http://hdl.handle.net/10985/18058 Sun, 08 Mar 2026 11:27:30 GMT 2026-03-08T11:27:30Z https://sam.ensam.eu:443/bitstream/id/e1cc11b3-327c-48e0-b7e9-44f117bf88ba/ http://hdl.handle.net/10985/18058 http://hdl.handle.net/10985/19215 An overview of filtration efficiency through the masks: Mechanisms of the aerosols penetration ABBASNEZHAD, Navideh; ZARBINI SEYDANI, Mohammad; ZIRAK, Nader; FARZANEH, Sedigheh; SHIRINBAYAN, Mohammadali; TCHARKHTCHI, Abbas The masks have always been mentioned as an effective tool against environmental threats. They are considered as protective equipment to preserve the respiratory system against the non-desirable air droplets and aerosols such as the viral or pollution particles. The aerosols can be pollution existence in the air, or the infectious airborne viruses initiated from the sneezing, coughing of the infected people. The filtration efficiency of the different masks against these aerosols are not the same, as the particles have different sizes, shapes, and properties. Therefore, the challenge is to fabricate the filtration masks with higher efficiency to decrease the penetration percentage at the nastiest conditions. To achieve this concept, knowledge about the mechanisms of the penetration of the aerosols through the masks at different effective environmental conditions is necessary. In this paper, the literature about the different kinds of face masks and respiratory masks, common cases of their application, and the advantages and disadvantages of them in this regard have been reviewed. Moreover, the related mechanisms of the penetration of the aerosols through the masks are discussed. The environmental conditions affecting the penetration as well as the quality of the fabrication are studied. Finally, special attention was given to the numerical simulation related to the different existing mechanisms. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/19215 2021-01-01T00:00:00Z ABBASNEZHAD, Navideh ZARBINI SEYDANI, Mohammad ZIRAK, Nader FARZANEH, Sedigheh SHIRINBAYAN, Mohammadali TCHARKHTCHI, Abbas The masks have always been mentioned as an effective tool against environmental threats. They are considered as protective equipment to preserve the respiratory system against the non-desirable air droplets and aerosols such as the viral or pollution particles. The aerosols can be pollution existence in the air, or the infectious airborne viruses initiated from the sneezing, coughing of the infected people. The filtration efficiency of the different masks against these aerosols are not the same, as the particles have different sizes, shapes, and properties. Therefore, the challenge is to fabricate the filtration masks with higher efficiency to decrease the penetration percentage at the nastiest conditions. To achieve this concept, knowledge about the mechanisms of the penetration of the aerosols through the masks at different effective environmental conditions is necessary. In this paper, the literature about the different kinds of face masks and respiratory masks, common cases of their application, and the advantages and disadvantages of them in this regard have been reviewed. Moreover, the related mechanisms of the penetration of the aerosols through the masks are discussed. The environmental conditions affecting the penetration as well as the quality of the fabrication are studied. Finally, special attention was given to the numerical simulation related to the different existing mechanisms. http://hdl.handle.net/10985/20155 On the importance of physical and mechanical properties of PLGA films during drug release ABBASNEZHAD, Navideh; ZIRAK, Nader; SHIRINBAYAN, Mohammadali; TCHARKHTCHI, Abbas; BAKIR, Farid Physical and mechanical properties of the drug-incorporated polymer play a significant role in the release behavior from the drug carriers. Understanding the relative extent of variation in the physical and mechanical properties of the polymer makes it possible to improve the design of polymer carriers to obtain better release profile and increase drug stability. Drug delivery from PLGA loaded with various percentages of diclofenac sodium (DS: 0, 5%, and 10%) at different flow rates of 0 and 7.5 ml/s (flow rate of the healthy internal carotid artery) in phosphate buffered saline (PBS) for different release intervals has been studied. In this research, the change of some physical properties such as free volume fraction, glass transition temperature (Tg) and mechanical properties before and during PLGA release have been investigated. In-vitro release tests have been performed in the PBS medium at the temperature of 37 °C. The results showed that during drug release, Youngs’ modulus and ultimate stress were increased while elongation at break was decreased for different drug loaded films and flow rates. In addition, the zero order kinetic model was found to best fit all the release-profiles obtained. