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http://hdl.handle.net/10985/23921
Numerical Investigation of Parietal Pressure Distribution on NACA0012 Wing Controlled by Micro-cylindrical Rod Arranged in Tandem
LARABI, Abderrahim; PEREIRA, Michael; RAVELET, Florent; AZZAM, Tarik; OUALLI, Hamid; MENFOUKH, Laiche; BAKIR, Farid
The aim of this study is to investigate the influence of disturbed freestream flow by a small cylinder on the laminar separated boundary layer over NACA0012 wing operating at a Reynolds number of Rec = 4.45 × 105. A detailed parametric investigations for the rod are performed using numerical simulations coupled with transition sensitive closure model (γ − ̃Reθ,t) seeking for the optimal passive control parameters. Firstly, the use of such steady RANS model has been successfully accurate in capturing the separation induced transition on the baseline wing suction surface. Secondly, the rod location was scaled according to the formation length of vortices behind the micro-cylinder for which the aerodynamic loads are very sensitive. The effects of three rod diameter ratios (d/c = 0.67%, 1.33% and 2%) on the laminar separation bubble and aerodynamic performances were examined. It was observed that the qualitative analysis of the flow structures revealed the mechanisms of the control device for the aerofoil performance improvements in which the rod wake exerted considerable effects on LSB size, pressure coefficient and flow streamlines. Particularly, it contributes to eliminate the boundary layer separation with pronounced decrease of 75% by energizing the shear layer over a significant extent, resulting in a mean drag dropping of 73% at 12◦ incidence, and a lift enhancement of about 23% at 15◦.
déjà sur hal, merci
Sat, 01 Jan 2022 00:00:00 GMThttp://hdl.handle.net/10985/239212022-01-01T00:00:00ZLARABI, AbderrahimPEREIRA, MichaelRAVELET, FlorentAZZAM, TarikOUALLI, HamidMENFOUKH, LaicheBAKIR, FaridThe aim of this study is to investigate the influence of disturbed freestream flow by a small cylinder on the laminar separated boundary layer over NACA0012 wing operating at a Reynolds number of Rec = 4.45 × 105. A detailed parametric investigations for the rod are performed using numerical simulations coupled with transition sensitive closure model (γ − ̃Reθ,t) seeking for the optimal passive control parameters. Firstly, the use of such steady RANS model has been successfully accurate in capturing the separation induced transition on the baseline wing suction surface. Secondly, the rod location was scaled according to the formation length of vortices behind the micro-cylinder for which the aerodynamic loads are very sensitive. The effects of three rod diameter ratios (d/c = 0.67%, 1.33% and 2%) on the laminar separation bubble and aerodynamic performances were examined. It was observed that the qualitative analysis of the flow structures revealed the mechanisms of the control device for the aerofoil performance improvements in which the rod wake exerted considerable effects on LSB size, pressure coefficient and flow streamlines. Particularly, it contributes to eliminate the boundary layer separation with pronounced decrease of 75% by energizing the shear layer over a significant extent, resulting in a mean drag dropping of 73% at 12◦ incidence, and a lift enhancement of about 23% at 15◦.Performance and flow characteristics of the optimum rotors of Betz, Joukowsky, and Glauert at low tip-speed ratio
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, Michael; 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 GMThttp://hdl.handle.net/10985/239232022-10-01T00:00:00ZBOURHIS, MartinPEREIRA, MichaelRAVELET, FlorentThe 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.Experimental investigation of the effects of the Reynolds number on the performance and near wake of a wind turbine
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, Michael; 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 GMThttp://hdl.handle.net/10985/239222023-06-01T00:00:00ZBOURHIS, MartinPEREIRA, MichaelRAVELET, FlorentWind 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.Effects of strain rate and temperature on the mechanical behavior of high-density polyethylene
http://hdl.handle.net/10985/18461
Effects of strain rate and temperature on the mechanical behavior of high-density polyethylene
LAMRI, Abderrahmane; SHIRINBAYAN, Mohammadali; PEREIRA, Michael; TRUFFAULT, Laurianne; FITOUSSI, Joseph; BAKIR, Farid; TCHARKHTCHI, Abbas
