Mostafa Fatehi

Bio: Mostafa Fatehi is an academic researcher from Isfahan University of Technology. The author has contributed to research in topics: Wind tunnel & Airfoil. The author has an hindex of 2, co-authored 2 publications receiving 18 citations.

Aerodynamic performance improvement of wind turbine blade by cavity shape optimization

Abstract: Many conventional airfoils, despite a good performance at their design points, get out of optimal conditions outside the design points. One passive way to enhance the airfoil performance is to use a cavity with an optimized shape. In this study, Riso_B1_18 airfoil, having a remarkable aerodynamic performance for wind turbine blades, is selected as a substrate for deploying an optimized cavity on the airfoil. For shape optimization of a cavity, its shape and downstream suction surface are parametrized to reach an optimum lift-to-drag ratio as the target function by using the genetic algorithm. The results of transient numerical solution indicate that the optimized cavity is well capable of draping vortex to control the stall margin, prevent flow fluctuations and significantly increase the lift-to-drag ratio at off-design conditions. To validate the performance improvement obtained from this numerical optimization, a force measurement setup is accomplished in a wind tunnel with 30 × 30 cm2 test section to measure the lift and drag forces of the Riso airfoil with and without optimized cavity. The experimental results shows that the lift-to-drag ratio increases 31% at AOA = 14° and 57% at AOA = 20° due to using the optimized cavity.

Evaluation of aerodynamic performance enhancement of Risø_B1 airfoil with an optimized cavity by PIV measurement

Abstract: Airfoils are mostly inefficient in their off-design conditions. In order to improve the aerodynamic performance of airfoils in these conditions, using an optimized cavity on airfoils as a passive method can be useful. In this study, a cavity on a Riso_B1_18 airfoil, which is used as a wind turbine airfoil, was optimized at an off-design angle of attack by incorporating a genetic algorithm into a RANS flow solver. For the cavity optimization, the geometry and downstream suction surface were defined by 16 parameters, and the lift-to-drag ratio was considered as the cost function at 14° angle of attack. The numerical solution showed that the optimized cavity traps a vortex, which postpones the stall. Due to the uncertainty of CFD especially at off-design conditions, it was necessary to evaluate the performance of the optimized cavity in a wide range of angles of attack. This study used the particle image velocimetry (PIV) measurement method to evaluate the improved flow structures over the optimized cavity. Two models of airfoils with and without the cavity were made of aluminum and installed inside the test section of an open-jet wind tunnel with an air speed of 30 m/s and a cross section of 30 × 30 cm2. The air flow on the suction side of the airfoils was measured at 7°–15° angles of attack by PIV. A comparison between the measured flow fields over the two airfoils showed that the optimized cavity postpones the stall angle by 3°. Furthermore, the cavity increases the momentum behind the airfoil at the angles of attack greater than 9°. After this angle, a further increase in the angle of attack increases the difference between the momentums behind the airfoils with and without cavity. The Riso_B1_18 airfoil with the optimized cavity can be used as a wind turbine airfoil at high angles of attack to increase the stall angle and decrease the instability and fluctuation at off-design conditions.

Damage detection techniques for wind turbine blades: A review

Abstract: Blades play a vital role in wind turbine system performances. However, they are susceptible to damage arising from complex and irregular loading or even cause catastrophic collapse, and they are expensive to maintain. Defects or damages on wind turbine blades (WTBs) not only reduce the lifespan and power generation efficiency of the wind turbine, but also increase monitoring errors, safety risks and maintenance costs. Therefore, damage detection for WTBs is of great importance for failure avoidance, maintenance planning, and operation sustainability of wind turbines. This paper provides a comprehensive review of state-of-the-art damage detection techniques for WTBs, including most of those updated methods based on strain measurement, acoustic emission, ultrasound, vibration, thermography and machine vision. Firstly, typical damages of WTBs are comprehensively introduced. Secondly, detection principles, development methods, pros and cons of the aforementioned techniques for blade inspection, and their fault indicators are reviewed. Finally, potential research directions of WTB damage detection techniques are addressed via a comparative analysis, and conclusions are drawn. It is expected that this review will provide guidelines for practical WTB inspections, as well as research prospects for damage detection techniques.

