https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Fri, 05 Jun 2026 22:53:06 GMT 2026-06-05T22:53:06Z http://hdl.handle.net/10985/22480 Experimental investigation of the effect of the Reynolds number on the performance of a micro-scale and low tip-speed ratio wind turbine BOURHIS, Martin; RAVELET, Florent; PEREIRA, Michaël Micro-scale wind turbines are of great interest to supply rechargeable batteries of autonomous sensors in the field of the Internet Of Things (IOT). However, they face the issue of lower dimensionless performance than large-scale wind turbines. Due to their small size and low operating wind speed, these runners operate mainly in low Reynolds number flow conditions at which the aerodynamic properties of the blades are not well-known. Even though promising results are reported on the Reynolds number effects on isolated and non rotating blades, their applicability to design efficient small rotating energy harvesters is questionable. This paper reports on the influence of the Reynolds number on the performance of high-solidity and low tip-speed ratio micro-scale wind turbines. Wind turbine’s power and torque coefficient vs. tip-speed ratio curves are measured in wind tunnel for a wide range of Reynolds number by changing either the turbine’s diameter or the free-stream wind velocity. This quantitative analysis will contribute to design more efficient wind energy harvesters. Sat, 01 Jan 2022 00:00:00 GMT http://hdl.handle.net/10985/22480 2022-01-01T00:00:00Z BOURHIS, Martin RAVELET, Florent PEREIRA, Michaël Micro-scale wind turbines are of great interest to supply rechargeable batteries of autonomous sensors in the field of the Internet Of Things (IOT). However, they face the issue of lower dimensionless performance than large-scale wind turbines. Due to their small size and low operating wind speed, these runners operate mainly in low Reynolds number flow conditions at which the aerodynamic properties of the blades are not well-known. Even though promising results are reported on the Reynolds number effects on isolated and non rotating blades, their applicability to design efficient small rotating energy harvesters is questionable. This paper reports on the influence of the Reynolds number on the performance of high-solidity and low tip-speed ratio micro-scale wind turbines. Wind turbine’s power and torque coefficient vs. tip-speed ratio curves are measured in wind tunnel for a wide range of Reynolds number by changing either the turbine’s diameter or the free-stream wind velocity. This quantitative analysis will contribute to design more efficient wind energy harvesters. http://hdl.handle.net/10985/21360 Innovative design method and experimental investigation of a small-scale and very low tip-speed ratio wind turbine BOURHIS, Martin; PEREIRA, Michaël; DOBREV, Ivan; RAVELET, Florent Small horizontal axis wind turbines operating at low wind speeds face the issue of low performance compared to large wind turbines. A high amount of torque is required to start producing power at low wind speed to overtake friction of mechanical parts. A low design tip-speed ratio (λ) is suitable for low power applications. The relevance of the classical blade-element/ momentum theory, traditionally used for the design of large wind turbines operating at high tip-speed ratio, is controversial at low tip-speed ratio. This paper presents a new design methodology for a 300 mm horizontal axis wind turbine operating at very low tip-speed ratio. Chord and blade angle distributions were computed by applying the Euler’s turbomachinery theorem. The new wind turbine has multiple fan-type blades and a high solidity. The rotor was tested in wind tunnel. The power and torque coefficients have been measured, and the velocities in the wake have been explored by stereoscopic particle image velocimetry. The results are compared to a conventional 3-bladed horizontal axis wind turbine operating at higher tip-speed ratio λ = 3. The new wind turbine achieves a maximum power coefficient of 0.31 for λ = 1. The conventional wind turbine achieves similar performance. At low tip-speed ratio, the torque coefficient (Cτ) is higher for the new wind turbine than for the conventional one and decreases linearly with the tip-speed ratio. The high magnitude of torque at low tip-speed ratio allows it to have lower instantaneous cut-in wind speed (2.4 m.s−1) than the conventional wind turbine (7.9 m.s−1). The order of magnitude of the axial and tangential velocities in the near wake are closed to the design requirements. The current method could still be improved in order to better predict the profiles. The analysis of the wake shows that the new wind turbine induces a highly stable and rotating wake, with lower wake expansion and deceleration than the conventional one. This could be useful to drive a contra-rotating rotor. