Chapter 9 Boundary Layer Theory
(i) at y = 0, v = 0
(ii) at y = d, v = V_{0} (d = boundary layer thickness V_{0} = free stream velocity)
(iii) at y = d, dv/dy = 0 [∵ v = V_{0} = constant]
The quantity (V_{0 }– v) is known as the velocity defect.
The ratio of displacement thickness to momentum thickness is called the shape factor (H)
H = d/q
(i) Boundary Layer thickness
(ii) Local coefficient of drag C*_{D}
(iii) Avg. Coefficient C_{D}
where
d = Boundary layer thickness
t = Shear stress at solid surface
x = Distance from where solid surface starts
For a given velocity it can be determined whether the B.L.(Boundary layer) has separated or on the verge of separation or will not separate from the following conditions :
1. If
< 0 : Flow has separated.
2. If
= 0 : Flow is on verge of separation.
3. If
> 0 : Flow is attached with the surface
(i) Rotating the boundary in the direction of flow.
(ii) Suction of the slow moving fluid by a suction slot.
(iii) Supplying additional energy from a blower.
(iv) Providing a bypass in the slotted wing.
(v) Providing guide blades in a bend.
(vi) Injecting fluid into boundary layer.
(vii)Streamlining of body shapes.