Flow cloaking... I wonder if there are aeronautical possibilities...

[sisu1a]

Interesting article about Duke engineers applying their passive,
engineered material light/sound cloaking techniques to water,
theoretically (substantially) reducing the amount of drag generated by
a boat's hull by 'tricking' the surrounding water into standing still.

http://www.eurekalert.org/pub_releases/2011-08/du-esw081111.php

-paul

[Martin Gregorie[_5_]]

On Sun, 14 Aug 2011 14:34:37 -0700, sisu1a wrote:

> Interesting article about Duke engineers applying their passive,
> engineered material light/sound cloaking techniques to water,
> theoretically (substantially) reducing the amount of drag generated by a
> boat's hull by 'tricking' the surrounding water into standing still.
>
> http://www.eurekalert.org/pub_releases/2011-08/du-esw081111.php
>
It will be interesting to see if it works, but I don't think it will help
us much, apart from the possibility of reducing friction drag in the
fuselage. The reason: since the whole point of this cloaking seems to be
to prevent momentum transfer to the surrounding fluid while a wing
generated lift by transferring momentum to the surrounding air, it ses to
me if you put the stuff on a wing, it would stop the wing from doing
anything useful.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Dan Marotta]

"Martin Gregorie" > wrote in message
...
> On Sun, 14 Aug 2011 14:34:37 -0700, sisu1a wrote:
>
>> Interesting article about Duke engineers applying their passive,
>> engineered material light/sound cloaking techniques to water,
>> theoretically (substantially) reducing the amount of drag generated by a
>> boat's hull by 'tricking' the surrounding water into standing still.
>>
>> http://www.eurekalert.org/pub_releases/2011-08/du-esw081111.php
>>
> It will be interesting to see if it works, but I don't think it will help
> us much, apart from the possibility of reducing friction drag in the
> fuselage. The reason: since the whole point of this cloaking seems to be
> to prevent momentum transfer to the surrounding fluid while a wing
> generated lift by transferring momentum to the surrounding air, it ses to
> me if you put the stuff on a wing, it would stop the wing from doing
> anything useful.
>
>
> --
> martin@ | Martin Gregorie
> gregorie. | Essex, UK
> org |

Are you saying, then, that the velocity of the air moving over the top of
the wing will be reduced relative to that over the bottom? What would
Bernoulli say?

[Martin Gregorie[_5_]]

On Mon, 15 Aug 2011 08:06:35 -0600, Dan Marotta wrote:

> "Martin Gregorie" > wrote in message
> ...
>> On Sun, 14 Aug 2011 14:34:37 -0700, sisu1a wrote:
>>
>>> Interesting article about Duke engineers applying their passive,
>>> engineered material light/sound cloaking techniques to water,
>>> theoretically (substantially) reducing the amount of drag generated by
>>> a boat's hull by 'tricking' the surrounding water into standing still.
>>>
>>> http://www.eurekalert.org/pub_releases/2011-08/du-esw081111.php
>>>
>> It will be interesting to see if it works, but I don't think it will
>> help us much, apart from the possibility of reducing friction drag in
>> the fuselage. The reason: since the whole point of this cloaking seems
>> to be to prevent momentum transfer to the surrounding fluid while a
>> wing generated lift by transferring momentum to the surrounding air, it
>> ses to me if you put the stuff on a wing, it would stop the wing from
>> doing anything useful.
>>
>
> Are you saying, then, that the velocity of the air moving over the top
> of the wing will be reduced relative to that over the bottom? What
> would Bernoulli say?

In the most general case a wing is a device that generates lift by
imparting downward momentum to the surrounding air in such a way that
that the resulting accelerating force counterbalances the force of
gravity acting on the aircraft. As the main effect of this 'cloaking'
seems to be to reduce momentum transfer from the moving body to the
surrounding fluid it seems to me that the 'cloaking' would also reduce
the amount of lift the wing would produce under normal flow conditions.

I wasn't being so specific about velocities or saying anything about
Bernoulli.

I don't much care for the application of Bernoulli to wing sections: that
theory applies to flow inside a pipe while airflow over a wing is not so
enclosed. Better aerodynamicists than I think its application to wing
sections is questionable. AFAICR straight application of Bernoulli can't
account for the upflow field in front of a wing and it certainly can't
account for the measured flow over a wing being so much faster than that
under it that air molecules separated by the LE don't rejoin at the TE:
the molecules passing over the top surface are long gone before molecules
passing under the lower surface arrive at the TE.

OTOH, if you were applying Prandtl..... My guess is that the cloaking
effect would reduce circulation.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Dan Marotta]

Thanks for a great explanation! My field is electrical engineering, though
I often wish I'd gone the aero path...


"Martin Gregorie" > wrote in message
...
> On Mon, 15 Aug 2011 08:06:35 -0600, Dan Marotta wrote:
>
>> "Martin Gregorie" > wrote in message
>> ...
>>> On Sun, 14 Aug 2011 14:34:37 -0700, sisu1a wrote:
>>>
>>>> Interesting article about Duke engineers applying their passive,
>>>> engineered material light/sound cloaking techniques to water,
>>>> theoretically (substantially) reducing the amount of drag generated by
>>>> a boat's hull by 'tricking' the surrounding water into standing still.
>>>>
>>>> http://www.eurekalert.org/pub_releases/2011-08/du-esw081111.php
>>>>
>>> It will be interesting to see if it works, but I don't think it will
>>> help us much, apart from the possibility of reducing friction drag in
>>> the fuselage. The reason: since the whole point of this cloaking seems
>>> to be to prevent momentum transfer to the surrounding fluid while a
>>> wing generated lift by transferring momentum to the surrounding air, it
>>> ses to me if you put the stuff on a wing, it would stop the wing from
>>> doing anything useful.
>>>
>>
>> Are you saying, then, that the velocity of the air moving over the top
>> of the wing will be reduced relative to that over the bottom? What
>> would Bernoulli say?
>
> In the most general case a wing is a device that generates lift by
> imparting downward momentum to the surrounding air in such a way that
> that the resulting accelerating force counterbalances the force of
> gravity acting on the aircraft. As the main effect of this 'cloaking'
> seems to be to reduce momentum transfer from the moving body to the
> surrounding fluid it seems to me that the 'cloaking' would also reduce
> the amount of lift the wing would produce under normal flow conditions.
>
> I wasn't being so specific about velocities or saying anything about
> Bernoulli.
>
> I don't much care for the application of Bernoulli to wing sections: that
> theory applies to flow inside a pipe while airflow over a wing is not so
> enclosed. Better aerodynamicists than I think its application to wing
> sections is questionable. AFAICR straight application of Bernoulli can't
> account for the upflow field in front of a wing and it certainly can't
> account for the measured flow over a wing being so much faster than that
> under it that air molecules separated by the LE don't rejoin at the TE:
> the molecules passing over the top surface are long gone before molecules
> passing under the lower surface arrive at the TE.
>
> OTOH, if you were applying Prandtl..... My guess is that the cloaking
> effect would reduce circulation.
>
>
> --
> martin@ | Martin Gregorie
> gregorie. | Essex, UK
> org |