Active Tollmien-Schlichting Wave Attenuation Device

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Aerospace & Defense
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The fluid dynamical boundary layer is fluid volume partially carried along by a moving body, due to adhesion to the body – then between molecules in the layer. Dependencies on velocity, body shape, fluid density, viscosity and surface characteristics affect how fluid behaves within this layer and defines Flow Condition, approximately predicted by nondimensional Reynolds Numbers. These associate with Laminar, Transitional, Reattached and Separated flow conditions, which affect Drag Coefficient.

Factors contributing to boundary layer growth involve boundary layer shear, which induces flow-perpendicular pressure differential gradients and flow curvature via Bernoulli Effect, vortical flow patterns, eddies and pressure anomalies.

Most drag reduction is passive – streamlining, boundary layer shedding, vortex mitigation and inducing reattached flow.

Tollmien-Schlichting Waves are inherent in boundary layers, contributing to their expansion, enlarging physical profile and increasing drag. They're poorly understood by most dynamicists, who incorrectly attribute surface imperfections. A flawless surface still induces them. Cause, besides pressure fluctuations from vortical flow consequences, are molecular collision shearing effects; inducing body resonances. These retransmit into the boundary layer and amplify bilaterally as body surface and boundary layer interact.

This concept applies sonic cancellation and custom sonic synthesis. Cause of TS Waves cannot be eliminated, but they can be neutralised to produce significant drag reduction, by inducing identical but phase-reversed waveforms in the body. Others have proposed this same method.

A network of sensors and actuators is deployed throughout the hull; also in internal machinery and possibly propshaft and screw. Sensors work like microphones. Actuators work like loudspeakers. The system may be best modelled on architecture of the human nervous system, using a central computer to analyse signal inputs, generate signals as required and direct them to the actuators.

Configuration depends on performance requirements, influenced by whether it's integral with a new vessel's original design, or retrofitted.

TS Wave attenuation is not ATSWAD's only application. Design objectives are:
1. Neutralise Tollmien-Schlichting Waves to reduce drag and enhance performance;
2. Enhance stealth capabilities by silencing noise or creating false acoustic signatures like biologicals and other submarines;
3. Integrate with the active and passive sonar system to enhance detection sensitivity;
4. Selectively modify fluid flow conditions over particular surfaces, providing trim and steerage enhancement, or partly compensating rudder/hydroplane damage/malfunction. Where repairs are impossible under duress, it may provide a survival edge.
5. Possibly mitigate a sonic weapon's harmful effects on crewmembers;
6. Enhance countermeasures with self-propelled decoys equipped with ATSWAD to produce acoustic effects - eg: screw cavitation, firing torpedoes, blowing ballast.

Whether similar systems are already in submarines is unknown. No commercial systems are currently known.

Applications are not limited to submarines. It can improve performance in avionics and commercial shipping and fuel efficiency, saving money and consumption of resources.

Manufacture hardly requires special considerations. Existing technologies are adequate for all essential system components.

No cost comparisons can be made.

If improving "quality of life” or “public safety and security” is a valid benefit, it's through national defence.

Economically, it may benefit an economy through employment and exports.

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  • ABOUT THE ENTRANT

  • Name:
    Ciarrai Macgiolla Comghail
  • Type of entry:
    individual
  • Profession:
    Student
  • Number of times previously entering contest:
    3
  • Ciarrai is inspired by:
    Science, technology & medicine.
  • Patent status:
    none