Why Does Fluid Accelerate and Decelerate Over a Convex Surface?

[KishoreAM]

Guys...Can anyone explain me why fluid accelerates and then decelerates when flowing over a convex surface
and also concept of flow attachment in simple terms

 

[jack action]

why fluid accelerates and then decelerates when flowing over a convex surface

It causes a reduction in cross-sectional area, so the velocity must be accelerated to keep up with the flow rate. It goes back to its original velocity once the obstruction is passed.

also concept of flow attachment in simple terms

As the cross-sectional area increases aft of the "bump", the fluid wants to fill the new enlarged area, so it tends to follow the shape of the part it gets around. Of course, the faster the fluid goes, the harder it will be for it to follow the shape.

If you imagine a solid part moving in a non-moving fluid, you can imagine that, as it moves, it leaves an empty space while displacing the fluid in front of it. The fluid just want to fill the void to equilibrate everything once more, thus it looks like the fluid "sticks" to the part. If the fluid moves and the part is fixed, the same thing happens.