Civil Engineering Reference
In-Depth Information
4
Basic bluff-body aerodynamics
4.1
Flow around bluff bodies
Structures of interest in this topic can generally be classified as
bluff
bodies with respect
to the air flow around them, in contrast to
streamlined
bodies such as aircraft wings and
yacht sails (when the boat is sailing across the wind). Figure 4.1 shows the flow patterns
around an airfoil (at low angle of attack) and around a two-dimensional body of
rectangular cross-section. The flow patterns are shown for steady free-stream flow;
turbulence in the approaching flow, which occurs in the atmospheric boundary layer, as
discussed in Chapter 3, can modify the flow around a bluff body, as will be discussed
later.
It can be seen in Figure 4.1 that the flow streamlines around the airfoil closely follow
the contours of the body. The free-stream flow is separated from the surface of the airfoil
by only a thin boundary layer, in which the tangential flow is brought to rest at the
surface. The flow around the rectangular section (a typical bluff body) in Figure 4.1 is
characterized by a 'separation' of the flow at the leading edge corners. The separated
flow region is divided from the outer flow by a thin region of high shear and vorticity, a
region known as a free shear layer, which is similar to the boundary layer on the airfoil
Figure 4.1
Flow around streamlined and bluff
bodies.
