Glaze Ice Conditions Research Articles

An experimental study on different plasma actuator layouts for aircraft icing mitigation

An experimental study was conducted to examine the effects of dielectric-barrier-discharge plasma (DBD) actuator layout on the plasma-induced thermal characteristics and evaluate their effectiveness for aircraft icing mitigation. The experimental investigation was performed in the Icing Research Tunnel of Iowa State University (i.e., ISU-IRT) with an airfoil/wing model embedded with an array of DBD plasma actuators around the airfoil leading edge. The plasma actuators were arranged in different layouts (e.g., orientation, number, and width of exposed electrodes) to evaluate their effects on the anti-icing performance under a typical glaze icing condition pertinent to aircraft inflight icing phenomena. While the dynamics ice accretion or anti-icing process over the airfoil surface before and after turning on the plasma actuators was recorded by using a high-resolution imaging system, a high-speed infrared thermal imaging system was used to quantitatively map the temperature distributions over the airfoil surface. The experimental results clearly reveal that, with the same power consumption level, the plasma actuators in streamwise layout would result in higher plasma-induced surface heating and faster runback of the unfrozen water over the airfoil surface, thereby, having a noticeably better anti-icing performance, in comparison to those in spanwise layout. The plasma actuators in streamwise layout were found to not only be able to prevent ice accretion near the airfoil leading edge, but also allow the plasma-induced surface heating to convect further downstream to delay/prevent the runback ice formation near the airfoil trailing edge. A proper combination of the plasma actuation strength and the plasma discharge coverage over the airfoil surface was found to result in the optimum performance for aircraft anti-icing applications.

Numerical Simulation of the Anti-Icing Performance of Electric Heaters for Icing on the NACA 0012 Airfoil

Ice accretion is a phenomenon whereby super-cooled water droplets impinge and accrete on wall surfaces. It is well known that the icing may cause severe accidents via the deformation of airfoil shape and the shedding of the growing adhered ice. To prevent ice accretion, electro-thermal heaters have recently been implemented as a de- and anti-icing device for aircraft wings. In this study, an icing simulation method for a two-dimensional airfoil with a heating surface was developed by modifying the extended Messinger model. The main modification is the computation of heat transfer from the airfoil wall and the run-back water temperature achieved by the heater. A numerical simulation is conducted based on an Euler–Lagrange method: a flow field around the airfoil is computed by an Eulerian method and droplet trajectories are computed by a Lagrangian method. The wall temperature distribution was validated by experiment. The results of the numerical and practical experiments were in reasonable agreement. The ice shape and aerodynamic performance of a NACA 0012 airfoil with a heater on the leading-edge surface were computed. The heating area changed from 1% to 10% of the chord length with a four-degree angle of attack. The simulation results reveal that the lift coefficient varies significantly with the heating area: when the heating area was 1.0% of the chord length, the lift coefficient was improved by up to 15%, owing to the flow separation instigated by the ice edge; increasing the heating area, the lift coefficient deteriorated, because the suction peak on the suction surface was attenuated by the ice formed. When the heating area exceeded 4.0% of the chord length, the lift coefficient recovered by up to 4%, because the large ice near the heater vanished. In contrast, the drag coefficient gradually decreased as the heating area increased. The present simulation method using the modified extended Messinger model is more suitable for de-icing simulations of both rime and glaze ice conditions, because it reproduces the thin ice layer formed behind the heater due to the runback phenomenon.

An experimental study on dynamic ice accretion and its effects on the aerodynamic characteristics of stay cables with and without helical fillets

