Formula 1 Car Vortices

The damp weather in US Grand Prix gave us a great chance to see some ‘aero porn’. Overnight everyone’s talking about the Y250 vortex as something magical that again Red Bull managed better than others. However Y250 vortex is not a new concept – check out Scarbs post back in 2011 and SomersF1 update after Austin. Here I’m going to introduce some basic principles on vortices and explain why Y250 vortex is important. This would contain some text book material for engineering students but hopefully it will be helpful for people with general interest in aerodynamics.

Wing Tip Vortices

Let’s start with a classic textbook picture of wing tip vortices…

trailing-vortex
Schematic description of wing tip vortices

Wing tip vortices are formed because of the pressure difference between the  top and bottom of the wing. For a wing generating lift, there’s high pressure at the bottom, low pressure at the top. So at the wing tip, the high pressure air below the wing tends to roll up to the low pressure region above the wing, forming two tip vortices running off trailing edge. This would subsequently cause a downwash in the middle of the span, which bends the air down as it comes off the wing. Recall that AoA is the angle between flow path and chord line, as the downwash bends the flow, effective AoA is reduced so that lift is reduced. It would also introduce a drag term called vortex drag, which is proportional to the lift and inversely proportional to aspect ratio.

On a formula 1 car, wing tip vortices can be often seen at the rear wing. However, the race car world is somehow an inversion of aeronautical world, whereby downforce and ‘upwash’ is generated.

Vortices coming off Ferrari rear wing
Vortices coming off Ferrari rear wing (Source: Suttton Image)

Vortex Lift

While wing tip vortices are associated with loss of lift, vortices can be used to generate lift as well. A typical case here is slender delta wings, where lift is generated from two strong leading edge vortices forming along the sharp edges. The high speed vortices reduce pressure above the wing based on Bernoulli equation so that more lift is generated from a suction effect. The vortex lift idea can also be applied to race cars on some plate components to add downforce.

Delta Wing Vortices
Delta wing vortices
delta wing cp
Delta wing pressure distribution (suction effect at the tip)

Vortices on F1 Cars

Here is a screenshot from one of the Sauber tech videos – Tech Bites: CFD – side wind, spinning car – Sauber F1 Team

Sauber CFD modelling of vorticity on F1 car
Sauber CFD modelling of vorticity on F1 car

The picture here shows vorticity in the air as the car heads towards wind coming from left. Highlighted by red regions, there is high vorticity flow coming off front wing, mirror, airbox, exhaust and rear wing/diffuser. There is highly turbulent, not necessarily vortex flow coming off front and rear wheels. The famous Y250 vortex sits in the middle 250mm from centreline, governing flow towards rear of the car. There are also vortices from front wing cascades/ auxiliary wings hanging from the endplates, which manages flow above the wheel. The endplates, correspondingly, guide the airflow outbound around the wheel. With regulation change in 2014, front wing will be 75mm narrower on each sides, which would make it tricker to direct the flow around. However there’s no change related to the Y250 vortex so we can still see them next year.

Y250 Vortex

The Y250 vortex, similarly to wing tip vortices is generated because of a pressure difference, in this case between the neutral middle section (250mm from centreline) and the rest of the wing. It is very important for controlling flow approaching leading edge of the floor. Here in analogy with the delta wing vortex lift, the Y250 vortex can potentially extract air at the edge of the floor, therefore producing a suction effect that improves aerodynamics efficiency in this area. On the other hand, the Y250 vortex may also have a benefit on managing front wheel wake by pushing it away from the car.

Comparison of Y250 vortices coming of Red Bull and Ferrari
Comparison of Y250 vortex coming of Red Bull and Ferrari

Skysports has edited a good video comparing Y250 coming of RBR and Ferrari and talking about how well-controlled the RBR vortices is. However ‘well-controlled’ is never a good word for engineers to use. To estimate vortices, we need to use some parameters like vortex core position, vortex strength and cleanness. These parameters are what the design of complex flaps/cascades is based on. I can’t agree with the Skysports’ explanation of vortices travelling down over sidepots as the vortex strength cannot be strong enough to affect area so far downstream. Nevertheless the Y250 vortex do interact with different parts of the car, which requires careful consideration in designing of front wing, floor and turning vanes, etc.

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British Grand Prix Aero Analysis

F1 came back to its home in England with a great race taken place at Silverstone. Most teams have made noticeable upgrades on their cars, although tyre issue caught all the attention by the end of the day. Pirelli states that “a series of different causes led to the failures, including rear tyres mounted the wrong way around, low tyre pressures, extreme camber angles and high kerbs”. Although they could blame a combination of various causes, it’s really the time for them to take a serious look at those tyres they made.

