RedNeck wind tunnel test

[Bob_n_Cincy]

Today Michael and I took our 818 out for a ride to test air flow around the back of the 818S.
We used tuft to see the airflow. We did about an hour of 60mph video.

My conclusions.
1. A lot of air is flowing into our opened up side scoops.
2. The air between the humps is turbulent and the tuft can't decide where to go.
3. The side if the hump on the outside of the car would be a great place to grab air for a TMIC.
4. The shoulder of the fender just behind the rear wheel would be a good place to grab air to cool the engine bay.
5. There in a lot of turbulence behind the rear bumper. The air flow through my rear radiator is the same at low speed as high speed.

We are going to add our belly pan and diffuser tomorrow and test again.

Attach is a crappy video.
Let me know your questions. Bob


https://youtu.be/Ojsyn40qvSY


In the picture below I circled the place I saw good steady flow.

good flow.jpg

[Bob_n_Cincy]

It's kind of interesting at 60 mph the wheels don't turn at 1/8 slow motion.
Kinda looks fake.
Bob

https://youtu.be/xR89QDqDZms

[Loring]

"Stop animation 818!!" Haha.

I was considering running one of these tests once my build is complete but using a thermal imager in the engine bay. This seems much more... efficient. Excellent post.

[Frank818]

Bob I am very interest into 2 locations:

1- The openings on the sides over the rear wheel (they are included in the hump cover);
2- The bottom of the rear bumper (I have my oil cooler there, which is same location as your rad).

If you get results with the belly pan and diffuser, I'd really like to study that.

[Bob_n_Cincy]

Bob I am very interest into 2 locations:

1- The openings on the sides over the rear wheel (they are included in the hump cover);
2- The bottom of the rear bumper (I have my oil cooler there, which is same location as your rad).

If you get results with the belly pan and diffuser, I'd really like to study that.

Number 1. our small slots in the hump cover is not cut out and I have no plan to do that.
Number 2. we are installing belly pan and diffuser today and will do more highway testing today our tomorrow.
Bob

[Santiago]

Thanks for sharing the results.

If I recall, Jim said that they tried ducts on the sides of the roll bar to feed air into the TMIC but didn't get good results - though he also said the area might produce better results with more refined ducts than those they used.

Wish I could find the pics they posted of their test set-up...
EDIT: Found it! Wasn't a pic, it was a video posted here: New 818 Configurations Windtunnel Tested

Best,
-j

[Bob_n_Cincy]

I Just posted another video of our test yesterday.
Take a look at the tuft on the left hump.
Bob

https://youtu.be/77COpwrJp3I

[bigAl]

The tufts on the outer side of the hump indicate good linear flow, NOT a high pressure area.
If the tuffs on the horizontal surface between the humps is helter skelter that could indicate a high pressure. Remember the tuffs show only the boundary layer flow, not the free stream flow directly above it.
You could definately use a better chase driver... I can't believe it is that hard to match the speed of the target vehicle.

[Bob_n_Cincy]

I can't believe it is that hard to match the speed of the target vehicle.

A 6000 lbs van can not match the speed change of an 1800 lbs rocket with equal horsepower.
We were out driving around for an hour, we were just playing around.
Bob

[Santiago]

Great video (well, the last half at least).

Also, your S-car rear hump is nowhere near as shrouded by the roll-bar hoop as it is with the R-car hoop. There might be a lot of flow volume available there for S-car builders relative to what the FFR team witnessed when they did their tests.

Best,
-j

[Bob_n_Cincy]

Watching the air coming out of our rear radiator.
I am disappointed the we seem to have the same airflow when we're stopped as when we are moving.
Bob and Mike


https://youtu.be/pDvr0Ic5iQs

[DMC7492]

Bob , this is great video and very useful,,I like the flow into the sides!! The rear video looks promising good steady airflow if you turn the radiator fans off how does the rear flow look?

[Bob_n_Cincy]

Bob , this is great video and very useful,,I like the flow into the sides!! The rear video looks promising good steady airflow if you turn the radiator fans off how does the rear flow look?

I have not shot video without fans running. I have another issue that is causing a CEL which forces the fans on.
Bob

[Bob_n_Cincy]

I will be doing some more videos this week. Is there anything particular someone wants to see?
Bob

[ssssly]

I would be interested in the flow 2" above than the side openings, 3" out from the side of the car.

Also interested in the flow directly above the midpoint of the rear wheel, at the body's highest point, 1" out from the body.

And the mid point of the door 2" out.

[DMC7492]

Hi Bob, could you stick a couple strands around the vents on the top of the hood? Interested to see if air is going in or out. And also across the rear trunk at the edge where the trunk meets the rear panel.
Once again thank you pioneers for the ongoing development of real life testing!!

[Bob_n_Cincy]

Rear vent air flow measurement.

With our rear radiator system. We were still having problems with coolant temperature creeping up while driving at 70-80 MPH.
Today we use an anemometer ( air flow meter) to measure the air speed going through our radiator.



Results in MPH,
Vehicle 0, Fans off 0, Fans low 5, Fans High 10.
Vehicle 60, Fans off 2, Fans low 4, Fans High 8.

