Development of Integrated Icing Shape Analysis Platform for Generic Aircraft

Abstract

thereby, the risk increases at high temperatures. However, ice horns cannot be observed under the stratiform clouds for HALE aircraft even in high temperature conditions. Since there is no ice horn, the high-risk region of HALE aircraft is diffident from that of fixed-wing aircraft. The high-risk region of icing for HALE aircraft appears under high humidity and low-temperature conditions. Third, when analyzing the icing on the body of the helicopter, accurate flow analysis should be accompanied. A relatively high-pressure and low-velocity region is formed under the rotor surface and above the fuselage. Due to the low-velocity region that is induced by rotor wake, the droplet trajectories and heat transfer rate are different from the cases of isolated fuselage. Consequently, the differences of the total amount of ice and the ice distribution are clearly distinguished between the isolated fuselage and including rotor wake effect. In addition, a large amount of icing occurs in the area where the tip vortex collides the body. This meant the necessity of the accurate simulation code that can predict the generation, movement, and collision with fuselage of the individual tip vortex.

Federal Aviation Regulations specify the aircraft class according to the maximum takeoff weight and the number of seats. The regulations present icing environments for the certification of airworthiness. Most aircraft icing studies are on fixed-wing aircraft, which has more than ten passengers by following Federal Aviation Regulations Part 25. The flight speed was focused on the stall speed of the presented aircraft in the regulations. In the case of rotorcraft aircraft, it follows the regulations and icing environments established for the fixed-wing aircraft. Moreover, there are no regulations for unmanned aerial vehicle (UAV). Under the regulations, research on aircraft icing has the following problems. First, the characteristics of icing shapes are not clear except for the aircraft types and regulations presented in regulations. It is difficult to apply the previous research results on the stall speed of fixed-wing aircraft to other aircraft, which is operating with low-speed, because the non-dimensional parameters governing the icing shape are in unknown. Therefore, it is necessary to analyze the characteristics of the icing shapes and its aerodynamic performance on the aircraft having the different mission profile. Second, it is the ultimate goal for aircraft icing research to determine the aviation safety of aircraft under given weather conditions. However, there have been no integrated procedures or methods for assessing the safety of aircraft. Under the given icing environment, icing research has been separately performed by following areas: the prediction of icing shape, the performance prediction of deformed shapes, the design of anti-/de- icing device, and the evaluation of operation safety. Third, simulation tools have been developed focusing on fixed-wing aircraft. There is no accurate numerical tool to predict the ice shapes on helicopter fuselage. It is essential to consider the rotor-airframe interaction. However, in the latest icing research, the technique performed to the fixed-wing aircraft is directly applied to helicopter fuselage. For example, the icing wind tunnel tests for the helicopter fuselage neglected the rotor blades. In numerical research, the simple inflow model which can not account for the blade tip vortices was applied. It is necessary to develop an accurate icing analysis solver to evaluate the validity of previous research results that ignored the rotor effects, and by using the accurate code, the icing characteristics should be identified under the conditions of rotor-airframe interaction. To this end, Ice Shape Estimation and Performance Analysis Code (ISEPAC), a simulation program to analyze icing phenomena occurring on the three-dimensional body, is developed by applying the latest numerical technique. ISEPAC is a second-generation icing analysis tool that is based on the Navier-Stoke equations, Eulerian droplet field calculation, and Messinger model with a shallow water film. ISEPAC can handle not only for the fixed-wing aircraft but also for the helicopter fuselage including rotor wake effects. The latest actuator surface model loaded on ISEPAC is able to capture the behavior of individual blade tip vortices. By using ISEPAC, the icing characteristics of HALE aircraft and helicopter fuselage are analyzed. As a result, the following conclusions were drawn. First, there are no ice horns on HALE aircraft and helicopter fuselages with low-speed flight (Mach number less than 0.1). The droplet with small inertia can avoid the body without collision, resulting in a small amount of water film on the surface. The generated water film flows by the shear force of the air, and concentrates on a specific region. At this time, the heat transfer is predicted to be small due to the low-speed characteristic, and only some of the concentrated water freeze. Therefore, the ice horn cannot be observed. Second, a new procedure is proposed to determine whether an aircraft can be operated at the given icing environment for HALE aircraft which does not have anti-/de- icing devices due to the ultra-light design. Preferentially, the ice shapes and its aerodynamic performance changes are obtained from ground to the mission altitude in the climbing stage under the given icing conditions. Then, the quantitative correlation between aerodynamic performance coefficients and icing environment variables was established. It was possible to judge the success of the mission by comparing the required power and the mounted battery to reach the mission altitude. The fixed-wing aircraft with high-speed is known to generate ice horns at high temperatures