260DET Posted July 5, 2008 Share Posted July 5, 2008 Am in the process of making an aluminium front undertray for the project Z and was thinking about getting some of those stick on vortex generators to attach to the underside. The undertray runs from the front of the spoiler back to the engine Xmember, its a bit over one meter long and 670mm wide. It slopes down a bit from front to back but not much so the airflow under it should remain attached. In that situation its my understanding that VG's should reduce air pressure but I'm not sure. For practical reasons the VG's would have to be mounted ~200mm back from the front but I can't see this as a problem as far as results are concerned. So what is the opinion of the aero learned forum members? The rest of you may comment as well Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted July 6, 2008 Share Posted July 6, 2008 I have not seen the bottom of a race car with any type of vortex generators.. They always have SMOOTH bellies Venturi tubes and front/rear diffusers are much different then a vortex (low pressure) generator Quote Link to comment Share on other sites More sharing options...
tube80z Posted July 6, 2008 Share Posted July 6, 2008 I've seen pictures of a number of the Dodge Vipers that had vortex generators on the underside of their splitters. These were in front of the tunnels that fed into the wheel wells. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 6, 2008 Share Posted July 6, 2008 There was also that article in the original aero thread where they put VGs on the leading edge of a Honda Insight air dam and got better mpg. I think the theory was that it helped the air to flow past the rough undercarriage. The strakes of a diffuser are also vortex generators in many cases. Lots of formula cars have VGs all over the sides, I think the bottoms are flat because the rules state they have to be. Quote Link to comment Share on other sites More sharing options...
260DET Posted July 6, 2008 Author Share Posted July 6, 2008 From a reading of McBeath's book Competition Car Aerodynamics it seems that the vortices created by VG's may inherantly lower air pressure slightly but this is not absolutely clear. However given that VG's are used on the top of aircraft wings I'm going to assume that they at least do not increase air pressure. What VG's will do is control air direction so this should assist in directing air along the length of the undertray, rather than have it spill off to the sides. Strakes would do the same thing but with them ground clearance becomes a problem whereas effective VG's can be just 15-25mm high. As Jon said, race car bottoms may be flat due to rules and, I guess, a lack of ground clearance given that bottoming out is not uncommon. Anyway if anyone can see a problem with the above comments please fire away. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 6, 2008 Share Posted July 6, 2008 From a reading of McBeath's book Competition Car Aerodynamics it seems that the vortices created by VG's may inherantly lower air pressure slightly but this is not absolutely clear. However given that VG's are used on the top of aircraft wings I'm going to assume that they at least do not increase air pressure. VG's on wings allow the flaps to work at higher angles of attack by preventing the flow of air from separating from the wing. It energizes the air that hits the flaps. It's a different use altogether. Correlates well to using them on the top to get better airflow to the wing or spoiler, but not to the bottom. VG's can lower the air pressure by design, like when used in a diffuser, and maybe this is what you're thinking of trying to use them for, but just sticking them on the bottom at the back of your splitter I don't think is going to have that effect. I think the airtabs usage correlates better for the bottom. Airtabs are used on semis to smooth the airflow past the large gap from the tractor to the trailer, and around the wheel openings. I would expect that this would be the kind of thing you'd be looking to do. A reminder of the airtab usage on the bottom of the Insight: http://www.autospeed.com/cms/A_3061/article.html That's how I'm seeing it, although I am not an expert by any means. Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted July 7, 2008 Share Posted July 7, 2008 Having VG's on the front splitter of the car will help organize the airflow.. like mentioned above.. but a full smooth underbelly/under tray like on race cars would be useless.. there is no flow separation UNDER the car except at the rear of the car.. which diffusers sort out. Now air separates and exits out of the sides as well.. but VG's would be pointless on the sides of a car.. thats why race cars are so low or add side skirts. In our case.. adding VG's on the front splitter for our Z's would help since our cars have a wild mess and lots of interference and parts sticking out... and I suppose adding VG's on the bottom of the stock gas tank would help too, but nothing noticeable. