An experimental study of deep water plunging breakers

Abstract

Plunging breaking waves are generated mechanically on the surface of essentially deep water in a two-dimensional wave tank by superposition of progressive waves with slowly decreasing frequency. The time evolution of the transient wave and the flow properties are measured using several experimental techniques, including nonintrusive surface elevation measurement, particle image velocimetry, and particle tracking velocimetry. The wave generation technique is such that the wave steepness is approximately constant across the amplitude spectrum. Major results include the appearance of a discontinuity in slope at the intersection of the lower surface of the plunging jet and the forward face of the wave that generates parasitic capillary waves; transverse irregularities occur along the upper surface of the falling, plunging jet while the leeward side of the wave remains very smooth and two dimensional; the velocity field is shown to decay rapidly with depth, even in this strongly nonlinear regime, and is similar to that expected from linear theory-the fluid is undisturbed for depths greater than one-half the wavelength; a focusing or convergence of particle velocities are shown to create the jet in the wave crest; vorticity levels determined from the measured, full-field velocity vectors show that the waves are essentially irrotational until incipient breaking occurs; and the magnitude of the largest water particle velocity is about 30% greater than the phase speed of the ͑equivalent͒ linear wave.

Surface tension effects on energy dissipation by small scale, experimental breaking waves

“…Longuet-Higgins and Cleaver (1994) have associated the presence of these waves with the induction of shear vorticity at the free surface and the subsequent increase on the wave crest instability. Perlin and He (1996) experimentally verified the formation of capillary waves on the faces of 0.8 m long plunging breakers. Evidence, however, presented by authors like Techet and McDonald (2005), Song and Sirviente (2004) and Liu and Duncan (2007) for spilling and plunging breakers relates the appearance of such waves to the magnitude of surface tension rather than the wavelength.…”

“…Linear theory was used for the estimation of the wave's velocity at the break point (C wb = ffiffiffiffiffiffiffi ffi gd b p ) and from this, particle celerity (C b ) was taken to be 1.03C wb for spilling breakers (Dimas, 2007), and 1.3C wb for plunging breakers (Perlin and He, 1996). C b , was preferred over any other characteristic velocity during breaking since it was found by Dimas (2007) to be unaffected by changes in We for spilling breakers.…”

Numerical modelling of wind effects on breaking waves in the surf zone

“…Much of our knowledge of breaking waves comes from laboratory measurements. Several systematic studies have been carried out for steady breaking waves (Duncan 1983), quasi-steady breaking waves (Lin and Rockwell 1995), unsteady deepwater breaking waves (Bonmarin 1989;Rapp and Melville 1990;Perlin et al 1996;Tulin and Waseda 1999;Melville et al 2002), and breaking waves in the laboratory surf zone (Nadaoka et al 1989;Ting and Kirby 1994;Stansby and Feng 2005;Kimmoun and Branger 2007).…”

Impulsive plunging wave breaking downstream of a bump in a shallow water flume—Part I: Experimental observations

“…The jet velocity is À0.2 m/s, i.e., the relative velocity is À 1.33 /U b S. /U b S is the ensemble average axial velocity averaged over the PIV field of view at t ¼t b . Chang and Liu (1998), Chen et al (1999), Perlin et al (1996), and Shakeri et al (2009) report jet relative velocities 0.5C, 0.45C, 0.3C, and 0.18-0.2C, respectively. The jet thickness is 0.2H w , which is similar to Bonmarin (1989), Grue and Jensen (2006), and Kimmoun and Branger (2007) value 0.14H w .…”