Thermal Ice Protection System Research Articles

Target temperature-based simulation method for predicting performance and designing aircraft thermal anti-icing systems

The prevention of ice build-up on aircraft surfaces is crucial for safe operations. Thermal ice protection systems, particularly electro-thermal systems, are commonly employed to mitigate ice formation. However, the weight of electric batteries used in these systems significantly impacts aircraft performance, necessitating the minimization of power load during design. Despite this requirement, effective anti-icing operation mandates a sufficient heat flux to maintain surface temperature above the freezing point and evaporate any runback water film. Previous research has utilized numerical simulation analysis to predict the performance of electro-thermal anti-icing systems. The conjugate heat transfer method has been commonly employed to predict temperature distribution on the protected surface. However, non-isothermal surfaces exhibit distinct local convective heat transfer coefficients that influence local thermal balance, unlike isothermal surfaces that adopt the loosely-coupled method for computational efficiency. In this study, we present a novel target temperature-based anti-icing simulation method that predicts the required heat flux for thermal ice protection systems without employing the conjugate heat transfer method. Our objective was to calculate the necessary heat flux to achieve the desired non-isothermal surface temperature for effective anti-icing. By eliminating the excessive iteration process associated with the coupling method for conjugate heat transfer, we have streamlined the simulation procedure. Through validation, target temperature-based anti-icing simulation method, when compared to the tight coupling method, demonstrated the ability to predict the same surface water flow rates while reducing computation time by up to 90 %. Furthermore, when applied to design problems, our method achieved approximately a 10 % reduction in the required heat capacity for anti-icing compared to experimental values. As a result, target temperature-based anti-icing simulation method offers a more efficient alternative to traditional conjugate heat transfer methods, providing valuable insights for both predicting anti-icing system performance and optimizing aircraft design.

A Preliminary Approach towards Rotor Icing Modeling Using the Unsteady Vortex Lattice Method

UAV rotors are at a high risk of ice accumulation during their operations in icing conditions. Thermal ice protection systems (IPSs) are being employed as a means of protecting rotor blades from ice, yet designing the appropriate IPS with the required heating density remains a challenge. In this work, a reduced-order modeling technique based on the Unsteady Vortex Lattice Method (UVLM) is proposed as a way to predicting rotor icing and to calculate the required anti-icing heat loads. The UVLM is gaining recent popularity for aircraft and rotor modeling. This method is flexible enough to model difficult aerodynamic problems, computationally efficient compared to higher-order CFD methods and accurate enough for conceptual design problems. A previously developed implementation of the UVLM for 3D rotor aerodynamic modeling is extended to incorporate a simplified steady-state icing thermodynamic model on the stagnation line of the blade. A viscous coupling algorithm based on a modified α-method incorporates viscous data into the originally inviscid calculations of the UVLM. The algorithm also predicts the effective angle of attack at each blade radial station (r/R), which is, in turn, used to calculate the convective heat transfer for each r/R using a CFD-based correlation for airfoils. The droplet collection efficiency at the stagnation line is calculated using a popular correlation from the literature. The icing mass and heat transfer balance includes terms for evaporation, sublimation, radiation, convection, water impingement, kinetic heating, and aerodynamic heating, as well as an anti-icing heat flux. The proposed UVLM-icing coupling technique is tested by replicating the experimental results for ice accretion and anti-icing of the 4-blade rotor of the APT70 drone. Aerodynamic predictions of the UVLM for the Figure of Merit, thrust, and torque coefficients agree within 10% of the experimental measurements. For icing conditions at −5 °C, the proposed approach overestimates the required anti-icing flux by around 50%, although it sufficiently predicts the effect of aerodynamic heating on the lack of ice formation near the blade tips. At −12 °C, visualizations of ice formation at different anti-icing heating powers agree well with UVLM predictions. However, a large discrepancy was found when predicting the required anti-icing heat load. Discrepancies between the numerical and experimental data are largely owed to the unaccounted transient and 3D effects related to the icing process on the rotating blades, which have been planned for in future work.

Numerical Simulation of an Electrothermal Ice Protection System in Anti-Icing and Deicing Mode

The design of efficient thermal ice protection systems is a challenging task as these systems operate in complex environments involving several coupled physical phenomena such as phase change, boundary-layer flow, and heat transfer. Moreover, certification rules are becoming more stringent, and there is a strong incentive for the reduction of fuel consumption. In this context, numerical tools provide a powerful asset during the design phase but also to gain insight into the physical mechanisms at play. This article presents modeling and simulation strategies for thermal ice protection systems. First, the model describing the behavior of the thermal protection system is presented. Second, a model and associated numerical method is presented for unsteady ice accretion. Third, the coupling methodology between the ice accretion solver and the heat conduction solver is described. In the fourth part, different methods to simulate the boundary-layer flow are described. Finally, some relevant examples are presented, both in steady and unsteady configurations.

열전달 결합 기법에 따른 열적 결빙보호장치 수치해석 개발

The numerical analysis of the thermal Ice Protection System(IPS) is conducted by heat transfer analysis between an icing simulation and an internal heat transfer simulation. For accurate heat transfer analysis, the coupling method is required since heat transfer occurs in each region. A loose-coupling method, which is used by most of the prior research, does not take into account the effect of the internal heat transfer on the convection heat of external flow. While the tight-coupling method takes longer to calculate than the loose-coupling method, it can result in high accuracy. In this study, a convective heat transfer coefficient is obtained by the tight-coupling method in dry conditions without water film. A comparative analysis was then performed with experimental results and other numerical analysis studies. The tight-coupling method showed more excellent agreement with the experiments than the loose-coupling method. Furthermore, it is confirmed that the developed numerical method has a great performance.