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/20155 2021-01-01T00:00:00Z ABBASNEZHAD, Navideh ZIRAK, Nader SHIRINBAYAN, Mohammadali TCHARKHTCHI, Abbas BAKIR, Farid Physical and mechanical properties of the drug-incorporated polymer play a significant role in the release behavior from the drug carriers. Understanding the relative extent of variation in the physical and mechanical properties of the polymer makes it possible to improve the design of polymer carriers to obtain better release profile and increase drug stability. Drug delivery from PLGA loaded with various percentages of diclofenac sodium (DS: 0, 5%, and 10%) at different flow rates of 0 and 7.5 ml/s (flow rate of the healthy internal carotid artery) in phosphate buffered saline (PBS) for different release intervals has been studied. In this research, the change of some physical properties such as free volume fraction, glass transition temperature (Tg) and mechanical properties before and during PLGA release have been investigated. In-vitro release tests have been performed in the PBS medium at the temperature of 37 °C. The results showed that during drug release, Youngs’ modulus and ultimate stress were increased while elongation at break was decreased for different drug loaded films and flow rates. In addition, the zero order kinetic model was found to best fit all the release-profiles obtained. http://hdl.handle.net/10985/18479 In vitro study of drug release from various loaded polyurethane samples and subjected to different non-pulsed flow rates ABBASNEZHAD, Navideh; SHIRINBAYAN, Mohammadali; TCHARKHTCHI, Abbas; BAKIR, Farid Drug-eluting implants with a polymeric matrix are currently widely used and the interest of modeling their behavior is increasing. This article aims to present preliminary results of an in vitro under steady flow, study the behavior of drug-loaded polyurethane samples used as drug delivery matrices. Polyisocyanate and polyol synthesis supplied the polyurethane studied in this work. A molding and heat at 50 °C for about 30 min make it possible to prepare films from these components. The prepared samples are placed in the impermeable Plexiglas tube and they are in contact with the medium (distilled water). Tests have been performed without flow and three other cases with steady flow, at a temperature of 37 °C. The substance active incorporated in these films, as the drug, for carrying out the release tests is the C20H24C12N2O3. This drug supplied in granular form is composed of a mixture in the following proportions, 15 mg of diclofenac epolamine and 50 mg of diclofenac-sodium. Four sample variants were carefully prepared: pure-PU and PU loaded in a mass ratio of 10, 20 or 30%. Weighing, DSC, FT-IR, and DMTA are the methods used to analyze the samples. In addition, SEM micrographs are used to explore qualitatively the microstructure during the release tests. The kinetics in vitro of the drug release and water absorption by the polyurethane films are discussed in detail. The results show that these two quantities depend on the initial drug loading and the flow rate value, as a function of the in vitro incubation time. Wed, 01 Jan 2020 00:00:00 GMT http://hdl.handle.net/10985/18479 2020-01-01T00:00:00Z ABBASNEZHAD, Navideh SHIRINBAYAN, Mohammadali TCHARKHTCHI, Abbas BAKIR, Farid Drug-eluting implants with a polymeric matrix are currently widely used and the interest of modeling their behavior is increasing. This article aims to present preliminary results of an in vitro under steady flow, study the behavior of drug-loaded polyurethane samples used as drug delivery matrices. Polyisocyanate and polyol synthesis supplied the polyurethane studied in this work. A molding and heat at 50 °C for about 30 min make it possible to prepare films from these components. The prepared samples are placed in the impermeable Plexiglas tube and they are in contact with the medium (distilled water). Tests have been