As per the title, I'm trying to learn more about the so called "vortex sealing". By that I mean using vortex to seal off the floor/wings to avoid leaking out low pressure air.
From a fluid-dynamic point of view, how does that actually work (if it does)? Does the vortex being clockwise or counter-clockwise influence its effect?
Let's consider the SF-90H and its curled front wing footplate for example: I'd imagine it creates a vortex which gets trapped in the little curled section. What is its scope, does it effectively "seal" the low pressure zone under the front wing? Wouldn't the vortex direction draw more air under the wing?
If you have any book/resources feel free to share them!
Thanks in advance
As per the title, I'm trying to learn more about the so called "vortex sealing". By that I mean using vortex to seal off the floor/wings to avoid leaking out low pressure air.
From a fluid-dynamic point of view, how does that actually work (if it does)? Does the vortex being clockwise or counter-clockwise influence its effect?
Let's consider the SF-90H and its curled front wing footplate for example: I'd imagine it creates a vortex which gets trapped in the little curled section. What is its scope, does it effectively "seal" the low pressure zone under the front wing? Wouldn't the vortex direction draw more air under the wing?
If you have any book/resources feel free to share them!
Thanks in advance
A vortex is a low pressure core and a high pressure wall. You can understand how vortices work if you understand the vortex ring. The spinning air pushes outward due to centrifugal force, lowering the pressure at the center. The static high pressure air tries to work against that centrifugal force by moving towards the low pressure. Because angular momentum is conserved, the air seeks the center via a spiral.
A vortex is a wall of air, and the direction of rotation has a kinetic component. For example, if you have a lateral counter clockwise rotating vortex, If you touch the vortex wall with your right hand, you'll feel an upwashing airflow, if you touch it with your left hand you'll feel a downwashing airflow.
I feel that "sealing" is a loaded term, I feel more accurate is to say separation, but then aero guys get confused because they use separation in a completely different way. You don't seal stuff with vortices, you separate high pressure from low pressure because the wall of the vortex is high pressure it repels high pressure air from moving across it. As long as the vortex maintains its integrity.
As per the title, I'm trying to learn more about the so called "vortex sealing". By that I mean using vortex to seal off the floor/wings to avoid leaking out low pressure air.
From a fluid-dynamic point of view, how does that actually work (if it does)? Does the vortex being clockwise or counter-clockwise influence its effect?
Let's consider the SF-90H and its curled front wing footplate for example: I'd imagine it creates a vortex which gets trapped in the little curled section. What is its scope, does it effectively "seal" the low pressure zone under the front wing? Wouldn't the vortex direction draw more air under the wing?
If you have any book/resources feel free to share them!
Thanks in advance
All you need to know with regards to vortex sealing, is that it is exactly what you'd think when you read the word "seal". For racing cars, this usually involves you creating a vortex in such a way, that ambient air cannot "get past the vortex" to reach a region of lower pressure. Often you'll hear of people sealing the underfloor or something like that... all that means, is we want to create a vortex which travels in such a way, that it follows the outer shaping of the floor, and stops the freestream air from being drawn into the underfloor aerodynamics, thus increasing the pressure, and reducing downforce.
It's quite difficult to get these to work, correctly, and you also need to be cognisant of their potential to "burst". Vortex bursting is one of those things that is never really clearly explained with exactness in my opinion... Based on my understanding of it, if I was to simplify it down as much as I could, then "once the rate of spiralling air exceeds that of a critical ratio to the (axial) flow speed that the vortex is travelling through the air at, the vortex will burst"... i.e. once you spin too fast relative to how fast you move forward, you blow up. Or something like that anyways I remember some theory somewhere that described the structure of the core of a vortex as a rotating inviscid ring, which had an inner viscous centre that was surrounded by the ring... something to do with the rate of the external flow, the rotational speed of that core-ring, and the velocity of that innermost core all somehow linked to vortex burst... But I digress... here's a really good video showing you the phenomenon:
To your question about footplates, not every vortex need be created by air rolling from the high pressure side of a wing to the lower... because the suction side of a wing generates a much larger delta pressure to ambient than that of the pressure side, you can also have ambient air being drawn in to the lower pressure suction side of a wing. That is, from the air just outside the endplate, under the footplate, and then under the front wing of the F1 car. What the footplate does, is increase the distance which that air needs to travel, before it can then be swept up into the main FW tunnel vortex (that blasts the front wheel to shut down some of the vortices that "it" generates). Because that air has to travel further, simply put, it's pressure drops even more than it would without the footplate. Having a curved footplate creates a mini-vortex in there that swirls around, which then aids in amplifying that same effect even more. In the image below, air would travel from the green, under the footplate, under that mini-vortex, under the corner vortex, and then be swept up into the main tunnel vortex (not shown).
This edge vortex under the front wing generates local "upwash", which affects downforce by reducing the local angle of attack. When you have vortex breakdown, however, you get reduced upwash, and an increase in effective angle of attack. As for your question about which direction they should go, the answer is which ever promotes outwash more; for example, on the left side of the car, you want a vortex rotating clockwise when looking from the back, to the front of the car, so that it's spiral motion counters that of the ambient air's desired path.
Hope this helps.
"And here you will stay, Gandalf the Grey, and rest from journeys. For I am Saruman the Wise, Saruman the Ring-maker, Saruman of Many Colours!"
I remember some theory somewhere that described the structure of the core of a vortex as a rotating inviscid ring, which had an inner viscous centre that was surrounded by the ring... something to do with the rate of the external flow, the rotational speed of that core-ring, and the velocity of that innermost core all somehow linked to vortex burst... But I digress... here's a really good video showing you the phenomenon: