream and beneath the leading edge vortex. The aerodynamic characteristics on the complete helicopter are similar to the ones attained for the isolated rotor simulation.

In the present paper, an experimental and numerical simulation of the turbulent cross-flow in a staggered tube bundle with transverse and longitudinal pitch-to-diameter ratios of 3.8 and 2.1, respectively, are performed. The bundle consists of 16 PVC tubes of 40 mm outer diameter arranged in a staggered configuration. Each cylinder has two grooves on the external surface at 90° and 270°. The experiments are carried out using a subsonic wind tunnel. The pressure distributions along the tubes are determined for a variation of the azimuthal angle from 0° to 360°. The drag and lift forces are measured using the TE 81 balance. The drag coefficients are also deduced from the resulting pressure force in order to compare with smooth cylinder configuration. The use of the grooved cylinder shows a reduction on the drag forces. The steady-state Reynolds-averaged Navier–Stokes equations are solved using a finite-volume method where Spalart–Allmaras, k–e realizable and k–ω SST, turbulence models are used to produce a closed system of solvable equations. The staggered tube bundle geometry simulations are performed at steady conditions. An adapted grid using static pressure, pressure coefficient and velocity gradient, furthermore, a second-order upwind scheme were used. The obtained results show that the numerical predictions are in good agreement with the experimental measurements.

The turbulent and thermal mixing in a vertically oriented T-junction is investigated numerically using ANSYS FLUENT software. By taking account the buoyancy forces, a steady state three-dimensional turbulent flow is considered with a Reynolds number of 0.4×105 at the cold inlet and 3.3×105 at the hot entrance. The k-ε standard model with standard wall function is chosen to provide closure for the Reynolds stress tensor. The numerical results presented in the form of velocity vectors field and contours of temperature distribution gave a good prediction of the dynamic and the thermal fields namely in the mixing region where a reversed flow is captured.

The present paper investigates the aerodynamic performances variations of straight-blades DARRIEUS wind turbine in two-dimensional steady flow with different low Reynolds numbers (30k, 40k, 55k and 80k). The numerical 6DOF approach (six degrees of freedom) is used to predict sequentially the angular positions according to the wind turbine mass properties (mass and moment of inertia) in real time. The numerical optimization requires a transient dynamic mesh technique for one degree of freedom around the rotation axis. The self-starting ability of the H-Darrieus wind turbine is expressed by increasing the inlet wind velocity, independently to the wind direction (angles of attack: 0°, 10°, and 20°). A 2D unsteady shear stress transport (SST k- ω) model has been employed to perform the present simulation. The various results of performance coefficients (lift and torque) obtained by a two blades design show a significant agreement with the available experimental data, as well as, an important increase in lift and torque according to the increase of the free stream wind velocity. However, the static stall still at the same azimuthal position (about 11°). That is a consequence of the appropriate modelling of the rotational speed, as well as, the stability that characterizes the 6DOF approach. The tangential force is maximum (wind turbine acceleration), where the blades axis are normal to the velocity field, and neglected at the braking position 0°.

This article presents a computational analysis of the turbulent flow of air in a pipe of rectangular section provided with two waved fins sequentially arranged in the top and the bottom of the channel wall. The governing equations, based on the k-? model with Low Reynolds Number (LRN) used to describe the turbulence phenomena, are solved by the finite volume method. The velocity and pressure terms of momentum equations are solved by the SIMPLEC algorithm. The profiles of axial velocity, the velocity fields and the drag coefficient were obtained and presented for all the geometry considered and for selected sections, namely, upstream, downstream and between the two waved baffles. This contribution lead to results which were analyzed by the use of the solid, plane baffles, waved and inclined with active degrees of 0? up to 45? with a step equal to 15 degree and directed towards the left. Over the range of the study, the undulation of the baffles induced with an improvement on the skin friction of about 9.91 % in the case of ?=15?, more than 16% in the other cases, and concerning the pressure loss, the undulation of the baffles was insured improvements starter from 10,43% in all cases compared with the baffles of plane form.

In the present paper an experimental investigation of drag reduction on in-line tube bundles with a configuration of seven by seven with a pitch ratio of 1.44 has been performed. Two longitudinal grooves are placed on the external surface of the circular cylinders as a passive control. The experiment is carried out using a subsonic wind tunnel. The pressure distributions for various azimuthal angles along the tubes are measured using a multi-channel differential pressure. Drag forces are also determined using a combined wire-strain gauge balance. The pressure drops are deduced from the resulting drag forces. The results obtained show an unexpected reduction in the pressure drop for the tube bundles. A reduction of 36.5% in the pressure drop for a Reynolds number of 1.33 × 10 4 is found compared to the configuration without grooves. Some correlations for the pressure drop are proposed.

