Concave Vs Convex?

[Lightspeedrt]

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Okay guys, thankyou very much for all your help. We competed in the National Finals last week and came 3rd overall, won Best Portfolio and Fastest Qualifying lap (1.085 car time 0.126 Reaction)

This was the design we used, im curious to know your guys thoughts, as we did not win we have 8 months to prepare for next comp, i will post any rule changes when i find out but until then im pretty sure all is the same.

Thoughts?

[flynfrog]

can we see some more angles like head on and also the rear of the car.

[Lightspeedrt]

Not the best renders but shows the shapes.

The idea of the bell shaped front is to try and reduce flow seperation. THoughts?

[MIKEY_!]

No curved hub caps??? I thought those were the best.

[Lightspeedrt]

Curved Hub Caps? Why would they be better than flat?

[kilcoo316]

Erm?

I take it the rules prevent you lengthening the wheelbase and placing the tank down between the wheels?


Drag is directly proportional to frontal cross section area.


I would also investigate splitters that don't extend to the full height of the wheels if you are not permitted to cover the wheels. OK, you'll get some friction from the counter-rotating wheel, but it should be less than from the stagnated pockets your creating with the full height surround.

Probably terminating 2/3rds the way up or so - but that number is a bit of a guess.


Oh and I'm sure this is so obvious you've looked at it - why are the wheels so big? Smaller wheels = smaller packaging problem!

[Lightspeedrt]

1. Yes, the canister is almost as low as possible, wheelbase is also about as large as possible.

2. You speak of stagnated pockets? What are these? Is this referring to pressure pockets?

3. Wheels are as small as possible

[kilcoo316]

Using Mikey's image:




There will be a stagnated pocket after the splitter and before the wheel - at the top. It is always going to exist to some degree - your job is to make it as small as possible.

If the splitter only extended to about 2/3rds wheel height, you'd minimise this.


Do the rules restrict you to 1 canister? Could you use 2 canisters in-line with the wheels?

[flynfrog]

That bubble is better than an uncovered wheel. The spinning wheel has much more drag.

Light Speed Why do you float the canister like that. If you were to smooth the rest of the body into it you would have a lot less area for separation.

[kilcoo316]

A spinning wheel with partial splitter (as compared to the current full height splitter) may have higher skin friction drag than the full height solution.


However, in my experience that is substantially smaller than the pressure drag caused by a stagnation pocket.

[flynfrog]

The stagnation pocket will form a rotating bubble much like a pickup bed this will help reduce the drag.

[kilcoo316]

Not quite the same - (1) because there is a downstream surface to act on, this region of stagnant flow will also cause (somewhat) corresponding forces to act on the wheel and (2) the reduced drag of a vertical cut is in comparison to that of a 'fast-back' car, which induces significant longitudinal vortices emanating from the region of the 3/4 panels (see the likes of the Ahmed body).

[Lightspeedrt]

Ok heres some CFD images of the car.










I have redone the car to blend the canister into the body more like you said flyn.









Im still a bit weary of the idea of directing airflow into the rotation of the wheel kilcoo, surely a small region of stagnant flow is better than the drag caused by directing into a rotating wheel?

[flynfrog]

Ok heres some CFD images of the car.
snip..
Im still a bit weary of the idea of directing airflow into the rotation of the wheel kilcoo, surely a small region of stagnant flow is better than the drag caused by directing into a rotating wheel?

Lightspeed why not humor Kilcoo and the rest of us watching run a sim with both ideas this is what the project is really about.

I would stretch the canister out to the side pods as well eliminating the tunnel in there. Might start to have a weight issue though.

[Lightspeedrt]

True i will run simulations on each when i get time probably late next week.

Stretching the canister all the way out would definitely create a weight issue, in your professional opinions, is this design better? Do you like the kick in the side pod?