performed without flow and three other cases with steady flow, at a temperature of 37 °C. The substance active incorporated in these films, as the drug, for carrying out the release tests is the C20H24C12N2O3. This drug supplied in granular form is composed of a mixture in the following proportions, 15 mg of diclofenac epolamine and 50 mg of diclofenac-sodium. Four sample variants were carefully prepared: pure-PU and PU loaded in a mass ratio of 10, 20 or 30%. Weighing, DSC, FT-IR, and DMTA are the methods used to analyze the samples. In addition, SEM micrographs are used to explore qualitatively the microstructure during the release tests. The kinetics in vitro of the drug release and water absorption by the polyurethane films are discussed in detail. The results show that these two quantities depend on the initial drug loading and the flow rate value, as a function of the in vitro incubation time. http://hdl.handle.net/10985/19932 Controlled release from polyurethane films: Drug release mechanisms ABBASNEZHAD, Navideh; ZIRAK, Nader; SHIRINBAYAN, Mohammadali; KOUIDRI, SMAINE; SALAHINEJAD, Erfan; TCHARKHTCHI, Abbas; BAKIR, Farid In this study, polyurethane-films loaded with diclofenac were used to analyze the drug release kinetics and mechanisms. For this purpose, the experimental procedures were developed under static and dynamic conditions with different initial drug loads of 10, 20, and 30%. In the dynamic condition, to better simulate the biological flow, drug release measurements were investigated at flow rates of 7.5 and 23.5 ml/s. These values indicate the flow rate of the internal carotid artery (ICA) for a normal state of a body and for a person during the exercise, respectively. The experimental data were analyzed and adjusted by Higuchi, Korsmeyer–Peppas, First-order, zero-order, and Peppas–Sahlin models in order to understand the mechanisms contributed. Finally, drug release mechanisms were specified by investigating the model correlation coefficients. Experimental results showed that increasing the flow rate and initial drug loads enhance drug liberation. In addition, the rate of release is more influenced by the drug dosage in the static state. The analysis revealed that diffusion, burst, and osmotic pressure are the principal mechanisms contributed. Moreover, Fickian type was the dominant mechanism at all duration of release. However, it was discovered using Peppas–Sahlin model that the contribution of the diffusion mechanism decreases with increasing flow rate and initial dosage. Furthermore, the tests at different drug dosages showed that the number of stages in medication release profile is independent of the flow rate and the medicine percentage. One can conclude that the drug release kinetic in static state is more influenced by drug dosage compared with dynamic state. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/19932 2021-01-01T00:00:00Z ABBASNEZHAD, Navideh ZIRAK, Nader SHIRINBAYAN, Mohammadali KOUIDRI, SMAINE SALAHINEJAD, Erfan TCHARKHTCHI, Abbas BAKIR, Farid In this study, polyurethane-films loaded with diclofenac were used to analyze the drug release kinetics and mechanisms. For this purpose, the experimental procedures were developed under static and dynamic conditions with different initial drug loads of 10, 20, and 30%. In the dynamic condition, to better simulate the biological flow, drug release measurements were investigated at flow rates of 7.5 and 23.5 ml/s. These values indicate the flow rate of the internal carotid artery (ICA) for a normal state of a body and for a person during the exercise, respectively. The experimental data were analyzed and adjusted by Higuchi, Korsmeyer–Peppas, First-order, zero-order, and Peppas–Sahlin models in order to understand the mechanisms contributed. Finally, drug release mechanisms were specified by investigating the model correlation coefficients. Experimental results showed that increasing the flow rate and initial drug loads enhance drug liberation. In addition, the rate of release is more influenced by the drug dosage in the static state. The analysis revealed that diffusion, burst, and osmotic pressure are the principal mechanisms contributed. Moreover, Fickian type was the dominant mechanism at all duration of release. However, it was discovered using Peppas–Sahlin model that the contribution of the diffusion mechanism decreases with increasing flow rate and initial