Posted On :

(i) Convergent flows: Negative pressure gradients (ii) Divergent flows: Positive pressure gradients (iii) A divergent duct or diffuser (iv) Tee-Junctions (v) Y-Junctions

**Boundary layer separation **

*(i)
**Convergent flows: Negative pressure gradients *

*If flow over a boundary occurs when there is a pressure decrease
in the direction of flow, the fluid will accelerate and the boundary layer will
become thinner.*

*This is the case for
convergent flows.*

*The accelerating fluid maintains the fluid close to the wall in
motion. Hence the flow remains stable and turbulence reduces. Boundary layer
separation does not occur.*

*(ii) Divergent flows:
Positive pressure gradients*

*When the pressure increases in
the direction of flow the situation is very different. Fluid outside
theboundary layer has enough momentum to overcome this pressure which is trying
to push it backwards. The fluid within the boundary layer has so little
momentum that it will very quickly be brought to rest,and possibly reversed in
direction. If this reversal occurs it lifts the boundary layer away from the
surfaceas shown below.*

*This phenomenon is known as boundary layer separation.*

*At the edge of the separated
boundary layer, where the velocities change direction, a line of vortices occur
(known as a vortex sheet). This happens because fluid to either side is moving
in the opposite direction.*

*This boundary layer separation and increase in the turbulence
because of the vortices results in very large energy losses in the flow.*

*These separating / divergent flows are inherently unstable and far
more energy is lost than in parallel or convergent flow.*

*(iii) A divergent duct
or diffuser*

*The increasing area of flow
causes a velocity drop (according to continuity) and hence a pressure
rise(according to the Bernoulli equation).*

*Increasing the angle of the
diffuser increases the probability of boundary layer separation. In a Venturi
meter it has been found that an angle of about 6**�** provides the optimum balance between length of meter and danger
of boundary layer separation which would cause unacceptable pressure energy
losses.*

*(iv) Tee-Junctions*

*Assuming equal sized pipes, as fluid is removed, the velocities at
2 and 3 are smaller than at 1, the entrance to the tee. Thus the pressure at 2
and 3 are higher than at 1. These two adverse pressure gradients can cause the
two separations shown in the diagram above.*

*(v) Y-Junctions*

*Tee junctions are special cases
of the Y-junction with similar separation zones occurring. See the diagram
below.*

*Downstream, away from the
junction, the boundary layer reattaches and normal flow occurs i.e. the effect
of the boundary layer separation is only local. Nevertheless fluid downstream
of the junction will have lost energy.*

Tags : Civil - Mechanics Of Fluids - Boundary Layer

Last 30 days 20 views
Related words : ### What is Mechanics Of Fluidsr: Boundary layer separation Define Mechanics Of Fluidsr: Boundary layer separation Definition of Mechanics Of Fluidsr: Boundary layer separation where how
meaning of Mechanics Of Fluidsr: Boundary layer separation
lecturing notes for Mechanics Of Fluidsr: Boundary layer separation lecture notes question and answer for Mechanics Of Fluidsr: Boundary layer separation answer
Mechanics Of Fluidsr: Boundary layer separation study material Mechanics Of Fluidsr: Boundary layer separation assignment Mechanics Of Fluidsr: Boundary layer separation reference description of Mechanics Of Fluidsr: Boundary layer separation
explanation of Mechanics Of Fluidsr: Boundary layer separation brief detail of Mechanics Of Fluidsr: Boundary layer separation easy explanation solution Mechanics Of Fluidsr: Boundary layer separation wiki
Mechanics Of Fluidsr: Boundary layer separation wikipedia how why is who were when is when did where did Mechanics Of Fluidsr: Boundary layer separation list of Mechanics Of Fluidsr: Boundary layer separation school assignment college assignment
Mechanics Of Fluidsr: Boundary layer separation college notes school notes kids with diagram or figure or image difference between Mechanics Of Fluidsr: Boundary layer separation www.readorrefer.in - Read Or Refer

Recent New Topics :
| Business Television (BTV) - Adaptations for Education | | Encryption | | System reliability and design lifetime | | Inter modulation and interference | | Downlink | | The Uplink | | Satellite uplink and downlink Analysis and Design | | TT&C Subsystem | | Thermal Control and Propulsion | | Attitude Control & Orbit Control | | The Power Supply- Satellite | | Spacecraft Technology- Structure | | Important Questions and Answers: Satellite Orbits | | Launch vehicles and propulsion | | Launching Procedures | | Eclipse | | Geo stationary and Non Geo-stationary orbits | | Station Keeping | | Orbital Parameters | | Newtonâ€™s law | | Keplerâ€™s laws | | Introduction to Satellite Communication | | Q and Phase Shift | | Measurement of SWR and Attunuation | | Measurement of Wavelength and Impeadence |