Transducer with Bernoulli Effect Aperture for Minimizing Rooster Tailing

Summary

A transom mounted sonar transducer of certain design may induce “rooster tailing” (an unwanted flow of water in the vertical direction) in higher speed recreational boat applications due to the use of transducers. The solution is to build in a Bernoulli Effect aperture within the transducer housing to utilize the flow of water over the top of the transducer to reduce the pressure and thus force the water downwards instead of into the rooster tail.

 

Background

In fluid dynamics, Bernoulli’s principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy. Bernoulli’s principle can be derived from the principle of conservation of energy. Which states that in a steady flow system, the sum of all forms of energy in a fluid along a streamline is the same at all points on that streamline. This requires that the sum of kinetic energy, potential energy and internal energy remains constant. Thus an increase in the speed of the fluid – implying an increase in both its dynamic pressure and kinetic energy – occurs with a simultaneous decrease in (the sum of) its static pressure, potential energy and internal energy. If the fluid is flowing out of a reservoir, the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit volume (the sum of pressure and gravitational potential ρ g h) is the same everywhere.

Fluid particles are subject only to pressure and their own weight. If a fluid is flowing horizontally and along a section of a streamline, when the speed increases, it can only be because the fluid on that section has moved from a region of higher pressure to a region of lower pressure. Furthermore, if its speed decreases, it can only be because it has moved from a region of lower pressure to a region of higher pressure. Consequently, within a fluid flowing horizontally, the highest speed occurs where the pressure is lowest, and the lowest speed occurs where the pressure is highest.1

Profylax

Description of Bernoulli Effect Transducer

The calculation of the ”real world” pressure in a constriction of a tube is difficult to do because of viscous losses, turbulence, and the assumptions that must be made about the velocity profile (which affect the calculated kinetic energy). The model calculation here assumes laminar flow (no turbulence), assumes that the distance from the larger diameter to the smaller is short enough that viscous losses can be neglected, and assumes that the velocity profile follows that of theoretical laminar flow. Specifically, this involves assuming that the effective flow velocity is one-half of the maximum velocity, and that the average kinetic energy density is given by one third of the maximum kinetic energy density.

Profylax2

Below are rough sketches of intended water flow characteristics in the use of transducers.  The Transducer may be used for transom mount transducers.

 

 

Side View

 

 

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Plan View

 

Profylax4

 

 

 

By Drew J. Gorman
Raymarine, Inc.
United Kingdom

 

References

1. https://en.wikipedia.org/wiki/Bernoulli%27s_principle
2. http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html
3. http://hydrogen.physik.uni-wuppertal.de/hyperphysics/hyperphysics/hbase/imgmec/bernoul.gif