Numerical Simulation of Airfoil Aerodynamic Penalties and Mechanisms in Heavy Rain

Numerical simulations that are conducted on a transport-type airfoil, NACA 64-210, at a Reynolds number of and LWC of 25？g/m3 explore the aerodynamic penalties and mechanisms that affect airfoil performance in heavy rain conditions. Our simulation results agree well with the experimental data and show significant aerodynamic penalties for the airfoil in heavy rain. The maximum percentage decrease in is reached by 13.2% and the maximum percentage increase in by 47.6%. Performance degradation in heavy rain at low angles of attack is emulated by an originally creative boundary-layer-tripped technique near the leading edge. Numerical flow visualization technique is used to show premature boundary-layer separation at high angles of attack and the particulate trajectories at various angles of attack. A mathematic model is established to qualitatively study the water film effect on the airfoil geometric changes. All above efforts indicate that two primary mechanisms are accountable for the airfoil aerodynamic penalties. One is to cause premature boundary-layer transition at low AOA and separation at high AOA. The other occurs at times scales consistent with the water film layer, which is thought to alter the airfoil geometry and increase the mass effectively. 1. Introduction The aerodynamic penalty of aircraft flight through heavy rain has been deemed to be a critical cause in many severe aviation accidents. The Eastern Flight 066 accident at Kennedy Airport (NTSB, 1976) is a telling example, though the factor of heavy rain was not taken into consideration at that time [1]. Three years later, another Flight named 693, a Boeing 727-25 civil airplane, suffered from an intense rainfall associated with wind shears on its eventual routine to the Atlanta International Airport [2]. Several severe aviation accidents in 1981 aroused people’s consciousness of the seriousness of rain influence on aircraft flight [3]. Investigation of rain effect on aircraft flight was begun with the wind tunnel test, and the earliest was conducted by Rhode in 1941 [4]. It dealt with the situation of an aircraft encountering heavy rain at moderate cruising altitude of about 5000？ft and concluded that, the heavy rain exposure time is not sufficient to force the aircraft to the ground. In 1982, Haines and Luers did a research concerning the frequency and intensity of very heavy rains and their effects on a landing aircraft [1]. In 1987, Hansman and Criag compared the aerodynamic performance degradation of NACA 64-210, NACA 0012, and Wortman FX 67-K170 airfoils under the low Reynolds numbers