Science Fair 04-05: Laminar Flow

Problem: What effect does the direction of a boat bow into the wind have on the laminar flow over a single sail?

Hypothesis: The laminar flow will be steadiest when the sail is properly sheeted at an angle to the wind, and more turnbulent when the bow is in, very near to, or far off the wind.

Materials: Small sailboat, large lawn with few or no windbreaks, wind indicator for visual comparison (in this case, mop handle), telltales (ribbon) and fastener (tape), camera, assistant to hold boat/sheet if necessary.
*This experiment requires some knowledge of wind and sailing.

Methods:
1. Gather materials.
2. Set up the experiment on the lawn. Before raising the sail, spread it out enough that you can get to the leech (the long edge on the outside, not attached to the mast or boom) and attach the tell-tales at even intervals. If you are installing permanent store-bought tell-tales, follow all manufacturer's instructions. Raise the sail properly; take care to raise the top of the sail all the way up the mast.
3. Aim the bow of the boat directly into the wind. Sheet in the sail so that it does not luff too badly. Take a picture from directly underneath the sail, looking as straight up as possible (depending on wind strength, hull shape, and sail shape, you may need to find another angle, as from directly behind the sail). If you are using a digital camera, you may need to take several pictures in order to ensure that at least one comes out clearly.
4. Lift the bow of the boat carefully and shift it left so that the boat is "sailing" forty-five degrees off the wind. Sheet in as necessary. Take pictures.
5. Sheet the sail out, so that it luffs. Take pictures. Then oversheet the sail and take pictures.
6. Shift the bow another forty-five degrees so that the boat is lying perpendicular to the wind. Sheet as necessary; take pictures (oversheeted, undersheeted, and properly sheeted).
7. Repeat the process on the "other tack" (to the right of the wind).
8. Bring the bow back into the wind to lower the sail. Unless they are permanent, remove the tell-tales. Stow the boat properly.
9. Develop/upload the pictures to a computer. Choose the best of each series of pictures (in the wind; oversheeted 45 degrees, undersheeted 45 degrees, properly sheeted 45 degrees, under/over/proper 90 degrees, etc.). Use these to determine and record the angle of the tell-tales to the leech edge. They will all be slightly different, especially if they are made of a light material; if necessary, take the measure of each angle and record the average.

Results: ((DO AT HOME TONIGHT))

Analysis; As the bow fell farther away from the ideal point of sailing, the laminar flow became more disturbed. At zero degrees off the wind the tell-tales all blew in the same direction, but they moved erratically. At forty-five degrees, there was some slight variation in direction but the tell-tales flapped considerably less. At ninety degrees, the tell-tales flapped wildly again and there was a large deviation in direction from one marker to the next.
*Errors in this experiment include the following:
1. Erratic gusts of wind
2. Windbreaks (trees and a hous) in the vicinity of the experiment
3. A slower shutter-closing time on the camera, which resulted in few clear pictures
4. A lack of an entirely accurate way to lay the boat off of the wind, due to irregularities in the ground and the curved shape of the hull

Conclusion: The hypothesis was correct. Laminar flow was strongest when the boat lay closer to the optimal point of sail, and more disturbed as it fell or climbed away.