Page 16 - Computational Fluid Dynamics for Engineers

^ Introduction

In this chapter we present five examples to demonstrate the application of
CFD techniques to solve real engineering problems. These examples are taken
from the literature and encompass flows which make use of solutions of invis-
cid, boundary-layer and Navier-Stokes equations. For some of these flows, the
reduced forms of the conservation equations, such as inviscid and boundary-
layer equations are more appropriate, and for others more general equations are
needed. In this way, the scope of this book is clarified further with additional
terminology and fluid-dynamics information.
The first example, discussed in Section 1.1, addresses the application of CFD
to reduce the drag of a wing by adjustment of pressure gradient by shaping and
by suction through slotted or perforated surfaces. The drag of an aircraft can
be reduced in a number of ways to provide increased range, increased speed,
decreased size and cost, and decreased fuel usage. The adjustment of pressure
gradient by shaping and using laminar boundary-layer control with suction are
two powerful and effective ways to reduce drag. This is demonstrated with a
calculation method for natural laminar flow (NLF) and hybrid laminar flow
control (HLFC) wings.
The second example, discussed in Section 1.2, addresses the calculation of the
maximum lift coefficient of a wing which corresponds to the stall speed, which
is the minimum speed at which level flight can be maintained. A calculation
method is described and used to predict the maximum lift coefficient of a high-
lift system; this coefficient plays a crucial role in the takeoff and landing of an
aircraft.
Aircraft design was traditionally based on theoretical aerodynamics and wind
tunnel testing, with flight-testing used for final validation. CFD emerged in the
late 1960's. Its role in aircraft design increased steadily as speed and memory
of computers increased. Today CFD is a principal aerodynamic technology for
aircraft configuration development, along with wind tunnel testing and flight-
testing. State-of-the-art capabilities in each of these technologies are needed to
achieve superior performance with reduced risk and low cost.