dosage. Furthermore, the tests at different drug dosages showed that the number of stages in medication release profile is independent of the flow rate and the medicine percentage. One can conclude that the drug release kinetic in static state is more influenced by drug dosage compared with dynamic state. http://hdl.handle.net/10985/26121 A Diffuse Interface Model for Cavitation, Taking Into Account Capillary Forces AIT‐ALI, Takfarines; KHELLADI, Sofiane; BAKIR, Farid; HANNOUN, Noureddine; NOGUEIRA, Xesús; RAMÍREZ, Luis We consider the moving least squares method to solve compressible two‐phase water‐water vapor flow with surface tension. A diffuse interface model based on the Navier–Stokes and Korteweg equations is coupled with a suitable system of state equations that allows for a more realistic estimation of the pressure jump across the liquid–vapor interface as a function of temperature. We propose a simple formulation for computing the capillarity coefficient based on the surface tension and the thickness of the diffuse interface. A convergence analysis using pressure jump in the test case of static bubble is conducted to verify our solver. We present several numerical test cases that illustrate the ability of our model to reproduce qualitatively and quantitatively the effects of surface tension on cavitation bubbles in general situations. Fri, 01 Nov 2024 00:00:00 GMT http://hdl.handle.net/10985/26121 2024-11-01T00:00:00Z AIT‐ALI, Takfarines KHELLADI, Sofiane BAKIR, Farid HANNOUN, Noureddine NOGUEIRA, Xesús RAMÍREZ, Luis We consider the moving least squares method to solve compressible two‐phase water‐water vapor flow with surface tension. A diffuse interface model based on the Navier–Stokes and Korteweg equations is coupled with a suitable system of state equations that allows for a more realistic estimation of the pressure jump across the liquid–vapor interface as a function of temperature. We propose a simple formulation for computing the capillarity coefficient based on the surface tension and the thickness of the diffuse interface. A convergence analysis using pressure jump in the test case of static bubble is conducted to verify our solver. We present several numerical test cases that illustrate the ability of our model to reproduce qualitatively and quantitatively the effects of surface tension on cavitation bubbles in general situations. http://hdl.handle.net/10985/18976 Micromechanical Modelling of Dynamic Behavior of Advanced Sheet Molding Compound (A-SMC) Composite AYARI, Houssem; SHIRINBAYAN, Mohammadali; IMADDAHEN, Amine; TAMBOURA, Sahbi; BEN DALY, Hachmi; TCHARKHTCHI, Abbas; FITOUSSI, Joseph Passive safety, particularly in the transport industry, requires maximizing the dissipation of energy and minimizing the decelerations undergone by a vehicle following a violent impact (crash). This paper proposes a strategy for identifying an anisotropic local damage criterion in a moderate dynamic loading for Advanced Sheet Molding Compound (A-SMC) composite materials. Multi-scale damage modelling based on the Mori-Tanaka approach is put forward. Previously, the results of an experimental campaign carried out on a range of strain rates varying from quasi static to 200 s−1 were used to identify a probabilistic local damage criterion based on Weibull’s formulation and integrate the effect of damage at a fiber-matrix interface scale. Therefore, the progressive local damage occurring under a fast loading may be described. A two-step homogenization procedure allows describing the strain rate effect on the stress-strain curves. The model gives also rise to the prediction of the progressive anisotropic loss of stiffness. Comparing between the experimental and numerical results confirms the ability of the proposed approach to describe the visco-damage effect (delay of damage threshold and decrease in damage kinetics) emphasized in A-SMC composites. Wed, 01 Jan 2020 00:00:00 GMT http://hdl.handle.net/10985/18976 2020-01-01T00:00:00Z AYARI, Houssem SHIRINBAYAN, Mohammadali IMADDAHEN, Amine TAMBOURA, Sahbi BEN DALY, Hachmi TCHARKHTCHI, Abbas FITOUSSI, Joseph Passive safety, particularly in the transport industry, requires maximizing the dissipation of energy and minimizing the decelerations undergone by a vehicle following a violent impact (crash). This paper proposes a strategy for identifying an anisotropic local damage criterion in a moderate dynamic loading for