In aerodynamics perspective, Lotus brought out the DRD systems that they’ve been developing since last year, Ferrari modified both their front and rear wing, and Red Bull made some change to their diffuser.

Lotus DRD
I have written about the DRD on Lotus E20 last year – Lotus E20 Drag Reduction Device. DRD is basically a passive air switch that operates by air velocity. Several teams have tried out this device including Red Bull, Mercedes and Sauber. However Lotus was the only one who insisted and has a possibly €12.5m budget on it. Lotus E21 is designed with DRD inlets, however it was mostly closed during the season. In Silverstone, DRD was put on Raikkonen’s car while kept closed on Grosjean’s car. Lotus have also made different modifications to the car body based on DRD.

Lotus E21 without DRD
Lotus E21 without DRD
Lotus E21 with DRD
Lotus E21 with DRD

There is an obvious periscope shape outlet on Kimi’s car with DRD fitted. Romain’s car however, without DRD, features a slimmer body with shark fin on it. And correspondingly a slimmer monkey seat was used on Romain’s car. The slimmer bodywork may improve the performance of diffuser and rear wing without DRD.

Lotus E21 Monkey Seat Variation with/without DRD
Lotus E21 Monkey Seat Variation with/without DRD

The different setup on two cars would enable Lotus to carry out direct comparison between the package with DRD and a whole new package without DRD. And hopefully they’ve got some valuable data from Silverstone so that we can see more of their development on the drag reduction device.

Ferrari’s Front and Rear Wing

Ferrari added a new cascade (green arrow below) on their front wing, which improves the airflow rearward by directing more air over the suspension into the sidepod.

Ferrari's Front WIng at Silverstone
Ferrari’s Front Wing at Silverstone

At the rear end, they added a vertical slot on the side of the rear wing endplate. This could potentially help dealing with the wake come off the rear wheel.

Ferrari's Rear Wing at Silverstone
Ferrari’s Rear Wing at Silverstone

Red Bull

Red Bull modified their diffuser with some additional slotted strakes to seek for more downforce.

Red Bull Diffuser at Silverstone
Red Bull Diffuser at Silverstone

Force India

Another obvious update is from Force India, who added some vortex generators on the front wing as Red Bull did in Canada. They would create more guidance to the air and re-energise the flow to make it better attached to the surface.

Force India - Small vortex generators on the wing
Force India – Small vortex generators on the wing

*Pictures from AMuS

Monza Low Downforce Setup

There is no circuit in F1 that looks simpler than Monza, a typical circuit dominated by long straights. In response to this, downforce is not that favourable here, on the contrary, low downforce setup aiming to reduce drag is the key to win the race.

Front Wing

Front wing is not often changed significantly from race to race as it is the part that determines downstream flow, therefore affecting the design of all following parts. However, for Monza, most teams have adjust their front wing by removing cascades, lower down AoA or reducing chord length.

McLaren has removed all the outer cascades and replaced their 2-section upper flap with one single upper flap.

Source: Formula1.com

McLaren Front Wing Change from Spa to Monza

Source: Sutton Image

McLaren Front Wing in Monza

Another noticeable change on front wing is from Ferrari, who has removed all the small upper cascades and made several changes to the flaps and endplates profile.

Source: Formula1.com

Ferrari Front Wing Comparison from Spa to Monza

Rear Wing

The rear wing design is closely related to exhaust/cooling, sidepod and rear diffuser. Teams have different adjustments based on their cars. Major methods to reduce downforce/drag in Monza includes slimming rear wings, introducing V-shape profile and use gurney flap on diffusers.

With Massa hitting 3rd in qualifying and Alonso finishing on podium from 10th start, Ferrari proved their speed in Monza. They modified the beam wing with a V-cut profile and slimmed outer span, fit gurneys along the trailing edge of the diffuser, and quite uniquely, added flaps above and below the diffuser. The V-cut supplies the car with enough downforce at corners with low downforce setup for straights. Use of gurneys and additional flaps help regulating the flow, correspondingly reducing drag.

farrari monza rear design
Source: ScarbsF1

Ferrari Rear Design for Monza

Similar to Ferrari, Red Bull also used a V-shaped beam wing, in combination with a rear wing of very small AoA. They’re among the teams that suffer the most from the ban of exhaust blown diffuser this year and quite obviously still haven’t found a ideal design for their underbody rear part. In Monza, they’ve also added an additional tier to the diffuser gurneys, though that didn’t seem to give them clear benefit.

Red Bull V-shaped Beam Wing

Source: Sutton Image

Additional Tier on RB8 Diffuser Gurney

As the low downforce rear wing has clearly given Button huge advantage in Spa, McLaren is quite happy using this setup for both cars in Monza with a few modifications to further reduce drag. Instead of slimming the wing as other teams, McLaren cleverly introduced a curved profile at the tip of their beam wing to smooth air flow.

