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Thread: Computational Fluid Dynamics and the Corvette?

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    Chest hair required Olitho's Avatar
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    Default Computational Fluid Dynamics and the Corvette?

    I am doing some aero work on my C5 Z06 Corvette. My immediate task is to vent the radiator and hood for better cooling and front end down-force.

    I have new ducting leading into the radiator from the nose and new ducting from the back of the radiator out of the top of the hood. I don't have many options on where to place the hot air from the radiator so that discussion is moot, although the planned venting seems to be in almost the optimal spot. My goal is to get the cooling I need when racing in 110 degrees and drafting another car. I hope to get the result I need as the stock set-up is not up to that task.

    In GT2 rules I am limited to louvered ducting of 600 square inches. If I have about 300 sq inches left to duct air from the engine compartment of the hood, based upon the CFD images below, where do you suggest I place the louvers? My goal is to reduce lift and pressure under the hood which is quite substantial at 150 MPH (as seen here just after the 2:10 mark of the video oli's flying hood - Bing Videos).

    080409_19.jpg

    092109_fieldview122.jpg

    chevrolet_corvette_c6r_09_02.jpg

    pres.png


    And here is a video:


    And this:
    GT1 cars CFD - Forum - F1technical.net
    Last edited by Olitho; 12-23-2013 at 07:46 PM.
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    Senior Member fatbillybob's Avatar
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    Quote Originally Posted by Olitho View Post
    I am doing some aero work on my C5 Z06 Corvette. My immediate task is to vent the radiator and hood for better cooling and front end down-force.

    I hope to get the result I need as the stock set-up is not up to that task.

    In GT2 rules I am limited to louvered ducting of 600 square inches. If I have about 300 sq inches left to duct air from the engine compartment of the hood, based upon the CFD images below, where do you suggest I place the louvers?

    If you really vent the radiator out the hood you have increased drag. Have you optimized the splitter? If yes do you have the horsepwer to add more front downforce and drag out the hood and more horsepower to add more rear wing to balance the new front down force? I don't see how you could do as you propose without lots of time and costly parts to test test test. The stop watch is the only answer. I'm not sure how to integrate CFD with power output to find the right balance on paper. Ask Tway but if I was him I'd be telling you that you need more ballast.

    Why does stock not work? It did fine in T1 and the venting you can do is more liberal than before. Is it because of the LS3 swap not making more heat?

    300 inches...hmm...why not vent the pressure out of the front wheel wells by perforating the inner fender liner and vent that out the hood? So you would have a central radiator vent, and 2 side hood vents over each wheel?

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    Chest hair required Olitho's Avatar
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    Quote Originally Posted by fatbillybob View Post
    If you really vent the radiator out the hood you have increased drag. Have you optimized the splitter? If yes do you have the horsepwer to add more front downforce and drag out the hood and more horsepower to add more rear wing to balance the new front down force? I don't see how you could do as you propose without lots of time and costly parts to test test test. The stop watch is the only answer. I'm not sure how to integrate CFD with power output to find the right balance on paper. Ask Tway but if I was him I'd be telling you that you need more ballast.

    Why does stock not work? It did fine in T1 and the venting you can do is more liberal than before. Is it because of the LS3 swap not making more heat?

    300 inches...hmm...why not vent the pressure out of the front wheel wells by perforating the inner fender liner and vent that out the hood? So you would have a central radiator vent, and 2 side hood vents over each wheel?

    Hey Fat Billy Bob:

    You present many good questions.

    I am not sure the drag will be any greater than my old vented hood. I think I had a lot of drag with that one while simultaneously having very poor cooling efficiency. I suspect I might have less drag with the new design as ultimately less air flow will be going into the front vents and all of it will be directed out of the hood. So in addition to have less drag, I hope to have less lift under the hood as well. That will hopefully help with my front grip, especially at speed. My rear wing is essentially flat which is good for drag, but not helping me with as much potential rear grip in the corners. My old design did not provide enough front grip, especially with the 335 rear tires.

