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

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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.