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I added some VG's.. ofcourse there are pics


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So why does the S130 have that "bump" above it's hatch? Were the designers addressing the exhaust fume issue of the S30? Is that all is needed to help the S30? These are my questions, especially since, personally, I'd rather NOT put a rear spoiler on my tail, but I'm not against something around the upper hatch area.

Pure conjecture to follow:

 

I think the bump on the 280ZX acts like a "trip strip". If you have a relatively smooth surface and you put a speed bump like obstruction in the airflow the air hits the bump and separates, creating a vacuum, and this causes the air to try and fill that vacuum and head in the direction of the bump.

 

This seems counterintuitive because you would expect that the fact that there is a low pressure boundary layer over the hatch would also try to suck air to the hatch. The fact is that this vacuum does want to be filled (with exhaust gasses mostly), but the trip strip works to create a stronger vacuum when the airflow is still attached, so it does it's bit before the air starts to separate naturally due to the shape of the object, and that means that it can redirect the air to curl back down onto the hatch before the separation begins.

 

I would suspect that the VGs would be the stronger method of keeping the flow attached, while the bump in the roof is the less conspicuous way of doing the same.

 

That's my theory anyway.

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I would suspect that the VGs would be the stronger method of keeping the flow attached, while the bump in the roof is the less conspicuous way of doing the same.

 

That's my theory anyway.

 

I tend to agree with you, although only more wind tunnel time will tell (airflow ideas are being swatted down like flies around here). Aesthetically, the VG's aren't my cup of tea for my street car, but if a more subtle "trip strip" could provide near the same function, I'm all for it.

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Scott.

 

I am working on a trip strip for my S30. If it works, I will end up making a mold of it. I want to paint it body colour, and I would like it inconspicuous as much as possible.

 

I posted a pic in this forum of my idea, though I used a strip of cardboard to illustrate a basic idea.

 

I'll post pics once my prototype is finished and ready for "seat of the pants" testing.

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  • 1 year later...
Hughdogz: the S130 already has a "bump" right above the hatch, supposedly put there by the Nissan engineers to seperate the boundary layer from the rear hatch, thereby reducing lift (TonyD and I butted heads about this awhile back). Which brings me to a larger question:

Isn't it the purpose of vortex generators to enhance boundary layer adhesion? Isn't this why they are useful on wings, because they enhance lift? Isn't that what we're trying avoid with our cars? I can understand the concept of trying to get air to the rear spoiler to enhance it's downforce properties, but it seems contradictory to increase lift in one spot, just to try and decrease it with a spoiler/wing 3 feet later. Please somebody, send me to school on this...

 

Just noticed this, particularly the first paragraph, only a few years behind, oh dear. Anyway, without thinking too much about it I think you are are on the right track in theory.

 

But I doubt that VG's will enhance boundary layer adhesion on the S130, given the gap created by the bump. So, unless you have a wing, I doubt that VG's will be of any benefit with the S130.

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  • 1 month later...

On that article, they have what looks like a computer engineered model of the Evo with the airflow speed shown with CFD. In other articles here I've read of individuals using that same software for seeing the airflow of different plenum designs, couldn't they use that same software for these threads as well?

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I was under the impression that the VGs reduced the swirling effect (think waterfalls and kayaks) at the hatch/rear deck area and allowed the air flow to enter the spoiler in a more straight forward manner.

 

Correct, which is why mitsu even states in the conclusion of their research paper that they actually decrease drag, due to the reduction of boundary layer. The increase of boundary layer size is a huge contributor to the swirl in the air behind a car. You're creating a vacuum that the air is trying desperately to fill.

 

By cleaning up this air you create a much more efficient flow path for your wing/spoiler. I think one of the biggest advantages I could see is that you don't need to run your wing as high up to get the same lift out of it, giving you better visibility, or possibly get good enough results from a wale tail type spoiler as would make street use of a wing impractical.

 

I don't really see any downside to them, other than looking odd at first.

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