Page 41 - Computational Fluid Dynamics for Engineers

26 1. Introduction

provide additional research capability for measuring component drag through
selective deicing. The aircraft is equipped with several standard instruments for
measuring icing cloud properties.
Wing leading edge ice shapes are measured in flight with a stereo photogra-
phy system. Wing section drag is measured with a wake survey probe mounted
on the wing behind the region where the stereo photos are taken. A noseboom
is used to measure airspeed, angle-of-attack, and sideslip. A flight test system
measures flight dynamics along a flight path. The system includes a data ac-
quisition system and an inertial package that contains rate gyros, directional
gyros, and servo accelerometers.
Subsection 1.4.1 describes the calculation of ice shapes on the lifting surfaces
of this aircraft, and subsection 1.4.2 describes the calculation of aerodynamic
performance characteristics of this aircraft, including the icing effects. In both
subsections calculated results are presented and compared with experimental
data to demonstrate the efficiency and accuracy of each calculation method.

1.4.1 Prediction of Ice Shapes

The prediction of ice shapes requires knowledge of aerodynamics and also of the
physics of ice accretion. The nature of the ice depends on meteorological param-
eters; glaze ice is formed at temperatures slightly below freezing and rime ice is
increasingly superimposed as the temperature decreases. Glaze ice is character-
ized by its buildup to large dimensions, as for example in the familiar "horns"
(Fig. 1.26a), and rime ice by its opaque appearance with fine-grained surface,
see Fig. 1.26b. The shape of the ice changes with time and is influenced by the
nature of the water droplets and ice particles which impinge on the body or are
carried past it, depending upon their size and the flow properties which, in turn,
depend upon the shape of the body. The resulting impingement, coalescence and
accretion depend on the temperatures of the surface and of the discrete and

(a) (b)
Fig. 1.26. (a) Glaze and (b) rime ice shapes.