Grooved surfaces

[amouzouris]

What about the relationship between your groove depth and body size? (length width etc).. what about the profile of the grooves? sharp round etc...

Believe me i would love to test all of those parameters! but i have no time!

[flynfrog]

Seriously how do you think there would be less skin drag? Increasing wetted area almost always results in increase in drag.

what if you had groves, golf ball dimples, and vortex generators you could have - drag then right?

Nope.. you are DECREASING the area. think very carefully about it...

not unless you area magically making your groves ignore the definition of a wetted area. if you do an equal depth to width you are doubling your wetted area. Not to mention you now have 100s more leading edges.

[Jersey Tom]

Let's rewind: What's the purpose of the grooves on the whale?

[Pierce89]

Let's rewind: What's the purpose of the grooves on the whale?

AFAIK, Whales use grooves on their fins to prevent spanwise flow migration.

[PlatinumZealot]

What about the relationship between your groove depth and body size? (length width etc).. what about the profile of the grooves? sharp round etc...

Believe me i would love to test all of those parameters! but i have no time!

That means you can't make a conlusion yet. With fluids things are not so straight forward. When I get the time i will try to set up a model and see what happens.. In my mind I think the drag can be reduced.. but it will take finding the right geometrical proportions that make it work.

[flynfrog]

It will take an already draggy body with large separation. Some bumps ridges dimples vgs ect. just before the point of separation to trip the air flown and keep it attached a while longer. This is nothing new. Its the same as the yearly thread that seams to pop up every year about shark skin gofl balls ect.

I would also disagree fluids are governed by equations just like every thing else thats why CFD works We get a little better understanding now and then and improve the equations. So it would seem that it is pretty strait forward.

[PlatinumZealot]

It's not straight forward to accurately demonstrate a problem like this one in CFD I can tell you that. CFD is just a tool. I have used CFD for many problems, and when I actually have a real life model things are not quite the same or sometime they behave totally different. As you get more experience you know how to fine tune the model, or you learn that certain regimes occur at different places, you have to change the shape, you have to change the type of cells etc or a different equation is needed etc. It's just a tool. How accurately the result depends on the user.

[flynfrog]

Its not a terribly hard problem to sim in CFD on a small scale. Doing an entire car would take add a lot of processing time. Like I said nothing new here http://www.f1technical.net/forum/viewto ... f=6&t=6649 scroll down to Ciros post that is pretty much all you need.

[No Lotus]

Let's rewind: What's the purpose of the grooves on the whale?

AFAIK, Whales use grooves on their fins to prevent spanwise flow migration.

I mentioned it earlier. The grooves allow the mouth and throat to expand to take in a greater amount of sea water. They don't serve a hydrodynamic function.

[olefud]

Seriously how do you think there would be less skin drag? Increasing wetted area almost always results in increase in drag.

what if you had groves, golf ball dimples, and vortex generators you could have - drag then right?

Nope.. you are DECREASING the area. think very carefully about it...

Dimples as on golf balls increase the boundary layer and, with a nonrotating, knuckleball condition, increase drag. However, when a golf ball rotates backspin wise, it creates lift by increasing pressure under the ball while decreasing it at the top and causes the ball to travel further. Highly skilled golfers like me can even rotate the spin axis 90° such that the ball takes a right turn after rather short travel.

[Pierce89]

Let's rewind: What's the purpose of the grooves on the whale?

AFAIK, Whales use grooves on their fins to prevent spanwise flow migration.

I mentioned it earlier. The grooves allow the mouth and throat to expand to take in a greater amount of sea water. They don't serve a hydrodynamic function.

If you'll read, I said the grooves on their fins, not their throats

[riff_raff]

Hydrodynamics are not the same as aerodynamics. Compressible fluids do not behave the same as incompressible fluids.

Another thing to consider is why do marine mammals, like whales and dolphins, have horizontal tail fins for propulsion, while marine fishes have vertical tail fins for propulsion?

[No Lotus]

AFAIK, Whales use grooves on their fins to prevent spanwise flow migration.

I mentioned it earlier. The grooves allow the mouth and throat to expand to take in a greater amount of sea water. They don't serve a hydrodynamic function.

If you'll read, I said the grooves on their fins, not their throats

Whales don't have grooves on their fins and the question and thread refer to the grooves on the venters of rorquals.

[autogyro]

Hydrodynamics are not the same as aerodynamics. Compressible fluids do not behave the same as incompressible fluids.

Another thing to consider is why do marine mammals, like whales and dolphins, have horizontal tail fins for propulsion, while marine fishes have vertical tail fins for propulsion?

Perhaps a large vertical fin on a whale takes to much energy to operate when on the surface and in air.
A horizontal tail fin is almost always supported by water.

[PlatinumZealot]

Hydrodynamics are not the same as aerodynamics. Compressible fluids do not behave the same as incompressible fluids.

Another thing to consider is why do marine mammals, like whales and dolphins, have horizontal tail fins for propulsion, while marine fishes have vertical tail fins for propulsion?

a mamal spine is different from fish spine. we bend your knees forward and back not side to side .