Icing Wind Tunnel Research Articles

Dense-HR-GAN: A High-Resolution GAN Model with Dense Connection for Image Dehazing in Icing Wind Tunnel Environment

To address the issue of blurred images generated during ice wind tunnel tests, we propose a high-resolution dense-connection GAN model, named Dense-HR-GAN. This issue is caused by attenuation due to scattering and absorption when light passes through cloud and fog droplets. Dense-HR-GAN is specifically designed for this environment. The model utilizes an atmospheric scattering model to dehaze images with a dense network structure for training. First, sub-pixel convolution is added to the network structure to remove image artifacts and generate high-resolution images. Secondly, we introduce instance normalization to eliminate the influence of batch size on the model and improve its generalization performance. Finally, PatchGAN is used in the discriminator to capture image details and local information, and then drive the generator to generate a clear and high-resolution dehazed image. Moreover, the model is jointly constrained by multiple loss functions during training to restore the texture information of the hazy image and reduce color distortion. Experimental results show that the proposed method can achieve the state-of-the-art performance on image dehazing the in icing wind tunnel environment.

An Experimental Study on Biochar/Polypyrrole Coating for Blade Anti-Icing of Wind Turbines

Wind turbines operating in cold regions are prone to freezing in winter, which can affect their performance and safety. To resolve this situation, the development of blade anti-icing technology has attracted widespread attention. In this study, a type of biochar/polypyrrole coating was obtained through synthesis on the surface of biochar. After characterization, it was found that the porous structure, irregular dents, and bumps on the surface of biochar/polypyrrole material contributed to the formation of a nanoscale roughness structure with a typical super-hydrophobic nanostructure. Additionally, it had a sufficient surface area. The wetting characteristics of the coating were analyzed with the assistance of a contact angle measurement instrument. The contact angle of the coating was determined as 151°, which indicates the excellent hydrophobic properties of the coating. Icing wind tunnel tests were carried out to evaluate the anti-icing effect of biochar coating and biochar/polypyrrole coating at different ambient temperatures and wind speeds. Compared with uncoated leaves, the icing area of biochar/polypyrrole coating was reduced. Additionally, the anti-icing effect of biochar/polypyrrole coating was most significant. This study provides a practical reference for the research of anti-icing coating on wind turbine blades.

Wind tunnel test of ice accretion on blade airfoil for wind turbine under offshore atmospheric condition

For wind turbines under offshore conditions, ice accretion occurs on the blade surface in winter because of the cold and humid environment, which leads to the performance degradation of the wind turbine. The characteristics of icing on the wind turbine blade surface under the in-cloud condition with salinity are explored. A blade segment with an airfoil of NACA0018 is selected. The tests of icing on the blade surface in different conditions of salinities, temperatures, and wind speeds are conducted in a return-flow icing wind tunnel. Two parameters are defined to evaluate icing characteristics. The distribution and amount of ice are analyzed quantitatively. Results show that salinity can restrain the amount of ice accretion. Oppositely, low temperatures and high wind speeds can increase the amount of ice. A self-developed device was manufactured to measure the adhesion strength of ice. The effects of salinity, temperature, and wind speed on adhesion strength are studied. Research indicates that adhesion strength decreases sharply first and then slowly with an increase in salinity. Even though low temperature and high wind speed both increase the adhesion strength, the growth rate decreases. The research provides a reference for anti- and de-icing technologies of offshore wind turbines.

A Wind Tunnel Test of the Anti-Icing Properties of MoS2/ZnO Hydrophobic Nano-Coatings for Wind Turbine Blades

Wind turbines operating in cold regions are prone to blade icing, which seriously affects their aerodynamic characteristics and safety performance. Coatings are one of the effective solutions to the icing problem on wind turbine blades. In this study, MoS2/ZnO/PDMS superhydrophobic nano-anti-icing coatings were prepared using the hydrothermal method and the liquid phase method. SEM revealed that the MoS2/ZnO coating was a typical superhydrophobic nanostructure with an ultra-thin sheet-like morphology of clusters and a hilly nano-rough structure, with contact angles (CA) of 152.1° and 4.7° with water droplets and the sliding angle (SA), respectively. The MoS2/ZnO/PDMS coating had an adhesion strength to ice of 78 kPa, which was 60.2% lower than an uncoated surface. The icing effects of the NACA0018 airfoil blade model with or without MoS2/ZnO coatings were studied at different ambient temperatures and wind speeds using the icing wind tunnel test. The results showed that, compared to uncoated blades, the level of icing was lower on the blade airfoil surface that was coated with MoS2/ZnO. At 10 m/s and −10 °C, the icing thickness and icing area of the leading edge of the blade airfoil were 13.7% and 28.3% lower, respectively. This study provides a valuable reference for the development of anti-icing coatings for wind turbine blades.

