contemplating a golf ball

PotatoSmack said:

I was contemplating the dimples on a golf ball and the ridges on a Frisbee. I noted that a little
turbulence was a good thing. Hence to make myself more aerodynamic on the bike I will shave the
front of my legs and leave the back of my legs hairy. What effect will this have. Comments and
opinions please.

It will make you look like a damn fool... er, I mean, really cool. All the chicks will be all over
you... yeah.

I say do it.

Jon Bond

In article <[email hidden]>, PotatoSmack

Quoted message said:

I was contemplating the dimples on a golf ball and the ridges on a Frisbee. I noted that a little
turbulence was a good thing. Hence to make myself more aerodynamic on the bike I will shave the
front of my legs and leave the back of my legs hairy. What effect will this have. Comments and
opinions please.

Rogaine on your back.

PotatoSmack said:

I was contemplating the dimples on a golf ball and the ridges on a Frisbee. I noted that a little
turbulence was a good thing. Hence to make myself more aerodynamic on the bike I will shave the
front of my legs and leave the back of my legs hairy. What effect will this have. Comments and
opinions please.

The ridges on the frisbee are there to equalize the lift from the front and rear edges. If they're
not pretty equal, the thing rolls left or right right away. As it happens, the center of lift shifts
from rear to front slightly as it slows down, so it starts by rolling right slowly and ends by
rolling left. The ridges took out the bias to center it around no-roll (right hand toss; reverse for
left hand toss).

On a golf ball, dimples thicken the boundary layer over which wind sheer happens. You don't want to
move air with a golf ball, as opposed to a lifting surface, where moving air is the whole point.
--
Ron Hardin [email hidden]

On the internet, nobody knows you're a jerk.

In article <[email hidden]>, PotatoSmack

Quoted message said:

I was contemplating the dimples on a golf ball and the ridges on a Frisbee. I noted that a little
turbulence was a good thing. Hence to make myself more aerodynamic on the bike I will shave the
front of my legs and leave the back of my legs hairy. What effect will this have.

It will slow you down-- you have it backwards. You are supposed to leave the front of your legs
hairy and shave the backs. Also, glue grains of sand to the leading edges of your frame tubes.

Eric

PotatoSmack said:

Hence to make myself more aerodynamic on the bike I will shave the front of my legs and leave the
back of my legs hairy. What effect will this have.

If you want to be more aerodynamic, the leading edge of a bluff body (like your legs) should be
rough. Some 80 grit sandpaper rubbed vigorously against your shin should suffice. Repeat when the
scabs come off.
--
terry morse Palo Alto, CA terrymorse.combikeOpen ↗

"PotatoSmack" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

I was contemplating the dimples on a golf ball and the ridges on a Frisbee. I noted that a little
turbulence was a good thing. Hence to make myself more aerodynamic on the bike I will shave the
front of my legs and leave the back of my legs hairy. What effect will this have. Comments and
opinions please.

That's half-hearted.

You can get the authentic "dimpled like a golf ball" effect by getting someone to vigorously beat
the whole of your body with a steak tenderising hammer.

If you survive this, you'll win the TDF.

If you don't, the guy who did the beating can rub a little oregano, chili and garlic into your body,
fire up the BBQ and enjoy succulent, tender prime cuts of you.

Tim.

PotatoSmack said:

I was contemplating the dimples on a golf ball and the ridges on a Frisbee. I noted that a little
turbulence was a good thing.

I've known people with skin texture similar to a golf ball and it did nothing for speed. <G>

Barry

Ron Hardin said:

On a golf ball, dimples thicken the boundary layer over which wind sheer happens. You don't
want to move air with a golf ball, as opposed to a lifting surface, where moving air is the
whole point.

I think you have hit a slice there. Golf ball dimples promote turbulence, and a turbulent boundary
layer will not separate from a body as readily as a laminar boundary layer. Separation is bad, as it
produces drag. A bluff body will almost always experience reduced drag when the flow is turbulent.
--
terry morse Palo Alto, CA terrymorse.combikeOpen ↗

Terry Morse said:

Quoted message said:

On a golf ball, dimples thicken the boundary layer over which wind sheer happens. You don't want
to move air with a golf ball, as opposed to a lifting surface, where moving air is the whole
point.

I think you have hit a slice there. Golf ball dimples promote turbulence, and a turbulent boundary
layer will not separate from a body as readily as a laminar boundary layer. Separation is bad, as
it produces drag. A bluff body will almost always experience reduced drag when the flow is
turbulent.

A turbulent boundary layer is very happy to separate from the body, that's why the drag is reduced.
The airflow doesn't follow the backside of the ball.
--
Ron Hardin [email hidden]

On the internet, nobody knows you're a jerk.