Advanced Sheet Molding Compound (A-SMC) composite materials. Multi-scale damage modelling based on the Mori-Tanaka approach is put forward. Previously, the results of an experimental campaign carried out on a range of strain rates varying from quasi static to 200 s−1 were used to identify a probabilistic local damage criterion based on Weibull’s formulation and integrate the effect of damage at a fiber-matrix interface scale. Therefore, the progressive local damage occurring under a fast loading may be described. A two-step homogenization procedure allows describing the strain rate effect on the stress-strain curves. The model gives also rise to the prediction of the progressive anisotropic loss of stiffness. Comparing between the experimental and numerical results confirms the ability of the proposed approach to describe the visco-damage effect (delay of damage threshold and decrease in damage kinetics) emphasized in A-SMC composites. http://hdl.handle.net/10985/26212 Numerical Investigations of Flows and Heat Transfer in Turbine Disk Cavities BEAUX, Jean-Hugues; GIRARDEAU, Julian; KHELLADI, Sofiane; DELIGANT, Michael; PERILHON, Christelle In gas turbines, the stator wells play a key role in the efficiency of the turbomachine. The research for performance gains requires a good understanding and an accurate modeling of the flows and heat transfers occurring in these areas. Within the framework of the European program main annulus gas path interaction (MAGPI) WP1, a two-stage axial turbine test rig provided an experimental database used to validate the computational fluid dynamics (CFD) models. The aim of this study is to setup a numerical methodology using the CFD solver ANSYSFluent to accurately predict the conjugate heat transfer in the stator well area. The validation of the methodology relies on thorough comparison of the results with the MAGPI WP1 experimental temperature/pressure measurements. A geometry with axial cooling injection through lock plate slot was chosen. A Reynolds-averaged Navier–Stokes (RANS) three-dimensional sectorized CFD model of the turbine with conjugate heat transfer was used. It includes main gas path, cavities with labyrinths, disks rotor, the casing, and the nozzle guide vanes (NGV). Mixing planes are placed between the static and rotating frames. Different influences (mesh, turbulence model, thermal boundary conditions, radial labyrinths clearances) were studied and compared with experimental data. As a baseline, the first calculations were performed with a cooling flowrate chosen so that hot gas ingresses from the main stream into the stator well cavity. Good agreements between predicted and measured temperatures/pressures were observed, especially in the vicinity of the stator well. Discrepancies were spotted at the first rotor hub endwall and at the upstream wheelspace and will be discussed. Two other cooling configurations were conducted, one with cooling air exiting from the disk rim cavity to the main gas path and the other with the lowest cooling flowrate and so the highest ingress. Finally, the turbine performance under nonadiabatic conditions has been evaluated with an appropriate efficiency definition. Sat, 01 Jun 2024 00:00:00 GMT http://hdl.handle.net/10985/26212 2024-06-01T00:00:00Z BEAUX, Jean-Hugues GIRARDEAU, Julian KHELLADI, Sofiane DELIGANT, Michael PERILHON, Christelle In gas turbines, the stator wells play a key role in the efficiency of the turbomachine. The research for performance gains requires a good understanding and an accurate modeling of the flows and heat transfers occurring in these areas. Within the framework of the European program main annulus gas path interaction (MAGPI) WP1, a two-stage axial turbine test rig provided an experimental database used to validate the computational fluid dynamics (CFD) models. The aim of this study is to setup a numerical methodology using the CFD solver ANSYSFluent to accurately predict the conjugate heat transfer in the stator well area. The validation of the methodology relies on thorough comparison of the results with the MAGPI WP1 experimental temperature/pressure measurements. A geometry with axial cooling injection through lock plate slot was chosen. A Reynolds-averaged Navier–Stokes (RANS) three-dimensional sectorized CFD model of the turbine with conjugate heat transfer was used. It includes main gas path, cavities with labyrinths, disks rotor, the