doG

What do you think happens at separation?

More turbulence, not significantly less turbulence as you asserted.

I put the graph to show what happens. It is a sphere. It goes down and up, but the derivative is a lot less when it is going down

Why then does it match the image in the paper I cited. In that paper it is the leg of an oil platform.

"As we can see from figure 2.4, there is a drop in drag at a certain Reynolds number (approximately 4 · 10⁵ Re 6 · 10⁵). This is the critical region, where the boundary layer around the body transitions from laminar to turbulent flow, explained in section 2.3.5. The turbulent mixing that takes place in the boundary layer gives the fluid a higher momentum toward the surface of the body, thus moving the separation point farther back. In the critical range, small variations in the Reynolds number cause considerable changes in the drag coefficient."

 

Can I just bold his words and hope you can understand them?

No you can't. Nowhere, even in the bolded section is there any mention that any turbulence has decreased, only the the point of separation has moved, In fact, in your bolded section he clearly states that their is higher momentum toward the surface of the body, not laminar to it, which indicates increased turbulence, not significantly reduced turbulence as you have tried to suggest by putting words in his mouth. Nowhere is your assertion that turbulence is decreased at higher reynolds numbers supported.

Read carefully what the Author is describing where you quoted him...more turbulence in the boundary layer (micro turbulence) moves the separation point (the start of much more significant larger turbulence) back further on the body...overall significantly less turbulence and drag

Read it again. The author says absolutely nothing of the sort, you don't get to randomly just insert words to make it mean what you want.

Additionally, Design Aerospace says simply:

For low values of Re, flow is laminar. For high values of Re, flow is turbulent.

 

I am by no means an expert on this, so I'm probably completely off. But, if our universe was infinite, wouldn't there be infinite gravity all around us?

Not necessarily. Infinite gravity would require infinite mass but an infinite universe need not be full of infinite mass...

I guarantee you that in that example their is significantly less turbulence at the lower coefficients of drag in this example.

Let me make sure I understand you. You are asserting that they have less turbulence at the lowest cd in that example, at an Re around 4 · 10⁵?

FWIW, that exact image is from section 2.4 of a white paper at http://www.diva-portal.org/smash/get/diva2:566139/FULLTEXT01.pdf The dip in drag coefficient is explained by the author:

pure alkali, white powder.

which one?

In both cases, the wing and a flat plate parallel to the flow, form drag is much less significant than skin friction. A change to a turbulent regime simply means more drag.

Sometimes. At others drag does go down with turbulence as shown by Endercreeper's post below...

And your point is? You do realize that this scenario is not true for all profiles?

By that reasoning you could say that subjective experiences don't exist because there is no evidence for them.

That looks to be intentionally obtuse.

Also note that your reference from the World of Physics - Drag Coefficient...includes a table where the drag coefficient of spheres (golf and tennis balls) increases at lower Reynolds numbers. I don't see where it helps your claim to the opposite.

Yes, and the same table shows that cd = 0.02 for a wing or 0.2 for a wing in turbulent flow where re > 30,000. Even the table at the wiki page shows a cd of 0.001 for a plate in laminar flow and 0.005 for a plate in turbulent flow.

In some cases for some shapes cd is higher at lower reynolds numbers and the reverse for others. It is different too for bodies moving through a fluid versus fluid moving through a body. In the case of a short sharp edged orifice versus a tube you can see values for cd go from 0.62 to 0.80. In the article I cited on cleaning fluid conductors it points out:

As N_R increases, flow conditions go from laminar, through the critical zone, to turbulent. It has been proven empirically that once N_R exceeds 3,000, resistance to fluid flow is a combination of the effects of turbulence and of viscous drag at the conductor wall.

For some conductors it points out that N_R needs to be as high as 25,000 to cause enough turbulence in order to cause enough drag to effectively clean the walls of the conductor.

