Changes in flow field around NACA23012 airfoil from a clean condition to a super-cooled large droplet （SLD） condition were simulated, and variations in aerodynamic parameters were calculated using FLUENT. In the cas...Changes in flow field around NACA23012 airfoil from a clean condition to a super-cooled large droplet （SLD） condition were simulated, and variations in aerodynamic parameters were calculated using FLUENT. In the case of numerical simulation for a clean airfoil, flow field characteristics simulated agreed well with theory analysis, indicating that turbulence models and parameters setting are feasible. Aerodynamic parameters for iced airfoil were calculated using the same method and agreed with those measured test data under the same environment in icing wind tunnels by S. Lee. Conclusion is made that the numerical simulation is valid, and it can be an alternative to study ice accretion effects at the SLD condition on airfoil aerodynamics, leading to reduction in research cycle time and cost.展开更多
Accurate prediction of droplet impingement on wind turbine blade is one of the most important premises of anti-icing and de-icing system design.In a super-cooled large droplets(SLD)conditions,droplet no longer maintai...Accurate prediction of droplet impingement on wind turbine blade is one of the most important premises of anti-icing and de-icing system design.In a super-cooled large droplets(SLD)conditions,droplet no longer maintains a sphere shape,and it may deform,break up,and splash when moving or impinging on the surface.Semi-empirical models of droplet dynamic behaviours are embedded into the Eulerian droplet model to improve the accuracy of the numerical simulation of droplet impingement limits and local collection efficiency.Eulerian droplet model(Model 1)for small droplets and improved Eulerian droplet model(Model 2)for large droplet are both validated by comparing to the wind tunnel experiment results.Using the proposed methods,droplet impingement limitation and local collection efficiency on the S809 airfoil are calculated in various conditions.A detailed derivation of Model 1and Model 2is presented along with a comparison of numerical trajectories,drag coefficient and collection efficiency distributions.The results show that droplet dynamic behaviours,including splashing,break-up and deforming,must be considered to accurately simulate the impingement behaviour in the SLD conditions.And with the increase of the droplet diameters,the effects of the droplet dynamic behaviors on the impingement characteristics are more obvious.展开更多
Information of droplet size and size distribution lays the basis for investigations of atomization mechanisms and performance optimization, However, the laser diffraction and phase Doppler particle analyzers have diff...Information of droplet size and size distribution lays the basis for investigations of atomization mechanisms and performance optimization, However, the laser diffraction and phase Doppler particle analyzers have difficulty in accurately characterizing sprays with a wide range of droplet sizes and very large droplets, especially ira large number of droplets are aspherical. A method to measure size in such large- droplet sprays based on digital imaging with backward illumination was developed, including an image acquisition system and image process programs. Calibration of the measurement system was performed using a dot calibration target with different dot sizes. An experimental setup was designed and established to characterize spray nozzles under different operation loads, as well as different nozzle arrangements. Results show that the droplet size of sprays ranges from dozens of microns to several millimeters. The superiority of wide load range for such nozzles was indicated by the size-measurement results under half-load to full-load operations. The present study revealed that the image processing technique can be effectively implemented for in-line size measurements of sprays with a wide distribution of droplet size and aspherical droplets, which would be difficult to characterize bv other methods.展开更多
Since the very early days of clinical liver transplantation(LT),transplant surgeons and professionals have been confronted with the increased risk of failure associated with the use of fatty liver grafts(1).Notwithsta...Since the very early days of clinical liver transplantation(LT),transplant surgeons and professionals have been confronted with the increased risk of failure associated with the use of fatty liver grafts(1).Notwithstanding the wide variability in steatosis assessment across different centers and pathologists(2),utilization of livers with moderate(≥30%)or severe(≥60%)macrovesicular steatosis has been consistently associated with an increased risk of primary non-function,early allograft dysfunction,acute kidney injury,as well as inferior graft and patient survival(3).The mechanisms behind the increased susceptibility of steatotic livers to ischemia-reperfusion injury(IRI)are multiple,including disturbances to microcirculation due to sinusoidal narrowing,increased oxidative stress upon reperfusion and enhanced lipid peroxidation,leading to an increased release of inflammatory mediators like IL6,IL1βand so-called damage associated molecular patterns(DAMP),like cell-free DNA and mitochondrial DNA.Histologically,this is reflected by hepatocyte death by necrosis rather than apoptosis,pseudopeliotic steatosis(i.e.,the expulsion of lipid droplets into the extracellular space)and lately,by tissue remodelling and fibrosis(4,5).展开更多