casing, and the nozzle guide vanes (NGV). Mixing planes are placed between the static and rotating frames. Different influences (mesh, turbulence model, thermal boundary conditions, radial labyrinths clearances) were studied and compared with experimental data. As a baseline, the first calculations were performed with a cooling flowrate chosen so that hot gas ingresses from the main stream into the stator well cavity. Good agreements between predicted and measured temperatures/pressures were observed, especially in the vicinity of the stator well. Discrepancies were spotted at the first rotor hub endwall and at the upstream wheelspace and will be discussed. Two other cooling configurations were conducted, one with cooling air exiting from the disk rim cavity to the main gas path and the other with the lowest cooling flowrate and so the highest ingress. Finally, the turbine performance under nonadiabatic conditions has been evaluated with an appropriate efficiency definition. http://hdl.handle.net/10985/26128 Investigation of asymmetric heating in Poiseuille-Rayleigh-Bénard water flow: A numerical study BENBEGHILA, Aymen; OUZANI, Riadh; BENDERRADJI, Ammar; ABID, Chérifa; KHELLADI, Sofiane In this paper, a numerical investigation of the impact of asymmetric heating on laminar mixed convection in Poiseuille-Rayleigh-Bénard water flow within parallel horizontal channels is presented. The study has been carried out in a rectangular channel with a transverse aspect ratio of 10, and considered both low (Ra = 1.28 × 10^4) and high (Ra = 1.4 × 10^5) Rayleigh numbers, with Reynolds numbers of 50 and 100. A uniform heat flux was applied to the top and bottom walls of the heated region to assess its effect on the system's thermoconvective behavior and heat transfer efficiency. Two flux ratio scenarios were considered: qt/qb = 1 and qt/qb = 2. The results indicate that increasing the flux ratio intensifies the destabilizing temperature gradient and significantly enhances buoyancy-induced flow, thereby influencing the patterns of thermoconvective structures. Specifically, flux ratios lead to an increased number of plumes originating from the bottom of the channel, while reducing their height and confining them between the bottom wall and the upper thermal boundary layer. It is also observed that flux ratios do not affect the mechanisms involved in the formation of longitudinal rolls. Furthermore, at low Rayleigh numbers, asymmetric heating has a pronounced impact on the establishment length. In contrast, this effect diminishes and becomes negligible at higher Rayleigh numbers. Numerical computations further reveal that near the bottom wall, the Nusselt number exhibits singular behavior, approaching infinity. Regardless of Reynolds and Rayleigh numbers, flux ratios significantly enhance heat transfer within the system. Additionally, near the top wall, the buoyancy effects from the bottom wall have negligible impact on heat transfer, except in the case where qt/qb = 2, Re = 50 and Ra = 1.4 × 10^5, where instability in the upper thermal layer was observed. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10985/26128 2025-01-01T00:00:00Z BENBEGHILA, Aymen OUZANI, Riadh BENDERRADJI, Ammar ABID, Chérifa KHELLADI, Sofiane In this paper, a numerical investigation of the impact of asymmetric heating on laminar mixed convection in Poiseuille-Rayleigh-Bénard water flow within parallel horizontal channels is presented. The study has been carried out in a rectangular channel with a transverse aspect ratio of 10, and considered both low (Ra = 1.28 × 10^4) and high (Ra = 1.4 × 10^5) Rayleigh numbers, with Reynolds numbers of 50 and 100. A uniform heat flux was applied to the top and bottom walls of the heated region to assess its effect on the system's thermoconvective behavior and heat transfer efficiency. Two flux ratio scenarios were considered: qt/qb = 1 and qt/qb = 2. The results indicate that increasing the flux ratio intensifies the destabilizing temperature gradient and significantly enhances buoyancy-induced flow, thereby influencing the patterns of thermoconvective structures. Specifically, flux ratios lead to an increased number of plumes originating from the bottom of the channel, while reducing their height and confining them between the bottom wall and the upper thermal boundary layer. It is also observed that flux ratios do not affect the mechanisms involved in the formation