ATLAS F1   Volume 6, Issue 47 Email to Friend   Printable Version

Atlas F1   Taking the Lid Off F1

Formula One Technical Analysis

  by Will Gray, England

Last year, Atlas F1 ran a series of articles that investigated the technical areas involved in design, development, and construction of an F1 car. Now, a year later, Will Gray picks up where he left off, and dives deeper into the technical analysis of Formula One.

8C. Cool Runnings: Internal Aerodynamics

Engines work hard. Their very nature of creating motive force from combustion means that there is a lot of waste heat to get rid of. Doing so in an efficient manner is down to the cooling system and internal aerodynamics - if it doesn't do its job, temperatures in the engine are going to rise, and she's gunna blow! It's all about heat transfer - moving heat from where it is not wanted, to a place which can cope with it - and the process runs in a constant loop. Heat from combustion in the engine is transferred to cooling fluids, which are constantly pumped around the car. These fluids flow out to the radiators where the heat is removed by an airflow, then return to the engine to do the job all over again.

The amount of cooling is affected by two criterion - the area of the radiators, and the amount of air flowing over them. The aim of the radiators (which should more correctly be called heat exchangers, but for simplicity will remain termed as normal!) is to obtain the most efficient cooling possible. Big is bad - mainly due to aerodynamics but also weight - and efficiency is achieved by getting the required cooling whilst minimising the drag created by them. To maximise cooling, the front of the radiator consists of a concentration of tiny air fins and liquid tubes, which increases the surface area used for cooling to much more than the frontal area seen by the airflow.

A BAR sidepod entry with bargeboardIt is important to know the speed of the airflow over the radiator, the speed the hot fluid is running around the radiator, and finally the temperature difference between them, as it is the combination of these three factors which dictate how much cooling the radiator will achieve. Cars have two fluids that require cooling - oil, and water - and will have a radiator set-up for each. But as race teams tend to purchase radiators from specialist companies, there is little they can do about their design apart from choosing the overall size. Also, with the cooling fluids pumped through at a rate specified by the engine company, all the teams can do here is concentrate on obtaining the best airflow through to the radiator. This bring us on to duct design.

To minimise the drag caused by the obstruction in the airflow, a duct is used to slow the air right down as it passes over the radiator - drag varies with speed, so decrease speed and you decrease drag. Simply, the laws of aerodynamics state that mass flow (which is related to both velocity and area) must be constant through a duct. Therefore, if the cross sectional area of a duct increases, the velocity will have to decrease, and bingo - less drag! Unfortunately it is not so simple, as when the airspeed across the radiator decreases, so does the cooling it can produce. However, a simple size increase will take care of this, and because drag increases linearly (i.e. one for one) with area, compared to increasing with the square of the speed, the engineer can reduce the drag overall.

A reduced, race trim, Jordan sidepod entryThe best position for a duct is in the sidepods, which is why the radiators are positioned there, either side of the engine. Unlike road cars, Formula One cars rely on the airflow caused by their own motion for cooling, so they do not have cooling fans - when you're travelling at average speeds close to 100mph, you don't need one! When the car is not moving, however, the teams use small fans which are fitted to the front of the sidepods.

In a nutshell, the duct (which is inside the sidepod covering) will decelerate the air coming in before it gets to the radiator, and once the air is past the radiator, the duct will accelerate the air back up towards the car's speed upon exit. In travelling through the duct, the air will pass through five areas. The first is the inlet, which must be designed to allow just the right amount of air to enter the duct. In an F1 car, there is little option in where the inlet face is positioned - with the radiators having to be close to the engine, they have to be side mounted, and with a low centre of gravity required, the lower to the floor these heavy items are, the better the car will handle. The unfortunate thing about this is that the track temperature means air close to it is hot - not much good for cooling, but there seems to be no other solution.

The McLaren sidepod chimneyThe air which has entered the duct is now expanded in a 'diffuser' which increases in cross sectional area (not to be confused this with the external diffuser at the rear of the car), and is steered in the direction of the radiator. A splitter is used in this section to bleed off the boundary layer, which is a low energy flow that develops on the car body ahead of the inlet, grows as the air travels along the surface and is not much use to anyone! The diffuser must also be designed so that very little boundary layer develops inside, as this will reduce the cooling potential at the edges of the radiator. Once the high energy flow reaches the radiator, the airflow undergoes the heat exchange, after which it is accelerated in a ‘nozzle’ which increases in area before returning the air to the airstream at the duct exit.

The positioning and size of this exit determines how much cooling air gets through the sidepods, and many teams have 'sideouts' of adjustable size. Once again, the type of track determines how big these need to be, as a track with slower average speed will not get as much cooling air accelerated into the sidepods as one with high speed straights. Ferrari providing extra airflowSome teams have tried to use the air exiting the sidepods to assist in other areas of aerodynamics, with recent trends being to put the sideouts beneath or in front of the winglets near the rear wheels, or to allow the air to exit through 'periscopes' as on this year's McLaren - if it works in the wind tunnel, then it will end up on the car!

Although you can’t see it, internal aerodynamics is one of the most important and oft-forgotten parts of racing car design. If the team doesn’t put its engine in as kind an environment as possible, its chances of lasting the race are much reduced, and with speed critical, a drag reduction such as this is something worth having - teams are beginning to look at internal aerodynamics more and more.

Next Week: "Are you sitting comfortably?" - Cockpit Comfort

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Will Gray© 2000 Kaizar.Com, Incorporated.
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