Page 49 - Computational Fluid Dynamics for Engineers

34 1. Introduction

flight 83-11, (b) mixed ice of 22 minute accumulation, flight 84-34, and (c) glaze
ice of 25 minute accumulation, flight 84-27. The comparisons also include the
airplane lift coefficient with the clean wing and tail. The results in Fig. 1.33b
also show the calculations for an iced airplane with the wings deiced. In this case
(deiced wing), all the ice accumulation between the wing tip and the propeller
was removed (deiced) but the wing ice between the propeller and the fuselage
was not removed. The calculations for this case were performed for a clean
wing between the wing tip and the propeller and for an iced wing between the
propeller and fuselage. The tail calculations were performed for an all iced-tail
conditions. Whereas the results are good at lower angles of attack, they are
not so good at higher angles. This may be due to the ice shape with horns.
Figure 1.34 shows a comparison between clean and iced section drag coefficients
obtained at 69% wing semi-span. The calculated drag coefficients have been
"corrected" such that the clean wing matches the experimental data. Figure
1.34a is for rime ice accumulation of 65 minutes and Fig. 1.34b is for mixed ice
accumulation of 15 minutes. Both figures clearly show the drag increase due to
ice on the wing.

1.5 Aerodynamics of Ground-Based Vehicles

In recent years, CFD has been increasingly utilized in the automobile industry
to reduce the time required to develop new products. As described in detail in
[29], the ability of a company to quickly react to the ever-changing needs of
the market must be given an even higher priority than simply cutting costs,
even though cost minimization is also very important. As a result, all compu-
tational methods must satisfy the following two conditions; the first condition
is necessary, and the second is sufficient.
1. The method must reproduce the related physics with adequate accuracy, and
2. The method must yield results faster than conducting an experiment.
At this time, however, the advances made in applying CFD to reducing product
development time in the automobile industry are somewhat limited, and CFD
is still more a subject of research than a practical development tool.
Before some of the applications of CFD to ground-based vehicles are de-
scribed in the subsection that follows, a brief overview of the aerodynamic
problems associated with ground-based vehicles (exemplified by a passenger
car) is presented below.
Aerodynamics affects vehicles on the ground in two ways: (1) fuel economy
and (2) the stability and controllability of the vehicle. The main difference
between airborne and landborne vehicle aerodynamics is that, for an airborne
vehicle the oncoming flow is essentially in the axial direction, whereas for a
landborne vehicle, the relative wind is not necessarily aligned with the path of