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Thread: Aerodynamics of the new Mirage (0.27-0.31 drag coefficient varies with options)

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    Quote Originally Posted by inuvik View Post
    Me thinks it's probably far simpler to bolt a 2017 spoiler on the current gen Mirage.
    It isn't necessarily mutually exclusive. C has a straight cut spoiler more similar to 2017 and it seems to benefit from it too. There was an scientific paper published which found that VGs improve performance of spoilers. In that research they had tried 26 different combinations of spoiler/VG location and found one position which eliminated low pressure zone behind the car.

    We do not have access to wind tunnel, and can't change spoilers, so the hope is that existing spoiler works and installed vgs improve their performance by increasing speed of flow.


    Last edited by cyclopathic; 12-08-2015 at 09:09 AM.

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        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 46.4 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.7 mpg (Imp)


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    Senior Member Cani Lupine's Avatar
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    The separation isn't caused by too steep of an angle, so VGs will only increase drag. If you want to eliminate that separation, try taping up the gap between the roof and the hatch. It's actually quite a large gap. I'm sure the flow remains smooth above the boundary layer, though. If someone has a GoPro, I'd like to see someone do a tuft test to prove my theory, with and without taping the gap.

    Also, the VGs aided the Mitsubishi Lancer Evo's spoiler because it's technically a wing, not a spoiler, and the VGs increased the airflow over the whole unit (top and bottom sides). Our spoiler is nothing more than a roofline extension, and the air underneath it is the wake.

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        click to view fuel log View my fuel log 2014 Mirage DE 1.2 manual: 49.2 mpg (US) ... 20.9 km/L ... 4.8 L/100 km ... 59.1 mpg (Imp)


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    inuvik (12-08-2015)

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    Moderator inuvik's Avatar
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    Quote Originally Posted by Cani Lupine View Post
    The separation isn't caused by too steep of an angle, so VGs will only increase drag. If you want to eliminate that separation, try taping up the gap between the roof and the hatch. It's actually quite a large gap. I'm sure the flow remains smooth above the boundary layer, though. If someone has a GoPro, I'd like to see someone do a tuft test to prove my theory, with and without taping the gap.

    Also, the VGs aided the Mitsubishi Lancer Evo's spoiler because it's technically a wing, not a spoiler, and the VGs increased the airflow over the whole unit (top and bottom sides). Our spoiler is nothing more than a roofline extension, and the air underneath it is the wake.

    I agree wholeheartedly on this. I haven't crawled umder the vehicle to look but I think you could gain much greater decrease in drag by installing panels underneath the car to smooth out the underside. Lots of air resistance underneath a vehicle because of it's irregular shape.

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        click to view fuel log View my fuel log 2015 Mirage ES 1.2 automatic: 40.5 mpg (US) ... 17.2 km/L ... 5.8 L/100 km ... 48.6 mpg (Imp)


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    Quote Originally Posted by inuvik View Post
    I haven't crawled umder the vehicle to look but I think you could gain much greater decrease in drag by installing panels underneath the car to smooth out the underside. Lots of air resistance underneath a vehicle because of it's irregular shape.
    Undercar will be our next step. Agree or not on VGs, I will run Cd calculations prior and after install and share results.

    By themselves VGs are nothing but added resistance. Where they become helpful is they remix boundary layer and increase its speed. This in return increases efficiency of the existing aero device (spoiler, wing).

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 46.4 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.7 mpg (Imp)


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    Senior Member Mitz's Avatar
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    Quote Originally Posted by inuvik View Post
    I agree wholeheartedly on this. I haven't crawled umder the vehicle to look but I think you could gain much greater decrease in drag by installing panels underneath the car to smooth out the underside. Lots of air resistance underneath a vehicle because of it's irregular shape.
    I can't imagine how to make the underchassis look like the belly of the AeroMobil.

    Quote Originally Posted by cyclopathic View Post
    Undercar will be our next step. Agree or not on VGs, I will run Cd calculations prior and after install and share results.

    By themselves VGs are nothing but added resistance. Where they become helpful is they remix boundary layer and increase its speed. This in return increases efficiency of the existing aero device (spoiler, wing).
    I intend to put Airtabs into my car early next year .. will wait for your test results.

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    Senior Member Cani Lupine's Avatar
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    Okay, so I did a bit of experimenting. Here's a morning commute:
    Name:  IMAG0196.jpg
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    Today, I taped off the gap between the hatch and the roof:
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    This stopped the flow from detaching, up until the little gap between the hatch and spoiler. I've taped up that gap, and we'll see tomorrow how that does.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage DE 1.2 manual: 49.2 mpg (US) ... 20.9 km/L ... 4.8 L/100 km ... 59.1 mpg (Imp)


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    Similar pics. First after 6mi drive to gas station, second after 1 hr drive

    The picture at the bottom showing C MPG improvements (it collects statistics by month. Sep Oct Nov are showing typical temperature related drop. VGs were installed on Thanksgiving at the end of November.
    Attached Images Attached Images    
    Last edited by cyclopathic; 12-13-2015 at 03:04 PM.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 46.4 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.7 mpg (Imp)


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    Senior Member Cani Lupine's Avatar
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    Yep, its definitely the gaps causing surface flow separation. I'm quite sure the flow is still attached without the tape, but with a thick boundary layer.

    Name:  IMAG0208.jpg
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    Name:  IMAG0209.jpg
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        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage DE 1.2 manual: 49.2 mpg (US) ... 20.9 km/L ... 4.8 L/100 km ... 59.1 mpg (Imp)


  10. #89
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    Quote Originally Posted by Cani Lupine View Post
    Yep, its definitely the gaps causing surface flow separation. I'm quite sure the flow is still attached without the tape, but with a thick boundary layer.
    I am 100% agree with you, the moisture on hatch door/spoiler looks exactly like on my C with VGs.

    If we were to fix it with vortex generators they would need to be installed ~12" in front of 1st gap or perhaps even more as there is a slight bend in the roof line. Unfortunately my son is categorically against VGs for aesthetic reasons (mystery to me), so I have no car to test this theory on. Have the set of EVO style VGs though.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 46.4 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.7 mpg (Imp)


  11. #90
    Senior Member Cani Lupine's Avatar
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    It's better to just seal the gaps, VGs would add some drag, which ends up with a lower net gain. The other reason is crosswind, you'd end up with a worse Cd.

    Overall, this gets into the "splitting hairs" category.


        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage DE 1.2 manual: 49.2 mpg (US) ... 20.9 km/L ... 4.8 L/100 km ... 59.1 mpg (Imp)


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