Hybrid airfoil design method to simulate full-scale ice accretion throughout a given α range

A design procedure is presented for hybrid airfoils with full-scale leading edges and redesigned aft sections that exhibit full-scale airfoil water droplet-impingement characteristics throughout a given angle of attack or a range, The design procedure is an extension of a previously published method 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 nap-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, this paper presents the design of two hybrid airfoils at two different angles of attack, such that they simulate both the full-scale velocity distribution as well as droplet-impingement characteristics at the respective design angles of attack, Both of the hybrid airfoils are half-scale airfoil models with the nose section matching the full-scale coordinates of the Learjet 305 airfoil back to 5% chord on the upper surface and 20% chord on the lower surface, The effect of nap 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. This paper also discusses important compromises that must be made to achieve full-scale ice accretion simulation throughout a desired a range and suggests alternatives such as applying a multipoint design approach.