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Old 10-22-2020, 09:41 AM   #1 (permalink)
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Oil drip aero testing - anyone here had good results ?

I searched the forum to see if anyone had posted on the topic, but the search feature doesn't work on Android.
( I consolidated my internet onto this phone I'm using to post )

I tried some oil drip tests on my car. It just made a mess.
The oil just runs down the side of the car.

So I thought I needed something with more viscosity and tried mollases.
I was thinking i could apply it cold even on an upright surface, and then it would thin as I drove - especially on a hot sunny day here in Texas.
It didn't work, and again made a sticky mess. ( At least it was easier to clean up than oil. )
But this was only giving it around 5 minutes or less to warm up.
My other thoughts are to take the water line that runs to my back window sprayer ( for the rear window wiper ) and add some colored dye.
Once up to speed, i could just squirt the area being tested .
I also tried drips of thin water base paint.
Both the paint test and the oil tests flowed downwards in the same direction on my Kammback.
They appeared to show MASSIVE vortexes on either side of the car.
Based on the tests, and the overall feeling I got after I applied the aero mods, It seemed to show that my mods had made the drag much, much worse than if I just left the car alone.
It was only after I did a tuft test, that I could see that the true direction of the airflow. ( with good results )
So what is the correct way to do oil drip tests ?
And how do the results compare to tuft tests ?
And since we are on the topic of tuft tests and such, why is it that it is no longer common to see tuft testing in wind tunnels ?
I have seen many smoke wand tests, and the results look the same for aerodynamic, and non aerodynsmic cars.

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Old 10-22-2020, 02:52 PM   #2 (permalink)
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I haven't tried any liquid flow visualization techniques, so I'm not much help unfortunately. But if anyone here has I'm curious to know more about it. I did a search a couple weeks ago that turned up a post on a land speed racer forum, IIRC, that had various recipes; I'll have to see if I can find it again.
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Old 10-22-2020, 03:50 PM   #3 (permalink)
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Quote:
Originally Posted by Vman455 View Post
I haven't tried any liquid flow visualization techniques, so I'm not much help unfortunately. But if anyone here has I'm curious to know more about it. I did a search a couple weeks ago that turned up a post on a land speed racer forum, IIRC, that had various recipes; I'll have to see if I can find it again.
The oil test on the Daytona ?
That's the post that inspired me to try it.
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Old 10-22-2020, 04:24 PM   #4 (permalink)
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I think it was a different forum altogether; I do remember there were various people's recipes (some with hi-viz paint compounds, etc.).
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Old 10-23-2020, 11:44 AM   #5 (permalink)
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oil drip

Cal Tech, FoMoCo, and others used a mixture of lamp-black and kerosene back in the 1950s - early 1960s.
Online, there's an iconic photograph from Cal Tech's wind tunnel, where the 1963 Chevrolet Corvette Sting Ray is undergoing this form of flow visualization.
The trick is to nail the proper viscosity of this mixture, so it won't just run all over the body before the tunnel gets up to supercritical Reynolds number and images can be captured.
And this technique will not reveal vorticity. Only tuft-screens or smoke will do that.
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Old 10-23-2020, 07:06 PM   #6 (permalink)
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Aerohead, I can't post images ( using my Android phone ) , but I have a picture of the " shelf" just behind my rear taillights.
Both the oil drip test and the paint test showed flow in the same direction as later tuft testing confirmed, but in other areas, the direction of the fluid was completely off.
I placed the drip on top of the Kammback in a depressed area where a bolt was.
As I got up to speed, the air blew it out of the depression, but gravity seemed to overcome it more than the force of the wind.
I know in the past we have spoke about something to use for creating smoke for aero testing.
This is just an observation, but after seeing kids vaping and the HUGE clouds of highly visible smoke coming from just a simple puff, I can't help but wonder if something could be created to use the same stuff they use in these things.
I come up with some pretty absurd ideas sometimes.
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Old 10-28-2020, 11:02 AM   #7 (permalink)
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vaping

Quote:
Originally Posted by Cd View Post
Aerohead, I can't post images ( using my Android phone ) , but I have a picture of the " shelf" just behind my rear taillights.
Both the oil drip test and the paint test showed flow in the same direction as later tuft testing confirmed, but in other areas, the direction of the fluid was completely off.
I placed the drip on top of the Kammback in a depressed area where a bolt was.
As I got up to speed, the air blew it out of the depression, but gravity seemed to overcome it more than the force of the wind.
I know in the past we have spoke about something to use for creating smoke for aero testing.
This is just an observation, but after seeing kids vaping and the HUGE clouds of highly visible smoke coming from just a simple puff, I can't help but wonder if something could be created to use the same stuff they use in these things.
I come up with some pretty absurd ideas sometimes.
I believe that the commercial smoke generators are just a larger version of a Vape 'cigarette.'
A heating element like a glow-plug in a Diesel heats propylene glycol to flash off the harmless white smoke.
Earlier, wind tunnels used heated SHELL's, 'ONDINA' oil to produce copious amounts of smoke.
A scale-model, locomotive power supply ( VARIAC ) might be a 'gateway' power supply to heat stainless steel wool, saturated in the glycol for home experiments.
The Halloween smoke generators are a version of the same.
Aroma therapy 'smoke' generators are too feeble.
Hydrosonic water vapor 'clouds' will condense before you can get any good out of them.
Hollywood special effects people also use 'smoke cookies'.
And there are smoke grenades, sport parachutists use, with up to around 50,000 cubic feet of smoke ratings.

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