My only point to begin with is the you cannot just calculate drag based on shape and angle of incidence. Velocity is an essential part of the equation. So is overall shape. A sphere will have a higher cd than a hemisphere ( with the round side facing flow) even though both present the same profile to oncoming flow. Drag is a complicated number than cannot be reduced to 2 variables.

the basis of all my calculations is high velocity relativity and the basic structure is purely mathematical and the conceptual make up is beyond the scope of this forum...

 

How arrogant...

Checkout Wolfram Alpha... http://www.wolframalpha.com/input/?i=sqrt%28i%29

See http://cmb.physics.wisc.edu/tutorial/light.html

I think that is the key. The friction is greater. But often with the drag of objects the form drag is significantly more important and makes up a higher portion of the drag. If it does not trigger less form drag (a straight pipe would not have any) you would just have the greater friction drag.

Actually a straight pipe does at significant flows. Flow is laminar at lower velocities but it becomes chaotic at greater velocities. An article from one of the magazines I get actually suggests using this principle for cleaning fluid conductors.

Here's a reference also from World of Physics - Drag Coefficient...

It's not empirical evidence. This is exactly the point I am making. Perhaps you missed my initial post on this.

The point you're missing is that evidence is not subjective....

High velocities and larger objects lead to higher lead to higher Reynolds numbers- the boundary layer transitions to turbulent relatively earlier on the object.

 

This boundary layer turbulence/mixing with the outer flow generally reduces the overall turbulence of the flow (swept downstream more readily and less build up of larger eddies)

 

Though shape dependant this generally means that higher Reynolds numbers lead to lower coefficients of drag.

 

At lower Reynolds numbers turbulence in the boundary layer are often induced for this reason, the earlier transition from laminar reducing drag (or increasing lift of a wing by delaying stall or assisting reattachment of the flow)

My own personal experience with orifices in hydraulics systems indicate the opposite. The higher the flow through an orifice, including a pipe which is just a long orifice, is that higher velocities create chaotic flows as opposed to laminar flow and the result is a higher pressure differential from the increased friction.

That someone has an opinion that something is incredible doesn't make it untrue.

You're missing the point. Just because someone has an opinion that something is credible doesn't mean that it is.

I just did. The problem here is that YOU don't find that credible. Others do. It's called a difference of opinion.

Ummmmmmmmm....no. Opinion doesn't make anything true. That someone has an opinion that something is credible doesn't make it credible.

 

Presumably you won't think the eye-witness accounts of say, Jesus miracles for example, credible but these are the kinds of evidences on which religious beliefs are often based.

What accounts? From the bible? That whole book is hearsay, there's not one word of first person testimony in that book. Like I said before, please cite some credible examples.

You're dismissing personal and historical testimony including eye-witness accounts and personal experience.

Eye witnesses of deities? Please cite some credible examples...

 

But until we know everything, literally everything, there's no room for science to say without a doubt that there is no existence of a deity.

Science will never look to prove that anything doesn't exist, the possibility always exists that there is some realm beyond our knowledge. In the end that's what science is about, knowledge. We do know that currently there is ZERO evidence for the existence of deities, leprechuans, unicorns, pegasus', SAnta Claus, the tooth fairy, the sandman, etc., etc. so there is no point trying to prove their existence or to accept the existence of any such mystical creatures as fact.

High fluid velocities lead to high reynold's numbers which indicates increased turbulence which increases drag. This simply means that cd is dependent on velocity and theories must account for that. It is not as simple as shape and angle of incidence.

I think cd increases with turbulent flow, i.e. high reynold's numbers...

Yes, but in this theory, you use the drag coefficient it would have if it was a flat 2D plate (based on Reynolds number) and you multiply that by the cosine of the average value of all angles less then 90 degrees.

For all velocities?

Ever heard of Reynold's number?

doG,

 

Exactly. There is a much difference between an apple and an orange, as there is between having an idea of God, and believing in the ideal.

 

Regards, TAR2

That's why it's OK to theorize deities but believing in them on faith alone is to be broken....