HYBRID AIRFOIL DESIGN METHOD TO SIMULATE FULL-SCALE ICE ACCRETION THROUGHOUT A GIVEN ALPHA-RANGE

A design procedure is presented for hybrid airfoils with full-scale le ading edges and redesigned aft sections that exhibit full-scale airfoi l water droplet-impingement characteristics throughout a given angle o f attack or a range, The design procedure is an extension of a previou sly published method in that it not only allows for subcritical and vi scous-flow analysis in the design but is also capable of off-design dr oplet-impingement simulation through the use of a flap system, The lim itations of the nap-system-based design for simulating both on-and off -design full-scale droplet-impingement characteristics and surface-vel ocity distribution are discussed with the help of specific design exam ples, In particular, this paper presents the design of two hybrid airf oils at two different angles of attack, such that they simulate both t he full-scale velocity distribution as well as droplet-impingement cha racteristics at the respective design angles of attack, Both of the hy brid airfoils are half-scale airfoil models with the nose section matc hing 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 eff ect of nap deflection and droplet size on droplet-impingement characte ristics is also presented to highlight the important limitations of th e present method both on-and off-design. This paper also discusses imp ortant compromises that must be made to achieve full-scale ice accreti on simulation throughout a desired a range and suggests alternatives s uch as applying a multipoint design approach.