Aquadynamics

[Nico]

Hi all.
Can anyone tell me if there are any differences between hydro/aquadynamics and aerodynamics ?
Aside from the element's density differences between liquids and gases, is there any aspect that I have to take into consideration when moving from one element to the other ?
I know this is a very general question but any enlightment will be most welcome.
Nico

[shawntkeating]

Well the only thing I can think of off the top of my head is that water viscosity decreases with temp, and the opposite happens for air.

This one difference becomes more and more apparent the more extreme you go in your comparisons.

[Antigrav]

A lot of the sums are the same or at least similar, just use different constants. It gets more complex when you have 2 fluids in action in the same area, ie board travelling through air and water. That's why ship science is such a hard subject

I'm an aero student so the only fluid I have to deal with is air

[consumer]

Yes I would assume the complexity is considering the interfacial dynamics between air/water.

[BWD]

Aerodynamics and hydrodynamics are both about fluids, but have lots of differences.
Many of these are due to density and the different relationships of density/viscosity/velocity in the different fluids.
If you haven't heard about the term "reynolds number" looking it up is one good start to get a perspective on some of the issues.

But to make a long story short, there are 2 obvious and important differences you might need to think about:

1. Density. -because water is so much denser and more viscous, the hydrodynamics of an object moving in water at typical boat or board speed (8-15 m/s)are more like the aerodynamics of a similar object moving in air at supersonic speed (>340m/s)!
So, part of the reason a speedboat looks like a rocket is fashion, but part is practical!

2. Air/water interface. -boards and boats are complicated because they move in both fluids at once. This is complicated, so I won't even try to explain it -leave that up to the engineers!

Those are some basic things to think about I guess. Others are how much lighter things can be in air (and sometimes need to be...), what the range of conditions of use is, how to keep control (flaps, rudders, sheeting, reefing, etc.???) depending on the specifics....
It's a very interesting area, design and engineering for ships, boats, and boards.
Now and then I try to learn a little more about it....

[RickI]

A more encompassing term is fluid dynamics, air (gas) and water are both fluids after all. What application are you considering? There is a great deal written on the subject with an overview at: http://www.bicambertechnology.com/how-it-works-3.html

[aeberl]

The main difference is that one is compressible, the other not. You cant test that: pull your safety at the apex of a mega jump and tell me later how the difference felt like!
If you do it in sub-zero temp. it becomes even more obvious

[El Rudo]

The main difference is that one is compressible, the other not. You cant test that: pull your safety at the apex of a mega jump and tell me later how the difference felt like!
If you do it in sub-zero temp. it becomes even more obvious

Spot on. Gas behaves elastically, which makes it behave totally different in every aspect when it comes to dynamics.

[Nico]

Hi guys.
Thanks for all the feedback, key words (fluids, compression, ...), and links.
All very stimulating and has helped me along quite a bit.
Should my plan work out, you are all on my VIP list .
Regards
Nico
PS Please don't hold your breath though as I have been on and off this for a few years already.

[alexrider]

Hi all.
Can anyone tell me if there are any differences between hydro/aquadynamics and aerodynamics ?
Aside from the element's density differences between liquids and gases, is there any aspect that I have to take into consideration when moving from one element to the other ?
I know this is a very general question but any enlightment will be most welcome.
Nico

Compressibility
Reynolds number