DRAG ON CYLINDER
DRAG ON CYLINDER
Consider a real fluid flowing over a circular cylinder of diameter D and length L, when a cylinder is placed in a fluid such that its length is perpendicular to the direction of flow.If the Reynolds number of the flow is less than 0.2, the inertia force is negligibly small as compared to viscous force and hence the flow pattern about the cylinder will be symmetrical.
As the Reynolds number increased, inertia force increases and hence they must be considered.
From experiments it has been observed that :
1. When Reynolds number Re<1,the drag force is directly proportional to velocity and hence the drag co-efficient 
is inversely proportional to Reynolds number
2. with the increase of Reynolds number from 1 to 2000, the drag coefficient decreases and reaches a minimum value of 0.95 at Re = 2000.
3. With the further increase of Reynolds number from 2000 to 30000, the coefficient of drag increases and attains maximum value of 1.2 at Re = 30000.
4. the value of coefficient of drag decreases if the Reynolds number is increased from 
to 
.At Re = , the value of = 0.3.
5. if the Reynolds number is increased beyond 
, the value of Cd increases and it becomes equal to 0.7 in the end.
Behavior of fluid according to magnitude of Reynolds number
Visualization of drag over cylinder.
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