A couple of people have asked about how flow gets determined in the tank so I may as well post it for everyone. The most common method uses yarn or plastic streamers. In some cases these get taped right to the hull and in others they get suspended away from the hull on small wires. Another clever method uses finely ground aluminum particles suspended in the water. This works best in observing the flow form overhead. Another method uses dye that is injected in front of the boat's path. This works OK but the dye soon dissipates. In wind tunnels smoke provides visual evidence of flow. Taylor coated the models with sesquichloride of iron mixed with glue. Then he injected pyrogalic acid through a small hole resulting in a smear of ink that revealed the flow. He would then drill a new hole where the ink smear lost definition until he eventually worked his way to the stern. For flow away from the he used meshes of fine string or wire coated with sesquichloride of iron and injected pyrogalic acid at known points. Taylor says," The relative flow indicated in the immediate vicinity of the model is found as regards to type quite a distance from the skin, so as regards motion near the hull we need consider only the disturbance close to the bottom, or the lines of flow as they may be called." These days I think this gets done mathematically since one doesn't mess up the tank or models. One of the things that impress me has to do with the similarity in flow lines for widely divergent hull shapes. The flow lines (crudely done with yarn I admit) I got on my sprint boats looked remarkably like those I got for my canoes and they looked remarkably like the ones Taylor got on his ship models. Matt asked why I thought the flow would dive under the hull and I must answer "I don't know" but the evidence points to something other than water being pushed only to the side. Cheers, John Winters Redwing Designs Specialists in Human Powered Watercraft http://home.ican.net/~735769/ *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************Received on Tue May 25 1999 - 04:40:21 PDT
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