I was expecting that the vacuum behind the vehicle at 60 mph would suck air out of the back of the car at 30-60 MPH.
I WAS WRONG

It seems that the spoiler on top and the open engine opening on the bottom is pulling the air right along with the car. That slow moving high pressure air is filling in right be hind the car.
So basically I have slow moving air at the same pressure on both side of my radiator. Then there is no increase in flow defendant on vehicle speed.

So now Mike and I have some decisions to make:
Option 1: Sick with the rear radiator, remove spoiler, close bottom of engine bay, and add ducting to radiator fans.

Option 2: Switch to a front radiator system.

Bob and Mike

[metros]

Wow, your testing showed a lot. You're better off sitting still with the fans on high than driving with the fans on.

I'd be curious to see if the spoiler had any effect at all and then if having the wing would provide enough clearance to get some airflow through the rear radiator.

[Bob_n_Cincy]

Wow, your testing showed a lot. You're better off sitting still with the fans on high than driving with the fans on.

I'd be curious to see if the spoiler had any effect at all and then if having the wing would provide enough clearance to get some airflow through the rear radiator.

Hi Metros,
We plan on doing the same test without the spoiler/wing.
The tuft test did show us that the air off the deck did go straight down.
Bob

[Santiago]

Good idea to do the same test without the wing - though I'm betting it doesn't help. When you go again, add more tufts along the edge of the rear deck (like one every 3") so you can get a better visual. When I look at the videos I see the single center tuft often straighten out, but then get pulled down. IOW, airflow off the rear deck is not always going straight down and more tufts would give a better sense of how it's flowing.

I hope I'm wrong, but I don't think the wing is the culprit. Part of the concern is that any bluff body has poor airflow directly behind it that's often recirculating. So you're fighting a pretty standard condition. Still, you might offset this with a good diffuser to close off the bottom of the engine bay. When ducting the fans be sure to try to diffuse the path after the entrance (if you can).

Lately I've noticed an increase in 18-wheelers using panels off the rear of their trailers to help reduce drag. I don't know for sure, but I think they're trying to gain distance from the back of the trailer and the recirculating region of air (as well as taper in the flow more gradually behind the rectangular trailer edges). Kind of lights the imagination on different routes to try. Just a thought.

Best,
-j

[Bob_n_Cincy]

Good idea to do the same test without the wing - though I'm betting it doesn't help. When you go again, add more tufts along the edge of the rear deck (like one every 3") so you can get a better visual. When I look at the videos I see the single center tuft often straighten out, but then get pulled down. IOW, airflow off the rear deck is not always going straight down and more tufts would give a better sense of how it's flowing.

I hope I'm wrong, but I don't think the wing is the culprit. Part of the concern is that any bluff body has poor airflow directly behind it that's often recirculating. So you're fighting a pretty standard condition. Still, you might offset this with a good diffuser to close off the bottom of the engine bay. When ducting the fans be sure to try to diffuse the path after the entrance (if you can).

Lately I've noticed an increase in 18-wheelers using panels off the rear of their trailers to help reduce drag. I don't know for sure, but I think they're trying to gain distance from the back of the trailer and the recirculating region of air (as well as taper in the flow more gradually behind the rectangular trailer edges). Kind of lights the imagination on different routes to try. Just a thought.

Best,
-j

Thanks Santiago for you insights.
No testing this week. It's below freezing for most of the week.
Bob

[apexanimal]

Bob,

I have a magnehelic gauge that has a sweep range appropriate for aerodynamic testing... i'd be willing to send it to you if it would be of use to you.

[Bob_n_Cincy]

Bob,

I have a magnehelic gauge that has a sweep range appropriate for aerodynamic testing... i'd be willing to send it to you if it would be of use to you.

Thanks Apex,
May take you up on that.
Can it measure pressure in a fast moving air stream?
Won't the Bernoulli cause the readings to be off?
Bob

[Frank818]

Bob, remind me, was this last test with or w/o the rear diffuser? Looks like no diffuser but it's too dark on the pic and too cropped in that area to see.

[Bob_n_Cincy]

Bob, remind me, was this last test with or w/o the rear diffuser? Looks like no diffuser but it's too dark on the pic and too cropped in that area to see.

All testing so far is with wing/spoiler, with engine belly pan and no diffuser.

Bob

[RetroRacing]

looks to me like reversion, air is curling around and pushing against the fan air (thus the reduced net with fans at full). We figured this might happen, that's why we went with such a big Hump duct on top of the rear cowl, for both the intercooler and the oil cooler. just a flat extension off the rear deck lid (about 4") and test again, I think it might help. A vent at the very back top of the deck lid, ducted to the rad might also help.

Or, just get a big Hump! (we did make a mold....)

[Bob_n_Cincy]

looks to me like reversion, air is curling around and pushing against the fan air (thus the reduced net with fans at full). We figured this might happen, that's why we went with such a big Hump duct on top of the rear cowl, for both the intercooler and the oil cooler. just a flat extension off the rear deck lid (about 4") and test again, I think it might help. A vent at the very back top of the deck lid, ducted to the rad might also help.
Or, just get a big Hump! (we did make a mold....)

