Aerodynamic implications of nose inlets

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horse
13
Joined: Fri Oct 23, 2009 4:53 pm
Location: Bilbao, ES

Aerodynamic implications of nose inlets

OK, so here is some maths.

According to Schlichting for high Reynolds number the boundary layer is approximately 5 * Re ^ (-1/2).

So lets choose the chassis height as a length scale, say 25cm and a velocity of about 200kph or 50 m/s.

Then the Reynolds number is about 1250000, so it's pretty high.

The boundary layer thickness is then going to be approximately 4.5mm.

That duct really isn't much deeper than that.
Adrian Newby wrote:I proposed that Newey was trying to peel off any turbulent air in that area, and then use that low-energy air to cool the KERS.
Yeah, I think the above is the calculation for laminar boundary layer. I just don't think that there will be a great deal of air induced by such an intake - perhaps they don't need much?
"Words are for meaning: when you've got the meaning, you can forget the words." - Chuang Tzu

-1
Joined: Tue Feb 07, 2012 10:05 pm

Re: Red Bull RB8 Renault

horse wrote:OK, so here is some maths.

According to Schlichting for high Reynolds number the boundary layer is approximately 5 * Re ^ (-1/2).

So lets choose the chassis height as a length scale, say 25cm and a velocity of about 200kph or 50 m/s.

Then the Reynolds number is about 1250000, so it's pretty high.

The boundary layer thickness is then going to be approximately 4.5mm.

That duct really isn't much deeper than that.
Adrian Newby wrote:I proposed that Newey was trying to peel off any turbulent air in that area, and then use that low-energy air to cool the KERS.

Yeah, I think the above is the calculation for laminar boundary layer. I just don't think that there will be a great deal of air induced by such an intake - perhaps they don't need much?

That is my thinking, that they don't need much, although, judging by KERS overheating last year, maybe a tad more than they calculated!

volarchico
0
Joined: Fri Feb 26, 2010 6:27 am

Re: Red Bull RB8 Renault

horse wrote:OK, so here is some maths.

According to Schlichting for high Reynolds number the boundary layer is approximately 5 * Re ^ (-1/2).

So lets choose the chassis height as a length scale, say 25cm and a velocity of about 200kph or 50 m/s.

Then the Reynolds number is about 1250000, so it's pretty high.

The boundary layer thickness is then going to be approximately 4.5mm.

That duct really isn't much deeper than that.
Why would we use the nose height as the length scale? The length scale should be the distance downstream from the start of the boundary layer. I know Wikipedia isn't authoritative, but my aerodynamics textbooks are at home buried away on the shelves somewhere. From my memory, the basic equations and principles presented here are correct:

http://en.wikipedia.org/wiki/Boundary-layer_thickness

Using turbulent boundary layer equation, and 50 m/s (180 kph), and a length scale from the tip of the nose to an approximate location of the inlet (~750 mm), the 99% thickness is 15 mm.

But keep in mind the turbulent boundary layer velocity profile is much steeper compared to a laminar one. So even scooping out the bottom 50% of a turbulent boundary layer is actually taking a good bit of air.

EDIT: Image of profile:

-1
Joined: Tue Feb 07, 2012 10:05 pm

Re: Red Bull RB8 Renault

volarchico wrote:
horse wrote:OK, so here is some maths.

According to Schlichting for high Reynolds number the boundary layer is approximately 5 * Re ^ (-1/2).

So lets choose the chassis height as a length scale, say 25cm and a velocity of about 200kph or 50 m/s.

Then the Reynolds number is about 1250000, so it's pretty high.

The boundary layer thickness is then going to be approximately 4.5mm.

That duct really isn't much deeper than that.
Why would we use the nose height as the length scale? The length scale should be the distance downstream from the start of the boundary layer. I know Wikipedia isn't authoritative, but my aerodynamics textbooks are at home buried away on the shelves somewhere. From my memory, the basic equations and principles presented here are correct:

http://en.wikipedia.org/wiki/Boundary-layer_thickness

Using turbulent boundary layer equation, and 50 m/s (180 kph), and a length scale from the tip of the nose to an approximate location of the inlet (~750 mm), the 99% thickness is 15 mm.

But keep in mind the turbulent boundary layer velocity profile is much steeper compared to a laminar one. So even scooping out the bottom 50% of a turbulent boundary layer is actually taking a good bit of air.

EDIT: Image of profile:
I agree with you on the length scale.

It seems that Newey made the lower duct as wide as possible to catch as much of the turbulent layer as he could, then calculated the height that would be needed for getting the amount of air he required for his purpose (KERS cooling, in my opinion).

kilcoo316
28
Joined: Wed Mar 09, 2005 3:45 pm
Location: Kilcoo, Ireland

Re: Red Bull RB8 Renault

That ducting wouldn't need to go very far; there will be a pretty adverse pressure gradient in a small duct that ingests only a boundary layer from outside.

Upon entering the narrow slit, the two expanding viscous sublayers (from upper and lower surfaces) will damp out the largest of the outer layer eddies somewhat, but you'll end up with further (form) pressure losses from both sides and a rapidly decreasing u(z). Indeed, which would in fact no longer exist if the flow becomes fully developed, it would be u(δ) instead which will decrease the further the flow travels down the duct.

Obviously, this adverse pressure gradient will perturb back upstream and affect the flow rate coming in (and the boundary layer under the nose/monocoque).

What do the rules say regarding ducting exits? Is it aft of the driver?

