Experimental Study on Turbulent Entrainment in an Enclosed Density Stratified Flow owing to Wind Action

研究了表面风应力作用下两层密度分层流中的界面湍流卷吸，观测到卷吸速度：(1)当浮力效应较大，风应力较小时，卷吸速度较小。(2)卷吸现象的形成机制可分为三种类型：扩散型、内波破碎型和穿透型。湍流结构：(1)湍流上层存在整体尺度和有组织的大尺度涡旋。(2)短寿命强的间歇性湍流会影响卷吸速度。(3)界面处的湍流动能方程有效地引入了卷吸速度定律。卷吸速度定律的推导：利用湍流动能方程的参数化，得到了风生卷吸速度方程，u_e/u_*=0.039(7.694+R_&lt；i*&gt；^&lt；1/2&gt；)/R_&lt；i*&gt；-2.5).Where Ri*是一个总的Richardson数，水摩擦速度u*，R&lt；i*&gt；=&lt；其中，u_e为夹带速度，&lt；Delta&gt；&lt；Rho&gt；g为重力加速度，h为上层深度。

A study is made of the interface turbulent entrainment in a two-layered density stratified flow owing to an imposed surface wind stress.Observed entrainment velocity : (1) When the buoyancy effeet is strong and the wind stress is weak, the entrainment velocity is small. (2) Mechanism of entrainment phenomenon are classified three types, which are diffusion,internal wave breaking and penetrating type.Turbulent structure : (1) lntegral scale and organized large scale vortex are existed in the upper turbulent layer. (2) A strong intermittent turbulence,which is short life time,influences entrainment velocity. (3) The kinetic turbulent energy equation at the interface is effectively to introduce the entrainment velocity law.Decission of entrainment velocity law : By using the parameterization of kinetic turbulent energy equation, We obtained an equation for wind-induced entrainment velocity,u_e/u_*=0.039(7.694+R_<i*>^<1/2>)/R_<i*>-2.5).Where Ri* is an over all Richardson number with a water friction velocity u_*, R_<i*>=<DELTA><rho>gh/<rho>u_*^2,u_e is the entrainment velocity, <DELTA><rho> is the density difference between upper and lower layer, g is the gravitational acceleration , and h is the upper layer depth.