Aircraft Ice Accretion Prediction Based on Neural Networks

Super-cooled large droplets (SLDs) present a unique experimental challenge for conventional horizontal spray icing wind tunnels due to gravity effects on the droplets and coalescence between the particles. Limited ice accretion shapes in this regime exist, making the verification of modeling tools and the validation of the applicability of scaling methods difficult. Furthermore, SLD accretions often occur in nature in a bimodal icing cloud, providing an additional facility challenge related to the reproduction of such clouds. The objective of this research effort is to expand the available SLD dataset to assess the capability of an existent ice accretion tool (LEWICE 2D) to predict such ice shapes. The effort also attempts to further verify the applicability of ice shape scaling methods in the SLD regime. Finally, bimodal SLD cloud reproduction and ice shape prediction is investigated. The Adverse Environment Rotor Test Stand (AERTS) at Penn State was assessed as an alternative facility to icing wind tunnels for ice accretion testing in the SLD regime. Laser diffraction measurement data analysis demonstrated that the icing nozzles used in the facility can produce an SLD within of requested values. Techniques to measure liquid water content (LWC) in the facility are also presented. LWC was controllable within . LEWICE ice shapes predicted were obtained using legacy empirical heat transfer models as well as an updated empirical heat transfer function developed at Penn State. When comparing modeling results to experimental shapes from the literature and the AERTS, LEWICE with the updated heat transfer function provided stagnation thicknesses within 5.6% of experimental values and horn protrusion within 16%. The modified Ruff scaling ice shape method was effective in the SLD regime, providing a mean deviations of 2.5% between reference and scaled ice shape characteristics. Finally, characteristics of a bimodal ice shapes were predicted by LEWICE. When comparing modeling results to experimental shapes, LEWICE with the updated heat transfer function provided predictions within 10.3% of the experimental stagnation thickness measured. It also provided horn angles with discrepancies of less than 12%. Icing limits of a bimodal icing cloud were observed to be that of a single mode SLD cloud of the same MVD, with an overall deviation of when comparing the experimental database to LEWICE.

Purpose The purpose of this paper is to analyse an actual representation of ice accretions, which are important during the certification process. Design/methodology/approach Ice accretion experiments are conducted in a low-speed subsonic wind tunnel testing facility to evaluate the influence of various ice shapes around the airfoil sections. Ice accumulation changes the shapes of local airfoil sections and thereby affects the aerodynamic performance characteristics of the considered NACA 23012 profile. The ice profiles are impregnated using balsa wood with glace, horn and mixed ice accretion cases for the detailed experimental investigation. Findings Computational fluid dynamics analysis is done to compute the influence of different ice shapes on the aerodynamic coefficients (Cl and Cd) while ice accretion occurs at the leading edge of the airfoil sections. It is observed that the Cl and Cd modified immediately more than 40% as compared to the clean wing configuration. In the same fashion, the skin friction coefficient also abruptly changes for different ice shapes that have the potential to induce flutter at the critical speed of the airplane. The computational solutions are further validated through wind tunnel experiments and recent literature concerning certification for flight in icing conditions. Social implications The ice accretion study on the aerodynamic surfaces can also be extended for wind turbine blades installed at different cold regions around the globe. Further, the propeller icing influences the entire rotorcraft aerodynamics at low temperature conditions and the findings of this study are strongly connected with such problems. Originality/value The aerodynamic characteristics of the baseline airfoil are greatly affected by the ice accretion problem. Although flight through icing condition endures for a short duration, the takeoff path and decision speed are determined based on airplane drag as per federal aviation regulations. Hence, the proposed study is focussed on a cost-effective approach to predict the effect of ice accretion to achieve optimum performance.

A computational study was conducted to evaluate the effectiveness of using a viscous flow solution in an ice accretion code and the resulting accuracy of aerodynamic performance prediction. Ice shapes were obtained for one single-element and one multi-element airfoil using both potential flow and Navier-Stokes flowfields in the LEWICE ice accretion code. Aerodynamics were then calculated using a Navier-Stokes flow solver.