of longitudinal rolls. Furthermore, at low Rayleigh numbers, asymmetric heating has a pronounced impact on the establishment length. In contrast, this effect diminishes and becomes negligible at higher Rayleigh numbers. Numerical computations further reveal that near the bottom wall, the Nusselt number exhibits singular behavior, approaching infinity. Regardless of Reynolds and Rayleigh numbers, flux ratios significantly enhance heat transfer within the system. Additionally, near the top wall, the buoyancy effects from the bottom wall have negligible impact on heat transfer, except in the case where qt/qb = 2, Re = 50 and Ra = 1.4 × 10^5, where instability in the upper thermal layer was observed. http://hdl.handle.net/10985/26209 Linear stability of Rayleigh-Bénard-Poiseuille flow of water near 4°C in a channel bounded by slip walls BENBEGHILA, Aymen; OUZANI, Riadh; BENDERRADJI, Ammar; ALLOUI, Zineddine; KHELLADI, Sofiane The onset of mixed convection of cold water in a horizontal channel is studied using linear stability analysis. The two walls of the channel are modeled using slip conditions and are maintained at different constant temperatures. A model with a parabolic relationship is used to predict the variation of density with temperature in the range around its maximum density. The finite difference method is used to solve numerically the linearized equations, and the critical eigenvalue is obtained using the iterative Newton-Raphson method. The effects of the dimensionless temperature ratio γ and the slip parameter Ω on the onset of thermal instabilities are studied. The obtained results showed that these two parameters induced modifications in the critical Rayleigh number and the corresponding critical wavenumber. The results also indicated that beyond a certain value of dimensionless temperature ratio the slip parameter of the upper wall no longer influences the critical threshold for the onset of mixed convection. Fri, 01 Nov 2024 00:00:00 GMT http://hdl.handle.net/10985/26209 2024-11-01T00:00:00Z BENBEGHILA, Aymen OUZANI, Riadh BENDERRADJI, Ammar ALLOUI, Zineddine KHELLADI, Sofiane The onset of mixed convection of cold water in a horizontal channel is studied using linear stability analysis. The two walls of the channel are modeled using slip conditions and are maintained at different constant temperatures. A model with a parabolic relationship is used to predict the variation of density with temperature in the range around its maximum density. The finite difference method is used to solve numerically the linearized equations, and the critical eigenvalue is obtained using the iterative Newton-Raphson method. The effects of the dimensionless temperature ratio γ and the slip parameter Ω on the onset of thermal instabilities are studied. The obtained results showed that these two parameters induced modifications in the critical Rayleigh number and the corresponding critical wavenumber. The results also indicated that beyond a certain value of dimensionless temperature ratio the slip parameter of the upper wall no longer influences the critical threshold for the onset of mixed convection. http://hdl.handle.net/10985/22476 Experimental investigation of the effect of blade solidity on micro-scale and low tip-speed ratio wind turbines BOURHIS, M.; RAVELET, Florent; PEREIRA, Michaël It is well-established that micro-scale wind turbines require high blade solidity in order to overtake friction torque of all mechanical parts and starts operating. Therefore, multi-bladed micro-scale rotors with a low design tip-speed ratio λ are advocated. However, no consensual blade solidity is admitted by the scientific community at low Reynolds number and low tip-speed ratio because the reliability of the airfoil data, used in the blade element momentum theory, is questionable. The vast majority of the open literature has focused on the number of blades rather than varying blade chord length to increase the solidity. This experimental study carried out in a wind tunnel serves two purposes: to examine blade solidity effect on the power C p and torque coefficients C τ vs. tip-speed ratio curves at a fixed number of blades and to investigate its effects on the velocity distributions using stereoscopic particle image velocimetry (SPIV) for three tip-speed ratio λ = 0.5, λ = 1 and λ = 1.4. Six 200 mm diameter runners with 8 blades and various blade solidity from σ = 1.5 