18
* Steady state flow
* Constant cross-sectional area
In this case, the drag force is caused by friction of fluid current flowing over the
tube. The drag force is a function of tube cross-sectional area, A, drag coefficient, CD,
external fluid density, p, and external flow velocity, V. Equation 2.1 defines the drag
force, Fdrag, on a cylinder based on applicable assumptions.
Fdr = CApV2 (2.1)
2
The cross-sectional area perpendicular to the flow direction is defined, A = Dh, with tube
diameter, D, and cross-sectional length perpendicular to flow, h. Figures 2.1 and 2.2
define h for a vertical tube and a tube inclined by angle, p, from the horizontal,
respectively.
Flow Direction h=L
1
Figure 2.1 Flow on a vertical tube
Flow Direction h = L sin (p
---- ^ /^
Figure 2.2 Flow on an inclined tube