|
Para
|
|
|
Group: Forum Members
Posts: 8,
Visits: 20
|
Dear Sir/Madam,
Is there an empirical data available on what the loads (lbs or Newton) are on a typical splitter for an average passenger car at various speeds?....or is there an easy way to calculate/estimate the force for a given splitter size/area ?
Thanks in advance
kindest regards
|
|
|
|
|
Para
|
|
|
Group: Forum Members
Posts: 8,
Visits: 20
|
Hi Guys,
First of all, thank you to everyone for getting back back....much appreciated.
I realise that the splitter itself does not actually create downforce (unlike an airfoil). All it does is to increase the surface area over which high pressure can build up. The more high pressure there is above the splitter...and the more low pressure below the splitter, the greater the net downforce.
Also, my understanding is that splitter function is also very sensitive to ride height.
The lower the car is to the ground the greater suction that will be created by the ground effects, hence the reason why the splitter is located at the lowest possible point. However if the splitter is too close to the ground it will stall, producing less downforce and more drag because air cannot flow through the bottom part of the splitter, so the speed of the flow there will decrease, increasing the pressure.
I read somewhere that this sensitivity can be reduced by designing anhedral shaped splitter. The idea being that in the case that the car touches the ground, part of the splitter will continue to function and hence create downforce.
So yes, i understand there is no one answer without CFD. The splitter will be unique to the vehicle it is being designed for...as frontal are, stagnation point etc are all different on different vehicle types...
But i was quite surprised to read that splitters can generate between 300-400 kg of load....astonishing !
Thanks once again everyone...much appreciated
|
|
|
|
|
Hanaldo
|
|
|
Group: Forum Members
Posts: 2.5K,
Visits: 28K
|
+xHi Guys, First of all, thank you to everyone for getting back back....much appreciated. I realise that the splitter itself does not actually create downforce (unlike an airfoil). All it does is to increase the surface area over which high pressure can build up. The more high pressure there is above the splitter...and the more low pressure below the splitter, the greater the net downforce. Also, my understanding is that splitter function is also very sensitive to ride height. The lower the car is to the ground the greater suction that will be created by the ground effects, hence the reason why the splitter is located at the lowest possible point. However if the splitter is too close to the ground it will stall, producing less downforce and more drag because air cannot flow through the bottom part of the splitter, so the speed of the flow there will decrease, increasing the pressure. I read somewhere that this sensitivity can be reduced by designing anhedral shaped splitter. The idea being that in the case that the car touches the ground, part of the splitter will continue to function and hence create downforce. So yes, i understand there is no one answer without CFD. The splitter will be unique to the vehicle it is being designed for...as frontal are, stagnation point etc are all different on different vehicle types... But i was quite surprised to read that splitters can generate between 300-400 kg of load....astonishing ! Thanks once again everyone...much appreciated Splitters do create downforce, just not as much as an airfoil. The main function of a splitter is to reduce the amount of air going underneath the car. As with all aero structures, the high pressure zone on top of the structure contributes very little to the negative lift being created, it is all about that low pressure zone on the bottom that does all the work. But the splitters role is much more important than just that; not only does it reduce positive lift by reducing the volume of air underneath the car, but by doing so it improves the performance of other aero components like any canards or front wings, side skirts, rear wing, rear diffuser if there is one, etc. So the net benefit can be huge because not only does the splitter itself produce negative lift, but it also let's the entire aero package produce more negative lift. They can actually produce significantly more than 400kg, mine is a relatively simple design. The splitter/front wing combinations on cars at the pointy end of Time Attack are making more than 800-1000kg of negative lift - to put that in perspective, it means you should be able to park a small car on top of the splitter and not see any deflection... So they can be absolutely massive, and are a hugely structural component. That said, a 20mm lip stuck to the bottom of the front bumper without proper rake or rear extension, is not going to do that and is really only contributing to drag. So most splitters that you see on street cars and the likes are not making any downforce at all. If you cant stand on it, its not doing anything for you!
|
|
|
|
|
Para
|
|
|
Group: Forum Members
Posts: 8,
Visits: 20
|
+x+xHi Guys, First of all, thank you to everyone for getting back back....much appreciated. I realise that the splitter itself does not actually create downforce (unlike an airfoil). All it does is to increase the surface area over which high pressure can build up. The more high pressure there is above the splitter...and the more low pressure below the splitter, the greater the net downforce. Also, my understanding is that splitter function is also very sensitive to ride height. The lower the car is to the ground the greater suction that will be created by the ground effects, hence the reason why the splitter is located at the lowest possible point. However if the splitter is too close to the ground it will stall, producing less downforce and more drag because air cannot flow through the bottom part of the splitter, so the speed of the flow there will decrease, increasing the pressure. I read somewhere that this sensitivity can be reduced by designing anhedral shaped splitter. The idea being that in the case that the car touches the ground, part of the splitter will continue to function and hence create downforce. So yes, i understand there is no one answer without CFD. The splitter will be unique to the vehicle it is being designed for...as frontal are, stagnation point etc are all different on different vehicle types... But i was quite surprised to read that splitters can generate between 300-400 kg of load....astonishing ! Thanks once again everyone...much appreciated Splitters do create downforce, just not as much as an airfoil. The main function of a splitter is to reduce the amount of air going underneath the car. As with all aero structures, the high pressure zone on top of the structure contributes very little to the negative lift being created, it is all about that low pressure zone on the bottom that does all the work. But the splitters role is much more important than just that; not only does it reduce positive lift by reducing the volume of air underneath the car, but by doing so it improves the performance of other aero components like any canards or front wings, side skirts, rear wing, rear diffuser if there is one, etc. So the net benefit can be huge because not only does the splitter itself produce negative lift, but it also let's the entire aero package produce more negative lift. They can actually produce significantly more than 400kg, mine is a relatively simple design. The splitter/front wing combinations on cars at the pointy end of Time Attack are making more than 800-1000kg of negative lift - to put that in perspective, it means you should be able to park a small car on top of the splitter and not see any deflection... So they can be absolutely massive, and are a hugely structural component. That said, a 20mm lip stuck to the bottom of the front bumper without proper rake or rear extension, is not going to do that and is really only contributing to drag. So most splitters that you see on street cars and the likes are not making any downforce at all. If you cant stand on it, its not doing anything for you!
