Aerodynamic Streamlining Mini-Course

[freebeard]

This is interesting, not only because the granularity of the turbulence is altered as well as it's onset. I wonder if they tried a 4" diameter ring or a 6" diameter circle and so forth.

[ERTW]

It's typical of spheres. Looking at the drag vs Re graphfor a sphere, there's a pronounced drop. Scale does not matter. Other shapes do not behave that way; so there's little transfer here. I suspect that once the patch is large enough, it stops seeing improvement.

Keeping the boundary layer energised is a good thing; especially on back slopes. Cars would look funny with shark wing denticles on them.

[aerohead]

Originally Posted by freebeard

This is interesting, not only because the granularity of the turbulence is altered as well as it's onset. I wonder if they tried a 4" diameter ring or a 6" diameter circle and so forth.

The NAVY used a circle and I don't recall that they experimented with different 'sizes.' Ludwig Prandtl used a trip wire ring in the 1920s to get the same results.
With the Reynolds numbers we have for our cars,at 20-mph we don't need a thing for the LBL-to-TBL transition to occur.
Ahmed Feysal reported that the nose of his RAM pickup had a total of 30mm of LBL before it exploded into fully-bloomed TBL.
Years back,BicycleBob remarked on how a spoiler might shatter major turbulence into smaller,more homogenous vortices and eddies.I like that mind picture.
The separation line does look more uniform with the TBL and the wake is remarkably less crenelated ( if that's an appropriate adjective).

[freebeard]

'[C]renelated' works for me. I'd bet that even if there wasn't a measurable difference in drag, you'd notice it acoustically.

[aerohead]

Originally Posted by freebeard

'[C]renelated' works for me. I'd bet that even if there wasn't a measurable difference in drag, you'd notice it acoustically.

Absolutely!
Especially regarding hunter/killer subs and torpedoes.The designers appear to take great care with all trailing surfaces to avoid eddies and turbulence and their attendant 'noise.'
And I believe that the submarine propulsor technologies are state secrets,on account of their 'stealth' advantages.
Really 'clean' hydrodynamics!
PS It would be interesting to compare the boat tail's boundary layer toroid thickness compared to the propulsor geometry and dimensions.
Here's a link to a submarine's noise-reducing 'lampshade.'
Sorry,wouldn't allow it
https://www.google.com/search?q=curt...ml%3B647%3B276
http://www.mycity-military.com/thumb...8521_image.jpg

[aerohead]

I've added six additional images on page-1,inserted at the bottom of the first table."Mod on Garth." "Mod on Wayne."

[freebeard]

I'll bet they can let the blade freewheel, and use hydrojets in the 'lampshade'.

[aerohead]

Originally Posted by freebeard

I'll bet they can let the blade freewheel, and use hydrojets in the 'lampshade'.

You gotta wonder if something like that is 'swimming' around out there somewhere.

[Otto]

Originally Posted by freebeard

I'll bet they can let the blade freewheel, and use hydrojets in the 'lampshade'.

I've wondered if such phenom could be used to propel an aircraft.

I also wonder if instead of a hollow ring foil, linear airfoils with air ejection could be used for spoilers and diffusers on the rear of cars, to fill and fair the turbulence behind the car, reducing drag.

Thoughts?

[Sven7]

I remember reading here that for every time you cut the scale of a car in half, you have to double the speed of airflow to get accurate wind tunnel results.

1/1, 15mph
1/2, 30mph
1/4, 60mph
1/8, 120mph
1/16, 240mph
1/32, 480mph

So if you were going to test a 1/18 scale car in a home made wind tunnel, you'd somehow have to get the air going at around 300mph to have any usable results. Now I learn that my 4th grade science project wasn't very accurate.