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Splitter Size Study

 
Old 07-06-2018, 08:00 PM
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Default Splitter Size Study

See results here: https://baero.tech/blog/2018/7/7/spl...ze-does-matter

Going to be making a splitter for a friend and fellow S2Ki member shortly and decided to do some research on best possible sizes. I'm going to be updating the post soon to account for some added 3D goodies, but the focus right now is a NASA TT legal splitter.

It was a super fun project that didn't take as long as I thought it would. I need to find a way to rent out some processing rigs to be able to analyze the entire body. I think one or two panels at a time are my limit at the moment.
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Old 07-06-2018, 09:39 PM
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At what vehicle speed was that simulation run at?

Also, you need to run the sim with the bumper attached. How the air is allowed to leave the bumper matters. Also, the flow through the bumper isn't nearly as open as your current sim indicates because, in reality, there is an entire car behind it... The radiator opening is not a straight shot... At least, simulate a massive restriction to airflow through the openings in the bumper if you don't want to simulate with an actual car behind it. I'm not doubting the trends your sim is showing but modeling against a more realistic scenario might actually amplify the 'gains'. Model at least the front end of the car from about half way up the windshield if possible.

Also, you need to include some supporting argument why 6lbf of drag is 'insignificant'. I'm assuming that total drag on the car is several magnitudes higher at the speed you tested, but it's not mentioned in the article.

That being said, I'm sure it's a no brainer to run the biggest splitter the rules allow. Supporting data is always appreciated though.
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Old 07-07-2018, 12:37 AM
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I'd take a peek at RHR's splitter work. The guy they were using was hired by Mercedes F1. https://rhrperf.com/blog/project-crusher-part-3/

Net: it is the diffusers that make the splitter work. You already have some channels. My recommendation, play with the diffusers (rules permitting) as much as size.
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Old 07-07-2018, 04:16 AM
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What about diffusers along the sides to block off the front wheels a bit? I recall seeing that this was very beneficial.
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Old 07-07-2018, 06:37 AM
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Originally Posted by bgoetz View Post
What about diffusers along the sides to block off the front wheels a bit? I recall seeing that this was very beneficial.
Against the rules, that's why they are omitted.

NASA rules only allow a completely flat 4" splitter, so I don't really have much room to play with.

Last edited by roel03; 07-07-2018 at 06:49 AM.
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Old 07-07-2018, 06:39 AM
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Originally Posted by shind3 View Post
At what vehicle speed was that simulation run at?

Also, you need to run the sim with the bumper attached. How the air is allowed to leave the bumper matters. Also, the flow through the bumper isn't nearly as open as your current sim indicates because, in reality, there is an entire car behind it... The radiator opening is not a straight shot... At least, simulate a massive restriction to airflow through the openings in the bumper if you don't want to simulate with an actual car behind it. I'm not doubting the trends your sim is showing but modeling against a more realistic scenario might actually amplify the 'gains'. Model at least the front end of the car from about half way up the windshield if possible.

Also, you need to include some supporting argument why 6lbf of drag is 'insignificant'. I'm assuming that total drag on the car is several magnitudes higher at the speed you tested, but it's not mentioned in the article.

That being said, I'm sure it's a no brainer to run the biggest splitter the rules allow. Supporting data is always appreciated though.
Testing is done at 100mph.

I'm not saying drag is insignificant, I was saying drag between the different sizes is so close I consider it constant.

If you read my post, the reason it's so simplified is because this is the extent my computer can handle. I tried running the entire front end and even half of it and my computer crashed.
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Old 07-07-2018, 09:14 AM
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Originally Posted by roel03 View Post
Against the rules, that's why they are omitted.

NASA rules only allow a completely flat 4" splitter, so I don't really have much room to play with.
Those are the rules for ST5/TT5. STU/1/2/3 allow aerodynamics close to/equal to unlimited WTAC cars. American Iron, another NASA class, also allows diffusers. The link I posed referenced those. RHR was doing development for both STU and AI aero.

When done with diffusers, limitations in rear downforce become the issues. With a flat plate spoiler, most racers seem to have their rear wings at close to 0° angle of attack.

For just a flat plate with no diffusers or endplates, why wouldn't the least expensive rigid material be used?

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Old 07-07-2018, 09:51 AM
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Old 07-07-2018, 02:14 PM
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DavidNJ, that image needs to come with a disclaimer every single time you post it. That "ST4" title in the image does not mean NASA's ST4. (is it a typo?)

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Old 07-07-2018, 08:08 PM
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Theres some serious potential for good information in this thread. What are other NASA TT people doing across the country?
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