An experimental investigation was conducted to examine the effects of helical fillets on dynamic ice accretion process over the surfaces of bridge stay cables and evaluate its effects on the aerodynamic characteristics of the stay cables under both dry rime and wet glaze icing conditions. The experimental study was performed in the Icing Research Tunnel of Iowa State University (i.e., ISU-IRT). Four bridge stay cable models, including a standard plain cable model and three helical filleted cable models of different helical pitch lengths, were used for the experimental investigation. During the experiment, in addition to using a high-speed imaging system to record the dynamic ice accretion process over the cable surfaces, a Digital Image Projection (DIP) based 3D scanning system was also utilized to quantify the 3D shapes of the ice structures accreted on the test models. While a high-resolution digital Particle Image Velocimetry (PIV) system was used to characterize the wake flows behind the cable models during the ice accreting process, the time variations of the aerodynamic drag forces acting on the test models were also measured by using a pair of force/moment transducers mounted at two ends of the cable models. It was found that, under the rime icing condition, the helical filleted cable models accreted more ice structures than the standard plain cable model. However, the helical filleted cable models were found to have less ice accretion under the wet glaze icing condition. The pitch length of the helical fillets was also found to affect the ice accretion process substantially. Under the rime icing condition, while the aerodynamic drag forces acting on the cable models were found to decrease continuously with more rime ice accreting over the cable surfaces, the drag reduction due to the rime ice accretion was found to be less obvious for the helical filleted cable models, in comparison with that obtained for the standard plain cable model. Under the glaze icing condition, the aerodynamic drag forces acting on the cable models were found to decrease quickly at the initial stage of the glaze icing process, and then increase gradually with the increasing ice accretion time at the later stage of the ice accreting process. PIV flow field measurements were correlated with the force measurement data to elucidate the underlying physics for a better understanding of the variation characteristics of the aerodynamic forces acting on the cable models under different icing conditions.

Correction of Local Collection Efficiency Based on Roughness Element Concept for Glaze Ice Simulation

ABSTRACTIn glaze ice conditions, beads on the surface usually grow to form roughness elements through coalescence, finally resulting in enhancement of local collection efficiency. However, the effects of roughness elements due to freezing of beads are not reflected on the local collection efficiency in CFD icing simulations. This is problematic for predicting the resultant ice shape, which may lead to inaccurate aerodynamic performance and load distribution. The aim of this study is to propose a macroscopic icing model which can reflect bead microscopic phenomena using the Eulerian approach. To this end, a correction was made for collection efficiency by introducing a novel parameter - the effective impinging angle- which is the angle to calculate the local collection efficiency depending on the physical state of surface. It is assumed that the parameter related to the contact angle represents the state of beads. The computational icing analysis of airfoil was performed using the proposed model both in the rime condition and glaze conditions. The results show that the icing characteristics in the feather region is captured with enhanced accuracy in both conditions.

Development of an icing simulation code for rotating wind turbines

This study aims to develop a three-dimensional icing simulation code named WISE (Wind turbine Icing Simulation code with performance Evaluation) integrated into OpenFOAM®. The freely available source code can contribute to icing simulations that require parallel computations. The rotational motion is explained by a Moving Reference Frame (MRF) in both aerodynamic and droplet fields. The thin water film theory is applied in the thermodynamic module. To verify WISE, ice accretion shapes on NREL Phase VI under rime and glaze icing conditions were considered. The ice accretion shapes obtained by WISE were compared against FENSAP-ICE and another numerical simulation without the MRF method for the droplet field. For the rime condition, the icing limits, maximum thickness, and its location are well predicted by WISE compared with FENSAP-ICE while the simulation without the MRF method overestimates the icing limits and maximum thickness. For the glaze condition, only WISE and FENSAP-ICE results are compared where the icing limits are slightly different. On the suction side, WISE accurately predicts the maximum thickness, ice growth direction, and icing limits. However, the thickness of ice on the pressure side is underestimated. It might be necessary to have a turbulence model that can predict the flow transition.

