Transactions of Nanjing University of Aeronautics & Astronautics
Issue 2,2023 Table of Contents
2023(2):115-123.
DOI: 10.16356/j.1005-1120.2023.02.001
Abstract:
Aircraft icing has a significant impact on flight safety， as ice accumulation on airfoils and engines can cause aircraft stalls. Developing anti-icing technology that can adapt to harsh and cold environment presents a challenge. Here， we propose a new anti-icing skin with micro-nano structure inspired by the bamboo leaf called Fargesia qinlingensis. A multilayer non-uniform height （MNH） micro-nano structure is proposed based on the Fargesia qinlingensis surface structure. The anti-icing mechanism of the MNH micro-nano structure is revealed. The flexible large-area MNH micro-nano structure is fabricated based on hierarchical assembly method. Compared with the smooth surface， the ice adhesion strength of the prepared bio-inspired surface is reduced by 80%， indicating that the MNH micro-nano structure inspired by Fargesia qinlingensis has ice-phobic effect. Based on this， an anti-icing hybrid skin based on bionics and electric heating is developed. The anti-icing hybrid skin has successfully completed the anti-icing function flight test on the UAV. To realize the effective anti-icing function under super cold conditions， the anti-icing hybrid skin has been applied on a certain type of UAVs. The bio-inspired anti-icing skin has broad application prospects in large transport aircraft， helicopters， wind power generation， and high-speed trains.
Aircraft icing has a significant impact on flight safety， as ice accumulation on airfoils and engines can cause aircraft stalls. Developing anti-icing technology that can adapt to harsh and cold environment presents a challenge. Here， we propose a new anti-icing skin with micro-nano structure inspired by the bamboo leaf called Fargesia qinlingensis. A multilayer non-uniform height （MNH） micro-nano structure is proposed based on the Fargesia qinlingensis surface structure. The anti-icing mechanism of the MNH micro-nano structure is revealed. The flexible large-area MNH micro-nano structure is fabricated based on hierarchical assembly method. Compared with the smooth surface， the ice adhesion strength of the prepared bio-inspired surface is reduced by 80%， indicating that the MNH micro-nano structure inspired by Fargesia qinlingensis has ice-phobic effect. Based on this， an anti-icing hybrid skin based on bionics and electric heating is developed. The anti-icing hybrid skin has successfully completed the anti-icing function flight test on the UAV. To realize the effective anti-icing function under super cold conditions， the anti-icing hybrid skin has been applied on a certain type of UAVs. The bio-inspired anti-icing skin has broad application prospects in large transport aircraft， helicopters， wind power generation， and high-speed trains.
2023(2):124-136.
DOI: 10.16356/j.1005-1120.2023.02.002
Abstract:
Flight safety is at risk due to complex icing meteorological conditions， highlighting the need for accurate prediction models that integrate geographical features. The mesoscale weather research and forecasting （WRF） model is utilized to simulate two icing events on Mt. Washington in the United States with four cloud microphysics configurations. Results indicate that the predicted liquid water content （LWC） and temperature are well matching results in the existing literature， and the Morrison configuration provides the most significant performance in the error analysis. Additionally， the sensitivity of horizontal resolution and cloud microphysics scheme for LWC and the mean effective diameter of cloud droplet （MVD） prediction is discussed， with higher horizontal resolution demonstrating greater accurate performance due to terrain-induced vertical motions. The study concludes with an analysis of icing intensity using the IC index， showing pronounced spatiotemporal variability and sensitivity to cloud microphysics schemes. Overall， this work enhances our understanding of cloud microphysics schemes and provides a base for selecting appropriate cloud microphysical solutions for icing weather prediction.
