摘要
在具有连续密度跃层的分层流体中,针对3种不同长径比拖曳潜体激发内波的运动学与动力学特性进行了系列实验.从拖曳潜体产生扰动密度场的动态时间序列测量结果入手,表明体积效应激发内波属于一种相对于拖曳潜体定常的多模态Lee波结构,而尾迹效应激发主控内波为相对于拖曳潜体非定常的拟Lee波结构,这是一类由湍流尾迹中大尺度相干结构作为移动源激发的内波结构.研究表明,在Lee波与拟Lee波之间存在一个与长径比近似为线性关系的临界转捩Froude数Frc,而且转捩后拟Lee波相关速度相应Froude数近似为一个常数0.8.研究进一步表明,存在一个与长径比近似为线性关系的Froude数Frp,当Fr<Frp时,Lee波为主控内波,无因次内波峰-峰幅值随Fr增大而增大;当Frp<Fr<Frc时,虽然Lee波仍为主控内波,但无因次内波峰-峰幅值随Fr增大而减小,而拟Lee波的影响逐渐增大;当Fr>Frc时,拟Lee波为主控内波,无因次内波峰-峰幅值随Fr增大近似线性增大,而且长径比的影响可以忽略,其中Fr为拖曳潜体特征直径Froude数.
Experiments are conducted for the kinematic and dynamic characteristics of the internal waves excited by horizontally towed bodies with three aspect ratios in a stratified fluid with a pycnocline. Based on the dynamic measurements of the density perturbation generated by towed bodies, it is shown that the body-generated waves are a type of stationary Lee wave structures with multi-modes; moreover the wake-generated waves are a type of non-stationary quasi-Lee wave structures with respect to the towed bodies, where the quasi-Lee waves are shown to be produced by the large-scale coherent structure in turbulent wakes acting as a moving excitation. Results show that the transition between the Lee and quasi-Lee waves occurs at a critical Froude number Fr c which is shown to be linearly dependent of the aspect ratio, and the Froude numbers with respect to the correlation velocities of the quasi-Lee waves remain at relatively constant value of approximately 0.8 regardless of the aspect ratios. Results further show that there exists a Froude number Fr p which is linearly dependent of the aspect ratio. The wave patterns for FrFr p are dominated by Lee waves and the dimensionless peak-to-peak amplitudes for such waves increase with Fr. Though the wave patterns for Fr p FrFr c are also dominated by Lee waves, the dimensionless peak-to-peak amplitudes for such waves decrease with Fr and the influence of quasi-Lee waves gradually increases; the wave patterns for FrFr c are dominated by quasi-Lee waves and the dimensionless peak-to-peak amplitudes for such waves linearly increase with Fr regardless of the aspect ratios, where Fr is the Froude number for the characteristic diameter of the submerged body.
出处
《科学通报》
CAS
CSCD
北大核心
2012年第8期606-617,共12页
Chinese Science Bulletin
基金
国家自然科学基金(11072153)
海洋工程国家重点实验室基金(GP010819)资助
