科研之友
微信
新浪微博
Facebook
分享链接
摘要
An experimental study of periodic waves interacting with near-orthogonal turbulent currents is presented in this paper. Mean velocity profiles for current-alone, wave-alone and combined wave-current flows are measured with Acoustic Doppler Velocimeters to resolve the changes in mean flow kinematics due to wave-current interaction. In this study, the near-bottom wave orbital velocity is approximately 1.5 times greater than the depth averaged current velocity, and the log-profile method is used to determine the bottom roughness from the measured velocity profiles. The primary focus is on 90 degrees wave-current interaction, while selected findings for 60 degrees and 120 degrees wave-current orientations are also presented. In the smooth bed experiment, the interaction is shown to be linear due to the relatively low Reynolds-number flows generated in the facility - a relatively common scenario in small-scale laboratory setups that has not received much attention in previous studies. The smooth turbulent flow equation, with modification of the input shear velocity, is found to accurately predict the mean flow roughness for linear interaction. The bottom roughness is subsequently increased with the introduction of a layer of uniform 12.5 mm marbles to achieve a more realistic rough turbulent flow regime. The results agree qualitatively with previous experimental findings that showed a reduction in the near-bottom mean velocity due to a wave-enhanced,(apparent) roughness. However, the Grant-Madsen (GM) model is found to over-estimate the apparent roughness when the angle of wave-current interaction is. large,. implying a lack of directional, sensitivity of this model under "strong-wave, weak-current" conditions. A tentative explanation of this shortcoming is given in the paper. However, it is not possible to extend the GM model analysis to the present near-orthogonal wave-current flows, as results suggest that both 60 degrees and 120 degrees wave-current cases are sufficiently contaminated by the wave-induced mass transport component in the current direction to invalidate the use of the log-profile method to resolve the bottom roughness. In addition to the modification of current profiles by waves, the present study also shows a drastic transformation of wave-induced mass transport profiles by the external turbulent currents. The veering of mean flow over depth is consistent with the superposition of a wave-induced return flow on the external current, while additional veering in the near-bottom region may be attributed to turbulence asymmetry induced by the current component in the direction of the near-bottom wave orbital velocity which is shown to vary locally by +/- 10 degrees due to parasitic waves emanating from the current inlet and outlet.
- 出版日期2016-10
- 单位MIT