Flight safety is at risk due to complex icing meteorological conditions， highlighting the need for accurate prediction models that integrate geographical features. The mesoscale weather research and forecasting （WRF） model is utilized to simulate two icing events on Mt. Washington in the United States with four cloud microphysics configurations. Results indicate that the predicted liquid water content （LWC） and temperature are well matching results in the existing literature， and the Morrison configuration provides the most significant performance in the error analysis. Additionally， the sensitivity of horizontal resolution and cloud microphysics scheme for LWC and the mean effective diameter of cloud droplet （MVD） prediction is discussed， with higher horizontal resolution demonstrating greater accurate performance due to terrain-induced vertical motions. The study concludes with an analysis of icing intensity using the IC index， showing pronounced spatiotemporal variability and sensitivity to cloud microphysics schemes. Overall， this work enhances our understanding of cloud microphysics schemes and provides a base for selecting appropriate cloud microphysical solutions for icing weather prediction.
2023(2):137-147.
DOI: 10.16356/j.1005-1120.2023.02.003
Abstract:
Superhydrophobic photothermal surface shows significant potential in the anti/de-icing field. In this work， we focus on the photothermal anti/de-icing performances of superhydrophobic surfaces with various micropatterns. A finite element simulation， coupling the wave optics and heat transfer models， is employed to illuminate the enhanced photothermal efficiency achieved by the reasonable design of surface micro/nano-structures. The effects of nanoparticle size， volume fraction， and coating thickness on the absorptivity and temperature rise of the photothermal coatings are discussed in detail. Furthermore， two hierarchical textures， including micropillars and microcones， are considered to expound the contribution of micro-scale structures on photothermal performances. Numerical results show that the surface with hierarchical textures has a better absorption efficiency of long waves than the single-scale surface， and the microcones topology presents the best photothermal efficiency. Moreover， the effects of geometric micropattern parameters， e.g. characteristic length and aspect ratio， are also discussed in detail. The illumination and ice melting test demonstrates the efficient anti/de-icing abilities of the superhydrophobic photothermal surfaces prepared in this study. The temperature rise of the optimal structure in this work can reach 45 ℃ under the 1 sun illumination. This work could shed new light on the design optimization of anti/de-icing materials.
Superhydrophobic photothermal surface shows significant potential in the anti/de-icing field. In this work， we focus on the photothermal anti/de-icing performances of superhydrophobic surfaces with various micropatterns. A finite element simulation， coupling the wave optics and heat transfer models， is employed to illuminate the enhanced photothermal efficiency achieved by the reasonable design of surface micro/nano-structures. The effects of nanoparticle size， volume fraction， and coating thickness on the absorptivity and temperature rise of the photothermal coatings are discussed in detail. Furthermore， two hierarchical textures， including micropillars and microcones， are considered to expound the contribution of micro-scale structures on photothermal performances. Numerical results show that the surface with hierarchical textures has a better absorption efficiency of long waves than the single-scale surface， and the microcones topology presents the best photothermal efficiency. Moreover， the effects of geometric micropattern parameters， e.g. characteristic length and aspect ratio， are also discussed in detail. The illumination and ice melting test demonstrates the efficient anti/de-icing abilities of the superhydrophobic photothermal surfaces prepared in this study. The temperature rise of the optimal structure in this work can reach 45 ℃ under the 1 sun illumination. This work could shed new light on the design optimization of anti/de-icing materials.
2023(2):148-158.
DOI: 10.16356/j.1005-1120.2023.02.004
Abstract:
The research of super-cooled water droplet impingement characteristics is the basis of the ice shape prediction and the aircraft anti-icing system performance analysis. The Eulerian method is frequently used to compute the droplet motion and impingement characteristics， so it is significant to analyze the accuracy of the Eulerian method when calculating the droplet impingement on complex surfaces. Taking a NACA 0012 airfoil， an icing wind tunnel， an S-shape duct and a multi-element airfoil as the research objects， the Eulerian method is used with different meshes to obtain the water droplet motion and collection efficiency. The results show that when the water droplet is not deflected or blocked by upstream components， the results obtained by the Eulerian method are slightly affected by the mesh. However， the results calculated by the Eulerian method are mesh-dependent with upstream trajectory deflections， and the liquid water content and collection efficiency calculated using different meshes are inconsistent. The impact of the mesh on the calculation of the Eulerian method needs to be considered when droplets are affected by upstream effects. The findings of this research are beneficial for the accuracy of aircraft icing simulation.
