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.