An experimental study to characterize the effects of initial ice roughness on the wind-driven water runback over an airfoil surface

In the present study, an experimental study was conducted to characterize the effects of initial ice roughness on the transient behaviors of surface water/ice run-back over a NACA 23012 airfoil model under a glaze icing condition. The experimental study was conducted in the Icing Research Tunnel of Iowa State University (i.e., ISU-IRT). A digital image projection (DIP) technique was applied to provide non-intrusive, temporally-and-spatially-resolved measurements of the thickness distributions of the dynamic water/ice flows over the airfoil surface. Two typical surface morphologies were observed for the surface water runback over the airfoil models: water film flow and water rivulets flow. While the surface water film flow modulated with one primary wave and multiple secondary waves is observed at lower wind speed conditions (i.e., U∞ = 10 m/s), the water rivulets flow is observed at relatively higher wind speed conditions (i.e., U∞ = 15 m/s). The initial ice roughness is found to retard and shorten the primary wave formation in the water film flow. It is also found that the initial ice roughness could trap and decelerate the water flow and decrease the inertia force in the film front, which essentially delays the formation of the rivulets. The water rivulet flow trapped by the initial roughness was found to have a meandering behavior, due to which, the initially formed narrow rivulets merged into wider rivulets as they move downstream. By recognizing the film/rivulets boundary during the dynamic surface water/ice runback process, the quantitative details were extracted, i.e., the formation, transition, and development of the rivulet flows. The initial ice roughness was found to have a significant effect on the rivulet characteristics (e.g., rivulet width, spacing, and height).

An experimental investigation on the dynamic glaze ice accretion process over a wind turbine airfoil surface

Icing events, particularly under precipitation-icing conditions in which high-liquidity glaze ice tends to form, could pose significant threats to the safe and effective operations of wind turbines in cold and wet environments. During the glaze ice accretion process, the wind-driven unfrozen water was coupled with the growth of ice structures and difficult to be quantified and characterized. In the present study, we introduced a Digital Image Projection (DIP) technique to quantitatively measure the unsteady water runback behaviors and dynamic ice accretion process under typical glaze icing conditions over a highly-cambered wind turbine airfoil surface, i.e., the pressure-side surface of DU91-W2-250 airfoil, in the Icing Research Tunnel at Iowa State University (ISU-IRT). DIP measurement results were found to be able to successfully capture the time-resolved three-dimensional information of the water transport behaviors over the ice accreting surface of the airfoil model during the glaze icing processes. The stumbling motions of the rivulet flows were observed during the icing processes, coupled with an increasing fluctuations induced by the underneath ice roughness. The forces acting on the rivulet flows were analyzed, and a theoretical model based on the force balance was built to predict the rivulet flows. The effects of the incoming airflow velocity on the glaze icing process over the airfoil surface were also studied, and it was found that, as the incoming flow velocity increased, the runback rivulet flows would move farther downstream and became thinner and narrower due to the increased aerodynamic stress acting on them. The rivulet bulged shape was found to have an inverse relationship with the inflow velocity squared. In addition, the ice accreted over the airfoil surface during an icing process was quantitatively decoupled from the unfrozen wind-driven water, and the quantitative results can be used to validate and optimize current ice accretion models.

Dynamic ice accretion process and its effects on the aerodynamic drag characteristics of a power transmission cable model

An experimental study was conducted to examine the dynamic ice accretion process over the surface of a high-voltage power transmission cable model and characterize the effects of the ice accretion on the aerodynamic forces acting on the test model. The experimental study was carried out by leveraging the unique Icing Research Tunnel of Iowa State University (i.e., ISU-IRT) to generate typical wet glaze and dry rime icing conditions experienced by power transmission cables. A cylindrical power cable model, which has the same diameter as that of typical power transmission cables, was mounted in ISU-IRT for the ice accretion experiments. In addition to using a high-speed digital imaging system to record the dynamic ice accretion process, a novel digital image projection (DIP) based technique was utilized to quantify the 3D shapes of the ice structures accreted on the surface of the power cable model as a function of the ice accretion time. The time variations of the aerodynamic drag force acting on the test model during the dynamic ice accretion process were also measured quantitatively by using high-sensitive force/moment traducers mounted at two ends of the test model. The ice structures accreted over the surface of the power cable model were found to change significantly under different icing conditions (i.e., rime icing vs. glaze icing). The characteristics of the aerodynamic drag acting on the test model was found to vary significantly during the dynamic ice accretion process depending on what types of ice structures were accreted on the test model. The acquired snapshots of the ice accretion images and the measured 3D shapes of the accreted ice structures on the test model are correlated with the aerodynamic force measurement results to elucidate the underlying physics.