Aircraft ice accretion is an important safety problem because of its degrading effects on aerodynamic performances. Simulation of this phenomenon using an icing wind tunnel is expensive, whereas numerical analyses offer several advantages in time and cost. The purpose of this paper is to simulate the ice shape on a multi-element airfoil. Icing accretion on a multi-element airfoil has already been analyzed in the past [Addy, Harold E., Jr., “Ice Accretions and IcingEffects forModernAirfoils,”NASATP-2000-210031.] [Tran, P., Brahimi,M.T., Tezok, F., and Paraschivoiu, I., Numerical Simulation of Ice Accretion on Multiple Element Configurations, ICAS Paper 96-2.7.5.]. Here different approaches are compared to identify the best in terms of a costs/benefits balance. Classical ice accretion models use a panel method to compute the aerodynamic field [Bragg, M. B., and Gregorek, G. M., “An Analytical Approach toAirfoil Icing,”AIAAPaper 81-0403, Jan. 1981.] [Gent, R.W., “Calculation ofWaterDroplet Trajectories About anAirfoil in Steady, Two-Dimensional, Compressible Flow,”RAETR-84060, Jun 1984.], but for high-lift configuration in the aerodynamic field there are large separation zones that are not simulated by panel codes, and that cannot be neglected. In this paper, ice accretion is calculated using several aerodynamics flow solvers [potential panel code, Euler, and Reynolds-averaged Navier-Stokes (RANS)] and several procedures for ice accretion simulation: single step, multistep time accretion strategy, and both single droplet and actual droplet spectrum for water impingement calculation.

Multi-physics simulation of 3D in-flight ice-shedding

In one of the most extensive applications to date of the NASA Lewis ice accretion code LEWI3DGR, certification of the Gulfstream GV ultra-long range business jet was obtained under FAR 25.1419. Analyses were performed to model water droplet impingement on lifting and nonlifting surfaces including those both protected and unprotected from accretion. Heat transfer rates for treating leading edges were determined from dry air flight testing. Ice shapes were calculated and fabricated for artificial ice shape testing. Flight tests were conducted with artificial shapes to verify aircraft performance with heavy ice accretion. The recently required zero-g horizontal stall pushover maneuver was flown. Flight into known icing natural ice tests were conducted to reaffirm aircraft performance and validate the ice protection system design. All testing was completed successfully, and certification was obtained. A list of lessons learned to streamline future icing certification was compiled.

PurposeThe main purpose of this paper is to investigate the effects of icing on unmanned aerial vehicles (UAVs) at low Reynolds numbers and to highlight the differences to icing on manned aircraft at high Reynolds numbers. This paper follows existing research on low Reynolds number effects on ice accretion. This study extends the focus to how variations of airspeed and chord length affect the ice accretions, and aerodynamic performance degradation is investigated.Design/methodology/approachA parametric study with independent variations of airspeed and chord lengths was conducted on a typical UAV airfoil (RG-15) using icing computational fluid dynamic methods. FENSAP-ICE was used to simulate ice shapes and aerodynamic performance penalties. Validation was performed with two experimental ice shapes obtained from a low-speed icing wind tunnel. Three meteorological conditions were chosen to represent the icing typologies of rime, glaze and mixed ice. A parameter study with different chord lengths and airspeeds was then conducted for rime, glaze and mixed icing conditions.FindingsThe simulation results showed that the effect of airspeed variation depended on the ice accretion regime. For rime, it led to a minor increase in ice accretion. For mixed and glaze, the impact on ice geometry and penalties was substantially larger. The variation of chord length had a substantial impact on relative ice thicknesses, ice area, ice limits and performance degradation, independent from the icing regime.Research limitations/implicationsThe implications of this manuscript are relevant for highlighting the differences between icing on manned and unmanned aircraft. Unmanned aircraft are typically smaller and fly slower than manned aircraft. Although previous research has documented the influence of this on the ice accretions, this paper investigates the effect on aerodynamic performance degradation. The findings in this work show that UAVs are more sensitive to icing conditions compared to larger and faster manned aircraft. By consequence, icing conditions are more severe for UAVs.Practical implicationsAtmospheric in-flight icing is a severe risk for fixed-wing UAVs and significantly limits their operational envelope. As UAVs are typically smaller and operate at lower airspeeds compared to manned aircraft, it is important to understand how the differences in airspeed and size affect ice accretion and aerodynamic performance penalties.Originality/valueEarlier work has described the effect of Reynolds number variations on the ice accretion characteristics for UAVs. This work is expanding on those findings by investigating the effect of airspeed and chord length on ice accretion shapes separately. In addition, this study also investigates how these parameters affect aerodynamic performance penalties (lift, drag and stall).