"Terry Morse" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

PotatoSmack said:

Hence to make myself more aerodynamic on the bike I will shave the front of my legs and leave
the back of my legs hairy. What effect will this have.

Personally, I have sharkskin tights and jersey. It's real hot, but it slices through the wind
real good.

Actually, I zipped my jersey, closed my mouth and laid off the beer so I wouldn't be so wide (what
was I thinking!!??)

Paul J Pharr

PotatoSmack, The golf ball dimples induce turbulence in the boundary layer, which will cause the
flow to travel farther against an adverse pressure gradient than laminar flow before it seperates
(and causes a lot of drag).

For a pipe, you can use a streamlined fairing on the back side of the pipe (see the nose gear of a
Grumman Tiger for an example). This should work the best for the bike. For your legs, you probably
need as much turbulence as you can get (low reynolds number), if you want to do the golf ball thing.
You'd probably do better (but look much dumber) if you tape triangular streamline fairings
(cardboard?) to your legs, or better yet, torso.

True science is never pretty.

Steve.

PotatoSmack said:

I was contemplating the dimples on a golf ball and the ridges on a Frisbee. I noted that a little
turbulence was a good thing. Hence to make myself more aerodynamic on the bike I will shave the
front of my legs and leave the back of my legs hairy. What effect will this have. Comments and
opinions please.

Quoted message said:

make myself more aerodynamic on the bike I will shave the front of my legs and leave the back of my
legs hairy. What effect will this have.

If you decide against the suggestions already offered, just wait a few years. Your body will begin
to mold itself into a fine variety of interesting shapes.

Ron Hardin said:

Terry Morse said:

I think you have hit a slice there. Golf ball dimples promote turbulence, and a turbulent
boundary layer will not separate from a body as readily as a laminar boundary layer. Separation
is bad, as it produces drag. A bluff body will almost always experience reduced drag when the
flow is turbulent.

A turbulent boundary layer is very happy to separate from the body, that's why the drag is
reduced. The airflow doesn't follow the backside of the ball.

A hook this time, but you're getting better. The point is that a turbulent boundary layer will
not separate as soon as a laminar one, and it is this fact that reduces the wake turbulence and
therefore the drag. This page visually shows the flow difference between a smooth ball and a
rough one:

tinyurl.comamecOpen ↗

One can see the difference clearly in the photos: the boundary layer separates much sooner on the
smooth ball.
--
terry morse Palo Alto, CA terrymorse.combikeOpen ↗

[email hidden] (PotatoSmack) wrote in message
news:<[email hidden]>...

Quoted message said:

I was contemplating the dimples on a golf ball and the ridges on a Frisbee. I noted that a little
turbulence was a good thing. Hence to make myself more aerodynamic on the bike I will shave the
front of my legs and leave the back of my legs hairy. What effect will this have. Comments and
opinions please.

I disagree with those that say that the roughness should start at the front of the bluff body. The
roughness should start just prior to the separation point. This is the order of boundary layer
conditions, in decreasing order of desirability:

Smooth boundary Layer Rough Boundary Layer Separated Boundary Layer

There's no reason to trip a smooth boundary layer prior to separation. It just increases the
boundary layer drag, and does not eliminate separation. Roughness just prior to separation energizes
the boundary layer, and delays separation. After separation, the surface treatment doesn't make much
difference.

Sailplane pilots will actually cover their wings with blackened (dirty?) oil and go up for a flight,
which will leave a pattern that indicates where separation has occurred. They then put a zig-zag
turbulator tape (similar to what the Dutch used on their speedskating skinsuits in 1998) to trip the
boundary layer just prior to separation. They operate at a Reynolds number somewhat comparable to
cyclists. See the following document from the Soaring Society of America.

ssa.org86 1997 05.pdfOpen ↗ ssa.org90 1998 05.pdfOpen ↗

What does this have to do with cycles? Just go into a wind tunnel, determine the separation line on
your legs using blackened oil, and epoxy a zig-zag turbulator strip to your legs just in front of
it. Simple, huh?

Seriously, the lesson here is that to see any improvement, you really need to carefully determine
the separation point prior to trying a turbulator. The minor waviness on these wings was causing
separation. I'm sure that your rippling calf and thigh muscles are causing the same effect. I doubt
that there is any gain, measurable or otherwise, in leaving the hair on your back of your legs.

PotatoSmack said:

Hence to make myself more aerodynamic on the bike I will shave the front of my legs and leave the
back of my legs hairy. What effect will this have.

People will laugh at you on the beach.

