downforce games
Mar 27, 2007, 12:26 PM
#16
so i promised to to talk about some aero **** here.
firstly if you exmamine the more "finely" made products (this includes evolutionary and JrCRXHF's undertray) that there are diffuser "ducts." these end up being very important. the basic precent of creating any fluiddynamic force is to turn flow. so how can you turn flow at the front of the car. you don't or usually can't have a fat wing sitting on top of the hood and anything you do under the car will just run up into the car.
this brings me to the second point, if you run fluid into a solid infinite wall you soon see that fluid dynamics turns into fluid statics. in order to generate fluid dynamic force you must turn FLOW, so you must have FLOW. this implies an intake and an exhaust (and yes even a brick in the wind has flow)
this being the case if you look at the underside of ferraris and other "finely" made cars you'll see they do something smart, they exhaust hte frontal air flow to the SIDES OF THE CAR and to the WHEEL WELLs. these areas will allow the airflow to go away after they've made their contribution to aerodynamicness of car.
that being said you can turn flow right into the wheel wells (and this is consequently good because you get hte df right at the wheel and tire where you need it) and the wheels wells do a great job of exhausting the flow.
this idea of turning flow of course also makes the rear diffusers angle of attack important. this is why the 9 bumper is cut higher. this is a good thing. this is why a good rear diffuser will slope up in a huge way like the kansai piece, or like the custom piece pictured above. cutting the bumper higher on the usdm would be a great idea.
now for the slats you see in both the front and the back. in order to keep the flow going fast you must keep the flow from laterally diverging as it sweeps across the surface of the aeroguide. some people call these slats venturi channels, i think this is very poor and loose nomenclature. a venturi would suggest a NARROWING of the channel and this is SELDOM observed in such diffuser media. so technically you'd want to call them like non diverging flow channels or vortex inhibitors, or like some **** like that. cuz basically they stop the flow from curling sideways and eventually curling back on themselves and slowing the whole show down.
fast is low pressure. this is a good thing that can be used in many aero applications and is used in the aforementioned vortex inhibitors. it's also used in those wheel well spats. when you make the wheel well spats jut out into the flow, the flow must cirumvent the obstruction and this speeds things up.
there is a major high pressure zone right at the front of the wheel where the wheel sort of "runs over" the on coming air. if you can create a low pressure zone here it will evacuate this high pressure zone and large antilift can be extracted. there have been tests done where people have made various kinds of ramps (canards) leading up to such a spat and those all produce nothing but drag. so a nice flat lip splitter leading up to basically a WALL at the leading edge of the wheel well is best. and you can make all kinds of splitters that have a tail that come up and bolt to the inner end of the bumper on the wheel well and that will accomplish this task well and easy.
now on the subject of canards, it's tempting to use them in conjunction with the wheel well spats but the problem is that canards will rob the spats of flow. personally i'm of the opinion that canards will probably produce more df in the long run as you can have multiple elements. also don't be fooled into thinking that the offshoot votrices from the canards will do anything for the high pressure zone in the wheel well as most canards with any decent angle of attack will shoot a vortex high over the desired high pressure zone to be evacuated. to use the spats as a supplement "can't hurt" i suppose... but i don't really know the results of the combined devices. the problem is that the underflow from the canard is essential for the canard's operation but this creates a diverging flow into the spat... while this will be accelerated by the spat i don't know if it'll end up being as hard core as the the spat alone, dedicated wtih all its own flow.
http://www.mattneal.co.uk/gallery/th...s.php?album=43
here's pics of the halford honda integra race car that employs this wheel well scavenging pressure thing.
this is bad
firstly if you exmamine the more "finely" made products (this includes evolutionary and JrCRXHF's undertray) that there are diffuser "ducts." these end up being very important. the basic precent of creating any fluiddynamic force is to turn flow. so how can you turn flow at the front of the car. you don't or usually can't have a fat wing sitting on top of the hood and anything you do under the car will just run up into the car.
this brings me to the second point, if you run fluid into a solid infinite wall you soon see that fluid dynamics turns into fluid statics. in order to generate fluid dynamic force you must turn FLOW, so you must have FLOW. this implies an intake and an exhaust (and yes even a brick in the wind has flow)
this being the case if you look at the underside of ferraris and other "finely" made cars you'll see they do something smart, they exhaust hte frontal air flow to the SIDES OF THE CAR and to the WHEEL WELLs. these areas will allow the airflow to go away after they've made their contribution to aerodynamicness of car.