The research of super-cooled water droplet impingement characteristics is the basis of the ice shape prediction and the aircraft anti-icing system performance analysis. The Eulerian method is frequently used to compute the droplet motion and impingement characteristics， so it is significant to analyze the accuracy of the Eulerian method when calculating the droplet impingement on complex surfaces. Taking a NACA 0012 airfoil， an icing wind tunnel， an S-shape duct and a multi-element airfoil as the research objects， the Eulerian method is used with different meshes to obtain the water droplet motion and collection efficiency. The results show that when the water droplet is not deflected or blocked by upstream components， the results obtained by the Eulerian method are slightly affected by the mesh. However， the results calculated by the Eulerian method are mesh-dependent with upstream trajectory deflections， and the liquid water content and collection efficiency calculated using different meshes are inconsistent. The impact of the mesh on the calculation of the Eulerian method needs to be considered when droplets are affected by upstream effects. The findings of this research are beneficial for the accuracy of aircraft icing simulation.
2023(2):159-168.
DOI: 10.16356/j.1005-1120.2023.02.005
Abstract:
Directional rebound of droplet impacting on solid surfaces is of great significance in engineering applications such as anti-icing/fogging and self-cleaning. Mixed-wettability surfaces have been shown to be as an effective way for droplet manipulation. The impact of droplet on hydrophobic substrate decorated with a hydrophilic stripe is investigated numerically. The validated diffuse interface method is adopted for interface capture. First， the formation of satellite droplets during the impact process is explored， and the role of mixed-wettability surfaces in the droplet spreading， retraction and rebound stages is clarified by analyzing the vertical and lateral velocities of the droplet. After that， the effect of the stripe width on the droplet rebound form and the contact time is studied systematically. Special attention is paid to the mechanisms of dynamics and energy transfer during the evolution of liquid film and droplet bouncing. The obtained results can provide useful guidance for the design of mixed-wettability surfaces and further optimize the control of droplet directional rebound.
Directional rebound of droplet impacting on solid surfaces is of great significance in engineering applications such as anti-icing/fogging and self-cleaning. Mixed-wettability surfaces have been shown to be as an effective way for droplet manipulation. The impact of droplet on hydrophobic substrate decorated with a hydrophilic stripe is investigated numerically. The validated diffuse interface method is adopted for interface capture. First， the formation of satellite droplets during the impact process is explored， and the role of mixed-wettability surfaces in the droplet spreading， retraction and rebound stages is clarified by analyzing the vertical and lateral velocities of the droplet. After that， the effect of the stripe width on the droplet rebound form and the contact time is studied systematically. Special attention is paid to the mechanisms of dynamics and energy transfer during the evolution of liquid film and droplet bouncing. The obtained results can provide useful guidance for the design of mixed-wettability surfaces and further optimize the control of droplet directional rebound.
2023(2):169-178.
DOI: 10.16356/j.1005-1120.2023.02.006
Abstract:
The shape of ice accretion on aircraft surfaces is crucial to icing wind tunnel tests. Currently， geometrical parameters of ice， such as height， angle， and location， are used to characterise the ice shape from a 2-D perspective. However， the surface roughness of ice-shape， which is crucial to aerodynamic analysis， is always ignored. In this paper， the fractal theory is used to characterise the ice roughness， and the corresponding characterisation method is explained. An aerofoil-icing test is conducted in a large icing wind tunnel to verify the feasibility and validity of the proposed method. In the test， the icing growth information of the aerofoil surface is collected using laser line scan technology. Then， the 3-D ice shape is reconstructed using the collected data. Subsequently， the 3-D ice shape is analyzed using fractal theory， where the profile curves at different positions of the ice shape are extracted. Additionally， the corresponding fractal dimension and joint roughness characterisation are calculated to summarise the linear regression equations of the fractal dimension. Then， the data points from profile curves are extracted to simulate the fractal interpolation functions of the ice. Correlation analyses show that ice accretion on the aircraft surface exhibits fractal features， and the fractal dimension is proportional to the joint roughness characterisation， which can be used as the assessment parameter of surface roughness of ice. Consequently， the fractal interpolation simulation of the ice-shape curves represent an excellent approximation of the ice accretion on aircraft surfaces. The fractal characterisation of rough surfaces provides a new approach for scientifically quantifying 3-D ice features.