Asymmetric Heat Transfer in Aircraft Electrothermal Anti-Icing

Aircraft icing is an important cause of air disasters, and electrothermal anti-icing is a common protection method. In this work, the influence of icing meteorological conditions on the anti-icing was studied through an icing wind tunnel experiment on the fairing. Based on the finite volume method, a transient heat transfer calculation method for electrothermal anti-icing was proposed. The calculated results were compared with the experimental results, and the influence of heating mode and structure layout on the anti-icing effect was analyzed. The results show that the calculated results are in good agreement with the experimental results, and the heat transfer of the anti-icing structure shows obvious asymmetry. First, during heating, the temperature gradient of the structural profile is large, the high temperature is concentrated in the heating layer, and the temperature distribution of the heating layer is relatively uniform. During cooling, the temperature distribution of the structural profile is more uniform, the high temperature is mainly concentrated in the back conduction layer, and the temperature of the outer wall increases first and then decreases from the center to the surroundings. Second, when the spray is turned on, the temperature of the outer wall is significantly reduced, but the temperature of the heating layer hardly changes. Third, the uniform heating mode can simultaneously raise the temperature of the outer wall and reduce the temperature of heating layer. Fourth, while the front conduction layer can significantly affect the temperature of the heating layer and the outer wall, the effect of the back conduction layer is small. However, the back one can be used to control the structural temperature more finely.

An experimental study of icing distribution on a symmetrical airfoil for wind turbine blade in the offshore environmental condition

For offshore installations in high-latitude regions, such as offshore wind turbines, ice accretion sometimes occurs on the blade surface due to cold and humid environments or splashed seawater. Hence, a potential hazard exists for the wind turbine. Icing destroys the aerodynamic characteristics of the blade airfoil and increases operational and maintenance fees. In this paper, icing tests of blade airfoils under offshore icing conditions are carried out. An icing wind tunnel is built by combining a conventional wind tunnel with a naturally low temperature in winter. A blade segment with NACA0018 airfoil is selected, while the effects of salinity, temperature, and wind speed on the icing area, the thickness of ice, and the icing scope on the blade surface are tested and analyzed. Experimental results show that the icing area and the thickness of ice both increase linearly with icing time. Salinity can decrease the icing area, and the thickness of ice compared to non-salinity conditions but has a minor effect on the icing scope. The icing scope is mainly in the range of −20%-20% at the relative position of the blade chord. Research findings lay an experimental foundation for in-depth exploration of the icing characteristics of an offshore wind turbine.

A corncob biochar-based superhydrophobic photothermal coating with micro-nano-porous rough-structure for ice-phobic properties

Biomass resource utilization promotes low-carbon technology advancement, and combining it with the superhydrophobic materials for ice-phobic coatings on wind turbine blades is conducive to environmental protection and developing clean energy. In this study, a Fe3O4-loaded biochar-based superhydrophobic ice-phobic coating with photothermal conversion effect was prepared from corncob. The decreased oxygen-to-carbon ratio of the carbon-based material reduced the surface energy, and its synergistic effect with the rough structure contributed to the superhydrophobicity of the coating. Icing wind tunnel experiments showed a reduction in blade icing mass of at most 32.71 % due to the generation of droplet bounce when colliding with the blade surface. Biochar-based materials efficiently absorbed optical energy and vibrational heat production of FeO bond during illumination, which enabled the coating to warm up to 55.9 °C and advance the de-icing rate by 42.71 %. This study provides new ideas for the application of biomass resources in the field of anti-icing/de-icing for wind energy.

