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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.

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.

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.

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.

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.