Heat exchanger ducting analysis

[Michael Moore]

I stumbled over this paper today

http://www.ansys.com/-/media/ansys/c...ormula-car.pdf

they do CFD on various ducting for the heat exchanger on an FSAE car. I think people will find it has some useful information. I had suspected that it was possible to basically stall the air in the duct to where it spills out around the duct opening instead of continuing to flow through and was pleased to see that confirmed in the paper.

cheers,
Michael

[freebeard]

That's a clear exposition of the result. I wasn't expecting that the by-pass air would give the most benefit.

Any idea why, if there is a single radiator, the off-side of the body is symmetrical?

[Michael Moore]

Perhaps they want a downforce tunnel in the other side pod, or they got points if both sides form safety crumple zones for the driver, or "it looks nicer if symmetric"? The last might go with the "the team desired the retro-look the bodywork that was styled along the theme of the Lotus Type 49 from 1967".

I don't think you read the results correctly if by by-pass air you mean case-2. The mass flow rate was increased by 206% with ducted-case 4 which "offers the highest cooling air flux to drag ratio of the tested configurations". The unsealed case- 2 was a 49.4% increase over the original.

[freebeard]

I've been wrong before, but...

Drag and Lift Forces
It is interesting to note that the cooling duct of case 3 has a positive effect on both the mass flow rate but also on the drag whereas the duct of case 4 only reduces drag slightly. As can be seen in figure 27 the cooling duct of case 3 decreases the drag by 8.7% or 51 drag counts over the baseline. It is, however interesting to note that the largest drag reduction come from removing the sealing in case 2. The drag reduction is close to 10% or 56 drag counts. This reduction happens as the flow passes around the sides of the radiator and is injected into the wake as previously mentioned.

[Michael Moore]

Perhaps we are both right, just looking at different things in the paper -- drag reduction vs mass flow. I was more interested by the mass flow because if you can improve that it seems like you could then go to a smaller heat exchanger and duct and still have adequate cooling and quite possibly reduce the drag some too.