Dominant features in three-dimensional turbulence structure: comparison of non-uniform accelerating and decelerating flows

The results are presented from an experimental study to investigate three-dimensional turbulence structure profiles, including turbulence intensity and Reynolds stress, of different non-uniform open channel flows over smooth bed in subcritical flow regime. In the analysis, the uniform flow profiles have been used to compare with those of the non-uniform flows to investigate their time-averaged spatial flow turbulence structure characteristics. The measured non-uniform velocity profiles are used to verify the von Karman constant κ and to estimate sets of log-law integration constant B r and wake parameter П, where their findings are also compared with values from previous studies. From κ, B r and П findings, it has been found that the log-wake law can sufficiently represent the non-uniform flow in its non-modified form, and all κ, B r and П follow universal rules for different bed roughness conditions. The non-uniform flow experiments also show that both the turbulence intensity and Reynolds stress are governed well by exponential pressure gradient parameter β equations. Their exponential constants are described by quadratic functions in the investigated β range. Through this experimental study, it has been observed that the decelerating flow shows higher empirical constants, in both the turbulence intensity and Reynolds stress compared to the accelerating flow. The decelerating flow also has stronger dominance to determine the flow non-uniformity, because it presents higher Reynolds stress profile than uniform flow, whereas the accelerating flow does not

Physical Modeling of Extreme Waves Propagating from the Open Sea to the Coastal Zone

International audienceThe evolution of solitary wave along the flume is investigated. Experiments were conducted in a smooth, rectangular sloping flume. Solitary waves are generated using a piston-type wave maker. These type of waves are generated by impulsive mechanism, close to the generation zone, their profile contains both elevation and depression components. These depressions are attached to the main solitary wave along the flume during the propagation. The main hydraulic parameters investigated are: energy damping along the flat bottom, wave height evolution on the slope (shoaling), breaking process and runup heights. It was found that experimental results are almost in good agreement with earlier studies. An empirical formula for runup heights determination is suggested. A good way for tracking the evolution of a solitary wave on flat and sloping bottom is presented thanks to spatiotemporal diagram. It is noted that for better accuracy, especially when investigating breaking, it is better to use camera

Effects of oscillatory flow on fertilization in the green sea urchin <em>Strongylocentrotus droebachiensis</em>

Broadcast spawning invertebrates that live in shallow, high-energy coastal habitats are subjected to oscillatory water motion that creates unsteady flow fields above the surface of animals. The frequency of the oscillatory fluctuations is driven by the wave period, which will influence the stability of local flow structures and may affect fertilization processes. Using an oscillatory water tunnel, we quantified the percentage of eggs fertilized on or near spawning green sea urchins, Strongylocentrotus droebachiensis. Eggs were sampled in the water column, wake eddy, substratum and aboral surface under a range of different periods (T = 4.5 - 12.7 s) and velocities of oscillatory flow. The root-mean-square wave velocity (rms(u(w))) was a good predictor of fertilization in oscillatory flow, although the root-mean-square of total velocity (rms(u)), which incorporates all the components of flow (current, wave and turbulence), also provided significant predictions. The percentage of eggs fertilized varied between 50 - 85% at low flows (rms(u(w)) < 0.02 m s(-1)), depending on the location sampled, but declined to below 10% for most locations at higher rms(u(w)). The water column was an important location for fertilization with a relative contribution greater than that of the aboral surface, especially at medium and high rms(u(w)) categories. We conclude that gametes can be successfully fertilized on or near the parent under a range of oscillatory flow conditions