A Hybrid Airfoil Design
Method to Simulate Full-Scale Ice Accretion Throughout a Given CL-Range
Saeed, F., Selig, M.S. and Bragg, M.B.
University of Illinois, Urbana, Illinois 61801
ABSTRACT
A design procedure for hybrid airfoils with full-scale leading edges
and redesigned aft-sections that exhibit full-scale airfoil water droplet
impingement characteristics throughout a given CL-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
half-scale airfoil models with a 5% upper and 20% lower full-scale surface
of the Learjet 305 airfoil leading-edge. 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
CL-range and suggests alternatives such as applying a multipoint design approach
for the design.