Sonic flow around F1 cars?

[tok-tokkie]

Is there no optimum relationship of length versus crossection distribution for optimum drag ?

Sure, there are Sears-Haack Bodies.

That is interesting. I have learned from Flynfrog's posts on the F1 in school threads & the Over & Under or Round the Sides thread that supersonic shapes look good but are not applicable when the speeds are nowhere near that. Egg & teardrop shape is best at those speeds. Is there a similar rule for these speeds?

[Robbobnob]

Streamlining decreased pressure drag by delaying the boundary layer separation, keeping flow attached, thus reducing the pressure difference between the front and back of the body and increases the friction drag by increasing the surface area. The end result depends on which effect dominates.

Basically in summation the thickness, D and the Length, L of the object both influence the aero-properties in subsonic flows, with a D/L ratio ~ 0 pressure drag is low but Frictional drag is high, where a D/L ratio ~ 0.5 the pressure drag is low and the frictional drag is high.

a conventional streamlined body has the optimal D/L ratio ~ 0.25



Source: Fundamentals of Thermo-Fluid Sciences, Cengel, Turner and Cimbala, 3rd Edition. Chapter 15-3

[HampusA]

How much differs subsonic vs sonic flows?

[hecti]

How much differs subsonic vs sonic flows?

how does sonic flow relate to an f1 car?? they are no were near fast enough to create any sonic flows or be affected by them. If you want to talk about sonic flows go start a topic under the aero section...

[horse]

Is there a similar rule for these speeds?

I think when you get down to subsonic speeds the argument becomes about Fineness ratio. This is the ratio of the length of a body to its maximum width. To quote wikipedia (oh dear):

At speeds below critical mach, one of the primary forms of drag is skin friction. As the name implies, this is drag caused by the interaction of the airflow with the aircraft's skin. To minimize this drag, the aircraft should be designed to minimize the exposed skin area, or "wetted surface", which generally implies the fuselage should be somewhat "egg shaped", with a fineness ratio about 4.5. A good example of such a design is the Questair Venture.

[PlatinumZealot]

In 201 we will have sonic flows..

Inside the turbocharger compressor!

[flynfrog]

That is interesting. I have learned from Flynfrog's posts on the F1 in school threads & the Over & Under or Round the Sides thread that supersonic shapes look good but are not applicable when the speeds are nowhere near that. Egg & teardrop shape is best at those speeds. Is there a similar rule for these speeds?[/quote]
I am honored to have been of use.

How much differs subsonic vs sonic flows?

usually the faster you go the narrow your aspect ratio becomes also the pointer your lead edge becomes. Look at the evolution the airplane wing. As engines got big planes went faster wings got thinner.

[Ciro Pabón]

How much differs subsonic vs sonic flows?

Well, flyn is correct, but I would like to add that the main difference I see is that at subsonic the air has "time" to move away from the wing or object, while at supersonic it hasn't.

Picture yourself as an atom, floating in the air. If you were to be "touched" by a wing moving at subsonic speeds, the waves created in the air by the leading edge of the wing would reach you before the wing does. So, you would move away from the edge of the wing and "follow" its contour.

If this wing moves at supersonic speeds you wouldn't receive any "warning" to move away before the wing or object hits you.

This is what creates a shock wave in front of objects moving at supersonic speeds: it is the result of the atoms of air being pushed away "directly" by the object, instead of being pushed around by the surrounding molecules, as they "usually" do.

At least that's how I've seen this business all my life.

[shelly]

Sometimes in the pat air was reaching transonic speeds in the front wing zone

[PNSD]

I thought the flow just before entering the underbody at that throat was transonic.

[mep]

This is what creates a shock wave in front of objects moving at supersonic speeds: it is the result of the atoms of air being pushed away "directly" by the object, instead of being pushed around by the surrounding molecules, as they "usually" do.

Is there still a shock wave in front of the object at supersonic speed?
I thought it is just behind it.


There already should be sonic flow at the exhaust valve (intake possible too) or simply when you push a hole into your tires.

[horse]

Is 'sonic' an Americanism or are we just using it mean non-subsonic? Is it common to use just 'sonic'? I come from a subsonic world. you see.

[DaveW]

I thought the flow just before entering the underbody at that throat was transonic.

I think that would imply a local airspeed of around vehicle speed times 5. Do you think that is likely?

[PNSD]

I guess not, but I'm sure I heard it somewhere.

Then again, at take off with full flaps extended flow over a 747 wing is transonic. So might be far from it.

[shelly]

The factor is less than 5; it is around 4 (if you consider 340m/s sound speed and 85 m/s car speed). Flow on high cuvature attached leading edge can reach those speeds