The drag coefficient / drag coefficient calculation!

Reading time 5 Min.

The Drag coefficient, or short c_w-Value (Cw value) describes the flow resistance of a body when a fluid flows around it. A fluid can be about Water be, but also Airwhich, from a physical point of view, also belongs to the fluids. Often there is also the name Drag coefficient for c_w-Value. This value is briefly referred to with the symbol Cw. It is a coefficient, that is, a dimensionless measure. At the same time, the flow resistance coefficient corresponds to the pressure loss coefficient of a body flowed through. From the c_w-Value the force of the flow resistance can be calculated taking into account the speed, the density of the fluid and the area of ​​the body.

following our c_w-Value calculator

Density of the flowing fluid (e.g. air) [kg / ㎥]
Resistance force [N]
body surface flowing against [㎡]
Approach velocity [m / s]
CW value

How can you do that c_w-Value measure up?

Usually the c_w-Value in you wind Tunnel determined. The body for which the calculation is to be made stands on a plate that is equipped with force sensors. The wind acts as a fluid. The force in the direction of the flow is then measured. This results in a value, the drag force Fw. Together with this and the already known quantities (namely the density of the fluid, air density) and the frontal area of ​​the object as well as the speed then becomes the c_w-Value calculated.

The following formula is used to calculate the drag coefficient: cw = Fw / qA, = 2 F w /? v² A

Fw describes the experimentally determined drag force. A is the reference area, ? describes the density of the object and v is the speed of the (undisturbed) flow. The reference surface is usually the face of the object against which the flow occurs. There are exceptions here, for example, in the aerodynamics of aircraft, where the Wing area for A is used. It should be noted that the designation Cw (with W for resistance) only is common in German usage. In the English-speaking world, the value is referred to as cd or cx (drag coefficient).

The value can also be calculated numerically depending on the model shape of the object. This works by integrating the distribution of the coefficient of friction and pressure over the model surface.

The c_w-Value in the application

Via the <strong>integrated datalog</strong> the measuring values can be stored on the humimeter RH5 paper moisture meter and additional data can be added. You also have the possibility to use the Autolog function. This function automatically saves measuring values in adjustable time intervals. c_w-Value For example, you can say how aerodynamic a vehicle is. The air resistance of a car makes indirect statements about the Consumption of the carriage. Even if the frontal area of ​​a vehicle is rarely specified by the manufacturer, there is still a way to calculate the drag force, if you can find out the area. The drag force is obtained by multiplying the drag coefficient by the reference area A.

The associated formula is the following: Fw = Cw * A

Fw as resistance force, Cw as c_w-Value and A as the end face of the vehicle.

A modern car has one c_w-Value of around 0,3. The lower the c_w-Valuethe more aerodynamic a vehicle is. Compared to this, Formula 1 cars, for example, are not as streamlined as one might think. Classic Formula 1 racing cars have a drag coefficient of around 1,2. That's because these racing cars have their speed not achieve that they are particularly aerodynamic, but rather that they are pressed firmly to the ground by their structure and the wind flowing around them. This gives them the opportunity to build up extreme speeds. Especially in curves! But that does not come without a price, because the pressure that is exerted on the vehicle can reach up to a ton at top speeds additional weight act on the car. But it is precisely this weight that ensures that the Formula 1 car not stands out from the track. A commercially available car would become lighter at such high speeds due to its construction and stand out from the road.

Incidentally, motorcycles are judged by theirs c_w-Value, not viewed as particularly economical. Even if its sleek shape would speak for it, many other factors play a role here.

Which statements does the c_w-Value in cars?

In a car, the fuel consumption depends on the c_w-Value. The fuel consumption increases with a higher air resistance. So the smaller the c_w-Value is, the less a car consumes. The most streamlined car to date comes from VW and has one c_w-Value of 0,189. The air resistance, which the c_w-Value significantly influenced, results from the frontal area of ​​the vehicle. If a car had a completely flat surface as an inflow surface, then a c_w-Value of 1,0 result.

By reducing the area, the c_w-Value be reduced and thus ultimately also the gasoline consumption. An aerodynamicist takes care of reducing this area as effectively as possible and keeping it as low as possible c_w-Value to reach. At the same time, aerodynamic vehicles also reduce CO2 emissions and are therefore more environmentally friendly. Another way to get the c_w-Value to influence positively is that Lowering of a vehicle. Other accessories, however, such as spoilers on the car, erhöhen the material moisture meter shows you the c_w-Value again.

By the way: tuningblog has other options for Calculation of various things on-line. The following gallery provides an overview of other computers.

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