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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.

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°.

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 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.

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.