It may be that this slit simply bleeds off the boundary layer prior to the splitter (to reduce interference 'drag' effects - not the drag itself, thats incidental in the grand scheme) and cools the driver's backside!

ringo
196
Joined: Sun Mar 29, 2009 9:57 am

Re: Red Bull RB8 Renault

The boundary layer discussion is not really relevant.
We are looking at a air crashing into a wall, not flowing along a surface.

The air will simply stagnate in that damn, you get some circulation going, a high pressure bubble if you will and less turbulent more streamlined flow will flow over it.
This will happen at high speeds.

This is cheap and dirty downforce from that high pressure static zone.

What is interesting about that part of the nosecone is that it is convex. Its worth investigating i think.
For Sure!!

-1
Joined: Tue Feb 07, 2012 10:05 pm

Re: Red Bull RB8 Renault

ringo wrote:The boundary layer discussion is not really relevant.
We are looking at a air crashing into a wall, not flowing along a surface.

The air will simply stagnate in that damn, you get some circulation going, a high pressure bubble if you will and less turbulent more streamlined flow will flow over it.
This will happen at high speeds.

This is cheap and dirty downforce from that high pressure static zone.

What is interesting about that part of the nosecone is that it is convex. Its worth investigating i think.
The boundary layer discussion is about the lower intake.

The upper intake is not an air dam. If anything, it is the opposite of that.

ringo
196
Joined: Sun Mar 29, 2009 9:57 am

Re: Red Bull RB8 Renault

On the lower surface, Bernoulli cannot be used in it's simple form. The equations will change because of gravitation and pressure potential.
The surface is curved and the air is underneath the surface.

What is the opposite of an air damn?
For Sure!!

-1
Joined: Tue Feb 07, 2012 10:05 pm

Re: Red Bull RB8 Renault

ringo wrote:On the lower surface, Bernoulli cannot be used in it's simple form. The equations will change because of gravitation and pressure potential.
The surface is curved and the air is underneath the surface.

What is the opposite of an air damn?
There are many, many things going on under the nose, behind the front wing, between spinning tires, etc.

The opposite of an air dam, which builds up a high pressure bubble, is to allow pressure to flow through an intake (in this case, the one in the hump on the nose).

bhall
370
Joined: Tue Feb 28, 2006 8:26 pm

Re: Red Bull RB8 Renault

Ringo wrote:What is the opposite of an air damn?
Adrian Newby wrote:The opposite of an air dam, which builds up a high pressure bubble, is to allow pressure to flow through an intake (in this case, the one in the hump on the nose).
Otherwise known as a vent?

(I'm just reminded of the joke in "Beavis and Butthead Do America" - oh, yes - where Beavis asks a Hoover Dam tour guide, "Is this a god damn?")

-1
Joined: Tue Feb 07, 2012 10:05 pm

Re: Red Bull RB8 Renault

bhallg2k wrote:
Ringo wrote:What is the opposite of an air damn?
Adrian Newby wrote:The opposite of an air dam, which builds up a high pressure bubble, is to allow pressure to flow through an intake (in this case, the one in the hump on the nose).
Otherwise known as a vent?

(I'm just reminded of the joke in "Beavis and Butthead Do America" - oh, yes - where Beavis asks a Hoover Dam tour guide, "Is this a god damn?")

Yes, exactly, a vent. Newey is venting that high pressure air into the chassis to "cool the driver" and then exiting it through the cockpit opening.

shelly
144
Joined: Tue May 05, 2009 11:18 am

Re: Red Bull RB8 Renault

I think boundary layer idea could aplly to bot tha lower an upper opening. Concave surface gives a steeper pressure gradient (basic theory of flow acceleartin on covex surface and decelerating on concave)

-1
Joined: Tue Feb 07, 2012 10:05 pm

Re: Red Bull RB8 Renault

shelly wrote:I think boundary layer idea could aplly to bot tha lower an upper opening. Concave surface gives a steeper pressure gradient (basic theory of flow acceleartin on covex surface and decelerating on concave)
Yes, that is correct.

PlatinumZealot
238
Joined: Thu Jun 12, 2008 2:45 am

Re: Red Bull RB8 Renault

bhallg2k wrote:
Ringo wrote:What is the opposite of an air damn?
Adrian Newby wrote:The opposite of an air dam, which builds up a high pressure bubble, is to allow pressure to flow through an intake (in this case, the one in the hump on the nose).
Otherwise known as a vent?

(I'm just reminded of the joke in "Beavis and Butthead Do America" - oh, yes - where Beavis asks a Hoover Dam tour guide, "Is this a god damn?")

Yes, exactly, a vent. Newey is venting that high pressure air into the chassis to "cool the driver" and then exiting it through the cockpit opening.
Air Dams can have vents. It's just a vent in the air dam.
"Raindrops .. drop top!"

-1
Joined: Tue Feb 07, 2012 10:05 pm

Re: Red Bull RB8 Renault

hardingfv32 wrote:
Adrian Newby wrote:Yes, exactly, a vent. Newey is venting that high pressure air into the chassis to "cool the driver" and then exiting it through the cockpit opening.
And you think that routing the air around the internal suspension components and the tightly packaged driver causes less drag than say Ferrari's ramp nose? Interesting

Brian
Nope. I think clean, high-energy airflow between the front tires is more important to Adrian Newey than drag on top of the nose, or inside a vent.

Many people here seem to be very hung up on drag, especially the drag of these new humps. F1 cars are very draggy things to begin with. And drag is relatively unimportant on the top of the nose.

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