The shape of ice accretion on aircraft surfaces is crucial to icing wind tunnel tests. Currently， geometrical parameters of ice， such as height， angle， and location， are used to characterise the ice shape from a 2-D perspective. However， the surface roughness of ice-shape， which is crucial to aerodynamic analysis， is always ignored. In this paper， the fractal theory is used to characterise the ice roughness， and the corresponding characterisation method is explained. An aerofoil-icing test is conducted in a large icing wind tunnel to verify the feasibility and validity of the proposed method. In the test， the icing growth information of the aerofoil surface is collected using laser line scan technology. Then， the 3-D ice shape is reconstructed using the collected data. Subsequently， the 3-D ice shape is analyzed using fractal theory， where the profile curves at different positions of the ice shape are extracted. Additionally， the corresponding fractal dimension and joint roughness characterisation are calculated to summarise the linear regression equations of the fractal dimension. Then， the data points from profile curves are extracted to simulate the fractal interpolation functions of the ice. Correlation analyses show that ice accretion on the aircraft surface exhibits fractal features， and the fractal dimension is proportional to the joint roughness characterisation， which can be used as the assessment parameter of surface roughness of ice. Consequently， the fractal interpolation simulation of the ice-shape curves represent an excellent approximation of the ice accretion on aircraft surfaces. The fractal characterisation of rough surfaces provides a new approach for scientifically quantifying 3-D ice features.
2023(2):179-192.
DOI: 10.16356/j.1005-1120.2023.02.007
Abstract:
The impact and freezing of micro-sized droplets on cold surface is simulated by the developed numerical methods which couple the multiphase lattice Boltzmann flux solver to simulate the flow field， the phase field method to track the droplet-air interface， and the enthalpy model to determine the liquid-ice interface. The accuracy and reliability of the numerical method are validated by the comparison between the predicted morphology of the droplet impact and freezing on the surface and that from the experiment. The dynamic freezing process is investigated considering the effects of the droplet size， the impact velocity and the temperature of the cold surface. The results show that the freezing of the droplet bottom inhibits the rebound after the droplet spreading， and it may even form a hat-like shape. For the droplet with higher velocity， the ice develops faster in the radial direction and the heat transfer between the droplet and surface is enhanced. In addition， the temperature governs the dynamic behavior of the droplet center. When the surface is colder， it may form a crater in the center. The analysis on the temperature distribution inside the droplet shows that the heat flux decreases with the increasing distance to the cold surface. Moreover， with the ice growing， the decreased temperature in symmetric axis is not proportional to the surface temperature. The dimensionless temperature inside the ice becomes lower for the colder surface due to the increased temperature difference.
The impact and freezing of micro-sized droplets on cold surface is simulated by the developed numerical methods which couple the multiphase lattice Boltzmann flux solver to simulate the flow field， the phase field method to track the droplet-air interface， and the enthalpy model to determine the liquid-ice interface. The accuracy and reliability of the numerical method are validated by the comparison between the predicted morphology of the droplet impact and freezing on the surface and that from the experiment. The dynamic freezing process is investigated considering the effects of the droplet size， the impact velocity and the temperature of the cold surface. The results show that the freezing of the droplet bottom inhibits the rebound after the droplet spreading， and it may even form a hat-like shape. For the droplet with higher velocity， the ice develops faster in the radial direction and the heat transfer between the droplet and surface is enhanced. In addition， the temperature governs the dynamic behavior of the droplet center. When the surface is colder， it may form a crater in the center. The analysis on the temperature distribution inside the droplet shows that the heat flux decreases with the increasing distance to the cold surface. Moreover， with the ice growing， the decreased temperature in symmetric axis is not proportional to the surface temperature. The dimensionless temperature inside the ice becomes lower for the colder surface due to the increased temperature difference.
