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Old 06-15-2015, 12:51 AM   #1 (permalink)
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Aero in the dust (El Mirage pics of my car)

Starting to go through my pics and vids from my trip to El Mirage for the SCTA event this weekend. My daughter was helper in taking the video that provided these stills. We just went off to a corner of the dry lake bed and let the dust do its thing.

Traveling between 45-50 mph:



and:



and the results collected on the back of the car:



I see evidence of spiraling vortexes off the c-pillars and the trunk lid. And while the dust reaches the trunk lid, it does not collect behind the read widow. And in the wake you can see down wash, with the dust height dropping at first, as the air washes off the rear decklid and hits the ground. Then the dust begins to rise again to a level as high or higher than the decklid in these pics.

In the last pic, you can faintly see dust collected on all the flay surfaces of the emblems. But it is slight. The heaviest layering of dust is on the bumper cover's top and the license plate framing.

The downwash and vortex is the most interesting thing to me here... no boat tails are in my future but I still love the idea of a substantial flat spoiler on the trunk lid. It seems to me it might reduce the power of these vortexes.

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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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Old 06-15-2015, 03:25 PM   #2 (permalink)
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Here's my favorite dry lakes picture, because you can see the dust off the front wheel against the dark body, conforming to the template:



The tread on the tire is carrying dust to 10-11 o'clock where the oncoming air clears it out.
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Old 06-15-2015, 06:18 PM   #3 (permalink)
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If you don't have a wind tunnel and smoke machine; make your own smoke! Thanks for sharing, wish you had cardboard to tape on a quick pro stock spoiler and see what the results might be.
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Old 06-15-2015, 06:37 PM   #4 (permalink)
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El Mirage

When I become rich,I'll setup a high contrast back drop to image against,like Muybridge did in his kinematics photography.
It would be nice to see every subtle detail the dust created.Denton has some huge dark tree rows along the highways,and during rain events,vehicle wakes stand out like a Venus transit across the face of the Sun.
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Old 06-15-2015, 07:26 PM   #5 (permalink)
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A black billboard on the side of a truck? If the camera is passing the car, the truck could be moving slower and vice versa.

Long telephoto to make the truck (& trailer?) look bigger.
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Old 06-15-2015, 08:34 PM   #6 (permalink)
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My daughter took the video on my tablet that supplies these shots. She is 12. Bright. Even a little informed about aerodynamics. But she made a hash of some of the video and we had difficulty locating terrain with sufficient "dustiness" and not taken up by the race event.

I'd love to see a Western EM gathering for aero tests with cardboard mods. Get a better camera onto the scene. With tripod. Camp for $15/day per car on the lake bed. Get some awesome photos and video
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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Old 06-15-2015, 09:38 PM   #7 (permalink)
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For me it would be 872 miles, vs 768 to Bonneville. Would there be cake?

Did you get the dust out of your car yet? Salt eats right into the metal.
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Old 06-17-2015, 10:23 AM   #8 (permalink)
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Close-up pictures of the recirculation zone

Here are a couple other pictures showing the recirculation zone in the photos in post #1. These are closeups showing how high the recirculation zone extended from the back bumper cover:

1) here you can see small amounts of dust on top of the "CVCC" badge (btw, the badge is for a history claim about the vehicle, not a technical claim about my particular engine):



2) here you can see fairly clearly what was totally apparent when looking at the car live. The recirculation zone at the tail of the car did not cross onto the trunk lid. A sharp line in the dust can been see where the radius from the taillight section meets the aft portion of the trunk lid.



I know from tuft test images of my car (see this link) that there is a recirculation zone behind the rear window too. But this shows that part of the flow briefly re-attaches and in doing so differentiates the tail light zone from the rear window zone.
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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Old 06-20-2015, 04:28 PM   #9 (permalink)
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some higher contrast images of flow visualization








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Old 06-20-2015, 07:55 PM   #10 (permalink)
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That is great and all, but the wake looks the same on the both the bus and the streamliner.

Just after a good rain on a humid day, you can see the mist kicked up behind vehicles quite well. In fact, you can clearly see a vortex 'tornado' just behind the cab on semis that are not towing a trailer. The mist flows over the cab and then goes UP in a circular vortex just behind the cab.

( Surely some of you other guys have seen this as well ! )

I think this, and perhaps a light snow are best at flow vis. I guess the dust is too light/heavy to conform to the true wake of the vehicle.

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