A Holistic Solution to Icing by Acoustic Waves: De‐Icing, Active Anti‐Icing, Sensing with Piezoelectric Crystals, and Synergy with Thin Film Passive Anti‐Icing Solutions

AbstractIcing has become a hot topic both in academia and in the industry given its implications in transport, wind turbines, photovoltaics, and telecommunications. Recently proposed de‐icing solutions involving the propagation of acoustic waves (AWs) at suitable substrates may open the path for a sustainable alternative to standard de‐icing or anti‐icing procedures. Herein, the fundamental interactions are unraveled that contribute to the de‐icing and/or hinder the icing on AW‐activated substrates. The response toward icing of a reliable model system consisting of a piezoelectric plate activated by extended electrodes is characterized at a laboratory scale and in an icing wind tunnel under realistic conditions. Experiments show that surface modification with anti‐icing functionalities provides a synergistic response when activated with AWs. A thoughtful analysis of the resonance frequency dependence on experimental variables such as temperature, ice formation, or wind velocity demonstrates the application of AW devices for real‐time monitoring of icing processes.

Passive Anti-Icing Performances of the Same Superhydrophobic Surfaces under Static Freezing, Dynamic Supercooled-Droplet Impinging, and Icing Wind Tunnel Tests.

Overcoming ice accretion on external aircraft wing surfaces plays a crucial role in aviation, and developing environmentally friendly passive anti-icing surfaces is considered to be a promising strategy. Superhydrophobic surfaces (SHSs) have attracted increasing attention due to their potential advantages of keeping the airframe dry without causing additional aerodynamic losses. However, the passive anti-icing performances of SHSs reported to date varied a lot under different icing test conditions. Therefore, a systematic investigation is necessary to elucidate the icing conditions where SHSs can remain effective and pave the way for SHSs toward practical anti-icing applications. Herein, we designed and fabricated a typical type of SHS featuring dual-scale hierarchical structures with arrayed micromountains (with both spacings and heights of tens of micrometers) covered by single-scale sandy-corrugation-like periodic structures (with both spacings and heights of only several micrometers) (termed SS1). Its anti-icing performances under three representative icing conditions, including static water freezing, dynamic supercooled-droplet impinging, and icing wind tunnel conditions, were comparatively investigated. The SS1 SHS maintained a lower static ice-adhesion strength (<60 kPa even after 50 deicing cycles at temperatures as low as -25 °C), which was attributed to a cumulative cracking effect facilitating the ice detachment. Within the laboratory dynamic icing tests, the SS1 SHSs with micromountain heights of 20-30 μm performed optimally in the antiadhesion of supercooled droplets (at an impinging velocity of 3.4 m/s and temperatures of -5 to -25 °C). In spite of the significant anti-icing performances of the SS1 SHSs in both static and dynamic laboratory tests, they could hardly sustain reliable passive anti-icing performances in harsher icing wind tunnel tests with supercooled droplets impinging their surfaces at velocities of up to 50 m/s at a temperature of -5 °C for 10 min. This study can inspire the development of improved SHSs for achieving satisfactory anti-icing performances in real-aviation conditions.

Experimental study on icing and anti-icing of a rotating conical spinner

Icing and hot-air anti-icing tests of a rotating conical spinner were carried out in an icing wind tunnel. The surface temperature was measured using a calibrated infrared thermal imager. The icing process and the water film flow on the spinner were recorded by a high-speed camera. In the icing test with temperature of −21.7 °C and LWC (liquid water content) of 0.5 g/m3, white rime ice grows and covers the entire surface. From the cone tip the ice thickness decreases from 5.8 mm to a minimum of 3.2 mm, while in the rear part the ice thickness increases. In the icing test with temperature of −9.4 °C and LWC of 1.0 g/m3, long pine needle-shaped ice forms downstream the cone tip area. The anti-icing surface temperature first increases and then decreases along the spinner generatrix, with a maximum value near the tip. Under nearly identical incoming flow conditions the higher the mass flow of hot air is, the greater the decrease in surface temperature is. For the anti-icing tests with LWC of 0.5 g/m3, from t = 40 s, as the mass flow of the hot air is low the spinner surface is completely covered by water film. There exists a complete evaporation area near the cone tip with a high mass flow. For the anti-icing tests with LWC of 1.0 g/m3, from t = 40 s the spinner surface is completely covered by water film in all test runs.

