Civil Engineering Reference
In-Depth Information
The fluctuating cross-wind force coefficient for a square cross-section with sharp
corners is higher than that for a circular section, due to the greater strength of the shed
vortices. In smooth flow, the r.m.s. fluctuating cross-wind force coefficient is about 1.3;
this drops to about 0.7 in turbulent flow of 10% intensity (Vickery, 1966).
Figure 4.24
Variation of fluctuating cross-
wind force coefficient per unit length with
Reynolds number for a circular cylinder
(smooth flow).
4.6.5
Correlation length
The spatial correlation coefficient for fluctuating forces at two points along a cross-
section is defined by:
(4.23)
where are the fluctuating forces per unit length at two sections along a
cylindrical or prismatic body. (This was previously discussed in relation to atmospheric
turbulence in Section 3.3.5.)
We have assumed that the mean-square fluctuating force per unit length is constant
along the body, so that:
