contemplating a golf ball

Discussion in 'Cycling Equipment' started by Potatosmack, Apr 29, 2003.

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  1. Potatosmack

    Potatosmack Guest

    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.
     
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  2. PotatoSmack wrote:
    > 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
     
  3. In article <[email protected]>, PotatoSmack
    <[email protected]> wrote:
    >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.
     
  4. Ron Hardin

    Ron Hardin Guest

    PotatoSmack wrote:
    >
    > 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 protected]

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

    Eric Murray Guest

    In article <[email protected]>, PotatoSmack
    <[email protected]> wrote:
    >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
     
  6. Terry Morse

    Terry Morse Guest

    PotatoSmack wrote:

    > 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 http://www.terrymorse.com/bike/
     
  7. Tim Cain

    Tim Cain Guest

    "PotatoSmack" <[email protected]> wrote in message
    news:[email protected]...
    > 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.
     
  8. PotatoSmack wrote:
    >
    > 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
     
  9. Terry Morse

    Terry Morse Guest

    Ron Hardin wrote:

    > 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 http://www.terrymorse.com/bike/
     
  10. Ron Hardin

    Ron Hardin Guest

    Terry Morse wrote:
    > > 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 protected]

    On the internet, nobody knows you're a jerk.
     
  11. Paul J Pharr

    Paul J Pharr Guest

    "Terry Morse" <[email protected]> wrote in message
    news:[email protected]...
    > PotatoSmack wrote:
    >
    > > 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
     
  12. 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 wrote:
    > 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.
     
  13. Vol

    Vol Guest

    >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.
     
  14. Terry Morse

    Terry Morse Guest

    Ron Hardin wrote:

    > Terry Morse wrote:
    > > 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:

    http://tinyurl.com/amec

    One can see the difference clearly in the photos: the boundary layer separates much sooner on the
    smooth ball.
    --
    terry morse Palo Alto, CA http://www.terrymorse.com/bike/
     
  15. Mike Zaharis

    Mike Zaharis Guest

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

    http://www.ssa.org/Johnson/86-1997-05.pdf http://www.ssa.org/Johnson/90-1998-05.pdf

    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.
     
  16. On Tue, 29 Apr 2003 15:34:30 +0000, PotatoSmack wrote:

    > 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. _`\(,_ | (_)/ (_) |
     
  17. Ron Hardin

    Ron Hardin Guest

    Terry Morse wrote:
    >
    > Ron Hardin wrote:
    >
    > > Terry Morse wrote:
    > > > 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:
    >
    > http://tinyurl.com/amec
    >
    > 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 protected]

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

    monkey Guest

    >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!
     
  19. Ron Hardin <[email protected]> wrote:

    > 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:

    http://www.rmcs.cranfield.ac.uk/aeroxtra/e348hsfmachn.htm

    http://www.rmcs.cranfield.ac.uk/aeroxtra/e348cont4.htm
     
  20. Ron Hardin

    Ron Hardin Guest

    Benjamin Weiner wrote:
    > > 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 protected]

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