2023(2):193-204.
DOI: 10.16356/j.1005-1120.2023.02.008
Abstract:
The icing of unmanned aerial vehicles （UAVs） poses a serious threat to flight safety. The available energy of UAVs is inadequate， so an energy-efficient ice protection strategy is required. In this paper，an integral fiberglass composite airfoil is tested， which has super-hydrophobic coating and embedded electro-thermal film （SHS-EET）. The proportional integral derivative method （PID） is used to adjust surface temperature and heating power. Experiments are conducted in an icing wind tunnel to verify the anti-icing/de-icing performance of the strategy. The results show that the super-hydrophobic coating without a heating source fails to avoid the formation of accreted ice. In addition， the ice shedding period of SHS-EET is reduced by 64.6% and the energy consumption is reduced by 72.3%. As the surface temperature is lower than 10 ℃ ![]()
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The icing of unmanned aerial vehicles （UAVs） poses a serious threat to flight safety. The available energy of UAVs is inadequate， so an energy-efficient ice protection strategy is required. In this paper，an integral fiberglass composite airfoil is tested， which has super-hydrophobic coating and embedded electro-thermal film （SHS-EET）. The proportional integral derivative method （PID） is used to adjust surface temperature and heating power. Experiments are conducted in an icing wind tunnel to verify the anti-icing/de-icing performance of the strategy. The results show that the super-hydrophobic coating without a heating source fails to avoid the formation of accreted ice. In addition， the ice shedding period of SHS-EET is reduced by 64.6% and the energy consumption is reduced by 72.3%. As the surface temperature is lower than 10
2023(2):205-215.
DOI: 10.16356/j.1005-1120.2023.02.009
Abstract:
This study investigates the dynamic behavior and heat transfer of ice crystals in high-temperature air flow after being ingested by an aero-engine. A numerical model under the Lagrange framework is built to simulate ice crystal motion， heat and mass transfer. Different ice crystal melting models and ice crystals with various shapes and sizes are also compared. The results show that when using the “naked” ice particle model， it takes longer to completely melt compared with the water cover model. It takes 0.04 s for a 20 μm particle to melt， but the melting rate of a “naked” ice particle is faster before 0.023 s. Under the same condition， the liquid water content of a spherical ice crystal is high， and that of a 20 μm spherical one is 49.05% at the outlet. The liquid water contents of ellipsoidal and hexagonal plate ice crystals are close， which are roughly 40% at the outlet. The smaller the size， the earlier the crystals start to melt， and the higher the liquid water content of the crystals. The liquid water content is 60.4% of a 20 μm ice crystal and only 15.5% of a 40 μm one at the outlet.
This study investigates the dynamic behavior and heat transfer of ice crystals in high-temperature air flow after being ingested by an aero-engine. A numerical model under the Lagrange framework is built to simulate ice crystal motion， heat and mass transfer. Different ice crystal melting models and ice crystals with various shapes and sizes are also compared. The results show that when using the “naked” ice particle model， it takes longer to completely melt compared with the water cover model. It takes 0.04 s for a 20 μm particle to melt， but the melting rate of a “naked” ice particle is faster before 0.023 s. Under the same condition， the liquid water content of a spherical ice crystal is high， and that of a 20 μm spherical one is 49.05% at the outlet. The liquid water contents of ellipsoidal and hexagonal plate ice crystals are close， which are roughly 40% at the outlet. The smaller the size， the earlier the crystals start to melt， and the higher the liquid water content of the crystals. The liquid water content is 60.4% of a 20 μm ice crystal and only 15.5% of a 40 μm one at the outlet.
