A hybrid airfoil design method to simulate full-scale ice accretion throughout a given C₁-range

A design procedure for hybrid airfoils with fullscale leading edges and redesigned aft-sections that exhibit full-scale airfoil water droplet impingement characteristics throughout a given Ci-range is presented. The design procedure is an extension of the method first published by Saeed, et al., in that it not only allows for subcritical and viscous flow analysis in the design but is also capable of off-design droplet impingement simulation through the use of a flap system. The limitations of the flap-system based design for simulating both on- and off-design full-scale droplet impingement characteristics and surface velocity distribution are discussed with the help of specific design examples. In particular, the paper presents the design of two hybrid airfoils at two different angles of attack, such that they simulate both full-scale velocity distribution as well as droplet impingement at the respective design angles of attack. Both of the hybrid airfoils are halfscale airfoil models with a 5% upper and 20% lower full-scale surface of the Learjet 305 airfoil leadingedge. The effect of flap deflection and droplet size on droplet impingement characteristics is also presented to highlight the important limitations of the present method both on and off design. The paper also discusses important compromises that must be made in order to achieve full-scale ice accretion simulation throughout a desired Cj-range and suggests alternatives such as applying a multipoint design approach for the design.