Blade design and optimization of a horizontal axis tidal turbine

Abstract: Tidal turbine is a device which converts the kinetic energy of water into electric energy. The blade element momentum theory (BEM) is used to design the blade in this paper. Although tidal power resources are abundant, the actual operation of hydraulic turbines is not very good due to the limitations of turbine conversion efficiency and production cost. Therefore, this paper establishes a neural network model for variables and objective functions, and then applies multi-objective optimization algorithm to genetic optimization of the power coefficient, the main index of hydraulic performance of tidal turbines. The optimized results are verified by model test and sea trial. The results show that after optimizing the blade chord length distribution and pitch Angle distribution, the power coefficient of the turbine increases by 2%, and the optimal tip speed ratio range is also expanded, which is more conducive to the actual tidal turbine power generation, and has certain engineering significance.

Wind Turbine Blade Optimal Design Considering Multi-Parameters and Response Surface Method

Abstract: Within the framework of blade aerodynamic design, the maximum aerodynamic efficiency, power production, and minimum thrust force are the targets to obtain. This paper describes an improved optimization framework for blade aerodynamic design under realistic conditions, while considering multiple design parameters. The relationship between the objective function and the design parameters, such as the chord length, maximum chord, and twist angle, were obtained by using the second-order response surface methodology (RSM). Moreover, the identified parameters were organized to optimize the aerodynamic design of the blades. Furthermore, the initial and optimized blade geometries were compared and showed that the performance of the optimized blade improved significantly. In fact, the efficiency was increased by approximately 10%, although its thrust was not varied. In addition, to demonstrate the improvement in the resulting optimized blades, the annual energy production (AEP) was estimated when installed in a specific regional location. The result showed a significant improvement when compared to the baseline blades. This result will be extended to a new perspective approach for a more robust optimal design of a wind turbine blade.

Development and validation of a hybrid aerodynamic design method for curved diffusers using genetic algorithm and ball-spine inverse design method

Abstract: The inverse design is one of the aerodynamic design methods, in which the pressure distribution along the wall is known, and the duct geometry is unknown. To obtain the best geometry by the inverse design, the target pressure distribution along the walls should be optimum. This paper presents an aerodynamic design of diffusers by optimizing the wall pressure distribution and applying it to the ball-spine inverse design method. A code was first developed to solve the boundary layer equations using the integration method, and then incorporated into a genetic algorithm to optimize the wall pressure distribution to achieve the maximum pressure recovery without separation occurrence. Depending on the type of the duct, a series of constraints was applied to the wall pressure distributions during the optimization process. The optimized pressure distribution was considered as the target pressure distribution for the inverse design problem. The duct geometry changes during the inverse design process to reach one satisfying the target pressure distribution. An offline connection was observed between the ball-spine inverse design method and the genetic algorithm. The boundary layer code was the medium for this offline connection. The optimized wall pressure distribution and inverse design process were evaluated for a straight diffuser and three S-shaped diffusers with different height to length ratios. The results revealed the robustness of the offline link of the inverse design and the genetic algorithm for the optimal aerodynamic design of ducts.

Evaluation of aerodynamic performance enhancement of Risø_B1 airfoil with an optimized cavity by PIV measurement

Abstract: Airfoils are mostly inefficient in their off-design conditions. In order to improve the aerodynamic performance of airfoils in these conditions, using an optimized cavity on airfoils as a passive method can be useful. In this study, a cavity on a Riso_B1_18 airfoil, which is used as a wind turbine airfoil, was optimized at an off-design angle of attack by incorporating a genetic algorithm into a RANS flow solver. For the cavity optimization, the geometry and downstream suction surface were defined by 16 parameters, and the lift-to-drag ratio was considered as the cost function at 14° angle of attack. The numerical solution showed that the optimized cavity traps a vortex, which postpones the stall. Due to the uncertainty of CFD especially at off-design conditions, it was necessary to evaluate the performance of the optimized cavity in a wide range of angles of attack. This study used the particle image velocimetry (PIV) measurement method to evaluate the improved flow structures over the optimized cavity. Two models of airfoils with and without the cavity were made of aluminum and installed inside the test section of an open-jet wind tunnel with an air speed of 30 m/s and a cross section of 30 × 30 cm2. The air flow on the suction side of the airfoils was measured at 7°–15° angles of attack by PIV. A comparison between the measured flow fields over the two airfoils showed that the optimized cavity postpones the stall angle by 3°. Furthermore, the cavity increases the momentum behind the airfoil at the angles of attack greater than 9°. After this angle, a further increase in the angle of attack increases the difference between the momentums behind the airfoils with and without cavity. The Riso_B1_18 airfoil with the optimized cavity can be used as a wind turbine airfoil at high angles of attack to increase the stall angle and decrease the instability and fluctuation at off-design conditions.