Drafting

Originally posted by Conniekat8 Here's an experiment that may answer some of your questions: Go to the bathtub, fill it up with water. Take your 3 hole punch and empty the confetty over the water surface. Put your hand in the water (slowly and carfully, to disturb the surface as little as possible) then pull your hand in a fast liner motion in one direction, as if it is a swimmer going in that direction. Watch what happens to the confetti. Do it again, at variable speeds and variable hand depth and cross section. I don't think that what happens with the confetti relates in any significant way to the drafting effects we are talking about. It just shows where the tail eddys and turbulence and, perhaps how it moves. The confetti is simply reacting to water that has already been accelerated by the passing of the hand - they are not significantly changing the water flow. Actually my question about how the phenomena experienced by birds and nascar drivers might relate to swimming regards the interplay of the leader swimmer's wake with the drafter and, in the case of the drafter creeping up along side of the leader's legs/hips, the effect of the drafter's wake on the leader. I also question whether the drafter actually gets close enough to the lead swimmer to mimic the Nascar paradigm (where the two cars effectively act as one long car as far as air flow is concerned). If not, then drafting will not necessarily be a boon to the lead swimmer. If so, then drafting is almost certainly a boon to the lead swimmer - though not as big a boon as it is to the drafting swimmer.

Originally posted by knelson Actually that is exactly what we are looking for. It tells us that a swimmer passing through the quiescent water will accelerate that water in the direction he/she is swimming. All it tells us is it's possible to draft, though. It tells us some of that swimmer's (or hand's) energy has been transferred into moving the water forward. It doesn't really help answer the question of whether the lead swimmer is helped or hindered by a drafting swimmer, though. I took it as obvious that the swimmer has accelerated some water. What the confetti is entirely unable to show us is how that accelerated water now affects another, similar size/mass, object that is placed in that space. The lone Nascar IS "pulling" air along behind it - which costs some energy. When the draft car tucks in behind that car the drafter now "pulls" a large portion of the tail air instead of the lead car pulling it. This shifts the work (fuel consumption) of pulling that air onto drafter and frees the lead car from that portion of the combined work. In return, the drafter is relieved of much of the frontal resistance which the lead car still labors under. Because the trailing end of a swimmer is quite tapered, the amount and nature of the tail eddys and turbulence is quite different than that of the rather blunt ended cars. A bit like the difference between the tail end of a Kayak vs the tail end of a rowboat. While a swimmer can get close enough to benefit from lower frontal resistance, I think the swimmer cannot get close enough to shift the tail resistance away from the lead swimmer.

The truth is that like cycling the person being drafted also gains an advantage. Same speed with less effort. Or if you wish greater speed with the same effort. If you have a person on each side of you even better. Add one behind better yet. Of course the benefit is not as great as the one drafting.

Originally posted by GNITE The truth is that like cycling the person being drafted also gains an advantage. Same speed with less effort. Or if you wish greater speed with the same effort. If you have a person on each side of you even better. Add one behind better yet. Of course the benefit is not as great as the one drafting. Are you aware of any research that bears this out for either swimmers or other surface penetrating moving objects?

Turbulence increase speed?? So that’s why the announcers are always asking for us to cheer on the swimmers! The increased commotion and turbulence decreases drag. I always wondered why we swam faster with a cheering crowd. Thanks! And back to the subject of drafting, I think USA-Swimming did some extensive studies a few years back. For those who are really interested in this, they should contact USA-Swimming to see if they can get the scientific results.

Lat night, I swam wiht the Unerv. of Ill. masters team. We did Indian Swimming. It used drafting by having us swim in a close line and sprinting. It was a lot of fun but drafting is a big no-no. Also, when you listen to peole after they've just swam a really fast time, thye will almost always mention that what was the best thing was that the water was either quiet or smooth. If you can get still water & move through it, you will swim faster. At least that is what I've always been told. Isn't that why you skull? So that your hand moves into still water through the length of the pull. Wave action is very tricky, it seems to me. Trying to move into & then stay in some one else's wave can be very deceiving. I don't know about all of this. When I think about it, it makes sense. But when I try it, I use a lot of energy trying to stay in the wave coming off of another person. Who knows? Some of this is talked about in Swimming Fastest. Physics is so confusing ot me, I was an Anthropology major. I could go on forever about the social and ecomonical dymanics of the division of swimmers in lanes

Turbulent flow actually decreases drag compared to laminar flow for a bluff (i.e., not streamlined) body because it reduces the size of the wake. A good swimmer tries to be streamlined, but we're still not exactly an airfoil!

I think you're confusing turbulence with wave action, but I see your point! What you want to do is ride the other swimmer's wave, not get swamped by it.

Originally posted by GNITE The truth is that like cycling the person being drafted also gains an advantage. Same speed with less effort. Or if you wish greater speed with the same effort. If you have a person on each side of you even better. Add one behind better yet. Of course the benefit is not as great as the one drafting. And if those drafting on either side are creating waves and other turbulence that disrupt what might otherwise be more laminar flow along the lead swimmer's lower body, this works against the lead swimmer.

Originally posted by knelson Turbulent flow actually decreases drag compared to laminar flow for a bluff (i.e., not streamlined) body because it reduces the size of the wake. A good swimmer tries to be streamlined, but we're still not exactly an airfoil! If swimmers benefit from turbulence projected at them from an outside source it would seem that getting rid of lane lines would help trim some time off those stubborn world records. :)