Saturday, January 19, 2013

Exhaust Comparison Using CFD

I carried out a CFD (Computational Fluid Dynamics) test to compare the two exhaust solutions that were used in the 2012 season, the McLaren style exhaust (1st Picture) and the Red Bull-Sauber Style exhaust (2nd Picture). There has been a lot of discussion about which one of the two solutions is the best and which solution teams will follow in 2013. 

I removed the drive shafts, suspension wishbones and pullrod, to keep the test as simple as possible. I did not include a rear wing to reduce the time needed for the test to be carried out. In general, I tried to keep things as simple as possible.

I used a road speed of 55 m/s (200 km/h, 124 mph) and the exhaust speed out of the pipe is at 350 m/s and 850 degrees Celsius. 

These are my results:

I obviously didn’t manage to get the exhaust plume to bend down to the diffuser in my first iteration of the McLaren style sidepods (1st Picture), but it is definitely possible. This indicates that using this solution it is harder to get the exhaust plume flowing exactly where you want it as opposed to the Red Bull – Sauber style sidepods which I got almost right on the first try (2nd Picture). 

It is believed that using the Red Bull ramp it is easier to get the plume where you want as it is continuously following bodywork to reach the diffuser. My results support this belief, and show a more consistent and predictable flow, which will in turn produce more consistent downforce. 

I believe that more teams will follow the trend set by Red Bull and Sauber in 2012 as it is, as I believe, the better solution. 

Here are some more shots of the CFD test:


  1. Absoloutly Briliant

  2. Perfect !!!.
    Very good explanation !!

  3. Hello
    nice job.
    I wondered how you got to those exhaust speed numbers. I would assume you assumed an exhaust diameter of about 5cm and an engine speed of 18000 U/min.
    Those pictures look pretty much like you did these in Ansys.
    I've just seen, that you forgot to put a Radius on the back of the engine in the McLaren.
    Anyway I really like your those two models.

  4. Very good. I got the same results for the McLaren style with a 2D simulation on The Powder Toy. It's harder, but the front vanes do make a difference to the coanda effect on the sidepods! All you needed to do was angle the channels outwards slightly, you would prefer for the exhaust plume to be directed down between the diffuser and the tyres, as it was used to seal the edge, to reduce tyre squirt.

  5. Excuse me, is possible add the radiators air under the exhaust gas? I think if hot radiators air pointing to diffuser, there's a good chance to increase Coanda effect and increase exhaust energy on the diffuser.

    1. ACtually the hot radiator airflow is the last thing you want to point at the diffuser..the airflow is very very slow

  6. This is great, shows the exhaust slow in such a clear way. Great exhausts should not interfere with the flow of air in any way.