2023(2):216-229.
DOI: 10.16356/j.1005-1120.2023.02.010
Abstract:
Compared with conventional wind tunnels， cryogenic wind tunnels can supply testing airflow with higher Reynolds numbers. However， the residual trace water vapor in the cryogenic wind tunnel may affect the accuracy of aerodynamic data at low temperatures. Due to the difficulty of experimental methods， the characteristics of trace water icing still need to be revealed. Based on the Eulerian method， a multiphase flow model of wet air， subcooled droplets and ice crystals is established in this paper. The icing process caused by subcooled droplets and ice crystals condensed from water vapor on the airfoil under the condition of cryogenic wind tunnels is simulated. The results show good consistency with experimental data. The effects of the total water content， melt ratio， airflow temperature， pressure， Mach number and other parameters on icing process are analyzed， and the effects of the airfoil icing on aerodynamic characteristics are also quantified， which may provide a theoretical reference for the actual operation of cryogenic wind tunnels.
Compared with conventional wind tunnels， cryogenic wind tunnels can supply testing airflow with higher Reynolds numbers. However， the residual trace water vapor in the cryogenic wind tunnel may affect the accuracy of aerodynamic data at low temperatures. Due to the difficulty of experimental methods， the characteristics of trace water icing still need to be revealed. Based on the Eulerian method， a multiphase flow model of wet air， subcooled droplets and ice crystals is established in this paper. The icing process caused by subcooled droplets and ice crystals condensed from water vapor on the airfoil under the condition of cryogenic wind tunnels is simulated. The results show good consistency with experimental data. The effects of the total water content， melt ratio， airflow temperature， pressure， Mach number and other parameters on icing process are analyzed， and the effects of the airfoil icing on aerodynamic characteristics are also quantified， which may provide a theoretical reference for the actual operation of cryogenic wind tunnels.
2023(2):230-238.
DOI: 10.16356/j.1005-1120.2023.02.011
Abstract:
When aircraft operate in a cold and humid environment， ice accretion occurs on the leading edge of wing at times， which threatens the flight safety. For developing anti-icing and de-icing technologies， it is necessary to explore the adhesive characteristic of ice covering on the blade airfoil surface. In this paper， a measurement system of ice adhesion for blade airfoil is designed and built. And an evaluation method of ice adhesion strength for the blade airfoil is proposed. The distribution and adhesion strength of ice on the blade segment with airfoil of NACA0018 are recorded and measured under different conditions. The experiment results show that icing time is less significant to the ice adhesion strength. As the ambient temperature decreases， the adhesion strength of ice on the blade airfoil surface increases， but the growth rate decreases. In addition， when the wind speed increases， the adhesion strength of ice on the blade airfoil surface decreases. The research findings provide a reference for deeply exploring the adhesion mechanism of ice covering on blade airfoil.
When aircraft operate in a cold and humid environment， ice accretion occurs on the leading edge of wing at times， which threatens the flight safety. For developing anti-icing and de-icing technologies， it is necessary to explore the adhesive characteristic of ice covering on the blade airfoil surface. In this paper， a measurement system of ice adhesion for blade airfoil is designed and built. And an evaluation method of ice adhesion strength for the blade airfoil is proposed. The distribution and adhesion strength of ice on the blade segment with airfoil of NACA0018 are recorded and measured under different conditions. The experiment results show that icing time is less significant to the ice adhesion strength. As the ambient temperature decreases， the adhesion strength of ice on the blade airfoil surface increases， but the growth rate decreases. In addition， when the wind speed increases， the adhesion strength of ice on the blade airfoil surface decreases. The research findings provide a reference for deeply exploring the adhesion mechanism of ice covering on blade airfoil.
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