The objective of this work is to initiate the discussion about multiphysics relationships between the molten and solid states of high-density polyethylene (HDPE). The extrusion and the injection processes are employed to prepare samples, and the experimental procedures, using differential scanning calorimetry, dynamic thermomechanical analysis (DMTA), thermal gravimetric analysis, and rheological measurements, are defined to choose the optimal variables. After different characterizations, the extrusion and injection temperatures of 220 and 230 °C have been chosen. To investigate the viscoelastic behavior of HDPE, the DMTA is used. To perform the high strain rate tensile tests, tensile machine was equipped with a specific furnace. Two temperatures, −20 and 20 °C, with strain rates varying from 0.001 to 100 seconds−1 were used to compare the flow characteristics. Results showed that by increasing the strain rate the molecular mobility of the HDPE chains is decreased. In addition, to the tests at −20 °C, the increase of Young's modulus can be properly observed, under high strain rates.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10985/184612020-01-01T00:00:00ZLAMRI, AbderrahmaneSHIRINBAYAN, MohammadaliPEREIRA, MichaelTRUFFAULT, LaurianneFITOUSSI, JosephBAKIR, FaridTCHARKHTCHI, AbbasThe objective of this work is to initiate the discussion about multiphysics relationships between the molten and solid states of high-density polyethylene (HDPE). The extrusion and the injection processes are employed to prepare samples, and the experimental procedures, using differential scanning calorimetry, dynamic thermomechanical analysis (DMTA), thermal gravimetric analysis, and rheological measurements, are defined to choose the optimal variables. After different characterizations, the extrusion and injection temperatures of 220 and 230 °C have been chosen. To investigate the viscoelastic behavior of HDPE, the DMTA is used. To perform the high strain rate tensile tests, tensile machine was equipped with a specific furnace. Two temperatures, −20 and 20 °C, with strain rates varying from 0.001 to 100 seconds−1 were used to compare the flow characteristics. Results showed that by increasing the strain rate the molecular mobility of the HDPE chains is decreased. In addition, to the tests at −20 °C, the increase of Young's modulus can be properly observed, under high strain rates.Innovative design method and experimental investigation of a small-scale and very low tip-speed ratio wind turbine
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, Michael; 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 GMThttp://hdl.handle.net/10985/213602021-01-01T00:00:00ZBOURHIS, MartinPEREIRA, MichaelDOBREV, IvanRAVELET, FlorentSmall 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.Numerical Study on the Effect of an Off-Surface Micro-Rod Vortex Generator Placed Upstream NACA0012 Aerofoil
http://hdl.handle.net/10985/21380
Numerical Study on the Effect of an Off-Surface Micro-Rod Vortex Generator Placed Upstream NACA0012 Aerofoil
LARABI, Abderrahim; PEREIRA, Michael; AZZAM, Tarik; OUALLI, Hamid; MENFOUKH, Laiche; BAKIR, Farid; RAVELET, Florent
In this paper, 3D numerical simulations have been carried out to enhance the understanding of a flow over a passive control device composed of micro cylinder with, d/c = 1.34% placed in the vicinity of NACA0012 aerofoil wing, by means of γ–Reθt transition sensitive turbulence model meant to predict the separation induced by transition achieved for aerofoils operating at moderate Reynolds number (Re = 4.45×105). Results show that the separation of the boundary layer has been eliminated by the passive static vortex generator at stall regime due to the injection of free-stream momentum to the boundary layer. The early transition to turbulent state overcomes the local flow deceleration of an adverse pressure gradient and remains sticked to the wall the boundary layer. Furthermore, the wing aerodynamic performance are improved as drag is reduced and lift is enhanced which is straight forward linked to the lift to drag ratio gain that varies from 22.68% to 134.17% at post stall angles of attack.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/213802021-01-01T00:00:00ZLARABI, AbderrahimPEREIRA, MichaelAZZAM, TarikOUALLI, HamidMENFOUKH, LaicheBAKIR, FaridRAVELET, FlorentIn this paper, 3D numerical simulations have been carried out to enhance the understanding of a flow over a passive control device composed of micro cylinder with, d/c = 1.34% placed in the vicinity of NACA0012 aerofoil wing, by means of γ–Reθt transition sensitive turbulence model meant to predict the separation induced by transition achieved for aerofoils operating at moderate Reynolds number (Re = 4.45×105). Results show that the separation of the boundary layer has been eliminated by the passive static vortex generator at stall regime due to the injection of free-stream momentum to the boundary layer. The early transition to turbulent state overcomes the local flow deceleration of an adverse pressure gradient and remains sticked to the wall the boundary layer. Furthermore, the wing aerodynamic performance are improved as drag is reduced and lift is enhanced which is straight forward linked to the lift to drag ratio gain that varies from 22.68% to 134.17% at post stall angles of attack.