Number of inlets

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Post Fri Nov 13, 2009 1:10 am

I read this book Aerodynamics (don't know the author) and he said that if the inlets had the same area that 1 inlet would have more drag that 2 inlets. Is this so and if it is then why haven't i heard anything about F1 doing something about it with the radiator inlets?
Spencer
Shrek
 
Joined: 5 Jun 2009
Location: right here

Post Fri Nov 13, 2009 5:10 am

Might have to do more with the area of the opening, vs the amount of air needed, vs how much drag, vs frontal area.

If drag penalty is less than say the cooling penalty of two openings, then they would go for the small penalty if no ideal compromise can be found.

I'm just sayin' that drag might not be the be all end all deciding variable.
Before I do anything I ask myself “Would an idiot do that?” And if the answer is yes, I do not do that thing. - Dwight Schrute
Giblet
 
Joined: 19 Mar 2007
Location: Downtown Canada

Post Sun Nov 15, 2009 8:32 am

Shrek,

I would disagree. All other things being equal, a single inlet would always be more aerodynamically efficient, since its more favorable surface area-to-volume ratio characteristics would mean less induced drag penalty.

Of course, there are always going to be exceptions, depending upon the exact geometries and flow conditions defined for each of the examples. And how each configuration might be best optimized. For example, jet aircraft with a single turbine engine sometimes use twin inlets, in order to always ensure that the engine always has sufficient airflow, even under excessive yaw conditions.

As for radiator ducts on an F1 chassis, the ducts are shaped and located as a result of where the radiator cores need to be, and what the rules dictate. The fluid-filled cores are relatively heavy and large, so they naturally want to be near the car's CofG to minimize polar MOI effects. The heat exchangers and ducts also provide a very effective side impact structure. And with regards to their induced drag penalty, a well designed heat exchanger installation should not impose any drag at all. In fact, it most likely produces a positive net thrust under most conditions, since there is a large amount of thermal energy being imparted into the airflow passing across the heat exchanger core matrices.

Regards,
Terry
"Q: How do you make a small fortune in racing?
A: Start with a large one!"
riff_raff
 
Joined: 24 Dec 2004

Post Sun Nov 15, 2009 8:43 am

Shrek wrote:I read this book Aerodynamics (don't know the author) and he said that if the inlets had the same area that 1 inlet would have more drag that 2 inlets. Is this so and if it is then why haven't i heard anything about F1 doing something about it with the radiator inlets?


That simply doesn't sound right, how about a dozen inlets with the same area?

As for Terry's theory about the heat-xchanger channel acting like a jet-engine xpanding the air, I doubt that as well.
"I spent most of my money on wine and women...I wasted the rest"
xpensive
 
Joined: 22 Nov 2008
Location: Somewhere in Scandinavia

Post Sun Nov 15, 2009 10:17 am

xpensive wrote:As for Terry's theory about the heat-xchanger channel acting like a jet-engine xpanding the air, I doubt that as well.

I do not know how important the effect could be but in fact that's the way jet engine is working - you adding heat into the flow (in case of jet engine by burning fuel) and thus increasing its speed.
noname
 
Joined: 13 Feb 2009
Location: EU

Post Sun Nov 15, 2009 12:51 pm

xpensive wrote:As for Terry's theory about the heat-xchanger channel acting like a jet-engine xpanding the air, I doubt that as well.

Have you read about the nuclear jets?)))
timbo
 
Joined: 22 Oct 2007

Post Sun Nov 15, 2009 6:54 pm

noname wrote:
xpensive wrote:As for Terry's theory about the heat-xchanger channel acting like a jet-engine xpanding the air, I doubt that as well.

I do not know how important the effect could be but in fact that's the way jet engine is working - you adding heat into the flow (in case of jet engine by burning fuel) and thus increasing its speed.


A turbine engine is also compressing the air to dense a mixture and igniting it, adding significantly more energy to the flow stream. The radiator ducting does not compress the flow, but actually expands it. The inlet is purposely smaller than the radiator core because that slows the flow so that heat exchanger-airstream exchange is more efficient.

The thrust per mass flow is the equal to the difference in velocity at the exit. There is no way that the radiator heat adds a sufficient amount of energy to make up for the total pressure loss through the heat exchanger core.

What was the title of this book? I'm curious and would like to read this myself. I think something may have been misinterpreted.
Mystery Steve
 
Joined: 25 Sep 2009
Location: Cincinnati, OH, USA

Post Sun Nov 15, 2009 8:26 pm

Mystery Steve wrote:A turbine engine is also compressing the air to dense a mixture and igniting it, adding significantly more energy to the flow stream. The radiator ducting does not compress the flow, but actually expands it. The inlet is purposely smaller than the radiator core because that slows the flow so that heat exchanger-airstream exchange is more efficient.

The thrust per mass flow is the equal to the difference in velocity at the exit. There is no way that the radiator heat adds a sufficient amount of energy to make up for the total pressure loss through the heat exchanger core.

