The efficiency of turbulent mixing in stratified fluids

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Title: The efficiency of turbulent mixing in stratified fluids
Author: Ebert, Guenther Wolfgang
Abstract: Mixing is a common feature of stratified fluids . In stratified fluids the density varies with the height . This is true for the most fluids in geophysical environments , like lakes , the atmosphere or the ocean . Turbulent mixing plays a crucial role for the overall energy budget of the earth and has therefore an huge impact on the global climate . By introducing the mixing efficiency , it is possible to quantify mixing . It is defined as the ratio of gain of potential energy to the injection of mechanical energy . In the ocean energy provided by tidal forces leads to turbulence and thus highly dense water is lifted up from the deep sea to the surface . For this process , a mixing efficiency of 0 .2 is estimated . Until now it is not completely understood how this high value can be achieved . Thus we measured the mixing efficiency by using a Couette -Taylor system , which can produce steady -state homogeneous turbulence . This is similar to what we find in the ocean . The Couette -Taylor system consists of two concentric cylinders that can be rotated independently . In between a stratified fluid is filled using salt as a stratifying agent . In the laboratory experiment , we obtained mixing efficiencies in the order of 0 .001 as a result . Moreover we found that the mixing efficiency decreases with decreasing stratification like previous laboratory experiments have shown . As this value is two orders of magnitude smaller than what we find in the ocean , further studies will be necessary .
URI: http : / /hdl .handle .net /2152 /ETD -UT -2010 -08 -1876
Date: 2011-01-03

Citation

The efficiency of turbulent mixing in stratified fluids. Master's thesis, University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /ETD -UT -2010 -08 -1876 .

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