| An experimental investigation of steady breaking waves produced by towing fully submerged two-dimensional hydrofoils at constant depth (d), speed (U) and angle of attack is presented. Three hydrofoils of chord (c) 15, 20 and 30 cm are used to create the breakers at speeds of 69, 80 and 98-cm/s, respectively. Each foil is towed at the same three d/c ratios, creating three sizes of Froude scaled breaking conditions at each of three different breaking intensities, to investigate the effect of viscous, capillary, gravitational and inertial forces on the nine breaking waves produced. Measurements include the temporal evolution of streamwise and cross-stream surface profiles of the breakers, and flow fields in the breaking region located on the forward face of the wave obtained by particle image velocimetry (PVI). Wake measurements behind the breaking region are also reported.; Over the length scales studied here, the frequencies of the dominant free surface disturbances and the variance of the surface profiles in the breaking region depart in some cases from exact Froude scaling to a confidence level of t80%. In addition, the wavenumbers of the dominant disturbances, and the breaker viscous drag appear to exhibit departures from Froude scaling. The nondimensional phase speed of the disturbances, however, is remarkably invariant with respect to scale and breaking intensity. Gradient spectra are somewhat dependent on scale, while the curvature spectra are very dependent on scale. Significant anisotropy of the height fluctuations in a wavenumber range {dollar}k/ksb0 < 20{dollar} is present in the height spectra, indicating that surface disturbances at these wavenumbers are approximately two-dimensional. The gradient spectra have the least anisotropy, while the magnitude of the curvature spectra display greater anisotropy.; Average flow fields obtained from PIV reveal a region of downslope flow on the forward face of the breakers. The aft end of this region at the surface defines a flow reversal point that is also on the forward slope of the waves. Mass flux from the upper region of the breakers is shown to result primarily from a previously undocumented mechanism operating in the hydrostatically unstable conditions near the toe of the breaker, while turbulent entrainment explains mass flux into the upper region. Finally, the mean flow paradigm of steady breaking waves has been improved by the incorporation of mass conservation, and an instantaneous flow paradigm is presented. |
