The Icing Safety Research Oriented To The SLD Requirement Of Airworthiness In Large Civil Aircraft Airfoil

Supercooled large droplet (SLD), whose particle diameter is greaterthan50μm, is beyond the envelope described in the Appendix C of FAR25. When the droplets impact the surface of airfoil, they will freeze as theshape of ridge, cause the flap gap icing or getting stuck, change the wingaerodynamic shape of the wing significantly, reduce aerodynamicperformance and then endanger the safety of the aircraft greatly.In this paper, under the guide of latest icing airworthiness regulation,we develop a method applied in multi-element airfoil SLD icingsimulation and aerodynamic analysis on runback ice, which fills up thedeficiencies in the existing icing safety research.Icing on each wing segment of MD-LB606b multi-element airfoilhas been simulated in this work, the results agree well with theexperimental data form NASA. Moreover, the numerical simulations ofmaximum lift coefficients and stalling angles of NACA23012m are carried out by using Reynolds Stress Model (RSM), the good agreementwith the experimental data shows that RSM is a powerful tool to analyzeflow separation resulting from runback ice. The research methods in thiswork can be used for the icing aerodynamic safety assessment of largecivil aircraft.For the safety assessment on single element airfoil SLD icing oflarge civil aircraft, the effect of runback ice varies on different airfoilgeometries, the aerodynamic studies of runback ice on wing airfoil andtail airfoil are represented respectively. Under the influence of therunback ice，the aerodynamic separation on supercritical airfoil occursahead of time, and then the lift decreases significantly; while on the tailairfoil, flow separation zone becomes smaller at high angles of attack.For the safety assessment on multi-element airfoil SLD icing of largecivil aircraft, the ice accretion on the each wing are much more than thenormal droplets icing, the height of the ice at the leading edge of flapdecreases sharply；the aerodynamic performances reduce, in which theperformance reduces most on the slat among the three-element airfoil.However, due to the high-lift device, the penalties of aerodynamicperformance on multi-element airfoil are relatively less than those onsingle element airfoil.The investigation of this paper is of certain directive significance toaircraft design and airworthiness certification for large civil aircraft.