|
|
|
|
|
Para
|
|
|
Group: Forum Members
Posts: 8,
Visits: 20
|
+x+xHi Guys, First of all, thank you to everyone for getting back back....much appreciated. I realise that the splitter itself does not actually create downforce (unlike an airfoil). All it does is to increase the surface area over which high pressure can build up. The more high pressure there is above the splitter...and the more low pressure below the splitter, the greater the net downforce. Also, my understanding is that splitter function is also very sensitive to ride height. The lower the car is to the ground the greater suction that will be created by the ground effects, hence the reason why the splitter is located at the lowest possible point. However if the splitter is too close to the ground it will stall, producing less downforce and more drag because air cannot flow through the bottom part of the splitter, so the speed of the flow there will decrease, increasing the pressure. I read somewhere that this sensitivity can be reduced by designing anhedral shaped splitter. The idea being that in the case that the car touches the ground, part of the splitter will continue to function and hence create downforce. So yes, i understand there is no one answer without CFD. The splitter will be unique to the vehicle it is being designed for...as frontal are, stagnation point etc are all different on different vehicle types... But i was quite surprised to read that splitters can generate between 300-400 kg of load....astonishing ! Thanks once again everyone...much appreciated Splitters do create downforce, just not as much as an airfoil. The main function of a splitter is to reduce the amount of air going underneath the car. As with all aero structures, the high pressure zone on top of the structure contributes very little to the negative lift being created, it is all about that low pressure zone on the bottom that does all the work. But the splitters role is much more important than just that; not only does it reduce positive lift by reducing the volume of air underneath the car, but by doing so it improves the performance of other aero components like any canards or front wings, side skirts, rear wing, rear diffuser if there is one, etc. So the net benefit can be huge because not only does the splitter itself produce negative lift, but it also let's the entire aero package produce more negative lift. They can actually produce significantly more than 400kg, mine is a relatively simple design. The splitter/front wing combinations on cars at the pointy end of Time Attack are making more than 800-1000kg of negative lift - to put that in perspective, it means you should be able to park a small car on top of the splitter and not see any deflection... So they can be absolutely massive, and are a hugely structural component. That said, a 20mm lip stuck to the bottom of the front bumper without proper rake or rear extension, is not going to do that and is really only contributing to drag. So most splitters that you see on street cars and the likes are not making any downforce at all. If you cant stand on it, its not doing anything for you! Hi Hanaldo, Thanks for that. Indeed those are huge loads. However if you look at data from passenger cars modified into track cars, you will see that no such vehicle capable of generating more than about 1.4g centripetal acceleration. I can only think this is due to unbalanced load as it difficult to get comparable loads at the back of the car without substantial aero bits such as diffusers and matching rear wings to ensure non turbulent return of the low pressure flow back up to ambient. On the contrary a proper race car generates half of it’s downforce by ground effects alone (flat bottom and diffusers….the Venturi effect) so a passenger car is never going to get into the 2.5g lateral acceleration as in a Radical of similar. Incidentally, has anybody modelled a front splitter with an aerofoil cross-section and noted the effects?...although this may not be work that well… as an aerofoil needs smooth flow over both surfaces to be effective….given that it is mounted on the front of a car where there is a massive stagnation point….so that may be pointless. Anyway the reason for the original post was to gauge what sort of loads we can get from a splitter so that I could work out the loads that the connecting rods and attachments would be subjected to….attached is an example showing a 90 kg downforce and it’s effects on attachments etc For this I have assumed that the 90 kg (198 lb) force will be evenly distributed along the splitter length. We can then model this force acting at a single point at the centre of the splitter and treat the whole set up as a framework that has external forces acting on it. From a framework perspective, the rods and the splitter itself carry out one of two operations: These can stop the framework from collapsing inwards by exerting an outward force, or THRUST….ie acting as a STRUT or prevent the joints from flying apart by exerting an inward pull (TENSION) at each end…acting as a TIE. The calculations show the thrust and tension loads on the rods and the retaining attachments. I solved for the various loads acting through the system simply by taking moments about appropriate points and resolving vertical and horizontal components of all the forces.  
|
|
|
|