Saturday, October 13, 2012

Red Bull's double-DRS

Is there a connection between Red Bull's new double-DRS system, and their unique 'underpass' duct?

To recall, the underpass is a means of separating the 'coke-bottle' flow along the flank of the sidepod, from the exhaust-flow, sweeping down from the top of the sidepod. The coke-bottle flow feeds the starter-motor slot and the top surface of the diffuser's trailing edge, while the exhaust jet partially seals the side of the diffuser and increases the flow over the rear brake-duct assembly.

The underpass is fed by the flow along the flanks of the sidepods, which in turn is fed by the front-wing wake. By connecting the flow along the flanks of the sidepods to the low pressure area under the beam wing, the underpass not only assists with rear downforce, but also pulls the air faster over the front-wing.

Red Bull's double-DRS system purportedly stalls the central section of the beam wing, (although Craig Scarborough suggests that it is the tips of the beam-wing which are being stalled, in order to reduce the wing-tip vortex drag). 

The central part of the beam wing is the section which is pulling the air out of the underpass. Thus, if the beam wing stalls, then the underpass stalls, the flow along the flanks of the sidepods weakens, and front-wing downforce and drag are reduced.

The image above here illustrates how the front-wing streamlines on a generic open-wheeled race-car are the same streamlines which pass along the flanks of the sidepods, and thence between the rear wheels, (although there is no sidepod undercut or beam wing in this illustrative case, courtesy of the 2012 University of Southampton Racecar Aerodynamics MSc Group Design Project).

Red Bull introduced a smaller underpass inlet for the Korean Grand Prix, and if the double-DRS really does stall the centre of the beam wing, it would certainly make sense to change the underpass as well. Autosport's Mark Hughes comments in his Korean Grand Prix report that the changes to the sidepod area gave "more downforce and more diffuser stall." 

One can speculate then, that Red Bull's double-DRS is a system which reduces front-wing drag as well as helping to stall the beam wing and diffuser.


Barry said...

Thank for the insight. It's a smart and complete solution which the other teams will not be able to match before the end of the season.

Alex M-C. A. said...

Thanks for the report! Very useful!
Just one question, maybe easy... Maybe not.
How does the flow over the beam wing could help the front wing downforce?
Thanks again.

Gordon McCabe said...

The low pressure produced by the lower surface of the beam wing pulls on the flow down the flanks of the sidepods, which in turn, pulls on the flow over the front-wing. The faster the flow over a wing, the greater the downforce and the greater the drag.

David said...

And I guess this external system avoids the issues the Mercedes internal system has with delayed reattachment on the front wing?

Gordon McCabe said...

Indeed. If I'm right, then the front-wing won't actually be stalled by stalling the beam wing; rather, the drag will be reduced. Hence, there will be no re-attachment delay as such, but then the amount of front-wing drag shed by the system will be less as well.

corner1 said...

your fantastic work has been making the rounds of sites and tweets that i usually follow but i was surprised it was mentioned by leo parente on a youtube channel called drive.

Gordon McCabe said...

Cheers corner. Yes, I spotted that Youtube link!