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/21360 2021-01-01T00:00:00Z BOURHIS, Martin PEREIRA, Michaël DOBREV, Ivan RAVELET, Florent Small horizontal axis wind turbines operating at low wind speeds face the issue of low performance compared to large wind turbines. A high amount of torque is required to start producing power at low wind speed to overtake friction of mechanical parts. A low design tip-speed ratio (λ) is suitable for low power applications. The relevance of the classical blade-element/ momentum theory, traditionally used for the design of large wind turbines operating at high tip-speed ratio, is controversial at low tip-speed ratio. This paper presents a new design methodology for a 300 mm horizontal axis wind turbine operating at very low tip-speed ratio. Chord and blade angle distributions were computed by applying the Euler’s turbomachinery theorem. The new wind turbine has multiple fan-type blades and a high solidity. The rotor was tested in wind tunnel. The power and torque coefficients have been measured, and the velocities in the wake have been explored by stereoscopic particle image velocimetry. The results are compared to a conventional 3-bladed horizontal axis wind turbine operating at higher tip-speed ratio λ = 3. The new wind turbine achieves a maximum power coefficient of 0.31 for λ = 1. The conventional wind turbine achieves similar performance. At low tip-speed ratio, the torque coefficient (Cτ) is higher for the new wind turbine than for the conventional one and decreases linearly with the tip-speed ratio. The high magnitude of torque at low tip-speed ratio allows it to have lower instantaneous cut-in wind speed (2.4 m.s−1) than the conventional wind turbine (7.9 m.s−1). The order of magnitude of the axial and tangential velocities in the near wake are closed to the design requirements. The current method could still be improved in order to better predict the profiles. The analysis of the wake shows that the new wind turbine induces a highly stable and rotating wake, with lower wake expansion and deceleration than the conventional one. This could be useful to drive a contra-rotating rotor. http://hdl.handle.net/10985/21379 Numerical Assesment of a Small-Scale and Very Low Tip Speed Ratio Wind Turbine BOURHIS, Martin; DOBREV, Ivan; RAVELET, Florent; PEREIRA, Michaël The aim of this paper is to study by CFD the performance and to characterize the velocity fields in the wake of an horizontal axis wind turbine. The design of this wind turbine is far from classical as it has been designed to work at very low angular velocity to promote torque. The 8 blades are not isolated but form a high solidity blade cascade. The numerical simulation compares well to experimental data regarding the power coefficients. The analysis of the wake does show that high tangential velocities, close to the order of magnitude that was used as a design requirement, are generated and form a stable rotating wake. This rotating kinetic energy in the wake may be used to rotate a second rotor in a counter-rotating arrangment. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/21379 2021-01-01T00:00:00Z BOURHIS, Martin DOBREV, Ivan RAVELET, Florent PEREIRA, Michaël The aim of this paper is to study by CFD the performance and to characterize the velocity fields in the wake of an horizontal axis wind turbine. The design of this wind turbine is far from classical as it has been designed to work at very low angular velocity to promote torque. The 8 blades are not isolated but form a high solidity blade cascade. The numerical simulation compares well to experimental data regarding the power coefficients. The analysis of the wake does show that high tangential velocities, close to the order of magnitude that was used as a design requirement, are generated and form a stable rotating wake. This rotating kinetic energy in the wake may be used to rotate a second rotor in a counter-rotating arrangment. http://hdl.handle.net/10985/23923 Performance and flow characteristics of the optimum rotors of Betz, Joukowsky, and Glauert at low tip-speed ratio BOURHIS, Martin; PEREIRA, Michaël; RAVELET, Florent The advent of the Internet of Things technology has led to a renewed interest in the use of low tip-speed ratio micro-scale wind turbines to supply power to battery-less microsystems. At low tip-speed ratio ( λ), the blade geometry varies significantly depending on the optimal flow conditions used in the classical design method and the blade element/momentum theory (BEMT), and very few papers have examined this controversy. This experimental study aims to investigate the airflow and power characteristics of three 200-cm wind turbines designed according to the BEMT with three different optimum flow conditions at λ = 1: the Betz model, the Glauert model, and the Joukowsky model. Glauert optimum rotor achieves higher maximum power coefficient ([Formula: see text]) than the optimum rotors of Betz ([Formula: see text]) and Joukowsky ([Formula: see text]). The two latter turbines have lower cut-in wind speed and their torque coefficient decreases linearly with the tip-speed ratio. Betz optimum rotor has a highly stable and persistent wake, whereas large recirculation bubbles and vortex breakdown are observed downstream the runners of Glauert and Joukowsky. The airflow velocity fields and induction factor distributions computed from stereoscopic particle image velocimetry acquisitions show significant differences between each rotor and also between the theoretical developments and the experimental results, especially for the Joukowsky rotor. In addition, even though the optimum flow conditions of Glauert or Betz appear to be the most appropriate models, a