The aim of the present paper is to investigate numerically the energy separation mechanism and flow phenomena within a vortex tube. A 3D computational domain has been generated considering the quarter of the geometry and assuming periodicity in the Azimuthal direction which was found to exhibit correctly the general behaviour expected from a vortex tube. Air is selected as the working fluid. The flow predictions reported here are based upon four turbulence models, namely, the ke 3, keu and SST keu two-equations models and the second moment closure model (RSM). The models results are compared to experimental data obtained from the literature. Four cases have been considered by changing the inlet pressure from 200 up to 380 kPa. It has been observed that all the above mentioned models are capable of predicting fairly well the general flow features but only the advanced RSM model is capable of matching correctly the measured cold and hot outlet temperatures. All the other models over predict the mean temperature difference by values up to twice the measured data.

A single phase computational fuel cells model is presented to elucidate three-dimensional interactions between mass transport and electrochemical kinetics in proton exchange membrane (PEM) fuel cells with straight gas channels. The governing differential equations are solved over a single computational domain, which consists of a gas channel, gas diffusion layer, and catalyst layer for both the anode and cathode sides of the cell as well as the solid polymer membrane. Emphasis is placed on obtaining a basic understanding of how three-dimensional flow and transport phenomena in the air cathode impact the electrochemical process in the flow field. The complete cell model has been validated against experimentally measured polarization curve, showing good accuracy in reproducing cell performance over moderate current density interval. Fully three-dimensional results of the flow structure and species profiles are presented for cathode flow field. The effects of pressure on oxygen transport and water removal are illustrated through main axis of the flow structure. The model results indicate that oxygen concentration in reaction sites is significantly affected by pressure increase which leads to rising fuel cells power.

In the present work, the influence of non-uniform boundary conditions on natural convection in inclined rectangular cavities differentially heated is studied. The hot wall is wavy with three undulations. The aspect ratio of the cavities has also been changed. Various inclination angles were performed. The flow and the heat transfer are calculated by solving both Navier–Stokes and the energy equations with finite volume method in the primitive formulation. The sinusoidal distribution of temperature is imposed at the vertical walls and was compared with isothermal boundary conditions. The flow and the heat transfer are also simulated for different wavelength of the sinusoidal distribution. It was found that this parameter has an effect on the trend of the local Nusselt number. The results obtained show that the trend of the local Nusselt number is wavy for all inclination angles and for all the configurations tested. The mean Nusselt number decreases comparing with the Nusselt number of the square cavity. Non-uniform boundary conditions of the temperature distribution in both vertical walls increase the local and the mean Nusselt number comparing with the isotherm walls. The sinusoidal distribution seems to reduce the heat transfer rate for two wavelengths and increasing aspect ratio results in a decrease of the Nusselt number.

The objective of this study is the comparison between the model of Darcy-Brinkman and the Navier-Stokes equations modified, in the case of the natural convection. The study is made in a porous vertical square cavity saturated by a Newtonian fluid. A cylindrical heat source maintained at a uniform heat flux is introduced into porous medium. The equations which describe the thermal transfer and the hydrodynamic flow of the two models are solved numerically by means of the software package Femlab 3.2 based on the finite element method. The results obtained are in the form of average kinetic energy per unit mass, the local and the average Nusselt numbers, the pressure and the viscous force per unit area.

The present work is a numerical computation of steady turbulent forced convection flow and pressure drop characteristics in a two-dimensional horizontal rectangular cross section channel with isothermal walls and with two and three transverse waved baffles disposed overlapping in a channel. The fluid is considered as Newtonian, incompressible with constant properties. The governing equations are solved by the method of finite volume using the SIMPLE-algorithm, in two-dimensions with the k-e Realizable model to describe the turbulence phenomena. Air is the working fluid with the flow rate in terms of Reynolds numbers ranging from 5.000 to 20.000. The effects of baffle shape geometries as well as Reynolds numbers on the flow patterns and heat transfer performances are investigated. To understand the characteristics of thermal enhancements, the friction factors are also computed. The numerical results are validated with available flat rectangular-shaped baffle measured data and found to agree well with measurement. The computational results reveal essentially, that the shape of the baffles can alter substantially the flow and heat transfer characteristics. In general, an increase in the flow Reynolds number causes a substantial increase in the convective Nusselt number other than the pressure loss is also very important. The detailed knowledge on the flow and heat transfer distribution in this computation provides the basis for further optimization of shell-and-tube heat exchangers.

