Aerodynamics of a racecar undertray

[Renegade]

This is a question about aerodynamics & lift/downforce created by a change in the undertray design of an IRL car..

The IRL racing series announced yesterday a number of changes to car design in order to keep cars from lifting off the ground, as they were for some unknown reason especially prone to do last year. One of the new changes is to the undertray of the car which was essentially 'flat' last year:

The plate(undertray) will now curve from its center up toward the wheels on each side, so that the outside edges are 10 mm higher than the center. The curved skid plate effectively raises ride height 10 mm, and serves two purposes, according to Barnhart: It reduces downforce and improves yaw stability. It does that by channeling air out the other side of the bottom of the car if it skids, rather than allowing the air to build up and thus create lift

.

Not sure that means too much to anyone, but basically the bottom of the car will be a *very-flat "V"* as you look at it from nose to tail.

Now imagine a car skidding sideways.
The diagram below is extremely crude & exaggerated(it is a curve in real life):

\______ _______/
_______V__________ <--flat ground
==> direction of air underneath car


My (non-physics-background)-thinking is that air encountered by the forward side of the undertray will get squeezed or "scooped" underneath and as it gets trapped towards the centreline the lowest(narrowest) point.
I would think this would create LIFT, the exact opposite of the desired affect.

Someone I was discussing this with mentioned aircraft wings & the Bernoulli prinicple, but an open-wheel racecar is not 'wing' shape when looking at it from the side!

Can someone explain how the airflow under a sideways-sliding car with a 'V' bottom would act?

 

[Cliff_J]

If the air is 'squeezed' so that more air is forced through a given space its velocity would increase. An increase in velocity would result in a drop in pressure.

Cliff

 

[ravenprp]

The aerodynamics of a racecar undertray are crucial for achieving optimal performance on the track. The undertray is responsible for generating downforce, which helps keep the car stable and grounded at high speeds. In the case of the IRL car, the changes to the undertray design are aimed at reducing lift and improving yaw stability.

The new curved undertray design creates a 'V' shape when viewed from the side, with the outside edges being 10 mm higher than the center. This design allows for better channeling of air underneath the car in the event of a skid, preventing the buildup of air and ultimately reducing lift.

To understand how this works, we can look at the Bernoulli principle, which states that as the speed of a fluid (in this case, air) increases, its pressure decreases. In the case of a sideways-sliding car with a 'V' bottom, the airflow underneath the car encounters the upward slope of the undertray first. This causes the air to speed up and create a low-pressure area, effectively pushing the car down and reducing lift.

Additionally, the curved undertray design also helps improve yaw stability. As the car turns, the outside wheels have a longer distance to travel than the inside wheels. This creates a difference in drag, which can cause the car to spin out of control. However, the 'V' shape of the undertray helps to equalize the drag and keep the car stable during turns.

In conclusion, the aerodynamics of a racecar undertray are complex and play a crucial role in the car's performance on the track. The new curved design of the IRL car's undertray is aimed at reducing lift and improving yaw stability, ultimately making the car safer and more efficient on the track.