    I am not sure how more ballast would help me. Please explain that one.

    I don't feel I have a problem with the LS3 making more heat. I ran into a problem in September racing with Chuck Mathews. I was able to follow him in the 100 degree heat, but when I was following him closely around the track waiting for an opportunity to pass my car temps went up. I would try and follow closely and draft, but we were so close I needed to be patient on the pass attempts. My car computer cut power twice and I had to fall back and then catch him again. The second time it happened on the last lap as I was really trying to put the pass pressure on. I don't want that to happen again. As you know the Corvette exhaust is right in the same spot as the radiator intake on the C5. Not a good combo for close racing so I needed a different solution. I think I have that now.

    Lastly, in all the research I have done, I have not been able to corroborate that there is a lot of inner fender air pressure on fendered race cars... at least not what I can tell from those images of the Corvettes. That area appears to be a low pressure zone. Certainly across the top of the front fenders and hood is a very low pressure area. That is where I presume I am going to put long thin louvered plates. Exhausting hot under-hood air pressure from those points and limiting the aimless air coming out of the stock radiator design under the hood will hopefully improve down-force, improve cooling and reduce drag from what I have in stock form. I am looking for critical input and feedback from others on this forum.
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    Sir flink
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    600 sq in sounds like quite a lot.

    If you want the best possible air flow through the rad then presumably you want to vent into the lowest-pressure area. That is said to be the point of highest curvature.

    I measure the over-hood pressures on the wife's 328.

    Pitot tube:


    Differential pressure gauge:


    Result:


    Decision:


    Tuft testing. Make of it what you will: 2011 01 07: Thunderhill: Hood Vents - YouTube

    I think a decent rule of thumb for all cars is "vent the hood as far forward as you can put it".

    Prepare to be disappointed - it doesn't make any difference, really. The flow rate through a radiator is very low, so the amount of low-pressure-zone-reduction over the hood is very small. I spent a year doing various things to try to reduce drag - mainly restricting cooling flow which in theory should reduce drag by a lot. None of it ever made any difference I could measure, even at Miller. Perhaps at ACS one could make a measurable difference.

    Spend an hour here: Windtunnel Testing the Datsun S-30 Z - Windtunnel Test Results and Analysis - HybridZ and here: Windtunnel Test Data - Windtunnel Test Results and Analysis - HybridZ.

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    Chest hair required Olitho's Avatar
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    Yes, 600 sq inches is a lot, but that is the limit so I can go up to that. They say the louvered area can be up to 600 inches. I am trying to guess does that mean the whole plate or just the actual louvers specifically.

    I did a string test a while back. I did find that the strings along the hood by the windshield got sucked back into the engine bay, so I sealed that area. I will watch your suggested video now.
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    Chest hair required Olitho's Avatar
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    Quote Originally Posted by flink View Post

    Tuft testing. Make of it what you will: 2011 01 07: Thunderhill: Hood Vents - YouTube
    That far rear most string seems to suggest that your BMW like the Corvette has a very low pressure zone right above the fender above the front wheels.
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    Sir flink
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    Quote Originally Posted by Olitho View Post
    I did find that the strings along the hood by the windshield got sucked back into the engine bay, so I sealed that area.
    Yep, the hood<->windshield gap is all bad. Increases drag and raises the pressure in the engine bay, hence worsens the pressure drop across the radiator.