The turbulent natural convection of air flow in a confined cavity with two differentially heated side walls is investigated numerically up to Rayleigh number of 1012. The objective of the present work is to study the effect of the inclination angle and the amplitude of the undulation on turbulent heat transfer. The low-Reynolds-number k–e, k–ω, k–ω–SST RANS models and a coarse DNS are used and compared to the experimental benchmark data of Ampofo and Karayiannis [F. Ampofo, T.G. Karayiannis, Experimental benchmark data for turbulent natural convection in an air filled square cavity, Int. J. Heat Mass Transfer 46 (2003) 3551–3572]. The k–ω–SST model is then used for the following test-cases as it gives the closest results to experimental data and coarse DNS for this case. The mean flow quantities and temperature field show good agreement with coarse DNS and measurements, but there are some slight discrepancies in the prediction of the turbulent statistics. Also, the numerical results of the heat flux at the hot wall are over predicted. The strong influence of the undulation of the cavity and its orientation is well shown. The trend of the local heat transfer is wavy with different frequencies for each undulation. The turbulence causes an increase in the convective heat transfer on the wavy wall surface compared to the square cavity for high Rayleigh numbers. A correlation of the mean Nusselt number function of the Rayleigh number is also proposed for the range of Rayleigh numbers of 109–1012.

Accurate simulation of turbulent free surface flows around surface ships has a central role in the optimal design of such naval vessels. The flow problem to be simulated is rich in complexity and poses many modeling challenges because of the existence of breaking waves around the ship hull, and because of the interaction of the two-phase flow with the turbulent boundary layer. In this paper, our goal is to estimate the lift and drag coefficients for NACA 0012 of hydrofoil advancing in calm water under steady conditions with free surface and emerged NACA 0015. The commercial CFD software FLUENT version 14 is used for the computations in the present study. The calculated grid is established using the code computer GAMBIT 2.3.26.The shear stress k-ωSST model is used for turbulence modeling and the volume of fluid technique is employed to simulate the free-surface motion. In this computation, the second order upwind scheme is used for discretizing the convection terms in the momentum transport equations, the Modified HRIC scheme for VOF discretisation. The results obtained compare well with the experimental data.

This paper presents the results of measurements and numerical predictions of turbulent cross-flow through an in-line 7×7 bundle configuration with a constant transverse and longitudinal pitch-to-diameter ratio of 1.44. The experiments are conducted to measure the pressure around tubes, using DPS differential pressure scanner with air flow, in square channel at a Reynolds number of 35000 based on the gap velocity and the tube diameter. The commercial ANSYS FLUENT is used to solve the unsteady Reynolds–Averaged Navier–Stokes (RANS) equations. The primary aim of the present study is to search for a turbulent model that could serve as an engineering design tool at a relatively low computational cost. The performances of the Spalart-Allmaras, the RNG k-e, the Shear Stress Transport k-ω and the second moment closure RSM models are evaluated by comparing their simulation results against experimental data. The second objective is to verify the validity of the periodicity assumption taken account in the most previous numerical works by considering the filled bundle geometry. The CFD results show that the Spalart-Allmaras model on the fine mesh are comparable to the experiments while the periodicity statement did not produce consistently the flow behavior in the 7×7 tube bundle configuration.

This paper presents a numerical study on flow structure and convective heat transfer in a plane channel with waved fins mounted alternatively on top and bottom of the walls in a rectangular channel. In this investigation or different bar sizes in the Reynolds number range (5000, 10000, 15000 and 20000) corresponding to steady turbulent flow. The governing equations (continuity, momentum, energy and the turbulence) are solved over the entire domain, using the corresponding properties for the solid and fluid regions. The control volume approach is employed in order to discredit the governing equations for their numerical solution. The k- ω model has been applied to the turbulent flow field. The SIMPLE algorithm was used for the convective terms in the solution equations. A computer code was developed to study the dynamic and thermal comportment for four values of Reynolds number and for different geometric positions of the fins. The axial velocity profiles, the structures represented by the convective Nusselt number, the coefficients of friction and pressure losses were obtained for various selected sections, namely, upstream, downstream and between the two waved fins. DOI: http://dx.doi.org/10.5755/j01.mech.19.2.4154

