On 12/04/2015 09:00, robin_d...@hotmail.com wrote:blades have a noticeable effect on a crew?
And how's about a golf-ball-textured film.
Enough for a Friday!
Another question which has come to mind after watching the Boat Races - in proper headwind conditions, would the reduced diameter of the scull-like C2 skinny sweep shafts compared to more conventional diameter of either normal C2 or Croker sweep
In short, yes.Hi Carl,
For a 5cm diameter cylinder transverse to a 10m/sec air flow, the
Reynolds number is about 450. At that point the drag coefficient for a smooth cylinder will have fallen almost to a plateau of around
1.2<Cd<1.4 & may rise only slightly as diameter, & hence Re, is reduced).
Since reduced diameter reduces frontal area, & since drag is
proportional to the product of frontal area times velocity squared,
slimmer oars should probably reduce wind drag, but not quite in direct proportion to the diameter reduction.
That said, it is within the range 50<Re<800 that you might expect the greatest benefit from fitting boundary layer trips as a means to
re-energise the surface flows & thus to reduce Cd by reattaching an otherwise separating boundary layer.
For the slimmer oar you must be sure that its bending and torsional stiffness remain within acceptable limits, but if the reality is that
you are outside the zone within which these become critical to your use
of the oar, then smaller diameter should be better.
Cheers -
Carl
--
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