Performance and mechanism analysis of nanosecond pulsed surface dielectric barrier discharge based plasma deicer

Ice accretion on aircraft surfaces, especially on wings, may do harm to the aerodynamic performance and safety of an aircraft. In this work, de-icing experiments on an NACA0012 airfoil model were conducted in an icing wind tunnel using nanosecond pulsed surface dielectric barrier discharge (nSDBD) actuator under typical glaze icing conditions. The spatial-temporal distribution of the temperature and the dynamic process of de-icing on the surface of the airfoil were obtained and analyzed. Accreted ice with an average thickness of 3 mm can be removed within 4 s by nSDBD, and then the ice never appeared again on the plasma-protected zone. In the whole de-icing process, the ice on the plasma-protected zone was “cut” and the adhesion force between the ice layer and airfoil surface was reduced by the heat generated by the plasma actuator. The “cut” ice layer was blown downstream by aerodynamic force of the incoming flow. It can be concluded that both the thermal effects of the nSDBD actuator and the aerodynamic force of the incoming flow contribute to the de-icing performance.

Novel Superhydrophobic Surface with Solar-Absorptive Material for Improved De-Icing Performance.

Ice accretion is detrimental to numerous industries, including infrastructure, power generation, and aviation applications. Currently, some of the leading de-icing technologies utilize a heating source coupled with a superhydrophobic surface. This superhydrophobic surface reduces the power consumption by the heating element. Further power consumption reduction in these systems can be achieved through an increase in passive heat generation through absorption of solar radiation. In this work, a superhydrophobic surface with increased solar radiation absorption is proposed and characterized. An existing icephobic surface based on a polytetrafluoroethylene (PTFE) microstructure was modified through the addition of graphite microparticles. The proposed surface maintains hydrophobic performance nearly identical to the original superhydrophobic coating as demonstrated by contact and roll-off angles within 2.5% of the original. The proposed graphite coating also has an absorptivity coefficient under exposure to solar radiation 35% greater than typical PTFE-based coatings. The proposed coating was subsequently tested in an icing wind tunnel, and showed an 8.5% and 50% decrease in melting time for rime and glaze ice conditions, respectively.

A three-dimensional aircraft ice accretion model based on the numerical solution of the unsteady Stefan problem

This paper develops a three-dimensional aircraft ice accretion model based on the numerical solution of the unsteady Stefan problem. In this model, for both rime and glaze ice situation, the heat conduction within the ice layer is considered as an unsteady process and the evolution of temperature distribution is numerically solved by Variable Space Grid (VSG) method. Unlike the Myers' state-of-the-art model and its extended model which introduces a posteriori correction factor α by assuming a linear temperature profile, current model does not need to tune the parameter α to match the experimental results. A hierarchical overset grid strategy is applied to ease the grid generation and shorten the workload on constructing complex icing configurations. Only the grid around the iced surface needs to be regenerated at each ice accretion step and complex flow characteristics near the ice horn can be captured accurately with such high-quality grid. First, simulations on NACA 0012 airfoil are conducted to validate current ice accretion model. Under rime and glaze ice condition, the predicted ice shapes agree well with experimental results. The predicted temperature evolution at iced surface reveals that ice accretion is a complex process influenced by heat and mass transfer. Then the computations on GLC-305 swept wing are performed to study the ice accretion process on the three-dimensional surface. The results show a good agreement with the experimental data. At the leading edge, the overall convective heat transfer coefficient and droplet collection efficiency increase along the direction from the wing root to the wing tip. This leads to very distinct ice horns at different wing sections.

