Renewable energy systems performance was studied by many researchers during the last decade in order to help in reducing greenhouse gas emissions as well as having energy at lower cost than that of conventional energy sources. Among the renewable energy sources is wind energy which is considered to be the most friendly renewable energy source. However, the design of wind turbine is not an easy task for engineers due to its large blades which are exposed to a wind velocity at high elevation causing vibration within the whole system. Rotor is another important component which needs to be controlled from speed point of view in the presence of gearbox which requires lubrication. Moreover, the exposure of wind turbine to very severe weather (ambient conditions) in cold countries causes turbine blades icing. In the paper titled “Static Mechanical Properties and Modal Analysis of a Kind of Lift-Drag Combined-Type Vertical Axis Wind Turbine,” F. Feng et al. developed a prototype of lift-drag-vertical axis wind turbine based on finite element methods to obtain structural design and vibration profile. The aerodynamics of S series airfoils on straight-bladed vertical axis wind turbine was investigated numerically and experimentally by F. Feng et al. in the paper titled “Research on Aerodynamic Characteristics of Straight-Bladed Vertical Axis Wind Turbine with S Series Airfoils.” These authors obtained that S series airfoil for SB-VAWT is worth researching deeply.

The control method for the speed of wind turbine under the fault of gearbox efficiency due to lack of lubrication was presented by Y. A. El Maati et al. in the paper titled “Fault Tolerant Control of Internal Faults in Wind Turbine: Case Study of Gearbox Efficiency Decrease.” The authors evaluated the effectiveness of this method and its convergence with the rotor parameter.

The dynamic oscillation load acting over a glazed-iced airfoil was simulated numerically by N. Tabatabaei et al. in the paper titled “Time-Dependent Effects of Glaze Ice on the Aerodynamic Characteristics of an Airfoil.” The authors found that the higher frequency has the same characteristics of shedding mode while the lower frequency has the flapping mode characteristics.

The integral influence of uniform ambient flow field on a single axial fan over a wide operating range was tested inside wind tunnel by T. Heinemann and S. Becker in the paper titled “Axial Fan Performance under the Influence of a Uniform Ambient Flow Field.” The authors found that the straight-bladed fan reacted less sensitively than the forward skewed fan.

The Pelton turbine for micro hydro potential site was studied by CFD in terms of design, modeling, and performance by T. Nigussie et al. in the paper titled “Design, Modeling, and CFD Analysis of a Micro Hydro Pelton Turbine Runner: For the Case of Selected Site in Ethiopia.” They showed that the model is highly dependent on the size of Pelton turbine.

The authors contributing to this special issue highlight the recent challenges in rotating machinery in renewable energy as in wind and hydro energy systems.

Finally, this special issue will provide guidance on how to design and control the performance of turbomachinery systems such as VAWT, axial fan, and Pelton turbine.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

M. El Haj Assad
Tareq Salameh
Ali Mostafaeipour
Ahmad Sedaghat
Rafat Al-Waked