Multi element airfoils (rear wing)

[Deano990]

I am doing a project at uni on rear wing shapes for formula 1 cars. I was wondering if you could help me with information on the reasons for using multi element airfoils, and any ideas on how 2 construct one on a smaller scale. It would also be useful if anyone had any ideas on a method to find the optimum angle of the ing to be set at?

thanks

[syguy]

Welcome to the forum Deano990,

In motor racing, such as Formula 1, there are limited volumes in which to position airfoils, especially at the rear. It would be difficult to fit a single optimal airfoil within the rear F1 rule mandated box. Instead, fitting multi-element airfoils is a better compromise in generating the required downforce.

Downforce in F1 is always more important than drag, so the extra drag associated with multi-element airfoils is something for the engine developers to counter with more horsepower.

Quote from http://www.symscape.com/blog/multi-element-airfoils

[Jersey Tom]

I would think a big thing is airfoil efficiency. If you look at tables of lift and drag coefficients for a given airfoil profile at varying Reynolds numbers and AoA's, the baseline number is given for an aspect ratio of infinity (ie there are no 'end' effects.. airfoil is infinitely wide). Obviously, this isn't practical to build! The lower the aspect ratio, the less efficient the airfoil will be (cL will be further away from the ideal scenario).

So for a given airfoil plan area, you could have one element with say an aspect ratio of 3.. or you could have 3 airfoils each with an aspect ratio of 9. Higher overall efficiency, more downforce for the least drag.

At least that's my understanding, but I'm not an aerodynamicist by trade..

[ReubenG]

Have a look at separation of the air flow from the wing surface - for any given profile there will be an angle of attack at which the flow separates from the wing surface and lift/downforce decreases dramatically (eventually leading to stalling). Beyond this angle of attack the aerofoil isn't useful. Given the space that and F1 wing must fit into, multiple smaller elements can be run at larger AoA (generating more downforce), than a single large element.

[MrT]

The purpose of multi element aerofoils is to re-energise the boundary layer on the lower surface to prevent boundary layer seperation which leads to total seperation of the flow and stalling. This is achieved by allowing air to pass through the slots between elements. By doing this you can run stacked elements with progressivly larger angles of attack without seperation and them stalling.

Mr T