Turbulence Models for Turbomachinery

Dear Colleagues,

Turbulent flow, characterized by chaotic changes in velocity and pressure, is still an unsolved problem. It occupies the attention of numerous researchers in theoretical and applied physics worldwide. The Kolmogorov turbulence theory, as a set of hypotheses, is one of a few great steps in the direction of revealing turbulence. However, a general theory of turbulence still does not exist.

Turbomachinery are the most used machines in all areas. They exist in almost every engineering system. Carrying out research on turbulence in these rotating systems is quite a challenging task. Numerous experimental techniques are applied in the complex research of turbulence in turbomachinery, from classical ones to the novel ones, such as the following:

• Fast-response multihole probes;
• Three-component velocimetry systems;
• High-speed stereo particle image velocimetry;
• Holographic particle image velocimetry.

On the basis of the acquired experimental data, numerous turbulence models for flows in turbomachinery can be developed and tested, with the roles of the RANSs (Reynolds-averaged Navier–Stokes equations), LESs (large eddy simulations), hybrid RANS-LES modeling, DNSs (direct numerical simulations), and data-driven turbulence modeling in turbomachinery industry having great importance and potential.

Thus, this Special Issue will present a discussion on various turbomachinery geometries (radial, diagonal, axial) inbuilt in pipes, diffusers, jets, etc.

Prof. Dr. Djordje Cantrak
Dr. Jelena Svorcan
Guest Editors

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• turbulence
• turbomachinery
• RANS
• LES
• hybrid RANS-LES
• DNS
• AI

Title: Insights from the Last Decade in CFD Design and Performance Enhancement of Darrieus Wind Turbines
Authors: Saïf ed-Dîn Fertahi, Shafiqur Rehman, Ernesto Benini, Abderrahim Samaouali, Asmae Arbaoui, Imad Kadiri, Rachid Agounoun
Affiliation: Thermodynamics and Energy” Research team, Energy Research Center, Physics Department, Faculty of Science, Mohammed V University in Rabat, 4 Avenue Ibn Batouta, B.P. 1014, Rabat, Morocco
Abstract: This review has provided a comprehensive analysis of the advancements in the design and performance of Darrieus wind turbines over the last decade, focusing specifically on the contributions of Computational Fluid Dynamics (CFD) to this field. The primary objective of this review was to offer insights from studies conducted between 2014 and 2024, emphasizing the enhancement of Darrieus wind turbine performance through various technological innovations. A wide range of recent investigations has been discussed, all of which have employed CFD modeling techniques, including both 2D and 3D simulations. The studies predominantly utilized the \textit{"Ansys-Fluent"} and \textit{"STAR CCM+"} solvers to evaluate the aerodynamic performance of Darrieus rotors. These technological advancements have focused on modifying the basic geometry of the Darrieus rotor, including alterations to blade profiles, chord length, rotor diameter, the 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 have been explored to enhance rotor efficiency. The review has highlighted the significant impact of these geometric modifications on key performance metrics, particularly the moment and power coefficients. A dedicated section presented CFD-derived visualizations, including vorticity fields, turbulence contours illustrated through Q-criterion, velocity vectors, and dynamic pressure contours. These visualizations provided a detailed understanding of the complex flow structures around the modified Darrieus rotors. Moreover, the review included an analysis of the dynamic performance curves of Darrieus rotors, which have shown improvements due to the modifications of the baseline design. This analysis covered the evolution of pressure coefficients, moment coefficients, and the increased power output of the Darrieus rotor. In summary, this review has consolidated the state-of-the-art in Darrieus wind turbine research, offering valuable insights into the design and optimization strategies that have been implemented to enhance their aerodynamic efficiency and energy harvesting capabilities, both in terrestrial and offshore environments.