To investigate the temperature effect on characteristics of icing distribution near the tip part of rotating blade of large-scale horizontal-axis wind turbine, numerical simulations were carried out on a horizontal-axis wind turbine rotor with rated power of 1.5 MW based on a quasi-three-dimensional computational method developed in this study. The icing simulation was focused on the part between blade tip and 30% length of blade from tip along span wise to blade root where the most serious icing area is according to the past researches. Eight sections along blade were selected, and the ice accretion on each airfoil was calculated. Eight temperature values from −6°C to −20°C were decided to investigate the effects of temperature on icing under the certain liquid water content and medium volume droplet. Three icing times were selected to research the ice accretion on blade surface with the increase in the time. According to the results, the icing distribution has the overall characteristics that the icing shape changes from horn icing shape to streamline icing shape with decrease in the temperature. The closer the blade airfoil section to blade tip, the more obvious the ice accretion is. This study can be a reference for the research on anti-icing and de-icing technologies for large-scale horizontal-axis wind turbine.

Investigations were conducted to examine ice accretion on a cascade of stator blades and its influence on the resulting aerodynamics. In particular, ice shapes and aerodynamic penalties were investigated on a stage 67A stator blade, which represents a part of a turbomachinery compressor stage. A steady Reynolds-averaged Navier-Stokes solver for the airflow was used with a Lagrangian continuous random walk for the droplet trajectory released upstream of the stator blade to predict impingement efficiencies. These results were coupled after finite icing intervals (ca. every 3 min) to update the ice shape around the stator blade using LEWICE. The overall methodology allowed the prediction of the impingement efficiency, the amount of ice accretion, and the adverse effects on the aerodynamic performance. Ice accretion is found to be significantly sensitive to droplet size, integration time, and temperature. However, relatively weak sensitivity was found with respect to the turbulence and angle of attack. Changes in the flowfield due to ice accretion can lead to boundary-layer separation, which causes a reduction in the flow turning angle and mass flow rate as well as an increase in the total pressure loss.

A research project is underway at NASA Lewis to produce a computer code which can accurately predict ice growth under any meteorological conditions for any aircraft surface. The most recent release of this code is LEWICE 1.6. This code is modular in design and can use flow codes other than the default potential flow code. Methods for assessing the capabilities of ice accretion prediction codes are examined by comparing geometric and aerodynamic characteristics of computationally generated and experimentally measured ice shapes. The data used in this paper comes from tests performed in the NASA Lewis Icing Research Tunnel (IRT). This paper will present comparisons with that data for both ice shape and performance results. A group of geometric characteristics for quantitatively describing ice shape profiles are introduced and used to assess the differences between profiles. An aerodynamic analysis of computational and experimental ice shapes is performed using a structured-grid, Navier-Stokes, flow code as an alternate method for assessing ice shape similarity. Results indicate that large differences in ice shape are reflected in the resulting aerodynamics but are not necessarily apparent in integrated force parameters such as lift or drag.

