Floor rules 2009+

[ringo]

I wonder if the curls also have to do with the body roll of the car and riding curbs?
Having the upward curls prevents the edge of the floor from coming too close to the ground when the car is in roll or when negotiating a curb. It has the little extra height to ensure the gap between the floor and car doesn't get too low at any time.

I aint no pro but i suspect if the curls are not of an airfoil shape but just a curled surface, the vertical area of the curls facing forward can add some drag and lift, and aft of that there can be flow separation over the top surface of the floor (due to the flow breaking over the edge of the curls) which is not good.
Mclaren did a good job by having an airfoil cross section.

[PlatinumZealot]

I think that floor design made less downforce as said before.

[Mystery Steve]

Feeding air underneath is just a way of making sure the air is energized to flow as fast as possible along the length of the car. I don't think the intention is to ram air under the floor. It's just to keep up the velocity.
In an ideal world there would be no boundary layer friction and no need to worry about friction losses, then less air is always better.

Exactly, unless you have the floor sealed off then you will have flow going under the car from the top side if you have a lower pressure on the bottom side (similar to wing tip vortices on aircraft). This flow is used to energize the boundary layer and reduce separation by generating vortices.

And from a quasi-1D perspective, "more air" is not necessarily a bad thing. The goal for reducing static pressure is achieved by increasing the velocity of the flow. If the cross-sectional area along most of the vehicle is nearly constant and since the flow isn't fast enough to consider compressibility, the only way to increase velocity is to increase mass flow.

That being said, ultimate downforce is not always the goal. It's all a balance of total downforce, drag, downforce distribution, pitch sensitivity, yaw sensitivity, roll sensitivity, etc. Yes, you do want a lot of downforce, but not at the expense of control.

[Balt23]

I would like to contend that these rolled edges of the floor are for "precisely" channeling the vortex that is rolling up around the edges of the floor. The edges are sculpted to deliver the vortex filament down the the edges of the floor. looking from the front view of the car with the vortex filaments perpendicular to your viewpoint, the vortex down the RHS of the car (LHS if your sitting in cockpit) will be counter-clockwise rotating vortex while the LHS vortex (RHS if sitting in cockpit) will be a clockwise rotating vortex. This will form an "invisible" skirt that will keep higher pressure air from migrating underneath the car along the sides.

Concerning feeding the diffuser, once you are past the throat, you would want to feed air into the diffuser to help in anyway possible with reducing the adverse pressure gradient. Recall that at the throat, the flow field has been accelerated to the maximum velocity, and also the lowest pressure. To prevent as much drag as possible and to increase the fluid mass passing through the C-D nozzle of the floor, you want to get the air out through the diffuser as fast as possible without separation while slowing the air down and bringing it back to ambient pressure. Brawn did some clever engineering by adding additional mass flow to the diffuser, something I'm still trying to figure out.

Please correct me or ask for clarification, I've just awoken from a Thanksgiving food coma and I'm still a little fuzzy.

[Mystery Steve]

I would like to contend that these rolled edges of the floor are for "precisely" channeling the vortex that is rolling up around the edges of the floor. The edges are sculpted to deliver the vortex filament down the the edges of the floor. looking from the front view of the car with the vortex filaments perpendicular to your viewpoint, the vortex down the RHS of the car (LHS if your sitting in cockpit) will be counter-clockwise rotating vortex while the LHS vortex (RHS if sitting in cockpit) will be a clockwise rotating vortex. This will form an "invisible" skirt that will keep higher pressure air from migrating underneath the car along the sides.

Assuming I've read that correctly, the vortices would be the other way around. The flow will go from on top to underneath, from high pressure to low pressure. This means from the front view the vortex on the left-side will be counter-clockwise, and on the right-side will be clockwise. If you can get your hands on a copy of Race Car Aerodynamics by Joseph Katz, check out pages 203-208:

Because of the low pressure created inside these channels, the flow from the sides of the vehicle enters the channels from the sides, creating strong concentrated vortices [as shown in an image]. The vortices in turn keep the flow attached inside the tunnels, and actually stabilize the underbody flow.