A Galerkin Method for the Simulation of Laminar Boundary Layers on Heated Walls

This paper presents a new solution method for the calculation of laminar thermal boundary layers. The method consists of a coupling between a modal method (Galerkin method) in the direction normal to the wall and a finite volume method in the direction(s) tangential to the wall. It is similar to an integral method in the sense that only a surface mesh is required and that the unknowns are integral quantities (corresponding to the moments up to a fixed order of the temperature profile in the direction normal to the wall). A specificity of the Galerkin method used is that the domain over which the integrals are computed has a variable size that is also an unknown of the problem. Using a series of numerical tests (representative of situations that can be encountered in aeronautics in the case of a wing equipped with a thermal ice protection system), we show that the new method allows us to predict the quantities of interest with a maximum error of a few percent, while a usual integral method (with only one unknown per mesh cell) is unable to treat the case of boundary layers on heated walls with a strong longitudinal temperature gradient, as shown in the literature.

Design and Development of an Experimental Setup of Electrically Powered Spinning Rotor Blades in Icing Wind Tunnel and Preliminary Testing with Surface Coatings as Hybrid Protection Solution

In order to study ice protection systems for rotating blades, a new experimental setup has been developed at the Anti-Icing Materials International Laboratory (AMIL). This system consists of two small-scale rotating blades in a refrigerated icing wind tunnel where atmospheric icing can be simulated. Power is brought to the blades through a slip ring, through which the signals of the different sensors that are installed on the blades also pass. As demonstrated by the literature review, this new setup will address the need of small-scale wind tunnel testing on electrically powered rotating blades. To test the newly designed apparatus, preliminary experimentation is done on a hybrid ice protection system. Electrothermal protection is combined with different surface coatings to measure the impact of those coatings on the power consumption of the system. In anti-icing mode, the coatings tested did not reduce the power consumption on the system required to prevent ice from accumulating on the leading edge. The coatings however, due to their hydrophobic/superhydrophobic nature, reduced the power required to prevent runback ice accumulation when the leading edge was protected. One of the coatings did not allow any runback accumulation, limiting the power to protect the whole blades to the power required to protect solely the leading edge, resulting in a potential 40% power reduction for the power consumption of the system. In de-icing mode, the results with all the substrates tested showed similar power to achieve ice shedding from the blade. Since the coatings tested have a low icephobicity, it would be interesting to perform additional testing with icephobic coatings. Also, a small unheated zone at the root of the blade prevented complete ice shedding from the blade. A small part of the ice layer was left on the blade after testing, meaning that a cohesive break had to occur within the ice layer, and therefore impacting the results. Improvements to the setup will be done to remedy the situation. Those preliminary testing performed with the newly developed test setup have demonstrated the potential of this new device which will now allow, among other things, to measure heat transfer, force magnitudes, ice nucleation, and thermal equilibrium during ice accretion, with different innovative thermal protection systems (conductive coating, carbon nanotubes, impulse, etc.) as well as mechanical systems. The next step, following the improvements, is to measure forced convection on a thermal ice protection system with and without precipitation and to test mechanical ice protection systems.

Numerical simulation of a thermal Ice Protection System including state-of-the-art liquid film model

In this work, a numerical model for the operation of an electro-thermal Ice Protection Systems (IPS) for an airfoil is presented. The present model solves the energy conservation laws and includes a boundary layer model to compute the relevant aerodynamic quantities based on previous works. Additionally, the computation of aerodynamic and water impingement properties is performed by means of open-source and in-house developed software. A state-of-the-art liquid film model based on lubrication theory has been deployed as an alternative to an element-wise mass balance. A simple ice formulation for the prediction of the formation of runback ice has been included. Moreover, a robust evaporation model based on the heat and mass transfer analogy is deployed. Finally, an interpolation scheme for the element-wise enthalpy variation is presented. The results obtained are in good agreement with the experimental data from the open literature for a range of different test cases including different operating modes, environmental and flight conditions.

Altitude Scaling of Thermal Ice Protection Systems in Running Wet Operation

A study into the effects of altitude on an aircraft thermal ice protection system (IPS) performance has been conducted by the National Research Council Canada (NRC) in collaboration with the NASA Glenn Research Center. The study included tests of an airfoil model, with a heated-air IPS, installed in the NRC’s Altitude Icing Wind Tunnel (AIWT) at altitude and ground level conditions. Two scaling strategies were employed based on Reynolds number and Weber number, the latter combined with matching the ratio of water loading and evaporative rates. The Reynolds number–scaled conditions resulted in greater mass of accreted ice that formed further back from the leading edge, whereas the Weber number approach provided a close match to reference altitude conditions in terms of ice mass, location, and shape.

Special Issue on Seventy Years of Aerospace Research and Technology Excellence at NASA Glenn Research Center

Special Issue on Seventy Years of Aerospace Research and Technology Excellence at NASA Glenn Research Center

Aircraft icing

Aircraft icing