1. Date of download: 11/8/2017
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From: Ventilation of Lifting Bodies: Review of the Physics and Discussion of Scaling Effects
Appl. Mech. Rev. 2017;69(1): doi: /
Figure Legend:
Measured hydrodynamic loads on a vertical surface-piercing strut with a symmetric semi-ogival section shape (c = 27.9 cm) in a towing tank at ARh = 1.0 and Fnh = 2.5. Load coefficients were also modeled using a modified lifting line method, plotted as dashed lines. In all the three plots, αb = 2.5 deg denotes the bifurcation angle and αs = 15 deg denotes the stall angle. Flow below α = 2.5 deg is exclusively fully wetted and flow above α = 15 deg is exclusively fully ventilated, leaving a range of bistable yaw angles of 2.5 deg ≤ α ≤ 15 deg. (Reprinted with permission from Harwood et al. [32]. Copyright 2016 by Cambridge University Press.) (a) Three-dimensional lift coefficient. Lift in the fully ventilated regime is significantly lower than that in the fully wetted regime at large yaw angles. At small yaw angles, lift coefficients in the two regimes are similar as a result of short, thin cavities, which neither reduce a0 significantly nor induce significant apparent camber. (b) Three-dimensional drag coefficient. The onset of ventilation reduces frictional and lift-induced drag, but incurs larger form and parasitic drag components. (c) Three-dimensional yawing moment coefficient, measured about midchord. Ventilation reduces both the lift and the moment arm of the lift about midchord. As a result, the yawing moment behaves as a sublinear (convex) function of α.