I happen to know a Ph.D on the subject, so I ran it by him : Probably a little more info than anyone needed, but that is Just what we do on this list!
<< Bill: The winglets and vortex shedding are unrelated. They both involve vortexes but they are different issues. When you have flow separation around a bluff body (like a shroud or a mast) you will get vortices shed in an alternating fashion from one side and then the other. This will cause a lateral sinusoidal force and if the frequency of the shedding matches the natural frequency of the object it will go into resonance which is what causes the noise. An airplane wing also produces vorticity but unless it's stalled it's not vortex shedding. The wing vorticity causes a change in the direction of the incoming flow which results in part of the lift vector pointing backwards - which is in the direction of drag - and is thus called lift-induced drag (or just induced drag). Winglets bascailly fake out the flow to make it think that the wing is longer than it is, and thus reduced the induced drag. If you google "vortex shedding" and "induced drag" I'm sure you will see some pictures or drawings explaining this. Cheers, Bill L >> -----Original Message----- From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Don Wagner via CnC-List Sent: Monday, July 25, 2016 8:08 PM To: cnc-list@cnc-list.com Cc: Don Wagner; Christian Tirtirau Subject: Re: Stus-List Singing Rigging This is technically known as "vortex shedding". It's a natural phenomena caused by the air flow around a round cylinder ( the rod or the wire) and occurs at certain wind speeds. At normal speeds, normal flow occurs, and there's no vibration. At certain higher speeds, vortexes develop, and induce vibrations in the rigging. Tightening or loosing the rigging will usually reduce the effect. You can find a more complete description on the internet. Note: Commercial airliners have observed the problem at their wing tips, and many recently added small winglets at the ends of their wings. I believe this reduces energy loss, reduces the vibration, and improves their fuel mileage. Don Wagner C&C 41 CB Der Baron West River MD -----Original Message----- From: Christian Tirtirau via CnC-List Sent: Monday, July 25, 2016 11:04 AM To: cnc-list@cnc-list.com Cc: Christian Tirtirau Subject: Stus-List Singing Rigging Hello fellow seers, I'm getting this humming in the mast as soon as I have a little breeze while on the mooring ball and it's really annoying. At first I thought it was a generator or an engine sound propagated by water but I realized it's the strings of this big violin that are singing. Any idea how you get rid of that without messing up the rig balance? Is it the baby stay? I have a lower that is a little loose and when I tension it the sound pitch changes but does not go away. Cheers, Christian Tirtirau C&C 37 Northern Light _______________________________________________ This list is supported by the generous donations of our members. If you like what we do, please help us pay for our costs by donating. All Contributions are greatly appreciated! _______________________________________________ This list is supported by the generous donations of our members. If you like what we do, please help us pay for our costs by donating. All Contributions are greatly appreciated! _______________________________________________ This list is supported by the generous donations of our members. If you like what we do, please help us pay for our costs by donating. All Contributions are greatly appreciated!