that being said you can turn flow right into the wheel wells (and this is consequently good because you get hte df right at the wheel and tire where you need it) and the wheels wells do a great job of exhausting the flow.
this idea of turning flow of course also makes the rear diffusers angle of attack important. this is why the 9 bumper is cut higher. this is a good thing. this is why a good rear diffuser will slope up in a huge way like the kansai piece, or like the custom piece pictured above. cutting the bumper higher on the usdm would be a great idea.
now for the slats you see in both the front and the back. in order to keep the flow going fast you must keep the flow from laterally diverging as it sweeps across the surface of the aeroguide. some people call these slats venturi channels, i think this is very poor and loose nomenclature. a venturi would suggest a NARROWING of the channel and this is SELDOM observed in such diffuser media. so technically you'd want to call them like non diverging flow channels or vortex inhibitors, or like some **** like that. cuz basically they stop the flow from curling sideways and eventually curling back on themselves and slowing the whole show down.
fast is low pressure. this is a good thing that can be used in many aero applications and is used in the aforementioned vortex inhibitors. it's also used in those wheel well spats. when you make the wheel well spats jut out into the flow, the flow must cirumvent the obstruction and this speeds things up.
there is a major high pressure zone right at the front of the wheel where the wheel sort of "runs over" the on coming air. if you can create a low pressure zone here it will evacuate this high pressure zone and large antilift can be extracted. there have been tests done where people have made various kinds of ramps (canards) leading up to such a spat and those all produce nothing but drag. so a nice flat lip splitter leading up to basically a WALL at the leading edge of the wheel well is best. and you can make all kinds of splitters that have a tail that come up and bolt to the inner end of the bumper on the wheel well and that will accomplish this task well and easy.
now on the subject of canards, it's tempting to use them in conjunction with the wheel well spats but the problem is that canards will rob the spats of flow. personally i'm of the opinion that canards will probably produce more df in the long run as you can have multiple elements. also don't be fooled into thinking that the offshoot votrices from the canards will do anything for the high pressure zone in the wheel well as most canards with any decent angle of attack will shoot a vortex high over the desired high pressure zone to be evacuated. to use the spats as a supplement "can't hurt" i suppose... but i don't really know the results of the combined devices. the problem is that the underflow from the canard is essential for the canard's operation but this creates a diverging flow into the spat... while this will be accelerated by the spat i don't know if it'll end up being as hard core as the the spat alone, dedicated wtih all its own flow.
http://www.mattneal.co.uk/gallery/th...s.php?album=43
here's pics of the halford honda integra race car that employs this wheel well scavenging pressure thing.
this is bad
Last edited by trinydex; Mar 27, 2007 at 04:34 PM.
Mar 27, 2007, 01:30 PM
#18
I researched this subject a few years back. Here's a great paper I came across. I did not write this paper. http://in3.dem.ist.utl.pt/lxlaser200...paper_35_2.pdf
You can also find good info and visuals of front and rear diffusers on www.mulsannescorner.com/
You can also find good info and visuals of front and rear diffusers on www.mulsannescorner.com/
Last edited by cmj; Mar 27, 2007 at 01:35 PM.
Apr 10, 2007, 03:08 AM
#26
Ok the Voltex front bumper / splitter makes sense and looks awesome, but the rear looks like it would act as a parachute. Also, it is great to vent the top of the wheel wells (if you can per your racing series) as that also helps reduce lift.
Any idea who made that nice Al. rear diffuser and if they are willing to make a few more
?
Any idea who made that nice Al. rear diffuser and if they are willing to make a few more
?
Apr 10, 2007, 08:44 AM
#27
i'm gonna make a rear diffuser.
but the voltex piece for the 9 bumper is not meant to be a diffuser, it's meant to be an underwing... the 9 bumper is very high cut the parachute effects are pretty well in check except on the sides where you could block off or cut holes... neither of which you expect an oem to do.
but the voltex piece for the 9 bumper is not meant to be a diffuser, it's meant to be an underwing... the 9 bumper is very high cut the parachute effects are pretty well in check except on the sides where you could block off or cut holes... neither of which you expect an oem to do.
Apr 10, 2007, 10:11 AM
#28
Great thread. Great information!
Wait till you see pictures of V2.0 of our splitter made for the Voltex front bumper. It should be done and installed in about 2 weeks. It will be completely different from the original unit we tested last year. I think you'll like it!
EVOlutionary
Wait till you see pictures of V2.0 of our splitter made for the Voltex front bumper. It should be done and installed in about 2 weeks. It will be completely different from the original unit we tested last year. I think you'll like it!
EVOlutionary