[Balt23]

MS -

You are correct, the vortices would be opposite direction to what I indicated in my post. My apologies.

I think what I was trying to say is that the flip up at the edge of the floor acts as a vortex generator upstream of the diffuser section of the undertray. This vortex is started further upstream, before the vortex created by the migration of the higher to lower pressure has started. The upstream vortex will have a very low pressure core, lets assume lower than the air that has smoothly fed to the undertray, and so will take higher pressure air from both above and below the floor into its core and carry it downstream, preventing the higher pressure air from above the floor migrating under the body.

I can't see where migration of high pressure air into the low pressure air of the floor would be beneficial, except in the diffuser section. I want as low of pressure for as much planform underneath the car as possible to maximize downforce. What I think Dr. Katz is talking about is feeding air to the underbody tunnels leading to the diffuser. If this promotes attachment and stabilizes the flow (likely due to the additional kinetic energy?) than it would be very beneficial to let the higher pressure air mix with the low pressure air to improve diffuser efficiency, and thus the rest of the floor. BUT I would want to prevent this from happening until I was into the diffusing portion of my floor. That quote takes me back to why feeding freestream air to Brawn's DD diffuser helped them so much...

I do not have a copy of Race Car Aerodynamics (its on the christmas wish list). Currently most of my time is spent on subsonic, Low RE# planes to give some background.

Let me know if you think I'm crazy. I always appreciate it

[ringo]

I suppose the vortex rotation is dependent on which side of the floor has the highest pressure.
If it does prevent air from going under the sides, I get that, what gets a little complicated is when you are dealing with feeding the diffuser. How will it accomplish both things at the same time.
I read the book you are talking about but i still feel like I never got enough info, especially when it comes to these new devices that are being used nowadays.

[Balt23]

ringo-

What I am trying to say is that they are different and separated mechanisms and devices. Alright, yes there will be interaction among all the devices, but if we relax that view of things for a moment.

I was trying to say, in response to MS post, that since there is a higher pressure area above the floor (otherwise the floor would not be generating downforce due to pressure differential) than yes, the vortices are rotating in the directions that MS indicates. (Front view, CW on LHS, CCW on RHS). My argument is that no matter the direction of the vortex, the very low pressure core will be the lowest pressure area and will pull air into the core and carry it downstream without allowing higher pressure air to migrate under the floor.

In regards to the diffuser and the quote that MS brings in from Dr. Katz book, I think that Dr. Katz is talking about having vortices in the underbody tunnels that will prevent separation and the associated loss in efficiency. My argument is that the diffuser section is where you would WANT migration of higher pressure air into the diffuser to generate vortices in the tunnels and prevent separation of the airflow from the tunnels.

The "vortex barrier" would be more important in the area between the front and rear tires.

The rear of the car is where you would actually want the migration of air into the underbody.

I think we've been discussing two separate areas of the floor.

[ringo]

Ok i get what you are saying.
And to add to that the diffuser strakes near the throat help a lot in terms of vortex formation.

[axle]

Concerning feeding the diffuser, once you are past the throat, you would want to feed air into the diffuser to help in anyway possible with reducing the adverse pressure gradient. Recall that at the throat, the flow field has been accelerated to the maximum velocity, and also the lowest pressure. To prevent as much drag as possible and to increase the fluid mass passing through the C-D nozzle of the floor, you want to get the air out through the diffuser as fast as possible without separation while slowing the air down and bringing it back to ambient pressure. Brawn did some clever engineering by adding additional mass flow to the diffuser, something I'm still trying to figure out.

Please correct me or ask for clarification, I've just awoken from a Thanksgiving food coma and I'm still a little fuzzy.

So os this where the DDD makes its big impact? Feeding the main diffuser? Or is the DDD simply an additional pressure reducing device? Or both?