Aircraft Icing

In the development of anti/de-icing systems for aeronautics, wind turbines or telecommunication antennas to date, less attention is paid to coating strategies. The majority of studies dealing with coatings have focused mainly on reducing ice adhesion forces, to easily remove ice, once it has formed. In this study we focused on an alternative strategy that consists of promoting the shedding of liquid water as a way to reduce the total amount of water present on the surface that can freeze. Shedding of liquid from the surface can be enhanced by modification of surface wettability, by means of the application of superhydrophobic coatings, i.e. water repellent coatings, characterized by low water adhesion forces.

This work was a part of an ongoing effort to develop technologies for safe and efficient flight into forecasted icing. Computational investigation was conducted to study the flowfield simulation and aerodynamic performance analysis of an NACA 23012 with 15 minute glaze ice shape. The aerodynamic parameters variation was calculated using commercial Fluent 6.3.26 code with multi-block grid technique to overcome the difficulty of generating structured grid on complex geometry and to save the storage and computational time .Aerodynamics were calculated using Navier-Stokes flow solver. With the application of the techniques outlined in this paper, the numerical simulation is valid with those measured test data under the same environment in icing wind tunnels by S. Lee. The numerical results with Spalart-allarams turbulence model are presented .The aerodynamic penalty of lift and drag coefficients were evaluated on the angle of attack range-5 to 20 degrees.

Icing accretions can modify the geometry of an airfoil significantly and they affect its performance. Two categories of icing accretions were analyzed in NACA 0012 airfoil through the effects in the force as well as in pressure distribution via numerical simulations. The results were compared with others computational experiments and measurements in wind tunnel of references in order to validate this research.

The present work is devoted to the numerical study of freezing processes which have become of major importance in aeronautical engineering. According to Caliskan and Hajiyev (2013), the most common causes of structural damage to aircrafts due to climacteric changes are the result of lightning strikes and icing at the wing's leading edge or empennage. The icing of a wing's leading edge turns the smooth airflow over the wing into a turbulent one, decreasing lift and increasing drag. At temperatures below zero, icing spreads to the trailing edge, affecting a greater percentage of the wing. Overall, icing has a negative effect on an aircraft's aerodynamic performance, especially during takeoff and landing and anti-icing systems on modern aircrafts make use of heat exhausted from the engines, to prevent the ice from forming, which increases fuel consumption and in turn the operational costs of the aircraft. Several authors, Yao and Schrock (1976) and Zarling (1980), have studied heat and mass transfer on freely-falling drops, in order to determine its rate of cooling under several humidity conditions, making use of the Ranz-Marshall relations for the Nusselt and Sherwood numbers. This model allows to calculate the heat and mass transfer maximum rates, however it does not take into account changes in temperature and air humidity as the drop falls. It is necessary to assume the drop internal movement be powerful enough, so that complete mix occurs – the temperature profile is planar and the heat and mass transfer happens only at the drop's surface – or there isn't mix in the drop, so the energy equation is reduced to a heat transfer problem in transient regime. The objective of the present work is to investigate numerically the freezing of free falling droplets for different diameters and air humidity. The predictions are compared with experimental data and the numerical analysis is conducted to provide insight into the heat transfer involved in the freezing process under several humidity conditions.