Civil Engineering Reference
In-Depth Information
The drag coefficients for two-dimensional rectangular prisms on the ground in
turbulent boundary-layer flow are shown in Figure 4.13. In comparison with rectangular
prisms in smooth uniform flow (Figure 4.9), the drag coefficients, based on the mean
wind speed at the height of the top of the prism, are much lower; because of the high
turbulence in the boundary-layer flow, they do not show any maximum value.
Melbourne (1995) has discussed the important effects of turbulence on flow around
bluff bodies in more detail.
4.4.4
Drag and pressures on a cube and a prism
The mean pressure distributions on a cube in a turbulent boundary-layer flow are shown
in Figure 4.14 (Baines, 1963). These pressure coefficients are based on the mean wind
speed at the height of the top of the cube. The drag coefficient of 0.8 is lower than that of
the two-dimensional square section prism (
d/h
equal to 1.0 in Figure 4.13). This is due to
the three-dimensional flows that occur around the side walls of the block which increase
the base pressure (decrease the negative pressure).
Figure 4.11
Effect of turbulence on shear
layers from rectangular prisms (Gartshore,
1973).