STUDY OF DRY ICE GROWTH ON DUPLEX CYLINDERS

A study of dry ice growth on bundled (duplex) cylinders has been performed using icing wind tunnel experiments and computational fluid dynamics (CFD) numerical simulations. The aim of this study is to "fill the gaps" in the works of Wagner (2010) and Qing et al. (2018). The numerical simulations cover a range of possible icing conditions by varying the operating wind speed, median volume diameter, and for some cases-the angle of incidence between the cylinders. The obtained results for the 0&amp;deg; AoA show that the accreted ice masses ratio between the leeward and windward cylinder varies from &amp;#126; 100&amp;#37; to &amp;#126; 30&amp;#37;. The accreted ice masses ratio decreases with the increase in the wind speed and/or median volume diameter. For the cases with non-zero AoA, the accreted ice masses become approximately equal, when the AoA is large enough to produce a vertical separation equal or greater to one cylinder diameter.

Icing wind tunnel measurements of supercooled large droplets using the 12 mm total water content cone of the Nevzorov probe

Abstract. Supercooled large droplet (SLD) icing can occur behind the protected surfaces of an aircraft and create severe aerodynamic disturbances, which represent a safety hazard for aviation. Liquid water content (LWC) measurements in icing conditions that contain SLDs require instruments that are able to sample unimodal and bimodal droplet size distributions with droplet diameters from 2 to 2000 µm. No standardized detection method exists for this task. A candidate instrument, which is currently used in icing wind tunnel (IWT) research, is the Nevzorov probe. In addition to the standard 8 mm total water content (TWC) collector cone, a novel instrument version also features a 12 mm diameter cone, which might be advantageous for collecting the large droplets characteristic of SLD conditions. In the scope of the two EU projects, SENSors and certifiable hybrid architectures for safer aviation in ICing Environment (SENS4ICE) and ICE GENESIS, we performed measurement campaigns in SLD icing conditions in IWTs in Germany, Austria and the USA. We obtained a comprehensive data set of measurements from the LWC sensor, the 8 mm cone sensor and the 12 mm cone sensor of the Nevzorov probe, and from the tunnel reference instrumentation. In combination with measurements of the particle size distribution, we experimentally derive a collision efficiency curve that is based on a suitable functional form for the new 12 mm cone for median volume diameters (MVDs) between 12 and 58 µm and wind tunnel speeds from 40 to 85 m s−1. Knowledge of this curve allows us to correct the LWC measurements of the 12 mm cone (LWC12) in particular for the inevitably high decrease in collision efficiency for small droplet diameters. In unimodal SLD conditions, with MVDs between 128 and 720 µm, LWC12 generally agrees within ±20 % with the tunnel LWC reference values from a WCM-2000 and an isokinetic probe. An increase in the difference between LWC12 and the WCM-2000 measurements at larger MVDs indicates better droplet collection properties of the 12 mm cone. Similarly, the favorable detector dimensions of the 12 mm cone explain a 7 % enhanced detection efficiency compared to the 8 mm cone; however this difference falls within the instrumental uncertainties. Data collected in various bimodal SLD conditions with MVDs between 16 and 534 µm and LWCs between 0.22 and 0.72 g m−3 also show an agreement within ±20 % between LWC12 and the tunnel LWC, which demonstrates the suitability of the Nevzorov sensor head with the 12 mm cone for measurements of LWC in Appendix O icing conditions.

Superhydrophobic coating induced anti-icing and deicing characteristics of an airfoil

Aircraft icing seriously threatens flight safety. The widely used electrothermal anti/de-icing technology has high energy consumption and poor performance. The bionic superhydrophobic surface has anti-icing potential, which can be combined with electric heater technology to achieve energy savings and efficiency improvement. In the previous research, we developed a superhydrophobic coating with mechanochemical robustness for aircraft anti-icing and proved its excellent anti-icing performance. This research combines this coating with the graphene electric heater to obtain a coupling system and explores its anti-icing effect under aviation conditions through the ice wind tunnel test. The results showed that the coating significantly improves the anti-icing properties, delaying the icing process for 10 s, saving the anti-icing energy consumption by 21% compared with graphene heating alone, and increasing the deicing efficiency by 250%. When the coating protection area reaches 30% chord, it can achieve a 'dry' anti-icing state, and this coupling system saves energy by 60% compared with wire heating. Furthermore, The ‘honeycomb structure’ coating is better in anti-icing effect, and the ‘island structure’ coating has stronger anti-icing stability. The hydrophobicity of the coating is less affected by the high-speed droplet impact, so it has a long life expectancy in the active anti-icing mode. This study can provide new ideas for solving the problem of aircraft icing.

