Turbulent flow decreases drag?

[SaintJude]

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Turbulent flow decreases drag? For real? How?

 

[chiddler]

i think it's drag causes turbulent flow.

no turbulence = la...that one word...la...lsomething.

edit: LAMINAR

 

[MedPR]

Turbulent flow decreases drag? For real? How?

This is a pretty dumb way to think about it, but it works for me.

Block the end of a water hose with your thumb and turn the water on. Now have someone stand 5 feet away from you and tell them to block every single stream of water from getting by them. Now remove your thumb and tell the person to block every single stream (now there's only 1 stream) of water from getting by them.

The second person is like drag, and your thumb in the water hose creates turbulent flow, which decreases the second person's ability to stop the flow of water.

Not technical at all, but it helps me remember :/

 

[SaintJude]

wait yes..or no? sorry, but i helps when the answer is really clear before I jump into your analogy

 

[typicalindian]

This is a pretty dumb way to think about it, but it works for me.

Block the end of a water hose with your thumb and turn the water on. Now have someone stand 5 feet away from you and tell them to block every single stream of water from getting by them. Now remove your thumb and tell the person to block every single stream (now there's only 1 stream) of water from getting by them.

The second person is like drag, and your thumb in the water hose creates turbulent flow, which decreases the second person's ability to stop the flow of water.

Not technical at all, but it helps me remember :/

Haha that is awesome! I definitely won't forget that one.

Also, isn't "drag" analogous to the friction that the fluid faces from the container as it flows? If so, would it make sense to say that by being turbulent you are in contact with the walls less consistently so the overall drag is reduced?

 

[chiddler]

This is a pretty dumb way to think about it, but it works for me.

Block the end of a water hose with your thumb and turn the water on. Now have someone stand 5 feet away from you and tell them to block every single stream of water from getting by them. Now remove your thumb and tell the person to block every single stream (now there's only 1 stream) of water from getting by them.

The second person is like drag, and your thumb in the water hose creates turbulent flow, which decreases the second person's ability to stop the flow of water.

Not technical at all, but it helps me remember :/

i don't understand this analogy.

explain, please?

 

[MedPR]

i don't understand this analogy.

explain, please?

Maybe you're not familiar with water hoses 🙂 Go to your bathroom sink (or kitchen, whatever) and stick your thumb where the water comes out of the faucet. Now turn the water on. See how the water sprays everywhere? That's like turbulent flow.. You can't block all of it and reduce it as easily (drag) as the laminar flow that comes out when you don't block it with your thumb.

 

[chiddler]

Maybe you're not familiar with water hoses 🙂 Go to your bathroom sink (or kitchen, whatever) and stick your thumb where the water comes out of the faucet. Now turn the water on. See how the water sprays everywhere? That's like turbulent flow.. You can't block all of it and reduce it as easily (drag) as the laminar flow that comes out when you don't block it with your thumb.

hmm, I understand this example, but I don't understand the conclusions to make of it!

You're saying that it's easier to add drag forces to laminar flow water? I would expect the contrary because laminar does not contact sides of hose.

 

[typicalindian]

hmm, I understand this example, but I don't understand the conclusions to make of it!

You're saying that it's easier to add drag forces to laminar flow water? I would expect the contrary because laminar does not contact sides of hose.

Woah what? I thought laminar flow DID contact te sides which is why it flows slowest on the aides an fastest in the middle

 

[chiddler]

Woah what? I thought laminar flow DID contact te sides which is why it flows slowest on the aides an fastest in the middle

wiki agrees with you.

does turbulent flow not contact sides of pipe?

 

[typicalindian]

wiki agrees with you.

does turbulent flow not contact sides of pipe?

Turbulent flow is really just the disturbance of laminar flow. The way I interpret it is, laminar flow is the ability for water layers to slide past each other nicely, like cars driving on the freeway. But turbulent flow is when the fluid deviates from the nice sliding motion and things just end up flowing every which way, which occurs at high speeds I believe.

So to answer your question, turbulent flow does contact the sides, but it's random, unlike laminar flow which always has the same fluid molecules sliding past the wall.

Think about it, have you ever seen a fluid pass through something without touching the sides? No matter what happens, it's going to touch the sides.

Edit : I'd just like to add that I'm not really a pro at physics so i can't be certain that all of the information I'm giving you is true. Take what I say with a grain of salt.

 

[chiddler]

Turbulent flow is really just the disturbance of laminar flow. The way I interpret it is, laminar flow is the ability for water layers to slide past each other nicely, like cars driving on the freeway. But turbulent flow is when the fluid deviates from the nice sliding motion and things just end up flowing every which way, which occurs at high speeds I believe.

So to answer your question, turbulent flow does contact the sides, but it's random, unlike laminar flow which always has the same fluid molecules sliding past the wall.

Think about it, have you ever seen a fluid pass through something without touching the sides? No matter what happens, it's going to touch the sides.

Ok! So I wasn't completely off. Then turbulent flow means that there is more friction during flow. Yes?

 

[typicalindian]

Ok! So I wasn't completely off. Then turbulent flow means that there is more friction during flow. Yes?

I can't give you a definitive answer on that. I'm not entirely sure myself so I'd rather not say and risk giving you incorrect info.

 

[milski]

It depends. There are conditions in which the boundary layer will change in a way resulting in less drag. There are examples where exactly the opposite is true. How does this relate to MCAT? Generally turbulent flows are well beyond anything that we would have to deal with except having some general idea that turbulence exists.

 

[chiddler]

generally turbulent flows are well beyond anything that we would have to deal with except having some general idea that turbulence exists.

🙂 🙂 🙂

 

[SaintJude]

Ok, so turbulent flow decreases drag.