Page 17 - Computational Fluid Dynamics for Engineers

2 1. Introduction

The third example, discussed in Section 1.3, deals with aircraft design and
power plant integration.
The fourth example, discussed in Section 1.4, corresponds to a calculation
method for predicting the performance degradation of an aircraft due to icing.
A NACA icing research aircraft is chosen to compare the calculated results
with measurements. The calculations are first performed by computing the ice
shapes that form on the leading edges of the lifting surfaces of the aircraft and
are followed by flowfield calculations to predict the loss in lift and increase in
drag due to ice.
The fifth example, discussed in Section 1.5 is the application of CFD to
ground-based vehicles, in particular to automobile aerodynamics development.
The use of CFD in this area has been continuously increasing because the aero-
dynamic characteristics have a significant influence on the driving stability and
fuel consumption on a highway. Since the aerodynamic characteristics of auto-
mobiles are closely coupled with their styling, it is impossible to improve them
much once styling is fixed. Therefore, it is necessary to consider aerodynamics
in the early design stage.
CFD also finds applications in internal flows and has been used to solve
real engineering problems such as subsonic, transonic and supersonic inlets,
compressors and turbines, as well as combustion chambers and rocket engines.
These applications are, however, beyond the scope of this book and the reader
is referred to the extensive literature available on these problems.

1.1 Skin-Friction Drag Reduction

There are several techniques for reducing the skin-friction drag of bodies. While
the emphasis in this section is on aircraft components, the arguments apply
equally to the reduction of skin-friction drag on all forms of transportation,
including underwater vehicles. The importance of the subject has been discussed
in a number of articles; a book edited by Bushnell and Heiner [1] summarizes
the research in this area and the reader is referred to this book for an in-depth
review of viscous drag reduction and for discussions of the possible savings which
can occur from the reduction of the drag. As an example of the argument in
support of the importance of the calculation methods used for reducing skin-
friction drag, it is useful to point out that a three-percent reduction in the
skin-friction drag of a typical long-range commercial transport, which burns
around ten million gallons of fuel per year, at 50 cents per gallon, would yield
yearly savings of around $ 150,000.
There have been many suggestions for reducing the skin-friction drag on
aircraft components including extension of regions of laminar flow, relaminar-
ization of turbulent flow and modification to the turbulence characteristics of the
near-wall flow. In general, these attempts to control the flow depend on changes