TURBULENCE FOIL

The invention relates to a layer for reducing air resistance of a forward-moving object. In forward-moving objects such as for instance a vehicle it is desirable to minimize the air friction, since optimum performance can hereby be obtained in respect of the forward movement of the vehicle. The performance of the moving object, such as a vehicle, is influenced to a great extent by the air resistance. The air resistance depends on the speed and the surface over which flow takes place. In addition, the so- called CW value is important in the air resistance. The CW value is a characteristic value that is related to the design of the object and how the air flows along this object .

The state in which the air flows along the object is also important for the air resistance. If the air flows along the object in a laminar state, the resistance will be less than if the air flows turbulently along the object. The case occurs in any forward-moving object, wherein the arriving airflow is laminar and somewhere on the surface of the object is transformed into a turbulent airflow. The further to the rear the transition point from laminar to turbulent lies, the lower the air resistance will be.

It is now an object of the invention to provide a layer which can be arranged on a forward-moving object and with which the air resistance can be reduced.

This object is achieved with a layer which comprises a pattern of surfaces rising in a first

direction, and channels running between the surfaces in a second direction at an angle to the first direction.

The rising surfaces ensure that the air is guided as far as the end of the rising surface and, at the transition to the following rising surface, enters a channel where the air becomes turbulent on a micro-scale. Owing to the rising surfaces a laminar flow is then created on a micro-scale in the channels. This laminar flow ensures that the possible beginning of turbulence in the main flow over the object is damped, whereby the transition point between laminar flow and turbulent flow can be displaced further in flow direction. Due to the channels running at an angle these zones of turbulent flow are distributed uniformly over the surface, thereby creating a uniform damping effect.

In a preferred embodiment the first and second directions form an angle of between 30 ^* and 60 ^" , preferably 45 ^° . In another embodiment each surface comprises at least one groove running in the first direction. During flow some of the air will run through this groove and, when running out into one of the channels between the surfaces, will ensure that the turbulent flow in these channels is blown away, whereby a flow of this turbulent air is generated which also contributes toward the damping effect, and thus displaces the transition point between laminar flow and turbulent flow in the main flow further to the rear as seen in the direction of the flow.

The width of at least one groove preferably lies in the range of 0.1-1 mm. In another preferred embodiment of the layer according to the invention, the quotient of the pitch distance in the first direction between adjacent surfaces and the desired cruising speed of the object is

substantially 20-65 kHz. Due to the alternating changes in height between the different rising surfaces vibrations occur in the air which can possibly cause a sound. The generation of these vibrations likewise causes air resistance, which is undesirable. By now modifying the distance between the surfaces to the desired cruising speed of the object it is possible to select the created vibrations such that a minimum amount of energy is lost herein. It has been found that this energy consumption is minimal at a frequency of around 20-65 kHz.

In yet another embodiment of the layer according to the invention the layer is a foil. The foil preferably comprises a PVC base layer and a teflon top layer. Through flow of the air along the teflon top layer the particles in the air brushing along the top layer become electrostatic. The advantage is that this electrostatically charged air layer has a viscosity other than the air lying thereabove, thereby reducing the possible occurrence of friction.

These and other features of the invention are further elucidated with reference to the accompanying drawing.

Figure 1 shows a perspective view of an embodiment of a layer according to the invention.

Figure 2 shows a cross-sectional view of the layer according to figure 1.

Figure 3 shows a top view of the layer according to figure 1.

Layer 1 has a number of separate surfaces 2 which rise in the direction R. Channels 3 are provided between surfaces 2.

Surfaces 2 are further provided with grooves 4.

Figure 2 shows a cross-sectional view of layer 1 of figure 1. When an airflow L passes over layer 1 in

direction R, swirling T will be created in channels 3 which provides a damping effect. The air layer L above this swirling T will thus be damped as soon as signs of turbulence occur. Air layer L thus remains laminar for a longer time, whereby the air resistance of an object on which this layer 1 is arranged is reduced.

Figure 3 shows the top view of layer 1 of figure 1. When air flows over layer 1 in direction R, swirling will occur in channels 3 as shown in figure 2. Through grooves 4 arranged in surfaces 2 occurs a flow S which distributes this turbulence over channels 3. The damping effect of the turbulent air in channels 3 will hereby damp the air flowing along layer 1 in uniform manner and thus delay the transition between laminar air and turbulent air, thereby creating a lower air resistance. The pitch distance X between two successive surfaces 2 as seen in direction R is chosen such that the quotient of distance X and the desired cruising speed of the object on which this layer is arranged substantially equals 20-65 kHz. At such a value the energy loss from the generation of air vibrations is minimal .

When layer 1 according to the invention is arranged on a vehicle, for instance a car, the pitch distance of the surfaces and the orientation thereof can then be adapted to the airflow over the surface of the car. Various aspects can thus be further optimized in order to obtain the lowest possible air resistance. The power of the engine is hereby utilized better, and this power can be used either to obtain a lower fuel consumption or a higher top speed.