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Old 08-01-2022, 11:27 AM   #171 (permalink)
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because

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Originally Posted by AeroMcAeroFace View Post
Was that because it is away from vortices from the A-pillar or because it created separation all down the side of the car in its wake?
The car's near-field flow interfered with the mirror, while the mirror's near-field flow interfered with the car.
By moving the mirror away from the body, to perhaps the initial outboard streamline's distance, it essentially began to 'fly in formation' with the car, neither affecting the flow of the car, or vice versa.
And this also relied on careful shaping of both the mirror housing and mounting strut.
An added side benefit was a lower acoustic signature ( noise-vibration-harshness ).

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Old 08-01-2022, 01:19 PM   #172 (permalink)
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Quote:
Originally Posted by aerohead View Post
The car's near-field flow interfered with the mirror, while the mirror's near-field flow interfered with the car.
By moving the mirror away from the body, to perhaps the initial outboard streamline's distance, it essentially began to 'fly in formation' with the car, neither affecting the flow of the car, or vice versa.
And this also relied on careful shaping of both the mirror housing and mounting strut.
An added side benefit was a lower acoustic signature ( noise-vibration-harshness ).
Is that why companies put vortex generators near the mirror if itís closer? So it controls the bigger and more wild vortexís between the car and mirror?
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Old 08-01-2022, 02:32 PM   #173 (permalink)
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VGs

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Is that why companies put vortex generators near the mirror if itís closer? So it controls the bigger and more wild vortexís between the car and mirror?
Sometimes the very presence of the VGs alters the natural frequency of the mirror housing, eliminating some unwanted noise that couldn't be modelled in CFD, and which hadn't shown up until they got the car into an acoustic wind tunnel.
And since 'adding' the VGs is a simple 'additive' modification to the existing tooling, it costs very little for the good it does.
All VGs are 'BAND-AIDs'. If they exist at all, it's because there was something wrong with the original design. If the 'local' flow turns out to be a disappointment, there's only so much a VG would be able to mitigate.
And whatever they come up with has got to be able to stand up to a commercial car wash.
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Old 08-02-2022, 06:28 AM   #174 (permalink)
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And this also relied on careful shaping of both the mirror housing and mounting strut.
An added side benefit was a lower acoustic signature ( noise-vibration-harshness ).
Although that is assuming that the length and stiffness of the arm and resonant frequencies of the attaching and detaching flow don't create mirror wobble or transmitted buffeting through the arm. But I don't know if that is a realistic problem because the frequencies without design may be so far off that it is a non-issue.
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Old 08-04-2022, 11:08 AM   #175 (permalink)
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non-issue

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Although that is assuming that the length and stiffness of the arm and resonant frequencies of the attaching and detaching flow don't create mirror wobble or transmitted buffeting through the arm. But I don't know if that is a realistic problem because the frequencies without design may be so far off that it is a non-issue.
It came up with BMW. They published information from research they performed during the development of one of their passenger cars.
Only in their aero-acoustic wind tunnel did an un-wanted interaction of the side mirrors with the main body reveal itself.
From the cabin's vantage point, the mirrors produced a really undesirable flow disruption down both sides of the beltline.
Master clay modelers were able to shave and enhance the mirrors, succeeding in tuning out the unwanted turbulence.
In the United States, automakers are held to certain legal noise pollution constraints, in order to market their products. One cannot sell a vehicle if it exhibits 'whistling', 'buffeting', 'booming', as well as splash and spray hazards.

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