Source: ScarbsF1

McLaren Rear Design for Monza – Note Curved Tips on Beam Wing

Lotus has drawn wide attention because of their so-called DDRS system – It’s still quite confusing how people call this device though. Anyway we’re not seeing it until Singapore since Monza is not a preferable circuit for this system. In Monza, Lotus runs on the shortest chord rear wing, which makes it look quite tiny from behind.

Source: F1 Technical

Lotus Rear Design for Monza

Check this post from ScrabsF1 for more detailed analysis of rear end design based on each car relating exhaust/cooling/sidepod to rear wing assembly.

McLaren Spa Updates

With a dominant win from Jenson Button in Spa, McLaren has demonstrated their aerodynamic excellence after two successional win. It’s shame that Lewis was crashed out at the beginning of race, leaving us curious about how those two differently set-up cars would actually do in the race. Instead of seeing huge impact from DDRS, what drew attention is actually McLaren’s rear wing adjustment and sidepod airflow conditioner, while their DDRS remains a mystery.

High Downforce vs Low Downforce – Hamilton’s Deleted Tweets

The hottest topic outside the track is definitely Hamilton’s tweets during the weekend. Three of them get delated in two days, among those ghost tweets, the most famous one is the telemetry chart of the two McLaren cars.

Source: F1Technical

McLaren Overlaid Telemetry Chart

It looks a bit completed as there are lots of information merged into one single chart. However, telemetry chart is simple to read when you know which property each line represents. As a common approach of F1 data collection and analysis, a telemetry chart in fact can’t leak out too much serious information. Here is an example of a telemetry chart from 2010, which as an coincidence, is from Lewis Hamilton again. From the top to the bottom, properties plotted on the y-axis are speed, engine revolutions/gear, throttle/brake usage, lateral/longitudinal G force.

Telemetry chart in Bahrain 2010

As we can guess in Lewis’ leaking out chart, the most fluctuated lines represent his speed and Jenson’s. It’s obvious that on straights, Lewis’ car accelerates slower and has lower top speed compared to Jenson’s. Basically Jenson’s car has a low downforce configuration while Lewis get a high downforce one. The picture below combines Lewis’ and Jenson’s car during qualifying – with lower angle of attack, Jenson’s car has reduced downforce and drag, which gives him huge advantage on straights.

Source: Sutton Image

Comparison between Jenson’s and Lewis’ Car During Qualifying

However, this doesn’t mean lower downforce is always better on high speed circuits like Spa – downforce at severe corners should always be considered; weather condition has vast impact as well. Nevertheless, McLaren has clearly found the best compromise this weekend for Jenson.

McLaren New Sidepod Airflow Conditioner

The most evident change on MP4-27 in Spa is these airflow conditioners added on top of the sidepods.

McLaren Sidepod Airflow Conditioner

Now the airflow conditioner is connected to the cockpit and runs all the way over the sidepod. It’s expected to further regulating flow around the sidepod and towards the exhaust channel. In Hungry before the summer break, McLaren was using 3 fins on top of the sidepod as vortex generator to improve airflow.

McLaren Sidepod in Hungry

These fins would help smoothing the air by generating controlled vortex flow:

Effect of Vortex Generator

Although vortex generator is a good idea, McLaren seems to find those L-shaped covers over the sidepod working better in controlling the air.

Curiosities – Flexible Front Wing? DDRS?

An interesting picture of McLaren front wing in Spa indicates that it’s flattened during the race:

McLaren Flattened Front Wing

There was suspicion from ScarbsF1 that McLaren use flexible front wing to achieve better aero balance last year in Valencia – McLaren European GP Wing Movement. However although the suspicion was broadly argued, this picture still arise doubts on McLaren tricking on their front wing. Theoretically flexible front wing uses a joint rather than a rigid structure that allows the wing to tilt slightly backwards at high speed. The reduction of angle of attack would reduce front downforce/drag so that it corresponds to the reduction of rear downforce when DRS is activated. Because of the increasing limitation on rear part design, McLaren has actually focused a lot on the front part this season, as reflected in their lifted nosecone earlier this season.

Source: F1Technical

McLaren Nosecone Update

Although the so-called McLaren DDRS was buzzing before the race, there was no clear technical sources leaking out regarding this part. Some says there’re strange bumps on the rear endplates, which could mount in tubes like the Mercedes DDRS. However we still need to wait for more information to make judgement.

Bumps in McLaren Endplate

Besides McLaren, most teams have noticeable updates in Spa. There were more information of Lotus DDRS leaking out though it was not used in this race and is expected to be used in Japan Grand Prix. Also closed cockpit looks favourable in the future considering the huge crash in this race. These topics are hopefully covered in my future posts.