It depends on the situation, but generally speaking an "uphill" flow closes in, kind of like a contraction with only one side. Conversely, a "downhill" flow opens up, and then there is more area. With a conserved mass flow rate, if area goes up, velocity goes down and vice versa.
Excellent question and a common source of misconception for me. I think it's more correct to consider it as the pressure is what's causing the separation. Adverse pressure gradients (going from low to high pressure) lead to separation, so when flow separates it relieves this gradient leading to lower pressures in regions where it has separated. What originally confused me is it is natural to think separation means lower velocity and Bernoulli says that means flow pressure should be relatively higher. However, separation is slowed only in the streamwise direction and can introduce vertical velocity components that didn't exist, so the total velocity might not have reduced.
![CFD - Computational Fluid Dynamics [Fluid Mechanics #17]](http://i.ytimg.com/vi/BdjPE9zxHCc/mqdefault.jpg)
![CFD - Computational Fluid Dynamics [Fluid Mechanics #17]](/img/tr.png)
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Your videos are amazing, man!!!! Congrats!!
Your explanations are very clear and make the subject even more interesting!
Aw thanks!
What a brilliant video, thank you very much!
Thank you!
i am so thankful for you becauce of your amazing explanation for seperation region and back flow...thank you
Glad you liked it!
Thank you very much for the explanation
You're welcome!
I have a question sir why does speed of wind slows down when it goes downhill but increases uphill ?
It depends on the situation, but generally speaking an "uphill" flow closes in, kind of like a contraction with only one side. Conversely, a "downhill" flow opens up, and then there is more area. With a conserved mass flow rate, if area goes up, velocity goes down and vice versa.
why pressure in the separation zone is low?
Excellent question and a common source of misconception for me. I think it's more correct to consider it as the pressure is what's causing the separation. Adverse pressure gradients (going from low to high pressure) lead to separation, so when flow separates it relieves this gradient leading to lower pressures in regions where it has separated.
What originally confused me is it is natural to think separation means lower velocity and Bernoulli says that means flow pressure should be relatively higher. However, separation is slowed only in the streamwise direction and can introduce vertical velocity components that didn't exist, so the total velocity might not have reduced.