I'm not sure what the word reversion means, but I think we are thinking the same thing.
Here is a picture of a smoke wand behind a ford .



I wish that FFR would have published a lot more videos and data on the tunnel testing. If I saw this before I did my rear radiator. I might have changed my direction.

https://youtu.be/d_Y53kdCG6c

https://youtu.be/0xOCYSTQx3E

Bob

[RetroRacing]

Yes, that is what I meant! just made up a word that sounded like what I meant....

[Bob_n_Cincy]

If I move my radiator to the front and add all the aluminum.
what percentage of air goes out the hood vents and the wheel wells?



Bob

[Hindsight]

I don't recall anyone testing that. Closest I have seen has been infrared pics showing body temps after a long drive. The hood vents were very hot so we know they work but not sure about %.

[Frank818]

Maybe the rear diffuser could also help, since it would drag air from underneath the entire engine bay (not just the belly pan) and away from the curvy rear bumper's bottom (mayb away from your rad too). Of course you need good air pressure in from the side scoops and top side scoops to push the air out behind. So far that's my assumption.

[RetroRacing]

If you duct it, and seal it like we did, then it all has to go up through the hood vents. Make the vents as big as possible, as close to equal to the intake sq" as possible.

[Sgt.Gator]

These links to Simon McBeath's webpages may be useful. I love his book, Competition Car Aerodynamics, New 3rd Edition: A Practical Handbook http://www.amazon.com/Competition-Ca.../dp/1845847768
51J69JMaZnL._SX353_BO1,204,203,200_.jpg


Here are the articles he's written:
http://www.sm-designs.co.uk/articles.html

In particular for the red neck wind tunnel discussion these two are on point:

http://www.sm-designs.co.uk/pdfs/tracktest1.pdf

http://www.sm-designs.co.uk/pdfs/tracktest2.pdf

[apexanimal]

Thanks Apex,
May take you up on that.
Can it measure pressure in a fast moving air stream?
Won't the Bernoulli cause the readings to be off?
Bob

absolutely.

the best method is to place the open tube end perpendicular with airflow. using it, i was able to test the outside and inside of the hood of my previous two cars to see where it would be beneficial to place louvers to decrease the engine bay pressure, where the highest pressure was at the front to determine where to place the intake for best results, as well as the rear bumper to determine if it would be beneficial to cut it or not...

it'll take an afternoon, a sheet of paper and a pencil, some tape, and a methodological plan, but it's well worth it - especially with all the aero/cooling issues that are going on...

[904svo]

I'm also trying to cool my engine with the radiator in the back on my kit car. I'm having the same problem with the engine overheating above 50 MPH. After
looking at the videos and pictures I can see where the Bernouill effect is causing the problem (I think). The radiator is not getting enough COOL air at high
speeds, the heat from the engine (Its a heat pump at high speeds) is being pull out of the bottom of the car. This heat and the low pressure behind the rear
of the car slows down the air flow, which when couple with the heat of the engine compartment ( In excess of 185 degrees ) will not allow cooling to take place.

This is what I think is happening.

[Bob_n_Cincy]

I'm also trying to cool my engine with the radiator in the back on my kit car. I'm having the same problem with the engine overheating above 50 MPH. After
looking at the videos and pictures I can see where the Bernouill effect is causing the problem (I think). The radiator is not getting enough COOL air at high
speeds, the heat from the engine (Its a heat pump at high speeds) is being pull out of the bottom of the car. This heat and the low pressure behind the rear of the car slows down the air flow, which when couple with the heat of the engine compartment ( In excess of 185 degrees ) will not allow cooling to take place.

This is what I think is happening.

Hello 904svo
Can you post a link to pictures of your car.
I think the problem is that there is not low pressure behind the car. I was hoping for low pressure.
The air is forming a big pillow behind the car that is high pressure which blocks the air from coming out of rear radiator.
This picture shows it best.

Bob568c0cf1.jpg

[bigAl]

Much appreciate this whole effort.

[129st]

absolutely.

the best method is to place the open tube end perpendicular with airflow. using it, i was able to test the outside and inside of the hood of my previous two cars to see where it would be beneficial to place louvers to decrease the engine bay pressure, where the highest pressure was at the front to determine where to place the intake for best results, as well as the rear bumper to determine if it would be beneficial to cut it or not...

it'll take an afternoon, a sheet of paper and a pencil, some tape, and a methodological plan, but it's well worth it - especially with all the aero/cooling issues that are going on...

A pitot tube is used to measure both static and dynamic pressure of a moving airstream. Good pitot tubes are rather expensive ($150+). If you only want to measure the static pressure, the below Dwyer tube is a low cost solution. Just point the tube in the direction of the moving air and the small side holes will measure static pressure. It is can be attached to a low cost inclined manometer for reading.


http://www.amazon.com/Dwyer®-Portabl...DAXNAJD0AFFZWG

[904svo]

Here are the pictures of my car. As you can see the profile is about the same with air flow.
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[904svo]

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