Preliminary study on icing and flashover characteristics of inverted T-type insulator strings

Insulator icing flashover has always been one of the important factors influencing the safety of power grids in winter. Due to the limitation of tower structure and distance between the conductor and the ground, the existing anti-icing flashover method has certain effects but still cannot fully meet the safety requirements of power grids. Based on the idea of changing the ice coverage and discharge path of insulator string, a brand-new insulator string that arranged as inverted T-type is proposed in this paper to achieve the purpose of reducing ice coating and increasing the ice flashover voltage. The icing and flashover experiments are simulated in an artificial climate room. The experiment results show that the ice amount of inverted T-type insulator is smaller than that of the same type and same creepage distance of suspension I-string, and the inclined portion of the inverted T-type arrangement is basically free from bridges under glaze and mixed-phase ice conditions. In the case of the same creepage distance, dry-arc distance, the same degree of contamination, and the ice-covering condition of the same type of insulator, the melting flashover voltage gradient E50 of the inverted T-type string is 14.8–16.3% higher than that of the suspended I-string. The results show that after the insulator adopts inverted T-type arrangement, the ice coating can be significantly reduced and the ice flashover voltage can be increased. The conclusions of the study provide a new solution for the anti-icing flashover treatment and design of the overhead lines.

An experimental study on dynamic ice accretion process over the surfaces of rotating aero-engine spinners

An experimental study was conducted to investigate the dynamic ice accretion process over the surfaces of rotating aero-engine spinners and to examine the detriment effects of the ice accretion on the airflow to be inhaled by aero-engines. Three scaled spinner-fan models with different spinner shapes (i.e., conical-shaped, coniptical-shaped, and elliptical-shaped spinners) were manufactured and exposed under typical rime and glaze icing conditions for a comparative study. During the experiments, while a high-speed imaging system was used to record the dynamic ice accretion process over the rotating spinner models, a high-resolution particle image velocimetry (PIV) system was utilized to examine the trajectories of super-cooled water droplets as they approach to the surfaces of the spinner models. It was found that, under typical rime conditions, while accreted ice layers were found to conform well with the original shapes of the spinner models in general, the total amount of the ice mass accreted over the spinner surfaces were found to be a strong dependent on the spinner shapes. While the conical-shaped spinner was found to have the largest amount of ice accretion (i.e., 60–80% more than those over the other two spinner models) over almost entire spinner surface, ice accretion was found to take place mainly in the front portion of the coniptical-shaped and elliptical-shaped spinners. Under the glaze icing condition, in addition to forming ice layers over the spinner surfaces, very complicated, needle-shaped icicles were also found to grow rapidly out from the spinner surfaces and extrude into the incoming airflow, due to the effects of the centrifugal forces associated with the rotation motion. The complex glaze ice structures accreted over the spinner surface were found to induce significant disturbances/distortions and even cause large-scale flow separations for the airflow near the iced spinner surfaces, which would significantly degrade the quality of the inlet airflow to be inhaled by aero-engines, thereby, adversely affecting the performance of aero-engines.

A hybrid strategy combining minimized leading-edge electric-heating and superhydro-/ice-phobic surface coating for wind turbine icing mitigation

A hybrid anti-icing strategy that combines minimized electro-heating at the blade leading edge and a superhydro-/ice-phobic coating to cover the blade surface was explored for wind turbine icing mitigation. The experimental study was conducted in an Icing Research Tunnel available at Iowa State University (ISU-IRT) with a turbine blade model with DU91-W2-250 airfoil in the model cross-section exposed under different icing conditions. While a superhydro-/ice-phobic surface coating was used to cover the entire blade surface, a strip of electric heating film was used to wrap around the leading edge of the blade model. By using the superhydro-/ice-phobic coating to cover the entire blade surface, the hybrid strategy with the electric heating element covering only 5%–10% of the blade front surface would be able to keep the entire blade surface ice free under both rime and glaze icing conditions. In comparison to the conventional strategy to brutally heating the entire hydrophilic blade surface to keep the blade ice free, the hybrid strategy was found to be able to achieve the same anti-/de-icing performance with substantially less power consumption (i.e., up to ∼90% saving in the required power consumption), making it a very promising strategy for wind turbine icing mitigation.

