Red Bull: Exhaust Driven Diffuser

Red Bull surprised everyone with their revised car that appeared on the last day of testing.  As the car sported revised exhaust systems with a low exit that aims the exhausts over the diffuser.  While exhaust driven diffusers were popular in the nineties before periscope exhausts became the norm, to have the exhaust play over the top of the diffuser is a relative novelty.  However the Newey designed solution on the RB6 is a little more complicated than it first appeared.  In one shot we can see the upper deck of the diffuser features a window (Arrowed) to allow the exhaust gas to pass inside the diffuser, rather than solely over it.  With the aim that the high speed exhaust gas will drive more flow through the diffuser to increase downforce.

One criticism aimed at exhaust driven diffuser is their sensitivity to the throttle position and hence the speed of the flow through the exhaust and in turn the amount of downforce it adds to the diffuser.  This issue was mainly related to when the exhausts   were placed right on the kickline between the floor and diffuser, thus their effect on downforce was much more pronounced.  Placing the diffuser further up the diffuser reduced this sensitivity.  Newey knows a thing or two about blown diffusers, the McLarens retained diffuser exhausts exits all the way to the MP4-17, even then the switch to periscope exhausts was largely driven by other  engine packaging factors.  Even the still born MP4-18 aimed to have diffuser exiting exhausts.  The placement of the exhaust some way upstream of the diffuser exit should allow a better compromise between downforce and sensitivity.

15 thoughts on “Red Bull: Exhaust Driven Diffuser

  1. I suspect this is designed to offset some of the compromises made to the diffuser by the packaging required for the pull-rod suspension. A good idea, but maybe one not necessitated by the other teams due to their push-rod setup.

    • No the ‘fake’ stickers were on top of the sidepods, the low placed exhausts were real. You can see the shading of the false exhaust sticker in between the two wishbones in the top right of the picture.

  2. Is it fair to say that flow separation would start farthest back in the diffuser, and therefor adding energy to the flow at this point could help when detachment is imminent, but without disrupting upstream flow when flow conditions are less marginal?

    I’m just thinking of normal boundary layer thickening, but I don’t know if flow through diffusers is limited by separation towards the back, or if they start to separate elsewhere.

  3. Excellent post Mr. Craig Scarborough, i have one technical question? with this hot air coming out of the RB6 trough the diffuser this can’t cause more turbulence to any car behind??

    Thanks in advance for your answer, looking forward to it!

      • thanks for your answer, i was thinking more because of the exhaust in the RB6 are low in the car and maybe having the heat coming directly into the diffuser and not directly to the rear wind works better creating more downforce to the diffuser and not to the rear wind!

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  6. Nice post Craig.
    Is it possible that another reason for the exhaust vent positioning is to allow more control over tyre temperature? Could a similar fluidic switching effect (either passive or active) as used to control the operation of the blown slot on, for example the Mclaren, also be channeled to work to switch the direction of the exhaust outlet? Perhaps at low car and engine speed (pre-quali run, pre-grid start) the path of the exhaust could be used to increase tyre temperature, but at higher speed be channeled in a different direction, such as into/over diffuser or to direct flow outside of the rear tyres?

    I know, lots of what ifs….

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