to σ = 0.5 were designed at λ = 1 without using airfoil data. The results emphasise that the maximum power coefficient increases with blade solidity up to a maximum value C p,max = 0.29 reached for σ = 1.25. High-solidity rotors have a very low cut-in wind speed V 0 = 3.8 m s −1 and their torque coefficient C τ decreases drastically and linearly while increasing the tip-speed ratio λ. These specificities could be of particular interest for energy harvesting of low speed air flow in order to power low-energy appliances. However, for low-solidity rotors, the C τ vs. λ curves present a similar trend than the lift coefficient vs. angle of attack polar plots of isolated airfoil which is characterised by a significant drop in C τ illustrating stall effect. An increase in blade solidity postpones and attenuates the stall effects due to greater mutual blade interactions. The SPIV recordings reveal that for high-solidity rotors the magnitude and radial profiles of axial and tangential induction factors and the flow deflection were close to the design settings. Moreover, the analysis exhibits that an increase in the blade solidity and tip-speed ratio leads to higher axial and tangential induction factors. The investigation of the wake highlights that the aerodynamic torque generated by a wind turbine is not produced in a same way as changing the blade solidity or the tip-speed ratio. To conclude, the best compromise between the maximum power coefficient, the cut-in wind speed, the mass of filament and the stability of the wake is achieved for the rotor with a blade solidity of σ = 1.25. déjà sur hal Sun, 01 Jan 2023 00:00:00 GMT http://hdl.handle.net/10985/22476 2023-01-01T00:00:00Z BOURHIS, M. RAVELET, Florent PEREIRA, Michaël It is well-established that micro-scale wind turbines require high blade solidity in order to overtake friction torque of all mechanical parts and starts operating. Therefore, multi-bladed micro-scale rotors with a low design tip-speed ratio λ are advocated. However, no consensual blade solidity is admitted by the scientific community at low Reynolds number and low tip-speed ratio because the reliability of the airfoil data, used in the blade element momentum theory, is questionable. The vast majority of the open literature has focused on the number of blades rather than varying blade chord length to increase the solidity. This experimental study carried out in a wind tunnel serves two purposes: to examine blade solidity effect on the power C p and torque coefficients C τ vs. tip-speed ratio curves at a fixed number of blades and to investigate its effects on the velocity distributions using stereoscopic particle image velocimetry (SPIV) for three tip-speed ratio λ = 0.5, λ = 1 and λ = 1.4. Six 200 mm diameter runners with 8 blades and various blade solidity from σ = 1.5 to σ = 0.5 were designed at λ = 1 without using airfoil data. The results emphasise that the maximum power coefficient increases with blade solidity up to a maximum value C p,max = 0.29 reached for σ = 1.25. High-solidity rotors have a very low cut-in wind speed V 0 = 3.8 m s −1 and their torque coefficient C τ decreases drastically and linearly while increasing the tip-speed ratio λ. These specificities could be of particular interest for energy harvesting of low speed air flow in order to power low-energy appliances. However, for low-solidity rotors, the C τ vs. λ curves present a similar trend than the lift coefficient vs. angle of attack polar plots of isolated airfoil which is characterised by a significant drop in C τ illustrating stall effect. An increase in blade solidity postpones and attenuates the stall effects due to greater mutual blade interactions. The SPIV recordings reveal that for high-solidity rotors the magnitude and radial profiles of axial and tangential induction factors and the flow deflection were close to the design settings. Moreover, the analysis exhibits that an increase in the blade solidity and tip-speed ratio leads to higher axial and tangential induction factors. The investigation of the wake highlights that the aerodynamic torque generated by a wind turbine is not produced in a same way as changing the blade solidity or the tip-speed ratio. To conclude, the best compromise between the maximum power coefficient, the cut-in wind speed, the mass of filament and the stability of the wake is achieved for the rotor with a blade solidity of σ = 1.25.