Science of Wakes: Low Pressure Region Explained

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Discussion Overview

The discussion centers around the nature of wakes produced by moving objects, particularly in fluid dynamics, and their associated low-pressure regions. Participants explore various aspects of wakes, including their undesirability, mechanisms of formation, and applications in different contexts such as hydrodynamics and plasma physics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that wakes are undesirable due to their low-pressure regions, though this claim is challenged by others.
  • One participant questions the assertion that wakes are generally low pressure, asking for clarification and examples.
  • A comparison is made between the drag force on a car and the drag associated with wakes, suggesting that understanding one can illuminate the other.
  • Another participant argues that the wake behind a ship involves more than just hydrodynamic drag, indicating a need for a more comprehensive explanation of the wake-forming mechanism.
  • It is noted that wakes in plasma can be beneficial, as they are being researched for applications in particle accelerators, which contrasts with the general perception of wakes as undesirable.
  • A participant describes the persistence of energy in wakes, emphasizing that they represent a significant portion of the energy output from a ship's engine.
  • One participant elaborates on the different types of wakes, specifically referencing the Kelvin wake pattern and its characteristics.

Areas of Agreement / Disagreement

Participants express differing views on the nature and implications of wakes, with no consensus reached on whether they are inherently undesirable or beneficial in certain contexts. The discussion remains unresolved regarding the mechanisms and characteristics of wakes.

Contextual Notes

Some claims about wakes depend on specific contexts, such as the type of fluid or the source of the wake, which may not have been fully explored in the discussion.

kundukoustav
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we all know wakes are very much undesirable. Also, wakes are of generally very low pressure region. Why is is so? Discussions are welcome
 
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kundukoustav, we all do not know wakes are very much undesirable. Will you please say why they are?

I see plenty of ship wakes while exploring on Google Earth. (Try in the Suez Canal, for example...there are some great ship wake examples to see.) I can't understand why you say they are "of generally very low pressure region". How can that be? Will you please explain that for me also? Thank you.
Bobbywhy
 
Consider a car moving! check the drag force (pressure drag) of air on the car! You will get the idea!
 
The wake behind a moving ship is more than hydrodynamic drag. That's not a sufficient description of the wake-forming mechanism.
 
kundukoustav said:
we all know wakes are very much undesirable. Also, wakes are of generally very low pressure region. Why is is so? Discussions are welcome

This is not always true. Wakes generated in a plasma are now being used to generate high gradients as part of a research for the next generation of particle accelerators.

http://physicsworld.com/cws/article...a-wakefield-turbocharges-particle-accelerator

Other groups are using wakefields generated in metallic and dielectric structures.

Zz.
 
A wake (from a boat and probably from any other source too) is surely a wave. The energy in it takes a long time to dispel because, once it has settled down, it has a straight wave front. Until it comes to a discontinuity (shallow water) it hardly disperses at all. It represents a huge proportion of the ship's engine output, I think.
 
kundukoustav, You must have noticed by now there are several kinds of wakes. The wakefield accelerator has great promise. From your mistaken comparison with aerodynamic drag on a car I am assuming you are referring to boat or ship wakes.

"Wake pattern of a boat:
Waterfowls and boats moving across the surface of water produce a wake pattern, first explained mathematically by Lord Kelvin and known today as the Kelvin wake pattern. This pattern consists of two wake lines that form the arms of a V, with the source of the wake at the point. Each wake line is offset from the path of the wake source by around 19° and is made up with feathery wavelets that are angled at roughly 53° to the path. The interior of the V is filled with transverse curved waves, each of which is an arc of a circle centered at a point lying on the path at a distance twice that of the arc to the wake source."
http://en.wikipedia.org/wiki/Wake

For a more detailed analysis of steel ship wakes see:
http://www.steelnavy.com/WavePatterns.htm
 

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