Audio anaylsis to determine aero setup of compeitiors?

[Krispy]

While watching the Friday practice session for the French Grand Prix last week, one of the announcers made a comment that the teams were using audio from the on board camera shots of competitors to determine the amount of aero each team was using. Can anybody shed some light on this?

[WhiteBlue]

by audio analysis you can determine the revs and the power on every point on the circuit. It is best done at the speed trap. If you compare power with speed you get an idea of drag.

[zac510]

Search for some posts here by 'Reca'

[Krispy]

I did a search for that author and pulled several hundred posts...after looking through a few pages of them I noticed he knows a bit about aero. However through my brief browsing I didn't see anything about this audio analysis. Do you know any details on how the analysis is performed. On a slightly related note, how is the on screen (tv broadcast) telemetry gathered?

[modbaraban]

However through my brief browsing I didn't see anything about this audio analysis.

I did.
viewtopic.php?p=22025#p22025

[Krispy]

Much appreciated

[ReubenG]

It is possible to extract the engine rpm (and hence vehicle speed) from an audio signal -Reca's post explains this very well. I am not sure that engine power can be determined with any great accuracy from an audio signal.

I have an alternative theory for the audio analysis - aero link: a distant memory from my aerodynamics lectures involves vortices and the the frequency at which they are formed / shed from any section. If the vortex shedding produces a detectable sound, then frequency analysis of this vortex shedding will give some indication of aero behaviour at a particular speed. Will someone with more aero knowledge please comment on my theory? I've done only one windtunnel test (several years ago) so I don't know whether vortex shedding is an audible phenomenon.

[Krispy]

I don't know whether vortex shedding is an audible phenomenon.

According to my fluids book by Cengel and Cimbala,

This phenomenon usually occurs during normal flow over long cylinders or spheres for Re>= 90.The vibrations generated by vortices near the body may cause the body to resonate to dangerous levels if the frequency of the vortices is close to the natural frequency of the body--a situation that must be avoided in the design of equipment that is subjected to high-velocity fluid flow such as the wings of airplanes and suspended bridges subjected to steady high winds

If vortex shedding is occurring, it seems to me that it would only be audible, or at least be most audible if it was approaching Wn. And even if it were audible, it would have to be heard over the exhaust tone...

[Conceptual]

I don't know whether vortex shedding is an audible phenomenon.

According to my fluids book by Cengel and Cimbala,

This phenomenon usually occurs during normal flow over long cylinders or spheres for Re>= 90.The vibrations generated by vortices near the body may cause the body to resonate to dangerous levels if the frequency of the vortices is close to the natural frequency of the body--a situation that must be avoided in the design of equipment that is subjected to high-velocity fluid flow such as the wings of airplanes and suspended bridges subjected to steady high winds

If vortex shedding is occurring, it seems to me that it would only be audible, or at least be most audible if it was approaching Wn. And even if it were audible, it would have to be heard over the exhaust tone...

Or seperated by a computer.

I wonder what team first used their CFD supercomputers to tear down someones onboard audio to the smallest possible part.

If it was found, and a predictable thing, then I could believe it. But without more info as to what range the harmonics are in, and the range of the onboard Microphone, it is a bit hard to tell.

chris

[ReubenG]

The amplitude of the noise from the vortex shedding would not be so important as its frequency range - F1 engines typically run between 10K and 19K rpm, which gives a frequency band of 160 to 320 Hz. I found a paper on ScienceDirect (McAlpine,Nash and Lowson, On the generation of discrete frequency tones by the flow around an aerofoil, Journal of Sound and Vibration, 1999, Vol 222, pg 753-799) where they investigated a similar phenomena. They found the amplitude of the vortex shedding to be 30dB higher than background and to occur at discrete frequencies (~1000-1400 Hz for 30<V<44 m/s). I can't link to this paper as it's a subscription journal - PM me if you don't have access yourself. So it seems that the frequencies of engine noise and vortex shedding would be distinguishable on a frequency spectrum.

And now I wait for the engines people to start about higher harmonics....

[Conceptual]

The amplitude of the noise from the vortex shedding would not be so important as its frequency range - F1 engines typically run between 10K and 19K rpm, which gives a frequency band of 160 to 320 Hz. I found a paper on ScienceDirect (McAlpine,Nash and Lowson, On the generation of discrete frequency tones by the flow around an aerofoil, Journal of Sound and Vibration, 1999, Vol 222, pg 753-799) where they investigated a similar phenomena. They found the amplitude of the vortex shedding to be 30dB higher than background and to occur at discrete frequencies (~1000-1400 Hz for 30<V<44 m/s). I can't link to this paper as it's a subscription journal - PM me if you don't have access yourself. So it seems that the frequencies of engine noise and vortex shedding would be distinguishable on a frequency spectrum.

And now I wait for the engines people to start about higher harmonics....

Wow.

If this could be tapped and used, you could open a whole new area of aerodynamic utilisation. Echoharmonic engineering that can use CFD simulations to auto tune the vortecies to specific notes.

It would be like a flute blowing the same chord at 200MPH.

This could get crazy. Does anyone know the range of the microphone? Or care to analyze the spectrum to determine teh difference?

Chris

[pitlaneimmigrant]

I think that might be getting carried away, then again if someone has the time and the money...

The most obvious method I can think of is that if the aero stalls at a certain speed, leading to a reduction in drag, the car will accelerate more quickly than would otherwise be expected. So when listening to the engine speed, if rate at which the engine speed is increasing suddenly changes, that is probably due to the aero stalling.

Monitoring the engine speed was was how Ferrari's flexible rear wing was proven to be affecting aero performance. At a particular speed the cars acceleration would change as the profile of the wing changed.

[Conceptual]

I think that might be getting carried away, then again if someone has the time and the money...

The most obvious method I can think of is that if the aero stalls at a certain speed, leading to a reduction in drag, the car will accelerate more quickly than would otherwise be expected. So when listening to the engine speed, if rate at which the engine speed is increasing suddenly changes, that is probably due to the aero stalling.

Monitoring the engine speed was was how Ferrari's flexible rear wing was proven to be affecting aero performance. At a particular speed the cars acceleration would change as the profile of the wing changed.

Are we watching the same F1? LMAO