Paging the scientists

Two turbulence question.

1. Why are fairings smooth? Golf balls are dimpled to generate boundary
layer turbulence which reduces drag. Why not a bike fairing?


2. Wind breaks allow some air through to reduce turbulence. Why don't
bike screens have very small holes to allow air through?

 

I've seen dimpled fairings, now you mention it.

Have you ever looked really closely at a fairing - full of holes, it
is.

 

cos I don't want my bike twatted by tiger woods!!

the first blades did have

 

I think the dimples are there to assist the directional stability
BICBW
Surely boundary layer turbulence increases drag rather than reducing
it, which is why high speed aircraft are highly polished.

Mine has two very nice slots on the windscreen, they supposedly reduce
the 'vacuum' that forms behind the screen.

Paging Michael Carley; do you still have the airflow pics of my old
Pan?

 

Paint yours with black paint mixed with sand, and see if it makes any
difference.

What, like that experimental plane with the holes that suck? Bit stupid
to have that on a bike that doesn't go that fast.

 

English Electric Lightning ?

Paul.

 

Naa.. the one I'm thinking about is an X plane.

 

Well I was thinking more of those windbreaks you see behind the seats of
a convertable cage

 

The dimples actually increase drag from the front side of
the golf ball. This is also true for other designs that
increase turbulence, you might have seen them on parts
of the upper surface on airplane wings.

The desired effect is to get a more "energetic" boundary
layer that will follow the surface as far as possible on the
rear side of the object. That way the golf ball does not
have to fight a large low pressure area where the air flow
has separated completely. And the wing will respond to
steering input or use of flaps instead of going into a stall.

Now, as bike fairings have no rear half to talk about, it is
of little use to create more drag on the front side as it
will separate totally at the edge of the fairing all the same.
Off course there may be designs of fairing or fairing +
rider that might benefit from increased boundary layer
turbulence and the designer would find this out by doing
wind tunnel testing (or computer simulation, I guess).

 

The CBR Thou has a slit at the base of the screen to reduce turbulence.

 

I don't take much notice.

 

Because it is the larger scale shape of the fairing that decides whether
the air that slides off it gets turbulent, or flows in a smooth laminar
way?

Because it would also allow rain water through, to make you wet and the
electrical system corrode?

My 2p's worth.

 

They also spin and create lift, you wouldn't want that on a bike.

Some do, the pan has little vents IIRC.

 

CBR thou and 'aerodynamics' don't sit comfortably with each other.

 

You've not really spent much time looking at anything post the early models
then, have you really.

 

"when fluid dynamics go wrong"

 

Gofl balls are made in such a way as to limit the distance they can be
hit with modern clubs. Otherwise, they would have to keep lengthening
the holes to avoid turning all the current courses into pitch and
putts.

 

Absolute tosh. Dimples are there to aid flight not reduce it.
Dimples or texturing have been on golf balls since the gutta percha balls of
the 1800's