Separation of flow occurs when pressure gradient:a)Tends to approach z...
Flow separation occurs when the boundary layer travels far enough against an adverse pressure gradient that the speed of the boundary layer relative to the object falls almost to zero.
It has been observed that the flow is reversed at the vicinity of the wall under certain conditions.
A favourable pressure gradient is one in which the pressure decreases in the flow direction (i.e., dp/dx < 0). It tends to overcome the slowing of fluid particles caused by friction in the boundary layer.
This pressure gradient arises when the freestream velocity U is increasing with x, for example, in the converging flow field in a nozzle.
On the other hand, an adverse pressure gradient is one in which pressure increases in the flow direction (i.e., dp/dx > 0). It will cause fluid particles in the boundary-layer to slow down at a greater rate than that due to boundary-layer friction alone.
If the adverse pressure gradient is severe enough, the fluid particles in the boundary layer will actually be brought to rest. When this occurs, the particles will be forced away from the body surface (a phenomenon called flow separation) as they make room for following particles, ultimately leading to a wake in which flow is turbulent.
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Separation of flow occurs when pressure gradient:a)Tends to approach z...
Explanation:
Separation of flow occurs when the pressure gradient changes abruptly. Pressure gradient is the change in pressure per unit length in a fluid flow. When the pressure gradient changes suddenly, it causes the flow to separate from the surface and become turbulent.
The separation occurs because the pressure gradient is no longer able to sustain the flow and the fluid particles start moving in random directions. This can lead to the formation of eddies and vortices, and the flow becomes highly turbulent.
The separation of flow can occur in a variety of situations, such as:
- Flow over a curved surface: When the flow encounters a curved surface, the pressure gradient changes abruptly, causing the flow to separate.
- Flow over a sudden expansion or contraction: Similar to flow over a curved surface, sudden changes in the cross-sectional area of a pipe can cause the pressure gradient to change abruptly and lead to flow separation.
- Flow over a rough surface: If the surface is rough, it can cause the flow to become turbulent and lead to separation.
In summary, the separation of flow occurs when the pressure gradient changes abruptly, causing the flow to separate from the surface and become turbulent. This can occur in a variety of situations, such as flow over a curved surface, a sudden expansion or contraction, or a rough surface.