Concave Vs Convex?

[kilcoo316]

I think it would be worth trying.

Put like this - it would be the first thing I'd do... and some eejits see fit to pay me quite a bit for my opinions!!


Another thing - what you want to do is accelerate a large massflow of air by a smaller amount = better propulsive efficiency.


You should look at trying nozzle mixers - such as an ejector nozzle. Something similar to below, only obviously your secondary flow inlet will be axially upstream your motive flow and will surrounding your primary flow nozzle.

[kilcoo316]

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.

What benefit would that bring?

Your only enlarging your frontal cross sectional area? (or am I missing something?)

[flynfrog]

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.

What benefit would that bring?

Your only enlarging your frontal cross sectional area? (or am I missing something?)

you are reducing your whetted area you also eliminate a bunch of edges where flows can spill over and have to attach and reattach.

Frontal area is only one part of the equation if you can lower you Cd at the expense of a little frontal area and keep under your weight its worth the gain.

[Lightspeedrt]

I think it would be worth trying.

Put like this - it would be the first thing I'd do... and some eejits see fit to pay me quite a bit for my opinions!!


Another thing - what you want to do is accelerate a large massflow of air by a smaller amount = better propulsive efficiency.


You should look at trying nozzle mixers - such as an ejector nozzle. Something similar to below, only obviously your secondary flow inlet will be axially upstream your motive flow and will surrounding your primary flow nozzle.

This is refering to a nozzle over the canister right? We are not allowded to alter power propulsion.

Flyn, What is whetted area? And would it work if i but some larger radi on those tunnel edges? that would reduce seperation too right? , plus it would allow me to keep the weight down?

[flynfrog]

Wetted area is basically the surface area of the part. It is the component of the drag that is skin friction.

[kilcoo316]

you are reducing your whetted area you also eliminate a bunch of edges where flows can spill over and have to attach and reattach.

Frontal area is only one part of the equation if you can lower you Cd at the expense of a little frontal area and keep under your weight its worth the gain.

Yes, however you do have to collapse the outer mould line (OML) back to the nozzle. Doing so would become tricky if you extend the OML of the canister out to the wheel wells.

Basically, I heavily doubt you'd see the improved Cd figures to offset your increase in frontal area. Indeed, you probably wouldn't see improved Cd figures at all.

[kilcoo316]

This is refering to a nozzle over the canister right? We are not allowded to alter power propulsion.

What is the exact wording of the ruling?


As the saying goes; there is more than one way of skinning a cat!

[flynfrog]

you are reducing your whetted area you also eliminate a bunch of edges where flows can spill over and have to attach and reattach.

Frontal area is only one part of the equation if you can lower you Cd at the expense of a little frontal area and keep under your weight its worth the gain.

Yes, however you do have to collapse the outer mould line (OML) back to the nozzle. Doing so would become tricky if you extend the OML of the canister out to the wheel wells.

Basically, I heavily doubt you'd see the improved Cd figures to offset your increase in frontal area. Indeed, you probably wouldn't see improved Cd figures at all.

I didn't mean make the canister bigger all over simply eliminate the gap between the canister and the wheel fairings. Tunnels are not good for drag.

You nozzle idea wont work the point you need to be feeding outside air is inside the CO chamber the nozzle is provided by the pin striking the CO canister. Also you are trading velocity for mass so instead of accelerating just the vehicle you now have to accelerate air as well.

[flynfrog]

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?

are you simulating spinning wheels in your CFD? This is very important for a car of this type.

Im not sure the kick in the side pod is going to help you much. remember you want to move the air the lease amount possible. It does look cool though.

[kilcoo316]

You nozzle idea wont work the point you need to be feeding outside air is inside the CO chamber the nozzle is provided by the pin striking the CO canister. Also you are trading velocity for mass so instead of accelerating just the vehicle you now have to accelerate air as well.

That is the idea of it - at low speeds it is always better to trade velocity for mass.

At its most basic:

T = mdot*(V2-V1)

KE = 0.5 * mdot * (V2-V1)^2

So it pays to maximise mdot and minimise V - for the same amount of energy in, you get more thrust.

If you can mix the flow more effectively immediately downstream the nozzle - by using a mixer of some kind, you will see a gain in thrust.

It would be like a jet pump.

[Lightspeedrt]

The cartridges provide the car propulsion and all cars MUST interface directly
with the standard track starting pod mechanism without the use of additional
launch equipment.

The cartridge MUST be able to be inserted and withdrawn without removal and
replacement of car parts.

Both would prevent me from doing anything useful with a nozzle.

Flynn, the simulations do use rotating wheels, im going to test that kick the see its effects also.

How do you purpose eliminating the gap between the canister and the fairings?