Low Froude Number Hydrodynamic Performance of a Flat Plate Hydrofoil.
DAVID W TAYLOR NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER BETHESDA MD SHIP PERFORMANCE DEPT
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Results of towing tank experiments are presented for lift, drag, moment, and center of pressure of an aspect ratio 4, rectangular planform, 5.21 thick, flat plate hydrofoil attached to a large strut and pod and operated beneath the free surface of water. The nominal range of the chord Froude number was 0.5 to 3.5 with corresponding chord Reynolds numbers of 740,000-5,200,000. Tests included foil submergence depths ranging from 0.25 to 3.5 chord lengths, and foil angles of attack varying from 0 -8 deg. These data fill an important gap in our experimental knowledge of near-surface, low speed hydrofoil performance. Experiments indicate that there are significant changes in lift and drag for operation at shallow and moderate submergences in the low chord Froude number range, especially around 0.75 to 1.5. Prediction of residual drag coefficients for an 18-foot-chord hydrofoil operating at constant lift shows that the wavemaking drag is significant and that the trend of increase in residual drag at froude numbers ranging from 3.5 down to 1.75 appears to be roughly parallel to the trend of induced drag alone. However, the magnitudes of residual drag coefficients are rather large, and there are indications that interference wave drag, due to the presence of a strut and a pod, is an important feature of the low speed drag variation.
- Fluid Mechanics