An experimental study on the thermal effects of duty-cycled plasma actuation pertinent to aircraft icing mitigation

An experimental study was performed to evaluate the effectiveness of utilizing the thermal effects induced by duty-cycled dielectric barrier discharge (DBD) plasma actuation for aircraft icing mitigation. The experimental study was carried out in the unique Icing Research Tunnel available at Iowa State University (i.e., ISU-IRT) with a NACA0012 airfoil model embedded with DBD plasma actuators exposed under a typical glaze icing condition. During the experiments, the DBD plasma actuators were operated in two different modes for a comparative study, i.e., in duty-cycled actuation mode vs. in conventional continuous actuation mode as the comparison baseline. While the anti-/de-icing performances of the DBD plasma actuators under different actuation modes were revealed clearly based on the snapshot images acquired by using a high-speed imaging system, an infrared (IR) thermal imaging system was also used to map the corresponding surface temperature distributions over the ice accreting airfoil surface in order to characterize the thermal effects induced by the plasma actuations. It was found that, with the same power input, the plasma actuation in duty-cycled mode would have a higher instantaneous voltage during the “on” periods, resulting in much stronger thermal effects for an improved anti-/de-icing performance, in comparison to the case in the continuous actuation mode. The thermal effects induced by the duty-cycled plasma actuation were found to be further enhanced by increasing of the modulating frequency of the duty cycles, which is a very promising approach to further improve the anti-/de-icing performance of DBD plasma actuation. The findings derived from the present study could be used to explore/optimize design paradigm for the development of novel DBD-plasma-based anti-/de-icing strategies tailored specifically for aircraft icing mitigation.

Study of ice accretion and icing effects on aerodynamic characteristics of DU96 wind turbine blade profile

In order to optimize the large wind turbines operation in ice prone cold regions, it is important to better understand the ice accretion physics and its effects on aerodynamic performance and power production losses. This paper describes a case study of ice accretion on DU96-W-180 airfoil, which has been used for large wind turbine blades such as NREL 5 MW. Analysis has been carried out for glaze and rime ice conditions using icing tunnel experimental data and multiphase Computational Fluid Dynamics (CFD) based numerical approach. Results show a difference in profile surface roughness and heat fluxes during rime and glaze ice accretion process, which leads to a significant change in rate and shape of ice accretion. More complex ice shapes are observed in case of glaze ice conditions that affects the aerodynamic performance differently from rime ice conditions. Numerical results are compared with the experimental data, where a good agreement is found. Results show higher aerodynamic performance degradation for glaze ice conditions particularly at higher angles of attack.

An experimental investigation of dynamic ice accretion process on a wind turbine airfoil model considering various icing conditions

In the present study, the dynamic ice accretion process over a typical wind turbine airfoil model (i.e., DU96-W-180 airfoil) was experimentally investigated under various icing conditions. The experimental study was conducted in the Icing Research Tunnel of Iowa State University (i.e., ISU-IRT). Different icing conditions (i.e., rime, mixed and glaze) that wind turbine may experience in winter were reproduced by manipulating the airflow temperature, velocity, and liquid water content (LWC) in ISU-IRT. While a high-speed imaging system was used to reveal the dynamic ice accretion process over the surface of the test model, an infrared (IR) thermal imaging system was used to map the corresponding temperature distributions over the ice accreting airfoil surface. Time variations of the ice thickness accreted along the leading edge (LE) of the test model were extracted based on the acquired high-resolution images of the ice accretion process under different test conditions. It was found that, due to the obvious runback of the impacted water (i.e., formation of water film and rivulets) over the airfoil surface, the growth rate of the ice layer accreted along the airfoil leading edge was much slower under the glaze icing condition, in comparison with those under the rime and mixed icing conditions. Such surface water transport behavior was also found to expand the ice influencing region. From the temperature evolutions during the dynamic icing processes, the transient processes of droplet impingement, water film/rivulets formation, and ice roughness growth were temporally resolved, providing comprehensive details of the unsteady heat transfer during the dynamic icing process. While the surface temperature increment due to the direct droplet impingement was found to decrease monotonously along the chord in rime case, a stream-wise ‘plateau’ region was observed in the glaze and mixed icing cases due to the complex multiphase mass/heat transfer associated with the surface water transport behaviors.

