[![wind3a23c.jpg](http://www.steemimg.com/images/2017/01/29/wind3a23c.jpg)](http://www.steemimg.com/image/s7uzw)
 
<div class="text-justify">In order to investigate and measure the aerodynamic and aeroacoustic properties of bodies such as aircraft or automobiles, a wind tunnel is used. The aim is to assess whether they are able to withstand the expected wind forces in their original size during storms. Wind tunnel is coupled to a commercial software and the following variables are measured:</div>

* Temperature at each measuring point
* Rotation speed n
* Resistance Fw

Pressure difference ∆p dyn can be directly measured using a Prandtl pitot tube.

<h2>1.	Flow velocity</h2>

To determine the flow velocity, the following formula is required:

[![Unbenannt73f55.png](http://www.steemimg.com/images/2017/01/29/Unbenannt73f55.png)](http://www.steemimg.com/image/s7Qo7)

<h2>2.	Density of air</h2>

In order to calculate the air density, the following formula is required:

The general gas equation ![lufta1045.png](http://www.steemimg.com/images/2017/01/29/lufta1045.png)

Ambient pressure  can be directly measured using a barometer.

The dimensionless resistance coefficient is calculated using the formula:

![wieder74092.png](http://www.steemimg.com/images/2017/01/29/wieder74092.png)
 
<h2>3.	Viskösität</h2>

The Reynolds number can be determined by calculating the viscosity of the air.

https://picload.org/image/rdowclcd/111.jpg  

 B = 1,503 . 10-6, C = 123,6 und T = t + 273,15K

The kinematic viscosity can be calculated by dividing the dynamic viscosity by the density of the air.

![17ff73.png](http://www.steemimg.com/images/2017/01/29/17ff73.png)

<h2>4.	Reynolds number</h2>

The Reynolds number is defined as:

![122cab4e.png](http://www.steemimg.com/images/2017/01/29/122cab4e.png)

<hr>
References:

[1] What Are Wind Tunnels? https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-are-wind-tunnels-k4.html

[2] Windkanal: https://de.wikipedia.org/wiki/Windkanal
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