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 7, 2008 Share Posted July 7, 2008 Having VG's on the front splitter of the car will help organize the airflow.. like mentioned above.. but a full smooth underbelly/under tray like on race cars would be useless.. there is no flow separation UNDER the car except at the rear of the car.. which diffusers sort out. Now air separates and exits out of the sides as well.. but VG's would be pointless on the sides of a car.. thats why race cars are so low or add side skirts. In our case.. adding VG's on the front splitter for our Z's would help since our cars have a wild mess and lots of interference and parts sticking out... and I suppose adding VG's on the bottom of the stock gas tank would help too, but nothing noticeable. Again, I think we need to realize that there is more than one use for a VG. With the air tabs installed on a semi, the idea is not to keep the flow attached to the surface. Instead the idea is to keep the flow "organized" as you put it to allow it to cross the huge gap between the truck and the trailer more smoothly and reduce drag. So if Richard wanted to use them at the back of his splitter to keep the flow organized and reduce drag of air hitting the suspension and chassis underneath I think that very well may work. It may also make a rear diffuser more effective. Alternatively if there were a control surface under the car a VG may make that surface more effective (thinking duct here, but could be anything trying to make use of the airflow underneath). I think maybe you're just taking me too literally regarding VG's on the sides of cars. You may not see a typical VG stuck directly to the side of a car, but formula cars use lots of little vortex generators and "flow directors" all over to direct the flow to the radiators and rear wing. More info: http://www.airtab.com/Files/MIRA3.pdf Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted July 7, 2008 Share Posted July 7, 2008 Oh Jon I didn't even think about your post about the airflow around the sides of the car.. oops! I was just thinking about where the air could go when under a car. I'm sorry! I should of read your post about the semi's lol. Otherwise Jon, I completely agree with you. Quote Link to comment Share on other sites More sharing options...
260DET Posted July 8, 2008 Author Share Posted July 8, 2008 Decided to do it, will make some VG's out of aluminium angle using the Mitsubishi 'delta wing' pattern and pop rivet them to the undertray. Will take some pics when its done, if I remember Quote Link to comment Share on other sites More sharing options...
johnc Posted July 8, 2008 Share Posted July 8, 2008 The VGs need to direct air towards a low pressure area. The ones on the front splitters of race cars are more flow control devices then VGs with the idea being to direct as much flow as possible towards a low pressure area (the front wheel wells typically). http://www.mulsannescorner.com/benzCLR2.html Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted July 8, 2008 Share Posted July 8, 2008 I remember reading an article about the Mitsubishi Evo 9 with aerodynamics work on the front bumper with small diffusers right before the front wheels. It was a really neat picture of the underside of the front bumper.. Now I can't find it.. grr. But it's exactly like what your talking about John! Quote Link to comment Share on other sites More sharing options...
jtl260z Posted July 10, 2008 Share Posted July 10, 2008 The idea is solid. The only foreseen issue would be ground clearance. Quote Link to comment Share on other sites More sharing options...
260DET Posted July 12, 2008 Author Share Posted July 12, 2008 Pic, looking from the front back. Orange patch is a jacking point. Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted July 13, 2008 Share Posted July 13, 2008 ohh cool! that is very nice!! good work!! Quote Link to comment Share on other sites More sharing options...
MoNkEyT88 Posted September 2, 2008 Share Posted September 2, 2008 Looks like the only ones on this one are near the wheels. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 2, 2008 Share Posted September 2, 2008 Those aren't really vortex generators, they're flow diverters (I'm sure there is a better term here that I don't know). They are trying to steer some of the air out from under the car through the fender and wheel, not trying to produce a vortex to smooth the airflow under the car.. Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted September 3, 2008 Share Posted September 3, 2008 Betcha that's a CT9A Evo in the last pic. Quote Link to comment Share on other sites More sharing options...
Vapour Posted January 28, 2009 Share Posted January 28, 2009 hey do you make those under car vortex gens or do you got a link for the guy who does so that i can get one Quote Link to comment Share on other sites More sharing options...
260DET Posted May 1, 2011 Author Share Posted May 1, 2011 Glad that pic of mine above no longer exists, after doing some more study I've concluded that its crap for downforce. Not because of the vortex generators, because it curves up in the middle when it should curve down towards the ground, keeping in mind my Z has to have 100mm minimum ground clearance. So I'm designing another one. Quote Link to comment Share on other sites More sharing options...
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