How Do Vortices Seal the Floor of an F1 Car?

The most well known and arguably important vortex in the flow field of an F1 car is the y250 vortex. This article will use CFD analysis of a front wing to help visualise this and explain how it works and why it’s useful in more detail.

The y250 vortex forms on the inner front wing tips, where a counter rotating vortex pair form off of each side of the front wing. The name is a result of the vortex forming 250mm from the centre line of the car, this is because the rules mandate a neutral section in this area.

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Front wing neutral section

Before going any further it will be useful to define a vortex, it is simply an area of the flow rotating about a single axis. Vortices can be characterised by circulation or vorticity. They are both measures of rotation in a flow, however vorticity defines the rotation about a specific point so gives a more microscopic view.

Circulation: \Gamma =\oint U\cdot dl

Vorticity: \omega =\nabla \times U

Relationship between the two: \Gamma =\iint \omega \cdot dS

The vortex then moves downstream to the bargeboards. Here the bargeboards direct the vortex towards the edge of the floor. There are also lots of smaller vanes all of which produce small vortices co-rotating with the y250.

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Complex bargeboard vanes on the Haas

What are the benefits of this over one large vane producing a larger vortex? The benefit of this is that a stronger vortex can be obtained when multiple co-rotating vortices merge. When two vortices merge the centres drift towards each other and the angular velocities of the two remain almost constant. Once merged the vorticity of the resulting vortex is a result of the vorticity of the properties of the two that merged, as shown below.

\omega =\left( \dfrac {\Gamma _{1}}{\pi a,2}e^{-\dfrac {r}{a^{2}_{1}}}\right) +\left( \dfrac {\Gamma _{2}}{\pi a^{2}_{2}}e^{-\dfrac {r}{a^{2}_{2}}}\right)

After multiple small vortices have merged with the y250, it results in a stronger vortex than would be possible simply be using the y250 or a combination of the y250 and a single bargeboard vortex. This better seals the floor.

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CFD pressure slice showing how pressure increseases towards the edge of the floor

The better the teams can seal the floor the more downforce they will produce. They use complex aerodynamic surfaces to achieve this now that skirts, which are more effective at this, have been banned. This strong vortex at the edge of the floor seals the floor because of the rotating and therefore angular momentum it possesses. Momentum transfer between fluid layers (from the vortex to surrounding flow) draws the air away from the floor, preventing it from being sucked under the floor by the low pressure. If this air was allowed to enter the under floor area, it would increase the dynamic pressure and reduce the downforce generated. If the air drawn under the car at the edges is turbulent is can also cause flow seperation in the diffuser, further affecting performnace.

References

Josserand, C. and Rossi, M. (2007). The merging of two co-rotating vortices: a numerical study. European Journal of Mechanics – B/Fluids, 26(6), pp.779-794.

Meunier, P., Le Dizès, S. and Leweke, T. (2005). Physics of vortex merging. Comptes Rendus Physique, 6(4-5), pp.431-450.

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