I agree there is probably not enough heat from the radiators to create significant amount of the thrust but it could be done (you can speed up the flow up to mach 1 just by adding heat to it). compression could be achieved by relative speed of the car and the air, similarly like in ramjets.

the problem is there is not enough speed and heat in case of F1 car ;)
noname
 
Joined: 13 Feb 2009
Location: EU

Post Sun Nov 15, 2009 11:20 pm

noname wrote:
Mystery Steve wrote:A turbine engine is also compressing the air to dense a mixture and igniting it, adding significantly more energy to the flow stream. The radiator ducting does not compress the flow, but actually expands it. The inlet is purposely smaller than the radiator core because that slows the flow so that heat exchanger-airstream exchange is more efficient.

The thrust per mass flow is the equal to the difference in velocity at the exit. There is no way that the radiator heat adds a sufficient amount of energy to make up for the total pressure loss through the heat exchanger core.

I agree there is probably not enough heat from the radiators to create significant amount of the thrust but it could be done (you can speed up the flow up to mach 1 just by adding heat to it). compression could be achieved by relative speed of the car and the air, similarly like in ramjets.

the problem is there is not enough speed and heat in case of F1 car ;)


Ramjets don't really work until you approach Mach 1 in the freestream as "significant" compression doesn't occur until you get into the higher Mach numbers. They would have to make the run off areas a bit bigger if they want to run at those speeds in F1 :wink:

Hypothetically, you could get the flow up to Mach one at the exit of the sidepod, but unfortunately you would have to either increase the pressure aft of the radiator (not really an option) or you would have to decrease the area of the sidepod exit duct. The problem is you would start to choke the flow which is not what you want because the priority is ensuring efficient flow through the heat exchanger.
Mystery Steve
 
Joined: 25 Sep 2009
Location: Cincinnati, OH, USA

Post Mon Nov 16, 2009 12:00 am

I read something similar in a book that I have (can't remember which one, since I have about 30 of them) and I seem to recall that it had something to do with the rim of the inlet having more area to condition the flow aft of the inlet.

I remember not seeing the logic when reading it, but after thinking about it, I could see that since the inlet "rim" is sculpted, that it may have some drag reducing character to it.

It would be interesting to see Kilcoo use his CAE-Linux distro to do a test!
Conceptual
 
Joined: 15 Nov 2007

Post Mon Nov 16, 2009 8:12 pm

I think something has been miss-read or the like.

2 inlets would generally increase drag force over a single duct of the same inlet area because of the increase in forces due to viscosity due to the increased wall surface area.
Ofcourse there are always going to be exception to every rule.
F1_eng
 
Joined: 5 Aug 2009

Post Mon Nov 16, 2009 11:08 pm

Aerodynamics is the name of the book Steve I don't know the author but on the cover is a guy with a car in the wind tunnel doing some smoke testing and i think the last chapter is about testing the aerodynamics of a car (tuft testing, smoke testing, wind tunnel)
Spencer
Shrek
 
Joined: 5 Jun 2009
Location: right here

Post Wed Nov 18, 2009 3:13 am

Guys, I know what the OP means..

I think He is correct.. But ONLY IN THE CASE OF CURRENT F1 CARS overall performance, not the specific performance of the radiator inlets.

Let me explain, In F1 you can only (or it is best to) put the radiator ducts at the side right? There are TWO small ducts at either side. Now imagine putting ONE single duct that has the same total area as the two before.. where would you put that huge single duct?

If you had it one one side of the car, your single radiator might be as tall as up to the lower lip of the engine air intake. Creating a massive amount of drag on one side. And the other side of the car would be left blank with a small bulge for the exhaust pipes.

You can not put it at the front of the car..lol.. because it would totally mess up the aerodymanics. So to split it in two and mount it low is the best aerodynamically in this scenario.
"You can't change what happened. But you can still change what will happen.
Sebastian Vettel"
n smikle
 
Joined: 12 Jun 2008

Post Wed Nov 25, 2009 8:52 am

F1_eng,

Thank you for your elightened reply. I'm glad somebody grasped the theory behind my post.

Now, would you please explain the principle of energy or momentum transfer to this board, since I have seemed to have failed miserably at my effort to do so.

Regards,
Terry
"Q: How do you make a small fortune in racing?
A: Start with a large one!"
riff_raff
 
Joined: 24 Dec 2004

Post Wed Nov 25, 2009 9:29 am

xpensive wrote:As for Terry's theory about the heat-xchanger channel acting like a jet-engine xpanding the air, I doubt that as well.


No, no... that is a well known benefit of a well designed rad duct.

Ok, you might not get positive net thrust out of the whole thing, but you can cut drag to absurdly low amounts.


For instance, the NA P-51 Mustang and DH Mosquito both contained carefully designed radiators that added thrust... and these were piston engined aircraft.


http://www.hq.nasa.gov/office/pao/Histo ... /ch5-5.htm
kilcoo316
 
Joined: 9 Mar 2005
Location: Kilcoo, Ireland

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