Automotive aerodynamics – How to Car aerodynamics

Automotive aerodynamics is the study of the aerodynamics of road vehicles. Its main goals are reducing drag and wind noise, minimizing noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds. Air is also considered a fluid in this case. For some classes of racing vehicles, it may also be important to produce down force to improve traction and thus cornering abilities.

As the cost of petrol rises, car manufacturers are taking more and more care in designing their cars to be fuel efficient. One aspect of car design that plays a part in saving fuel is aerodynamic efficiency – in other words, ensuring a car meets as little resistance as possible from the air it travels through. The more aerodynamically efficient it’s, the less fuel it’ll use to follow at any given speed. The faster the car moves, the more important it’s to stay the air resistance – drag – to a minimum.

What is Automotive aerodynamics

Automotive aerodynamics is that the study of the aerodynamics of road vehicles. Its main goals are reducing drag and wind noise, minimizing noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds. Air is also considered a fluid during this case. for a few classes of racing vehicles, it’s going to even be important to supply down force to improve traction and thus cornering abilities.

Drag coefficient

The aerodynamic efficiency of a car’s shape is measured by its co-efficient of drag (generally known as its Cd figure). for instance , a flat plate held at right angles to the airflow features a Cd of 1.25, whereas the foremost efficient production car shapes at the instant have a Cd of about 0.28. However, this Cd figure can’t be used by itself to calculate a car’s aerodynamic drag because it doesn’t take under consideration the car’s frontal area. The frontal area is that the car’s total cross-section, or the total amount of space it occupies when viewed from the front.

A full-size car and a scale model of an equivalent thing would both have an equivalent Cd figure, but the larger version would wish tons more power to propel it at speed because its frontal area is larger. For this reason, the important figure is that the CdA (coefficient of drag multiplied by frontal area), which provides the entire amount of drag working on the body. Thus, if you’re comparing two cars, you want to compare the CdA figure instead of the Cd.

Wind tunnels

Car manufacturers use wind tunnels to ascertain how prototypes of their cars behave. in a structure , the car is anchored down and a stream of air is blown past it to simulate the conditions that the car would meet when driven forward. The car is connected to instruments that record how much down-force or how much lift is being generated at each end of the car. The flow of air past the car is formed visible by attaching small tufts of wool to the car’s body, or by blowing a stream of smoke past it.

In both cases the trail that the wind takes because it flows over the car are often seen by how the wool or smoke behaves. Smoke also shows the behavior of the air ahead of and behind the car. Woolen tufts arrange themselves along the lines of the airflow over the body but cannot show the air behavior in front of or behind the car. The model or car within the structure are often turned round at various angles to the airflow in order that the engineers can see how the body shape behaves in side winds.

Reducing drag

Drag and speed

  • As cars became faster over the years, their aerodynamic efficiency has become more crucial because the quantity of power needed to propel a car at high speed rises with the cube of the speed. The faster you’re going, the more power it takes to travel even faster. for example, if a two-liter Ford Sierra developing 100bhp can reach about 115mph, you’ll compute how fast a similar car with twice the facility should go, ignoring rolling resistance. The root of two (from 200bhp) is 1.26, therefore the second car should reach 115x 1.26 = 145mph— roughly the actual top speed of the 200bhp Sierra Cos worth.

Once the car is about up in the wind tunnel, its drag is measured by the amount of force that the car exerts on its anchored-down wheels because the wind blows past it. As modifications are made, the effects on drag are often measured and recorded. Usually, the car’s designers will have produced a prototype that appears as if it’ll slip through the air easily, but once items like air intakes and door handles are added, the efficiency falls.

Some of the features that help to smooth the airflow are often seen on cars like the Valhalla Astra. The Astra features a low, smoothly sloping nose to chop through the air, a windscreen that’s almost flush with the encompassing bodywork in order that the airflow isn’t disturbed, side windows that also are nearly flush with the bodywork and wheel trims with a minimum of contours. Careful attention to details like recessing the door handles and streamlining outside mirrors helps to scale back the aerodynamic drag by allowing the air to flow more smoothly and lowering the tendency for eddies to make.

Other techniques used on modern aerodynamic cars include recessing the windscreen wipers under the scuttle panel when not in use, having pop-up headlamps that fit flush to the nose of the car when transitioned , and eliminating raised gutters round the edges of the car’s roof. By careful attention to detail, the airflow can even be made to stay the taillight lenses clean.

Using wind tunnels to research good airflow

Good airflow means the car slips through the atmosphere with minimal disturbance while remaining stable. a particular amount of down force is required at either end of the body for stability, but any turbulence should ideally happen behind the rear of the car —this also helps to stay it clean.

Wind tunnels use an outsized motor-driven fan to suck a stream of air past a car to simulate driving through still air at speed. The car sits on pressure-sensitive pads within the middle of the tunnel and a viewing screen within the side of the tunnel allows the engineers to see what is going on.

Practicalities

When a car is being developed for production, some of the aerodynamic purity of the first design is typically lost. Sometimes the changes are made for reasons of cost. for instance, fitting a smooth under tray can improve the efficiency of a car’s shape, but this panel would cost extra cash to supply and will make access to components like the gearbox harder.

On other occasions, practical considerations, like the necessity to suit wider tires, can make the car less aerodynamic than the slim-tired prototype. If the car is to be mass-produced, its sales could also be held back if it includes features that are too unfamiliar.

An example of this is often the fired-in k streamlined) front wheels of Ford’s concept car, the Probe. The Sierra, which looks very almost like the Probe but without the fired-in front wheels, sold slowly until the public got wont to it. If it had fired-in front wheels, sales may need been further held back.

Stability

It is relatively easy to design a car which will slip through the air in a line when there’s no wind blowing, but it’s harder to make sure that the car will be stable when a wind is blowing on thereto from the side, or when it’s cornering at high speed, which creates a force on the side of the car. There is a theoretical point on the side of a car called the center of pressure which is where the wind pressure effectively acts. By paying attention to the center of pressure and therefore the balance of forces, engineers can design more stable cars.

For example, if the center of pressure were well above the center of gravity of the car, a side wind would make the car roll also as trying to push it off line. If the center of pressure is well ahead of the car’s center of gravity, a strong and gusty side wind will make the car attempt to turn round to place the center of gravity ahead.

However, the situation of the center of pressure shifts with changes within the car’s speed, and in some cases can even shift in order that it’s ahead of the car itself. the answer is first to make sure that the car’s center of gravity is well forward. this is often one of the reasons for the popularity of front-wheel drive layout, which features a forward weight bias. The center of pressure also tends to be kept further back if there’s a greater area of bodywork towards the rear of the car. Some racing cars of the past had tail fins which improved their stability at speed by increasing the world to the rear. The low, sloping bonnet line which gives good penetration through the air also helps to stay down the side area at the front of the car.

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