Icing(or ice accretion) is a phenomenon in which super-cooled water droplets impinge and accrete on a body.It is well known that ice accretion on blades and vanes leads to performance degradation and has caused severe...Icing(or ice accretion) is a phenomenon in which super-cooled water droplets impinge and accrete on a body.It is well known that ice accretion on blades and vanes leads to performance degradation and has caused severe accidents.Although various anti-icing and deicing systems have been developed,such accidents still occur.Therefore,it is important to clarify the phenomenon of ice accretion on an aircraft and in a jet engine.However,flight tests for ice accretion are very expensive,and in the wind tunnel it is difficult to reproduce all climate conditions where ice accretion can occur.Therefore,it is expected that computational fluid dynamics(CFD),which can estimate ice accretion in various climate conditions,will be a useful way to predict and understand the ice accretion phenomenon.On the other hand,although the icing caused by super-cooled large droplets(SLD) is very dangerous,the numerical method has not been established yet.This is why SLD icing is characterized by splash and bounce phenomena of droplets and they are very complex in nature.In the present study,we develop an ice accretion code considering the splash and bounce phenomena to predict SLD icing,and the code is applied to a fan rotor blade.The numerical results with and without the SLD icing model are compared.Through this study,the influence of the SLD icing model is numerically clarified.展开更多
During the coronavirus disease 2019 pandemic,short-range virus transmission has been observed to have a higher risk of causing infection than long-range virus transmission.However,the roles played by the inhalation an...During the coronavirus disease 2019 pandemic,short-range virus transmission has been observed to have a higher risk of causing infection than long-range virus transmission.However,the roles played by the inhalation and large droplet routes cannot be distinguished in practice.A recent analytical study revealed the predominance of short-range inhalation over the large droplet spray route as causes of respiratory infections.In the current study,short-range exposure was analyzed via computational fluid dynamics(CFD)simulations using a discrete phase model.Detailed facial membranes,including eyes,nostrils,and a mouth,were considered.In CFD simulations,there is no need for a spherical approximation of the human head for estimating deposition nor the“anisokinetic aerosol sampling”approximation for estimating inhalation in the analytical model.We considered two scenarios(with two spheres[Scenario 1]and two human manikins[Scenario 2]),source-target distances of 0.2 to 2 m,and droplet diameters of 3 to 1,500μm.The overall CFD exposure results agree well with data previously obtained from a simple analytical model.The CFD results confirm the predominance of the short-range inhalation route beyond 0.2 m for expiratory droplets smaller than 50μm during talking and coughing.A critical droplet size of 87.5μm was found to differentiate droplet behaviors.The number of droplets deposited on the target head exceeded those exposed to facial membranes,which implies a risk of exposure through the immediate surface route over a short range.展开更多
基金supported by the Fund of the CAAC Scientific Research Base of Civil Aviation Flight Technology and Safety (No. F2010KF02)
文摘Changes in flow field around NACA23012 airfoil from a clean condition to a super-cooled large droplet （SLD） condition were simulated, and variations in aerodynamic parameters were calculated using FLUENT. In the case of numerical simulation for a clean airfoil, flow field characteristics simulated agreed well with theory analysis, indicating that turbulence models and parameters setting are feasible. Aerodynamic parameters for iced airfoil were calculated using the same method and agreed with those measured test data under the same environment in icing wind tunnels by S. Lee. Conclusion is made that the numerical simulation is valid, and it can be an alternative to study ice accretion effects at the SLD condition on airfoil aerodynamics, leading to reduction in research cycle time and cost.
基金supported by the National Basic Research Program of China(″973″Program)(No.2014CB046200)the National Natural Science Foundation of China(Nos.11402114,51506089)+1 种基金the Fundamental Research Funds for Central UniversitiesNanjing University of Aeronautics,and Astronautics Basic Scientific Research Projects for Youth Science(No.NS2014014)
文摘Accurate prediction of droplet impingement on wind turbine blade is one of the most important premises of anti-icing and de-icing system design.In a super-cooled large droplets(SLD)conditions,droplet no longer maintains a sphere shape,and it may deform,break up,and splash when moving or impinging on the surface.Semi-empirical models of droplet dynamic behaviours are embedded into the Eulerian droplet model to improve the accuracy of the numerical simulation of droplet impingement limits and local collection efficiency.Eulerian droplet model(Model 1)for small droplets and improved Eulerian droplet model(Model 2)for large droplet are both validated by comparing to the wind tunnel experiment results.Using the proposed methods,droplet impingement limitation and local collection efficiency on the S809 airfoil are calculated in various conditions.A detailed derivation of Model 1and Model 2is presented along with a comparison of numerical trajectories,drag coefficient and collection efficiency distributions.The results show that droplet dynamic behaviours,including splashing,break-up and deforming,must be considered to accurately simulate the impingement behaviour in the SLD conditions.And with the increase of the droplet diameters,the effects of the droplet dynamic behaviors on the impingement characteristics are more obvious.
