Ben's Guide to VD: Lotus Finally Gets a Shot
The VD consists of the following components: two intakes (white, one on each side of the air box), a duct (blue), two duct vents (red), and a diffuser (green). The purpose of the system is to shed drag/downforce without any reliance on DRS whatsoever. This system operates at all times without any direct
influence from the driver, which is why it's passive by FIA standards.
Obviously, the forward motion of the car causes the intakes to draw in air. This causes static pressure to build within the duct. When the duct simply cannot accept any more pressure, excess pressure is bled through the lower vent (2) to move toward equilibrium. This action is assisted by a small diffuser that creates a low-pressure area behind the vent into which excess pressure readily migrates. The specific pressure threshold required to facilitate this action is adjustable according to the demands of the circuit.
Eventually the car reaches an airspeed in which the lower vent can no longer relieve static pressure within the duct, because that pressure is simply accumulating too quickly. When this happens, pressure is bled through the top vent (1) to move toward equilibrium. The specific pressure threshold required to facilitate this
action is also
adjustable according to the demands of the circuit.
Both of the aforementioned actions happen in quick succession.
It should be noted that two vents are required else the duct would very quickly become completely pressurized, and the VD would not work. The air box scoops would then be nothing more than air dam(n)s. Instead, when pressure is relieved by vent 2, the intended effect of the VD begins.
The air vented from vent 2 expands rapidly as it escapes the pressurized duct into the lower-pressure atmosphere behind the wing. The expanded air then deflects the laminar flow on the underside of the wing, which essentially is where downforce/drag is born. The specific flow targeted for deflection is that which passes over the trailing edge of the main plane. When this area of the wing is stalled it results in a substantial loss of downforce/drag, and that gives the car a higher top speed without any loss in useful downforce, because downforce effectively comes and goes as needed. As I've said before, this is a self-adjusting, stealth wing.
EDIT: It's also why I expect Lotus to have a blast at Spa and Monza. Maybe.