Contrast Icing Wind Tunnel Tests between Normal Droplets and Supercooled Large Droplets

In order to compare and analyze the similarities and differences between normal droplet icing shapes and supercooled large droplet icing shapes, SADRI carried out normal droplet and supercooled large droplet icing wind tunnel tests in the NRC−AIWT icing wind tunnel. Taking the typical glaze ice in normal droplet icing conditions as the reference, the freezing drizzle and freezing rain icing tests under the supercooled large droplet conditions were carried out. The test results show that compared with normal droplets, the ice horn height of supercooled large droplets decreases with the increase in droplet particle size, and even the ice horn characteristics are not obvious when the icing condition is freezing rain. At the same time, the range and height of rough element ice shape after the main ice horn of supercooled large droplets are significantly larger and higher than those of the normal droplets, while the difference in the rough element in different supercooled large droplet icing conditions is small.

Considering Thermal Diffusivity as a Design Factor in Multilayer Hybrid Ice Protection Systems

Icing is a major problem that affects the aeronautical sector, which is forced to use anti- and de-icing systems to ensure flight safety. The currently used systems are effective but exhibit high energy consumption. Resistive heating is used to prevent ice accretion or to release it once it has formed. To satisfy all the imposed airworthiness requirements, such as low aerodynamic impact, resistance to lightning strikes, no overheating, etc., multilayer systems are commonly configured with different layers fulfilling specific functions. For example, the Boeing 787 Dreamliner uses dry woven glass fiber fabric on top of the heating element to provide galvanic insulation and dielectric resistance. It satisfies the above-mentioned requirements, but its thermal conductivity is very low, therefore reducing energy efficiency. The thermal distribution of two materials (AA6061 aluminum alloy and PTFE) with significantly different thermal and electrical properties in contact with a heating element was studied. Finite element calculations and experimental testing in an icing wind tunnel were carried out at −12 °C under different convection conditions: natural (0 m/s) and forced (35 and 70 m/s), using specimens of different sizes. Heating elements areas were also varied. AA6061 showed homogeneous heating, whereas differences of up to 80 °C were observed when using PTFE. In addition, the test results highlighted the effect of forced convection and the need to evaluate these systems “in close to operative” conditions. The calculation results proved to it be an interesting tool for studying the behavior of the systems avoiding extensive testing.

A computational strategy for determining the optimal scaled wind speed in icing wind tunnel experiments

The icing wind tunnel experiment is one of the most important methods to investigate icing problems. Due to the blockage or capability limitations of icing wind tunnels, the geometric size of the testing model is usually needed to be sub-scaled and the corresponding icing conditions are required to be converted. However, the icing phenomenon is affected by various parameters, and how to determine the optimal subscale wind speed remains inconclusive. To solve this problem, a new computational strategy, named Improved Ruff Icing Scaling Method (IRISM), is proposed. In IRISM, the Ruff icing scaling theory is firstly applied to calculate the basic sub-scale temperature and the related cloudy parameters, etc., and then the icing numerical computation is utilized to evaluate the influence of sub-scale icing conditions on the similarity of the reference and subscale ice shapes. Finally, the optimal scaled wind speed is calculated by Differential Evolution Genetic Algorithm based on a high-efficient surrogate model, in which the ice shape consistency especially the ice horn structure is set as the optimization objective. The IRISM is comprehensively analyzed by icing numerical computations as well as icing wind tunnel experiments. The results show that the IRISM is capable of automatically providing the optimal scaled wind speed with the acceptable icing scaling error. As an important supplement to the current icing scaling methods, the IRISM can find the reasonable experimental parameters of scaled icing wind tunnel tests, which provides a new way for icing scaling analysis.

