Saïf Ed-Dîn Fertahi

The aim of this article is to improve the aerodynamic performance of a three-bladed vertical axis H-Darrieus wind turbine, which is equipped with different types of fairings. To this end, a 2D CFD simulation combined with calculations based on the resolution of the Steady Reynolds-Averaged Navier-Stokes equations (RANS) and the SST turbulence model was used. In addition, the multiple reference frame (MRF) method was applied for the simulation. The simulation results show that the power coefficient () reaches maximum values equal to 0.561, 0.580 and 0.607 for the NACA2412, Eppler 423 and DAE-11 profiles respectively, for a chord length C = 3 and a tip speed ratio (TSR) equal to 2.5. Then, the torque coefficient () reaches the highest value of = 0.354 at = 20° for the DAE-11 fairing, which means that this profile performs better, particularly at higher angles of attack. These results confirm that the DAE-11 fairing surpassed the Eppler 423 and NACA2412 profiles. Unstable vortex field formation has been observed between the turbine and the fairing, at the leading and trailing edges, for both low and high fairing chord lengths. This phenomenon can increase torque and disrupt flow direction at low velocity. On the other hand, when the chord length reaches a medium value, a more stable flow zone appears. It can therefore be concluded that the addition of a fairing to the H-Darrieus rotor with a suitable chord length improves the turbine aerodynamic performance, particularly in terms of flow stabilization and reduction of the stagnation zone.

This review provides an analysis of advancements in the design and performance assessment of Darrieus wind turbines over the past decade, with a focus on the contributions of computational fluid dynamics (CFD) to this field. The primary objective is to present insights from studies conducted between 2014 and 2024, emphasizing the enhancement of Darrieus wind turbine performance through various technological innovations. The research methodology employed for this review includes a critical analysis of published articles related to Darrieus turbines. The focus on the period from 2014 to 2024 was considered to highlight recent parametric CFD studies on Darrieus turbines, avoiding overlap with previously published reviews and maintaining originality relative to existing review works in the literature. By synthesizing a collection of articles, the review discusses a wide range of recent investigations utilizing CFD modeling techniques, including both 2D and 3D simulations. These studies predominantly utilize the “Ansys-Fluent” V12.0 and “STAR CCM+” V9.02 solvers to evaluate the aerodynamic performance of Darrieus rotors. Technological advancements focus on modifying the geometry of Darrieus, including alterations to blade profiles, chord length, rotor diameter, number of blades, turbine height, rotor solidity, and the integration of multiple rotors in various configurations. Additionally, the incorporation of flow deflectors, the use of advanced blade shapes, such as V-shaped or twisted blades, and the application of an opening ratio on the blades are explored to enhance rotor efficiency. The review highlights the significant impact of these geometric modifications on key performance metrics, particularly the moment and power coefficients. A dedicated section presents CFD-derived visualizations, including vorticity fields, turbulence contours illustrated through the Q-criterion, velocity vectors, and dynamic pressure contours. These visualizations provide a description of the flow structures around the modified Darrieus rotors. Moreover, the review includes an analysis of the dynamic performance curves of Darrieus, which show improvements resulting from the modifications of the baseline design. This analysis covers the evolution of pressure coefficients, moment coefficients, and the increased power output of Darrieus.

The study of H-Darrieus rotor attracted considerable attention due to its environmental advantages among generating electricity from renewable energy source. However, this rotor present reduced aerodynamic efficiency. In the present study, two-dimensional (2D) computational fluid dynamics (CFD) simulations of vertical axis H-Darrieus wind turbine (VAWT) rotor, characterized by a NACA0018 aerodynamic profile has been conducted using Ansys Fluent software. The air flow around three-bladed wind turbine has been simulated in order to improve the aerodynamic performance of this rotor. The numerical approach adopted consists on the resolution of unsteady Reynolds-averaged Navier-Stokes equations (URANS) applying k-ω shear stress transport (SST) and k-ε Realizable turbulence models. The obtained results indicate a good agreement with the available experimental data in terms of the variation in the power coefficient (Cp) as a function of the tip speed ratio (TSR). Furthermore, the results affirm the superiority of the k-ω SST turbulence model over the k-ε Realizable model regarding Cp which takes maximum values of 36%, 38% and 35% for velocity U∞ equal to 10, 15 and 20 respectively, in the case of k-ω SST. This result is valid also for the velocity magnitude contours. A parametric study has been established based on the variation of the torque coefficient with the azimuth angle, for different values of velocity

Offshore wind power resources in the Red Sea waters of Saudi Arabia are yet to be explored. The objective of the present study is to assess offshore wind power resources at 49 locations in the Saudi waters of the Red Sea and prioritize the sites based on wind characteristics. To accomplish the set objective, long-term hourly mean wind speed (WS) and wind direction (WD) at 100 m above mean sea level, temperature, and pressure data near the surface were used at sites L1-L49 over 43 years from 1979 to 2021. The long-term mean WS and wind power density (WPD) varied between 3.83 m/s and 66.6 W/m², and 6.39 m/s and 280.9 W/m² corresponding to sites L44 and L8. However, higher magnitudes of WS >5 m/s were observed at 34 sites and WPD of > 200 W/m² at 21 sites. In general, WS, WPD, annual energy yield, mean windy site identifier, plant capacity factor, etc. were found to be increasing from east to west and from south to north. Similarly, the mean wind variability index and cost of energy were observed to be decreasing as one moves from east to west and south to north in the Saudi waters of the Red Sea.

Solar dryers are traditional devices used for drying various products. Different indirect solar dryer (ISD) geometries were theoretically examined using computational fluid dynamics (CFD). This paper presents a numerical investigation of two indirect solar dryers using CFD simulation, comparing the velocity and thermal performance of dryers with smooth and corrugated absorber plates. The temperature values obtained by numerical simulations were compared to the experimental measurements and found a maximum variation difference of 1.26%. The maximum velocity in the solar air collector (SAC) and the value of average temperature at the SAC outlet were found to be 0.58 m/s and 336 K for the smooth absorber ISD, and 0.77 m/s and 350 K for the corrugated absorber ISD. It was observed that the corrugated absorber plate exhibited superior thermal performance and a higher maximum velocity compared to the smooth absorber plate. Within the cabinet, a uniform temperature profile was observed, particularly for the corrugated case. V-shaped absorber plates offer higher heat transfer rates, increased turbulence, and greater surface area for heat transfer, making them more efficient for drying processes compared to smooth absorber plates. Therefore, corrugated absorber plates in solar air collectors are a more efficient option than using smooth absorber plates.