In this work, two-dimensional and three-dimensional simulations on the flow in a room coupled with a facade of passive heating system type In-In (Trombe wall) were conducted numerically to determine the temperature and velocity fields in the influence of the variation of the modified Rayleigh number, which itself depends on the characteristics of the fluid and heat flow due to sunshine. The behavior of boundary layers in natural convection is analyzed along the Trombe wall in our periodically heated imposed flow. Thermal and dynamics modeling of the problem were made by a computational fluid dynamics (CFD) calculation, based on the finite volume method to model both the fluid flow and heat transfer. To take account of the strong temperature gradient and velocity near the walls, we chose a structured tight mesh near the walls and a little wider mesh elsewhere. The results have shown that for Grh > 4 × 108, the flow regime is laminar, while for Grh > 109, the flow regime becomes turbulent.

International audience; The objective of this research is the study the influence of aspect ratio A1 of fluid portion compared to the height of cavity, on the natural convection in a partially porous enclosure. A cylindrical heat source maintained at a uniform temperature is introduced into porous portion. The equations which describe the thermal transfer and the hydrodynamic flow are described by the Navier-Stokes equations modified by using the extension of Darcy-Brinkman and the energy equation. The results obtained are in the form of isotherm`s distribution, stream`s functions, the local and the average Nusselt numbers and the pressure. Correlations between these parameters and the aspect ratio are considered.

The aim of this paper is to develop a thermodynamic model for a water-to-water heat pump using propane as refrigerant. This model is based on the thermodynamic principals and heat transfer fundamental laws. The performances of the heat pump have been looked at as function of the water temperatures at the entry of the evaporator and the condenser. The results show that the cooling and heating COP of the system increase slightly when increasing the evaporator water inlet temperature and decrease when increasing the condenser inlet water temperature. However, in cooling mode, the exergy efficiency decreases when increasing the inlet water temperatures to evaporator and condenser, while, in heating mode, it increases. Furthermore, it is shown that the exergy efficiency in the cooling mode does not produce the same behaviour as that of the COP.

Free convection in an inclined square cavity with partial partitions has been investigated, by numerically solving the partial differential balance equations of mass, momentum, and energy. The analysed configuration has three undulations and three partitions. Investigations have been performed for different inclination angles, partition lengths and Rayleigh numbers, while keeping the Prandtl number constant. The results show that the hot wall geometry with partitions affects the heat transfer rate in the cavity. It has been found in the present numerical study that the mean Nusselt number decreases notably compared with the heat transfer in the square undulated cavity without partitions.

The aim of the present paper is to carry out a detailed exergy analysis of a two-stage vapour compression cycle by calculating its components exergetic losses. The exergy equations have been developed using refrigerant thermodynamic properties computed by means of a simple model of local equations of states. The results of the exergy analysis of a two-stage refrigeration system operating between a constant evaporating temperature of -30°C and condensation temperatures of 30, 40, 50 and 60°C with two natural substitutes of HCFC22, namely, propane (R290) and ammonia (R717) as working fluids, are presented. It is found that the most significant losses occur in the compressors, expansion valves and condenser. Furthermore, it is shown that the optimum inter-stage pressure for a two-stage refrigeration system is very close to the saturation pressure corresponding to the arithmetical mean of the refrigerant condensation and evaporation temperatures.

This paper presents photovoltaic-hydrogen power system for mobile phone station. This base transceiver station (BTS) is located in neighboring Ouargla city (in the south of Algeria). The power system includes a photovoltaic (PV) field, water electrolyzer and two fuel cells. Each fuel cell is used according to daily and seasonal load of the station. A biphasic model is adopted for the simulation of fuel cell stacks. The governing equations are solved using a program written under Matlab. Multi-criteria optimization with weighting between two opposite objectives is used to determine the compromise solutions between maximum efficiency and minimal fuel cells size. Genetic algorithm coupled with Quasi-Newton method is used to achieve optimal fuel cells operations. The optimal solutions in Pareto sense are plotted according to weighting coefficient. The obtained results show that PV modules number for the summer period is relatively high which requires introducing some technical improvements on shelter walls for reducing air-conditioning loads.