Trans RINA, Vol 152, Part B1, Intl J Small Craft Tech, 2010 Jan-Jun particular, with regard to the comment by Grant
Spanhake, the luff flaps at 1.4 Hz in trim #1, while does not flap in all the other trims. Figure 12 shows the auto- correlation of the pressure signal measured on the leeward side at the leading edge for the three trims #1, #2 and #3.
many points of view to allow the flying shapes to be post-processed with photogrammetric
technique. The
Yacht Research Unit is consistently investing in flying shape detecting systems, and is developing a real-time photogrammetric
system named VSPARS, which is
already used for commercial testing, and increasing the capabilities of an existing devoted laser scanner.
With regard to the comments by Grant Spanhake, Figure 13 shows one of the pressure tap adopted. The tap is a truncated cone with a rectangular base, the base of which is 17x10 mm2. The transparency of the material allows the hole on the base to be seen, and is connected with a stainless steel tube to a plastic pressure tube.
Figure 12: Auto-correlation of the pressure signals for three trims.
The drive force achieved by trim #1 is lower than the drive force achieved by trim #2. However, in the unstable full-scale condition, trim #2 and trim #3 might be unrealistic, because to stabilize the luff, the sheet has to be tightened significantly (as in trim #4). Hence, in full- scale condition the flapping trim would result in a larger drive force than the non-flapping trim.
With regard to the comment by Robert Ranzenbach, the pressure coefficient measured on the windward side of the A3 is presented on figure 10 of the paper for four trims, named #1, #3, #5 and #7 respectively. The luff is flapping in trim #1, while the sheet is tightened enough to stabilize the luff in trim #3, and it is over-trimmed in trim #5 and #7. When the luff is not flapping, the pressure coefficient is almost one over the whole section; it is at the same pressure of the stagnation point. When the luff
flaps, the stagnation point moves from the
windward to the leeward side and vice versa repeatedly. When the stagnation point is on the leeward side, the pressure coefficient over the windward side should be lower than one, due to the higher velocity of the flow. Hence, a flapping trim leads to two values of the pressure coefficient: one when the luff is straight the pressure coefficient is almost 1.0, and another when the luff is curled the pressure coefficient is lower than 1.0. The pressure coefficient during flapping trim results in the average of these two values, which would be lower than 1.0. In fact, the pressure coefficient correlated to trim #1 is roughly Cp=0.7.
With regard to the comments by Michael Richelsen, the test was performed also with the aim to provide suitable CFD benchmarks, and cameras recorded each trim from
Figure 13: Photograph of the pressure tap.
We thank the reviewers for their insightful and interesting comments about our paper. We will take note of their input in our future research on this topic.
© 2010: The Royal Institution of Naval Architects
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