--

David L. Johnson

__o | Become MicroSoft-free forever. Ask me how. _`\(,_ | (_)/ (_) |

Terry Morse said:

Ron Hardin said:

Terry Morse said:

I think you have hit a slice there. Golf ball dimples promote turbulence, and a turbulent
boundary layer will not separate from a body as readily as a laminar boundary layer.
Separation is bad, as it produces drag. A bluff body will almost always experience reduced
drag when the flow is turbulent.

A turbulent boundary layer is very happy to separate from the body, that's why the drag is
reduced. The airflow doesn't follow the backside of the ball.

A hook this time, but you're getting better. The point is that a turbulent boundary layer will
not separate as soon as a laminar one, and it is this fact that reduces the wake turbulence and
therefore the drag. This page visually shows the flow difference between a smooth ball and a
rough one:

tinyurl.comamecOpen ↗

One can see the difference clearly in the photos: the boundary layer separates much sooner on the
smooth ball.

Alas the explanation is wrong. Imagine the golf ball extended into a nice symmetrical wing or tear
shape at the point it separates in laminar flow. How would the flow know a wing was coming up (that
it should stick to) instead of a ball (that it should separate from)?

It's not _separation_ that's happening. What you see is wake turbulence, reduced in coverage by its
forming on a wider boundary layer. There's some instability involved, the one I know being that
turbulence forms on an inflection point of a shear-velocity profile and grows under some condition
or other; the less the underlying sheer, the more benign, or anyway it waits until the ball is past
and gathers up less air in the process. My best guess is that roughness reduces the scale size of
the turbulence and so reduces the amount of air that can be engulfed in the end, growing like a
square root instead of linearly over time as the ball goes by and the turbulence grows.

In effect the more turbulence, the less body shape matters. If you have a really bad shape (ball)
then you get less drag with deliberate turbulence. If you have a good shape, you get less drag
without turbulence. The flow can't organize into a huge drag-inducing pressure drop behind the ball
but breaks up and adds randomly in smaller pieces.

If you put spoilers on the top of a wing, the flow separates _earlier_ not later, another
inconvenient fact. To extend adhesion, some wings have blowers sucking air off the top surface to
reduce even the regular turbulence there. Wings want drag, just not in the forward direction. They
want a large organized motion to be left behind, downwards. Turbulence in the boundary layer reduces
lift by reducing the size that organized motion can be organized into, and thus the downward
deflection of air, which is precisely the lift of the wing.
--
Ron Hardin [email hidden]

On the internet, nobody knows you're a jerk.

Quoted message said:

People will laugh at you on the beach.

Who cares if they laugh when he's the next TDF winner because of his aerodynamic advantage he's
discovered!

Ron Hardin said:

Alas the explanation is wrong. Imagine the golf ball extended into a nice symmetrical wing or tear
shape at the point it separates in laminar flow. How would the flow know a wing was coming up
(that it should stick to) instead of a ball (that it should separate from)?

Actually, in subsonic flow, the flow does know that a wing is coming up. One way to think about this
is that information about the flow is propagated forward and back along streamlines at the speed of
sound. (Formally, this is probably a statement about solving the partial differential equations of
fluid flow by the method of characteristics.) When the shape of the body is changed, the entire
streamline pattern changes.

In contrast, in supersonic flow, there are shock waves at which dissipation occurs, the equations of
fluid flow are irreversible, and information cannot propagate back through the shock (this means
that backward-propagating characteristics meet up at the shock). The preshock flow does not know
anything about the details of the postshock flow.

There are a couple of good illustrations of this at:

rmcs.cranfield.ac.uke348hsfmachn.htmOpen ↗

rmcs.cranfield.ac.uke348cont4.htmOpen ↗

Benjamin Weiner said:

Quoted message said:

Alas the explanation is wrong. Imagine the golf ball extended into a nice symmetrical wing or
tear shape at the point it separates in laminar flow. How would the flow know a wing was coming
up (that it should stick to) instead of a ball (that it should separate from)?

Actually, in subsonic flow, the flow does know that a wing is coming up. One way to think about
this is that information about the flow is propagated forward and back along streamlines at the
speed of sound. (Formally, this is probably a statement about solving the partial differential
equations of fluid flow by the method of characteristics.) When the shape of the body is changed,
the entire streamline pattern changes.

Exactly what I am saying. The cause of the _apparent adhesion_ is a lack of large scale motion
downstream, not turbulence upstream. The turbulence reduces the scale size of downstream motions.
Downstream affects upstream as well as the reverse.

It's easier to intuit with the air stationary and the ball moving. If you're a bit of air a little
way away to the side, a ball covered with turbulence disturbs you less than a ball with large scale
motions following it around.
--
Ron Hardin [email hidden]

On the internet, nobody knows you're a jerk.