Source or Sink
Source flow -
A flow with straight streamlines emerging from a point.
Velocity along each streamline varies inversely with distance from the point (shown in Fig. 20.3).
Only the radial component of velocity is non-trivial. (vθ=0, vz=0 ).
In a steady source flow the amount of fluid crossing any given cylindrical surface of radius r and unit length is constant
(20.10a)
(which shows that velocity is inversely proportional to the distance )
where, K is the source strength is the volume flow rate
The definition of stream function in cylindrical polar coordinate states that
(20.11)
For the source flow,
(20.13)
Combining Eqs (20 .12) and (20.13) , we get
(20.14)
Thus
Because the flow is irrotational, we can write
(20.15)
The integration constants C1 and C2 in Eqs (20.14) and (20.15) have no effect on the basic structure of velocity and pressure in the flow.
The equations for streamlines and velocity potential lines for source flow become
(20.16)
K = source strength and is proportional to the rate of volume flow from the source per unit depth perpendicular to the page |
Sink flow
When is negative , we get sink flow,
here the flow is in the opposite direction of the source flow.
In Fig. 20.3, the point 0 is the origin of the radial streamlines. We visualize that point O is a point source or sink that induces radial flow in the neighbourhood .
The point source or sink is a point of singularity in the flow field (because vr becomes infinite).
The stream function and velocity potential function are
(20.17)
1. What are the assumptions made in analyzing inviscid, incompressible, irrotational flows? |
2. What is the significance of inviscid flow in civil engineering? |
3. How does the assumption of incompressibility affect the analysis of fluid flow? |
4. What is the significance of irrotational flow in civil engineering applications? |
5. What are the limitations of assuming inviscid, incompressible, irrotational flows? |
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