Effects of thermal conductivity of airframe substrate on the dynamic ice accretion process pertinent to UAS inflight icing phenomena

An experimental investigation was conducted to quantify the dynamic ice accretion and the unsteady heat transfer process over the ice accreting surfaces of composite-based airframes widely used for light-weight, Unmanned-Aerial-Systems (UAS), in comparison to those over the surfaces of metal-based airframes used by conventional manned aircraft, in order to elucidate the underlying icing physics specifically pertinent to UAS inflight icing phenomena. Two airfoil/wing models with the same airfoil shape, but made of different materials (i.e., thermoplastic material with the thermal conductivity being only ∼0.2 W/m⋅K to represent typical UAS airframe substrates vs. Aluminum with the thermal conductivity being ∼200 W/m⋅K widely used for conventional manned aircraft). The two test models were mounted side-by-side inside an Icing Research Tunnel available at Iowa State University (i.e., ISU-IRT) under the same wet glaze or dry rime icing condition. During the icing experiment, while a high-speed imaging system was used to record the dynamic ice accretion process over the surfaces of the test models, an infrared thermal imaging system was also used to map the corresponding surface temperature distributions over the ice accreting airfoil surfaces. It was found that, upon the impacting of the airborne, super-cooled water droplets in ISU-IRT, ice would start to accrete rapidly on the surfaces of the test models with a significant amount of the latent heat of fusion being released associated with the phase changing of the impacted super-cooled water mass over the airfoil surfaces. The thermal conductivity of the airframe substrate was found to affect the dynamic ice accretion and unsteady heat transfer processes over the ice accreting surfaces significantly. With the two test models being exposed under the same icing conditions, the released latent heat of fusion was found to be dissipated much slower over the surface of the thermoplastic model, due to the much lower thermal conductivity of the thermoplastic substrate. In comparison with those on the surface of the Aluminum model, the slower dissipation of the released latent heat of fusion on the surface of the thermoplastic model was found to cause higher surface temperatures and greater “heated” regions near the airfoil leading edge, more obvious surface water runback over the airfoil surface, and formation of more complex rivulet-shaped ice structures at further downstream locations beyond the direct impinging zone of the super-cooled water droplets.

An experimental study on the aerodynamic performance degradation of a wind turbine blade model induced by ice accretion process

Abstract An experimental study was conducted to characterize aerodynamic performance degradation of wind turbine blades induced by dynamic ice accretion process. The experimental study was performed in an Icing Research Tunnel with a turbine blade model under a typical glaze icing condition. Ice structures were found to accrete rapidly over both the upper and lower surfaces of the blade model after starting the ice accretion experiment. Irregular-shaped ice structures were found to disturb the airflow around the blade model greatly, resulting in large-scale flow separations and shedding of unsteady vortex structures from the ice accreting surface. The aerodynamic performance of the blade model was found to degrade significantly. The performance degradation induced by the ice accretion was found to be a strong function of the angle of attack of the blade model with more significant degradations at lower angles of attack. For the test case at the angle of attack of 5.0°, while the lift decreases to only ∼12% of its original value after 600 s of the ice accretion experiment, the drag was found to increase 4.5 times correspondingly. The detailed flow field measurements were correlated with the aerodynamic force data to elucidate the underlying physics.

Experimental investigation of the icing scaling test method for a rotating cone

One of the reliable methods of studying engine icing is to carry out testing in an icing wind tunnel. Due to the operational limitations of test facility, model-size scaling is adopted. An icing scaling test method for the rotating cone is established based on the dimensional analysis coupled with similarity theory and evaluated by considering the rotating effect. Similarity parameters are determined in the following five aspects: flow field similarity, droplet trajectory similarity, water catch similarity, heat balance similarity, and rotating characteristics similarity. Experimental icing tests have been performed at rime and glaze ice conditions to evaluate the scaling method in a closed-loop icing wind tunnel. Results show that the maximum error between the reference and scale ice shapes occurs at the stagnant point. On the areas apart from this, there is a significantly smaller error. Hence, the scaling test method is proven to be effective and reliable and can provide a theoretical basis for parameter selection of the ice wind tunnel tests.