Icing will occur when wind turbines are installed in cold and humid regions. Blade icing will reduce the efficiency of wind turbines. In this paper, a numerical simulation method is proposed for glaze, mixed, and rime ice accretion on three-dimensional wind turbine blades. The air flow field is calculated by the multiple reference frame model and droplet trajectories are obtained using the Eulerian two-phase flow method. In the ice accretion calculation, a three-dimensional icing calculation model is established and a new water flow distribution method based on shear force and centrifugal force is presented. The calculation results of ice shapes are compared with the experimental results and the good agreement proves the validity of the icing numerical simulation method. Based on the calculation results, the influence of centrifugal force on the ice shape is studied. Finally, the droplet impingement characteristics and ice shapes of the wind turbine blade are simulated. The results show that the in-cloud icing of wind turbine blades occurs mainly near the leading edge. The icing thickness is thicker and the icing range is wider with the increase of spanwise length.

<div class="section abstract"><div class="htmlview paragraph">Computational ice shapes were generated on the boundary layer ingesting engine nacelle of the D8 Double Bubble aircraft. The computations were generated using LEWICE3D, a well-known CFD icing post processor. A 50-bin global drop diameter discretization was used to capture the collection efficiency due to the direct impingement of water onto the engine nacelle. These discrete results were superposed in a weighted fashion to generate six drop size distributions that span the Appendix C and O regimes. Due to the presence of upstream geometries, i.e. the fuselage nose, the trajectories of the water drops are highly complex. Since the ice shapes are significantly correlated with the collection efficiency, the upstream fuselage nose has a significant impact on the ice accretion on the engine nacelle. These complex trajectories are caused by the ballistic nature of the particles and are thus exacerbated as particle size increases. Shadowzones are generated on the engine nacelle, and due to the curvature of the nose of the aircraft the shadowzone boundary moves from lower inboard to upper outboard as particle size increases. The largest particle impinging one the engine nacelle from the 50-bin discretization was the 47 μm drop diameter. As a result, the MVD greater than 40 μm Appendix O conditions were characterized by extremely low collection efficiency on the engine nacelle for these direct impingement simulations.</div></div>

Ice accretion and aerodynamic effects on a turbofan engine nacelle under takeoff conditions

In-flight ice accretion poses a major safety concern in aviation. It occurs due to the icing from clouds of supercooled water droplets, the accumulation of ice crystals at high altitudes, or snow buildup. Assessing the detrimental effects of ice accretion on aircraft performance and handling qualities is a complex, multidisciplinary task, as it requires modeling the dynamics of the dispersed phase (water droplets, ice crystals, and snowflakes), the particle impact dynamics and its interaction with the aircraft surfaces, the liquid film dynamics, the solidification process, and possibly ice shedding. The ice protection systems must also be modeled. The present review addresses the status of ice accretion models and simulation tools. The intrinsically stochastic nature of ice accretion, combined with substantial operational and modeling uncertainties, makes it challenging to validate these tools against experimental observations and use simulation as a reliable means of compliance for certification in icing conditions, especially for innovative aircraft configurations such as wing-body and advanced urban air mobility vehicles.

Unmanned aerial vehicles (UAVs) encounter significant challenges in freezing climates, as atmospheric ice accretion adversely impacts both flight safety and aerodynamic performance. This study provides an in-depth numerical investigation into the ice accretion process and its implications on the aerodynamic performance of UAV propeller. The analysis explores at various propeller blade pitching angles and rotational speeds. Detailed flow field analysis around propeller blade surfaces is conducted to address the performance degradations associated with ice accretion. The investigation reveals a noteworthy shift in ice shapes and extents with varying pitching angles and rotational speeds. The iced propeller demonstrates increased aerodynamic losses, marked by large size separation bubbles aft the ice shapes at outer radial locations. Remarkably, at higher pitching angles, the iced propeller outperforms the baseline propeller, followed by a propeller with increased rotating speed. For both baseline and higher pitching angles, the most significant losses in thrust coefficient 57.60% and 25.39%, respectively, occur at −2 °C, accompanied by maximum spikes in power coefficient of 140.08% and 93.92% at −4 °C. Meanwhile, an increase in rotating speed results in a decrease in thrust coefficient by 48.60% and an increase in power coefficient by 150.66% at an icing temperature of −4 °C.