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    Senior Member bellwilliam's Avatar
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    Oli:
    1. you want to place vents where "blue" area are in your first picture. in general, it means a V (looking at the hood from top) shaped area on the hood.
    2. you want to place a small lip at leading edge of the louver
    3. maximize your louver area. I am no engineer, I am sure smart people will come on and explain why even a small louver makes a huge difference on a hood. It has to do with large area of a hood. it generates a lots of lift. so even a small vent makes a big difference.
    4. even if you don't get a lot of down force, as long as car runs cooler, it means you can close up front radiator intake, which gets you better down force and lower drag.
    5. another tip is NOT to install brake duct intake at front bumper's red area (look at how big the "red" area are). instead install sideway inside radiator duct. this cuts drag.
    6. fender vent definitely helps. wheel wells are a high pressure area, so venting that is always a good idea.
    Last edited by bellwilliam; 12-23-2013 at 11:54 PM.
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    Quote Originally Posted by bellwilliam View Post
    Oli:

    2. you want to place a small lip at leading edge of the louver

    5. another tip is NOT to install brake duct intake at front bumper's red area. instead install sideway inside radiator duct. this cuts drag.

    2. Don't you mean the trailing edge of the louver like a Gurney Lip?

    5. I might tape them over. I am going to 380mm rotors and six piston calipers. I have heard from some racers that these larger rotors don't need/benefit from brake ducting that is somewhat dubious in ROI anyway.
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    Senior Member bellwilliam's Avatar
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    Quote Originally Posted by Olitho View Post
    2. Don't you mean the trailing edge of the louver like a Gurney Lip?.
    nope, gurney lip at leading edge.
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    I wanna go fast! thepass's Avatar
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    I think you guys are confusing terms on the louvre edge/gurney placement even though you mean the same thing. Gurney goes ahead of vent opening. If you have a louvre, the louvre shape partially serves the same function as a gurney does on a simple hole in the hood, since the louvre is angled up ahead of the hole. But, even a set of louvres will benefit from one big gurney flap in front of them, or from making the forward most louvre in a row of louvres larger than the ones behind it.

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    Senior Member bellwilliam's Avatar
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    What Pass said.

    I would also add - avoid using wire mess for openings or radiator intake. Even ones has biggest "holes", actually flows 66% at best. This is an example on Pegasus racing, it describes percentage of flow of various mesh. Most cars I see use fine mesh that's 50%
    https://www.pegasusautoracing.com/pr...p?Product=3642
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    Chest hair required Olitho's Avatar
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    Here are a couple of pictures of my revised radiator positioning and the relocated intake as we prepare the car for the ducted radiator exhaust out of the hood.

    I will post pictures later of the ducting work and the hood.

    photo-1.jpg


    photo-2.jpg
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    Senior Member bellwilliam's Avatar
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    Oli: hottest air is blowing on intake tube..........
    either do a heat wrap, or/and do a simple shield to deflect hot air
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    Chest hair required Olitho's Avatar
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    Quote Originally Posted by bellwilliam View Post
    Oli: hottest air is blowing on intake tube..........
    either do a heat wrap, or/and do a simple shield to deflect hot air
    I am figuring on wrapping it with locks of hair from Miata driver hair salons. I will glue it into place with finger nail extension glue from your trailer.
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    Quote Originally Posted by bellwilliam View Post
    Oli: hottest air is blowing on intake tube..........
    either do a heat wrap, or/and do a simple shield to deflect hot air
    That is so,but considering of how much air flows inside the tube the heat transfer is less than negligible.

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    Quote Originally Posted by Olitho View Post
    Here are a couple of pictures of my revised radiator positioning and the relocated intake as we prepare the car for the ducted radiator exhaust out of the hood.

    I will post pictures later of the ducting work and the hood.
    Oli,glad to see that your engine bay looks much better than last year on the Sevensonly's dyno Taking care of the things that move you always pays off.
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    Car cools well in open air, so you only need help in draft?

    I would look at fans...

    BID
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    Chest hair required Olitho's Avatar
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    Quote Originally Posted by bikeindirt View Post
    Car cools well in open air, so you only need help in draft?

    I would look at fans...

    BID
    The car does have a larger fan now, plus I opened up another radiator intake that won't pick up the wickedly hot exhaust of an LS3 spinning at 7000 RPM WOT.
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    Does that vent flow in the first three images produce any downforce?
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