基金support from the National Natural Science Foundation of China(Grant nos.51206112, 51327803,51176128)the Natural Science Foundation of Shanghai (Grant no.12ZR1446900)Innovation Project of Scientific Research of Shanghai Municipal Education Commission(Grant no. 12YZ110)
文摘Information of droplet size and size distribution lays the basis for investigations of atomization mechanisms and performance optimization, However, the laser diffraction and phase Doppler particle analyzers have difficulty in accurately characterizing sprays with a wide range of droplet sizes and very large droplets, especially ira large number of droplets are aspherical. A method to measure size in such large- droplet sprays based on digital imaging with backward illumination was developed, including an image acquisition system and image process programs. Calibration of the measurement system was performed using a dot calibration target with different dot sizes. An experimental setup was designed and established to characterize spray nozzles under different operation loads, as well as different nozzle arrangements. Results show that the droplet size of sprays ranges from dozens of microns to several millimeters. The superiority of wide load range for such nozzles was indicated by the size-measurement results under half-load to full-load operations. The present study revealed that the image processing technique can be effectively implemented for in-line size measurements of sprays with a wide distribution of droplet size and aspherical droplets, which would be difficult to characterize bv other methods.
文摘Since the very early days of clinical liver transplantation(LT),transplant surgeons and professionals have been confronted with the increased risk of failure associated with the use of fatty liver grafts(1).Notwithstanding the wide variability in steatosis assessment across different centers and pathologists(2),utilization of livers with moderate(≥30%)or severe(≥60%)macrovesicular steatosis has been consistently associated with an increased risk of primary non-function,early allograft dysfunction,acute kidney injury,as well as inferior graft and patient survival(3).The mechanisms behind the increased susceptibility of steatotic livers to ischemia-reperfusion injury(IRI)are multiple,including disturbances to microcirculation due to sinusoidal narrowing,increased oxidative stress upon reperfusion and enhanced lipid peroxidation,leading to an increased release of inflammatory mediators like IL6,IL1βand so-called damage associated molecular patterns(DAMP),like cell-free DNA and mitochondrial DNA.Histologically,this is reflected by hepatocyte death by necrosis rather than apoptosis,pseudopeliotic steatosis(i.e.,the expulsion of lipid droplets into the extracellular space)and lately,by tissue remodelling and fibrosis(4,5).
文摘Icing(or ice accretion) is a phenomenon in which super-cooled water droplets impinge and accrete on a body.It is well known that ice accretion on blades and vanes leads to performance degradation and has caused severe accidents.Although various anti-icing and deicing systems have been developed,such accidents still occur.Therefore,it is important to clarify the phenomenon of ice accretion on an aircraft and in a jet engine.However,flight tests for ice accretion are very expensive,and in the wind tunnel it is difficult to reproduce all climate conditions where ice accretion can occur.Therefore,it is expected that computational fluid dynamics(CFD),which can estimate ice accretion in various climate conditions,will be a useful way to predict and understand the ice accretion phenomenon.On the other hand,although the icing caused by super-cooled large droplets(SLD) is very dangerous,the numerical method has not been established yet.This is why SLD icing is characterized by splash and bounce phenomena of droplets and they are very complex in nature.In the present study,we develop an ice accretion code considering the splash and bounce phenomena to predict SLD icing,and the code is applied to a fan rotor blade.The numerical results with and without the SLD icing model are compared.Through this study,the influence of the SLD icing model is numerically clarified.
基金supported by a General Research Fund(grant number 17202719)provided by the Research Grants Council of Hong Kong.
文摘During the coronavirus disease 2019 pandemic,short-range virus transmission has been observed to have a higher risk of causing infection than long-range virus transmission.However,the roles played by the inhalation and large droplet routes cannot be distinguished in practice.A recent analytical study revealed the predominance of short-range inhalation over the large droplet spray route as causes of respiratory infections.In the current study,short-range exposure was analyzed via computational fluid dynamics(CFD)simulations using a discrete phase model.Detailed facial membranes,including eyes,nostrils,and a mouth,were considered.In CFD simulations,there is no need for a spherical approximation of the human head for estimating deposition nor the“anisokinetic aerosol sampling”approximation for estimating inhalation in the analytical model.We considered two scenarios(with two spheres[Scenario 1]and two human manikins[Scenario 2]),source-target distances of 0.2 to 2 m,and droplet diameters of 3 to 1,500μm.The overall CFD exposure results agree well with data previously obtained from a simple analytical model.The CFD results confirm the predominance of the short-range inhalation route beyond 0.2 m for expiratory droplets smaller than 50μm during talking and coughing.A critical droplet size of 87.5μm was found to differentiate droplet behaviors.The number of droplets deposited on the target head exceeded those exposed to facial membranes,which implies a risk of exposure through the immediate surface route over a short range.
