Aero induced sounds...

[mzivtins]

Hi Guys,

I Apologise if this seems like nothing more than a brain-fart!

I was reading some points on hot air vs ambient air over wing surfaces, thick boundary layers etc. I started thinking about the school-boy fact that the warmer air will just have more energy, and if you wanted to seal a diffuser, what could you use in place of hot gas?

We know that sound is important in Aerodynamics around the mach numbers, so would it be possible to re-create the skirt effect from that beautiful Lotus88 just using sound to energise the air to give an artificial seal?

First instincts tell me the effect would be so weak it would almost fail at anything other than making the air passing under the car in-audible.

But my question is, even if the effect is too weak to even bother thinking about in the real world... is it possible to achieve on a minescule level?

[timbo]

But my question is, even if the effect is too weak to even bother thinking about in the real world... is it possible to achieve on a minescule level?

Quite likely.

[Just_a_fan]

One issue would be energy use. Using the exhaust stream is quite cheap because it's effectively a waste product (albeit in hot blowing there is some fuel used, in cold blowing it's effectively almost free). To get the same effect with sound energy means having a dedicated system to generate the required sound waves (there will probably be a limited set of wavelengths at which this will be effective). This will mean carrying around the kit to generate the sound waves (an amplifier and a number of speakers of some form) as well as using fuel to generate the electricity to run the things.

Don't forget that the energy that you put in to the air stream will be coming from the speakers and hence the engine.

Assuming just using speakers (without some form of wave guide) would be adequate one might be able to use a flat panel type which could be incorporated in to the floor itself.

Of course, the entire thing would be illegal as the speakers would probably be considered to be "moveable aero devices" and thus banned.

The really clever thing to so would be to use the engine's own noise and channel that but I doubt there is suffcient space to channel it, nor sufficient energy in the right wavelengths, to be effective.

[mzivtins]

Hmm what if the speakers were the solid state type, that would surely not be a moveable aerodynamic device? You could also mount that behind any medium, meaning it doesnt actually contact the airflow it is influencing... again though, practically zero use

The interesting thing would be what the affect specific frequencies would have on the airflow, i wonder even further if you could create airflows that move as if they are passing vanes etc over entire flat surfaces.

It could be really interesting to see this happen, although i really think it would need a LOT of energy used to start to take affect.

[strad]

school-boy fact that the warmer air will just have more energy, and if you wanted to seal a diffuser, what could you use in place of hot gas?

How? Cold air is more dense

[mzivtins]

school-boy fact that the warmer air will just have more energy, and if you wanted to seal a diffuser, what could you use in place of hot gas?

How? Cold air is more dense

Sorry strad I literally meant in a non aero (also non ebd) situation, just more heat energy. I understand that cold air being more dense will be better for aero (just like another thread around points to exhaust gas making a much thicker boundary layer causing it to on paper; be less efficient than cold air blowing)

[strad]

Was an honest question...There is often angles I don't understand that go contrary to my sense of logic.

[humble sabot]

I'm not sure this idea even could be used effectively. Sound waves have a habit of diffusing. There's also the fact that we're talking about vibration which is more likely to upset a productive smooth stream of air, than it is to seal that stream off. Assuming i'm wrong, you'd still have to apply extremely high power to achieve the acoustic output sufficient to control such a strong stream of air.

I think the more productive direction would be similar to an acoustic heat pump. You could use vibrating panels create a low pressure directly. I'm sure it wouldn't be accepted by the FIA or ACO, but an interesting idea.

[mzivtins]

Hi Humble, Sound waves dont diffuse, they just reflect don't they?

I think the path of sound waves is a lot more accurate than some may think, a silk dome tweeter at full power will drop off consirderably in audibility by even 2 inches of movement off centre.

I've seen (or heard haha) high frequency sound (high than a human can hear) be used to create a wall effect within a loud club, simply walking under a solidstate sinewave strip will give you almost complete silnce even in a room with 120db music.

I do think though, like you say, the energy required to retain and effect on 200mph of air would be stupid! Still it would be interesting to see if someone could create a vaned diffuser with nothing but a completely flat survace and many tiny tweeting devices, purely just to be amazed tbh

[humble sabot]

The effect is called 'beaming' and happens when the frequency reproduced is of shorter wavelengths than the dimension of the radiating surface. If you imagine any thing that might be making noise, the sound is produced by the portion that is moving or vibrating in response to the movement. That movement or vibration happens in three dimensions. The natural thing is for this movement to excite the air in all directions. In the case of an audio transducer we're trying to reproduce the waveform as accurately as possible and so moving the diaphragm on only one axis makes things far more doable.


The usual trick for creating a silence is to replicate the 'noise' but with the phase inverted. The frequencies of the noise get cancelled by waves of their opposite.

[MaysEffect]

I have been thinking of this formula for a while. To me i don't think this type of application would work to well in a formula car but maybe work to an advantage on a gt car. I agree with what a commenter(just_a_fan) posted early on, the tools and accessories needed would take up space and add extra weight which would mean the car would have to produce more torque to move at the same speed it currently did(before this mod).

my idea behind using frequency processing in an aerodynamic way is to follow the process of "energy dumping" which is a slang term for releasing the energy load in a stored medium. where i'm trying to go with this is, When a car is increasing its velocity it also increases drag. This drag works as a stored energy or weight on the car, so if you where to use sound frequency(particularly low FQ) to resonate the frequency position of the car to release the drag or disturb the drag flow(which would separate the load away from the car), in practice the car should create a Vacuum seal or bubble in its air space where it decreases or eliminates drag in the surrounding area.

where i see this being put into place is with the use of KERS in passing situations or a defensive situation to subdue overtakes(dangerous outcomes). KERS in current regulation(FIA GP) can only be used in a designated strait of a track. This is where most cars pick up the most drag while increasing speed, but also this is when a driver is increasing speed before making a PASS,in this "slip stream" approach they are behind the back wash of the car in front which is good in decreasing there cars drag. but as soon as they leave that stream the car instantly picks up that drag on the frontal portion of the car creating instability(loss of downforce, uneven tire load) and can lead to an unsuccessful pass.now this slip stream technique isn't much of a value in most formula cars simply because they don't have a large drag area(oppose to a GT,DTM,Nascar or truck), so a Grand Prix or prototype car cant really take advantage of this technique to actively.

But it is in this occasion where the overtaking or defensive car can deploy a kind of "energy bump" i would like to call it a subsonic bump or drag release, where in a frequency pattern can eliminate or diffuse that drag so for example the overtakers car stability is undisturbed as if they never left the slip stream of the car in front of them, which would result a increase in strait line stability, increase of velocity for the pass and still being able to keep down force in the front of the car for the braking at the end of the strait. This design should mimic the exhaust blow which was created to decrease drag. But it should work even greater because the drag decrease is not limited to only the rear of the car but instead the front and central gravity allowing the ENTIRE car to reduce drag.

So with that i try to make clear this is attended to work along side of KERS and could be a replacement for Exhaust blowing.This feature would not likely be useful for any other area besides the straits. In corners you need down force. The energy bump would not increase downforce, In most cases it would upset the aerodynamic load, and in my estimates this was the problem with exhaust blowing,when exiting corners and other instability issues.

i think all in all the idea of using sound is, to mimic the thermal dynamic aspect of "exhaust blowing" or pressure diffusing. but cons of this style is much more likely to happen then the positive aspects. thus my reason why it wouldn't work in F1.

MZIVTNS - sound waves can be reflected, but the sound wave from the sound origin does not reflect it is diffused through mass, one of the reasons why the sound wave extension is measured in spl db's. from the point of origin the sound is moved across the mass area within its zone.