principle of fluidic logic control

PRINCIPLE OF FLUIDIC LOGIC CONTROL

('Coanda Effect' or 'Wall-Attachment' Effect)

1. What is a 'Coanda Effect' ?

• The 'Coanda effect', also known as 'wall-attachment effect', is the basis for functioning of many fluidic components and the fluidic technology itself.

• 'Coanda effect' defined: "When a stream of fluid meets other stream, the effect is to change its direction of flow and effect is the fluid sticks to the wall.”

2. Illustration of Coanda Phenomenon

Figs.15.1(a), (b) and (c) illustrate the wall-attachment phenomenon.

As shown in Fig.15.1(a), a free fluid jet (i.e., a stream of air/liquid) passing through an orifice will continue in a given direction, pulling in with it any available fluid that surrounds the jet as it leaves the orifice.

When there is greater availability of this entraining air from one side than from the other (Fig.15.1(b)), then a small vertex area ( having a low pressure) is created near the nozzle exit. This low pressure area tends to attract the free jet, distorting it and pulling it toward the angled wall.

• It is named after a Rumanian engineer Henn Marie Coanda who has developed it in 1932.

Once this free jet is pulled tangent to the exit wall, the continued existence of this vortex tends to hold the jet attached to that wall, as shown in Fig.15.1(c). That's why this phenomenon is termed as the 'wall-attachment' phenomenon.

3. Visual Demonstration of Coanda Effect

Fig.15.2 illustrates a simple self-explanatory, visual demonstration of Coanda effect. When a finger is held near the stream of water flowing at from the water-tap, then one can see that the water attaches itself to the figure as shown. This is clearly due to the Coanda effect.