The use of wind tunnels in automotive

Some people may not be aware that in the beginning, wind tunnel testing was used mainly for conducting aerodynamic research on aircraft. The enclosed wind tunnel, which was the first ever created and operated for aeronautical purposes in 1871, delivered a lot of fundamental discoveries. Nevertheless, wind tunnel experiments and testing was only done to automobiles nearly a century after, following years of using computer simulations rather than real-life procedures.

This was delayed since automotive aerodynamics are different from aircraft aerodynamics in several ways. As an example, the shape of a vehicle used on the road is a lot less streamlined than an aircraft. Also, it does not move in free air so its motion is not so affected by aerodynamic forces and its operating speeds are a lot lower.

In general, a wind tunnel consists of a test area where a model/vehicle is mounted and viewed while air is blown or oftentimes sucked above it by one fan or more. Usually, data can be collected from a balance upon which the model/vehicle is mounted and adding smoke trails to airflow, among other visualization techniques, can help in understanding the way some geometric features impact its aerodynamic performance.

The following data can be acquired by means of wind tunnels: aero-acoustic data; aerodynamic forces; lift, drag, side force and moments; yaw, roll, pitch: differences of aerodynamic forces plus moments with yaw; vehicle cooling drag; surface pressure distribution; influence of various vehicle details on the above, brake cooling flow assessment; and effect of aerodynamic features and aids.

Various selections of non-automotive products often rely on aerodynamics expertise. These include some forms of transport like trains and bicycles as well as totally unrelated products such as aerials, lifeboats, sports clothing and world class skiers.

Model Scale Testing

It is typical for models to fall between 30% to 60%, depending on the vehicle’s size and the test facility limitations. Model scale testing is best for the early assessment of how various body styles and features affect a vehicle’s aerodynamics. It is natural for model scale testing to use smaller facilities that have lower running costs as compared to their full scale equivalent. Sophisticated testing methods, like hiring a moving ground plane, is possible without spending too much. As a matter of fact, model testing can be a cost efficient way to develop a vehicle’s aerodynamics.

Full Scale Testing

It is fast becoming more common to remove the model scale stage, which is part of the aerodynamic development program, and go straight to full scale testing. This can be on program where a large portion of the styling assessments are virtually carried out using CFD to predict the aerodynamic performance of the vehicles or where full scale styling models are produced. When there are full scale styling models then there is no need to spend on model production.

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