Side pod & cooling

[Dark Cobalt]

We got the air box done, see my other discussion.
So it's time for a new project or two.
The left side side pod holds the radiator. The intake of the side pod is very F1 in shape. With the bottom opening fairly small 3-4 inches then flairs out at the top to about 10-12 inches. Similar to the number 7.??? Similar in looks to a Mclaren F1 side pod. The radiator fits fairly snug with foam between the pod & the radiator for a tight fit. The radiator itself is 18in tall by about 12in wide. Plenty of radiator.
Right now there are 3-4 gills for the radiator air to exit. They're about 1 wide 8 in. long and wrap from the top side of the pod down the side equally.
Sorry I don't have pictures, it's 30 minutes away & I can only help every couple of weeks.
Anyway, the air exit seems small compared to the intake.
We're thinking of a square opening on the side of the pod about 1/3 larger than the intake.
Not sure if this is too large and will allow the air to go through too quickly (less drag) and not cool the water down. This will allow the air a direct exit to the back of the car past the suspension pieces.

The other side has the oil cooler about 12x8. The air just dumps into that pod & goes where ever it wants.
So, we can duct it, but what do we do with the rest of the air coming in?
Direct it straight out?
Does the motor need an extra air circulating around it?

We 'think' we know what we're trying to do.
We 'think' we know what to do, but would be happy to hear others experiences.

[S Lathrop]

I asume that the radiator is forward of the roll bar.

I would have as much of the radiator air exit into the engine compartment as possible. Especially around the exhaust system.

On my cars the side pod diminishes in size to the rear and ends just past the leading edge of the rear tire. At that point the back of the side pod is open.

[brownslane]

Air can be made to move through a radiator in two ways...."pushing" it through higher pressure an the front , and "extracting" it via lower pressure behind it. In low-drag trim, you are trying to pull air in from an area that would normally be in a high pressure area (like the top of the side pod) and must be done in a way that does not create turbulence (both externally AND internally).. Look through your Carroll Smith books and you will see how to create a smooth intake mouth.....

Once you have drawn air in through the intake area it is often best to slow it down. Good old Bernoulli tells us that if you increase the volume of the air duct you will slow its speed....so often the best way is to create an internal duct that takes the (relatively) small air intake, expands it to the size of the radiator, then ducts it back to the rear of the car.

If you duct the exhaust air (from the cooler and radiator) back into a low-pressure area (often in the wake of the car) you can actually reduce overall drag and further improve air flow through the intake....on the cooler side you can split the air into two ducts; one supplying air to the cooler, the other directing air over the engine. These cars need all the engine bay cooling they can get. A better way might be to reduce the air intake size on the oil cooler side of the car for less drag.

Depending on the pressure variant, how close the outlet is to the wake of the car etc affects how you treat the exhausted air....but any time you can stuff high-pressure air into a low pressure wake you will go faster! Some times an exhaust duct actually reduces in size as it approaches its exit...this is done to increase its pressure (and consequently velocity)...which can be used to accelerate air from under a diffuser for example....

This is incredibly important in a car that is at 190 mph....it is less important in a car traveling at 130 mph....often simply venting the air into the engine bay is sufficient. Spend your time in the front of the ducts, where creating drag is most critical. A radiused opening is needed.....no sharp edges!!

I would not suggest any openings in the side pods at all if you can get away with it; there is pretty well no way (at least without a wind tunnel and really good CFD) that amateurs like us can create openings that will not create all sorts of drag.


Sometimes pictures help us in making suggestions.

Best, Tom

[Marty Nygard]

Tom,

It is a common misunderstanding that "Good old Bernoulli tells us that if you increase the volume of the air duct you will slow its speed". In fact, for non-compressible flows (i.e. liquids) or mildly compressed gases, the velocity varies in direct proportion to the area ratio.

What Bernoulli actually discussed was the effects of velocity changes on pressures generally expressed as a function of the velocity squared as (stolen from Wikipedia):
"In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.[1][2] The principle is named after Daniel Bernoulli who published it in his book Hydrodynamica in 1738.["

Marty

[brownslane]

Tom,

It is a common misunderstanding that "Good old Bernoulli tells us that if you increase the volume of the air duct you will slow its speed". In fact, for non-compressible flows (i.e. liquids) or mildly compressed gases, the velocity varies in direct proportion to the area ratio.

What Bernoulli actually discussed was the effects of velocity changes on pressures generally expressed as a function of the velocity squared as (stolen from Wikipedia):
"In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.[1][2] The principle is named after Daniel Bernoulli who published it in his book Hydrodynamica in 1738.["

Marty

Hi Marty. You are absolutely correct; there is a difference between speed and density.


" In fact, for non-compressible flows (i.e. liquids) or mildly compressed gases, the velocity varies in direct proportion to the area ratio."