Fiber Bragg Grating Sensors ice detection: Methodologies and performance

New Researches have been done recently in order to create and adapt new systems to the recent Appendix O FAR 25 Aeronautical aircraft icing regulations. One important issue are the Supercooled Large Droplets (SLD) that are an important hazard in many cases. Novel sensor technologies for aircraft are being developed in order to assess the ice severity and to discriminate between large size droplets and small size droplets ice accretions. The European SENS4ICE project gives founding for the research and development of several aeronautical ice detection systems that can discriminate between Appendix C and Appendix O conditions. In the present paper, the strengths and weaknesses of the Fiber Optic ice Detector (FOD) developed by INTA are discussed using a test matrix from the Canadian National Research Council (NRC). The FOD has presented good performance at the NRC ice wind tunnel tests in the ice detection time, detecting ice in most cases earlier than required by the actual standard (ED-103). Its lightness, low intrusiveness and small size, makes the FOD ideal for aeronautical applications. It measures indirectly the icing cloud characteristics, such as the liquid water content (LWC) and the ice accretion rate, so only an approximate severity assessment could be done. • FBG sensors are useful for fast detection. • The Optic Fiber sensors can estimate the icing conditions in rime conditions • The optic fiber sensor can provide of information about the type of ice and its location

Prediction of evaporator outlet temperature of icing windtunnel using deep neural network

This paper presents a deep neural network-based model for predicting the evaporator outlet&apos;s airflow temperature. Particularly, the Bi-directional Long Short-Term Memory (BiLSTM) neural network and Self-Attention mechanism are combined to establish the proposed prediction model. Using the cooling condition parameters and the evaporator outlet&apos;s airflow temperature as the input and output, respectively, an airflow temperature prediction model was trained in a supervision fashion. Then, through evaluations, we found that the mean square error (MSE) between the predicted temperature and the actual temperature is about 0.28, and the mean absolute error (MAE) between them is around 0.21°C. The preliminary study demonstrated that the airflow temperature inferred from cooling condition parameters was feasible.

Analysis of Numerical Methods for Droplet Impingement Characteristics under Aircraft Icing Conditions

The investigation of super-cooled droplet impingement characteristics is the most important step for aircraft icing and anti-icing/de-icing analyses. The Lagrangian method and the Eulerian method are widely used to compute the droplet motion and collection efficiency, and the two methods are considered to obtain almost the same results for surface impingement characteristics under icing conditions. The models and implementation approaches of the two methods were established in this work, and the simulations of droplet motion were carried out for a NACA 0012 airfoil, a 2D section of an A320 head, a multi-element airfoil, and an icing wind tunnel. The collection efficiencies of the NACA 0012 airfoil obtained by the present Lagrangian and Eulerian methods show good agreement with the results in the literature, validating the established methods. The droplet impingement characteristics of the two methods are consistent for the aircraft surfaces without upstream trajectory deflections. However, when the droplet motion is deflected by the frontal body before hitting the rear surfaces, the results obtained by the two methods are different whether the droplet trajectories intersect or not, which subverts the traditional opinion that the Lagrangian and Eulerian methods would obtain the same result of the droplet impingement characteristics. The reason is studied in detail according to the droplet motion results in the icing wind tunnel. The findings of this work are helpful for the accuracy of aircraft icing and anti-icing/de-icing simulations, and useful for the development of airworthiness certification.

Durable Metallic Surfaces Capable of Passive and Active De‐Icing

Ice accretion has adverse effects on several industrial sectors worldwide. Sparsely suspended, thin metallic sheets (buckling elastomer‐like anti‐icing metallic surfaces, or BEAMS) recently demonstrated extremely low ice adhesion strengths while maintaining durability. Here, BEAMS are designed using elastomeric suspension points shaped as channels, enabling active de‐icing by flowing air underneath the suspended sheet. The channel geometry is optimized using computational fluid dynamics by iterating through various channel dimensions and flow conditions. An experimental setup is constructed and utilized to assess BEAMS comprised of 1–4 channels. Active de‐icing is achieved by pressurizing the air within the channels to bulge the sheet outward and delaminate accreted ice from the interface. Active de‐icing is achieved by flowing room temperature air through the channels to heat the surface and melt the interface. Passive de‐icing is also observed under atmospheric icing conditions. Rime is accreted within an icing wind tunnel on multichannel BEAMS. Ice adhesion strengths &lt;8 kPa are maintained after ten consecutive icing/de‐icing runs, demonstrating substantial durability. The active and passive de‐icing capability of channeled BEAMS makes it a promising candidate for improving the operational efficiency of infrastructure in cold environments.