method based on flow deflection rather than on airfoil polar plots may be more pertinent for the design of low tip-speed ratio micro-scale wind turbines. déjà sur hal, merci de ne pas interférer. merci. Merci de plus de me désassocier définitivement de "dynfluid", je n'ai plus rien à voir avec ces gens. Sat, 01 Oct 2022 00:00:00 GMT http://hdl.handle.net/10985/23923 2022-10-01T00:00:00Z BOURHIS, Martin PEREIRA, Michaël RAVELET, Florent The advent of the Internet of Things technology has led to a renewed interest in the use of low tip-speed ratio micro-scale wind turbines to supply power to battery-less microsystems. At low tip-speed ratio ( λ), the blade geometry varies significantly depending on the optimal flow conditions used in the classical design method and the blade element/momentum theory (BEMT), and very few papers have examined this controversy. This experimental study aims to investigate the airflow and power characteristics of three 200-cm wind turbines designed according to the BEMT with three different optimum flow conditions at λ = 1: the Betz model, the Glauert model, and the Joukowsky model. Glauert optimum rotor achieves higher maximum power coefficient ([Formula: see text]) than the optimum rotors of Betz ([Formula: see text]) and Joukowsky ([Formula: see text]). The two latter turbines have lower cut-in wind speed and their torque coefficient decreases linearly with the tip-speed ratio. Betz optimum rotor has a highly stable and persistent wake, whereas large recirculation bubbles and vortex breakdown are observed downstream the runners of Glauert and Joukowsky. The airflow velocity fields and induction factor distributions computed from stereoscopic particle image velocimetry acquisitions show significant differences between each rotor and also between the theoretical developments and the experimental results, especially for the Joukowsky rotor. In addition, even though the optimum flow conditions of Glauert or Betz appear to be the most appropriate models, a method based on flow deflection rather than on airfoil polar plots may be more pertinent for the design of low tip-speed ratio micro-scale wind turbines. http://hdl.handle.net/10985/23922 Experimental investigation of the effects of the Reynolds number on the performance and near wake of a wind turbine BOURHIS, Martin; PEREIRA, Michaël; RAVELET, Florent Wind tunnel experiments provide worthwhile insights for designing efficient micro wind energy harvesters and large-scale wind turbines. As wind tunnel tests with large-scale wind turbines are expensive and not always feasible, most experiments are conducted with geometrically scaled rotors. Furthermore, micro-scale runners used for wind energy harvesting face the issue of lower efficiency than large turbines. A better understanding of Reynolds number effects induced by the downsizing of a turbine would help to design more efficient wind energy harvesters and more faithfully scaled experiments. This paper reports on Reynolds number effects on the performance and wake of micro-scale wind turbines. Wind turbines’ power and torque coefficients are measured in a wind tunnel for a wide range of Reynolds numbers. The wake axial velocity fields and the vortex core locations are collected for three Reynolds numbers using phase-averaged and phase-locked stereoscopic particle image velocimetry techniques. The results emphasize that an increase in the Reynolds number leads to larger power coefficients, torque coefficients, and optimum tip-speed ratios. Higher Reynolds numbers induce wider wake expansion and a larger axial velocity defect. This quantitative analysis will contribute to a clearer understanding of the scaling effects and help to design more efficient wind energy harvesters. déjà dans hal Thu, 01 Jun 2023 00:00:00 GMT http://hdl.handle.net/10985/23922 2023-06-01T00:00:00Z BOURHIS, Martin PEREIRA, Michaël RAVELET, Florent Wind tunnel experiments provide worthwhile insights for designing efficient micro wind energy harvesters and large-scale wind turbines. As wind tunnel tests with large-scale wind turbines are expensive and not always feasible, most experiments are conducted with geometrically scaled rotors. Furthermore, micro-scale runners used for wind energy harvesting face the issue of lower efficiency than large turbines. A better understanding of Reynolds number effects induced by the downsizing of a turbine would help to design more efficient wind energy harvesters and more faithfully scaled experiments. This paper reports on Reynolds number effects on the performance and wake of micro-scale wind turbines. Wind turbines’ power and torque coefficients are measured in a wind tunnel for a wide range of Reynolds numbers. The wake axial velocity fields and the vortex core locations are collected for three Reynolds numbers using phase-averaged and phase-locked stereoscopic particle image velocimetry techniques. The results emphasize that an increase in the Reynolds number leads to larger power coefficients, torque coefficients, and optimum tip-speed ratios. Higher Reynolds numbers induce wider wake expansion and a larger axial velocity defect. This quantitative analysis will contribute to a clearer understanding of the scaling effects and help to design more efficient wind energy harvesters.