Following Lotus’ use of DRD in British Grand Prix, Mercedes tested their updated DRD system in Germany GP practice. The basic idea of Mercedes DRD is similar to that of Lotus, although the mechanism for turning on/off the air switch might be different.
Instead of having two ears besides the airbox as Lotus did, Mercedes has two additional inlets at the back of airbox. This is easily fitted as Mercedes has integrated some removable design to their bodywork around roll hoop this season. The combination of a big and a small inlet may act as the control system for the air switch.
In terms of outlet, there are two outlets with the upper one below the main plain of the rear wing and lower one below the monkey seat/ beam wing. Above a certain high speed, such as long straights and high speed corners where less downforce is needed, the upper outlet switches on. The air blowing out under the rear wing disturbs the flow and therefore stall the wing for less downforce and drag. This would give an extra boost on the speed of the car.
Another noticeable detail is that both Lotus and Mercedes now have an extra small outlet below the rear wing. This is used to let out leaked air under the rear wing when the upper outlet is not supposed to be switched on.
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.
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.
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.
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.
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.
Red Bull modified their diffuser with some additional slotted strakes to seek for more downforce.
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.
There’re quite a few comprehensive analysis on Lotus E20 Drag Reduction Device, however I’m trying here to put on a simple explanation to the system so that everyone can understand.
Lotus DRD, we call it DRD instead of DDRS as this system is nothing related to DRS, although the function is the same – reducing drag. It’s completely passively controlled by car speed to achieve drag reduction. The benefit of isolating from DRS (compared to the Mercedes DDRS system) is that it’s not limited use to the specific DRS area on the circuits and does not have a delay over activation – the Mercedes DDRS needs to go all the way from the rear wing to the front wing, causing delay.
The whole structure of this device looks like this:
It basically contains two inlets – the airbox and the ‘ears’ and two outlets – the periscope/L duct and the mini diffuser/monkey seat. I’m not going through the internal ducting as it’s purely speculation going into this area, for which I’m not very sure about.
Besides the normal airbox inlet, Lotus places two additional inlets along each side of it like two ears. Those ears help directing excess flow into the rear part, thus reducing turbulence from air spillage and help generating more downforce when DRD is not activated. In addition, it’s suspected that the air that goes into the ears and airbox subsequently flows into different route through internal ducting to the rear outlets. However, as I’ve mentioned, I’m not going into detail on this.
Airbox and ‘Ears’ On Lotus E20 Airbox
There are two ways that the air can goes out of the car, either through the mini diffuser or the L duct. The path that the air goes depends on the speed, or air pressure.In a relatively low speed, i.e. off throttle condition, air mainly goes through the mini diffuser since higher pressure is required to push air through the narrow L duct. As the critical speed reaches, air can pass into the L duct then exit through 2 slots on each side of the duct, causing stall on the main plain of rear wing.
The structure of both the mini diffuser and the L duct is quite tricky if you look into the detail.
For the mini diffuser, there’s actually a small internal part inside which aids downforce generation when device is not activated.
Lotus E20 Mini Diffuser/ Monkey Seat Detail
The L duct is very narrow to ensure that it’s only activated when a certain speed is reached, those tiny air exiting slots make huge difference to the airflow pattern – cause flow separation to stall the wing. The FlowViz picture can clearly show this effect:
Lotus E20 Flow Viz Interpretation
Basically Flow Visualization paint is a special liquid sprayed to the car in order to study airflow on the surface. When the car runs, flow pattern is recorded as the paint redistribute due to the air goes over. So as can be seen in the Lotus Flow Viz illustration, there’s a V-shape pattern beneath the main rear plain right in the middle at the exit of the L duct, indicating flow separation, i.e. drag reduction. Also those 3-5 cm slots are shown clearly once zooming in to this area:
Lotus E20 L duct/ Periscope Slots Detail
The device need to be adjusted from race to race to modify the speed of activation, mainly by modifying the cross section of the mini diffuser and the L duct.
So as Mercedes came up with the intelligent DDRS which is activated by DRS, Lotus brought out a entirely passive system DRD. However, neither of the systems has given distinctive advantage to their cars. Regardless of that, it’s still a very clever idea that may inspire engineers for more innovation.