DocumentCode :
705638
Title :
Turbulent kinetic energy and temperature variance dissipation in laboratory generated Rayleigh-B??nard turbulence designed to study the distortion of light by underwater microstructure fluctuations
Author :
Matt, Silvia ; Weilin Hou ; Goode, Wesley ; Josset, Damien
Author_Institution :
Oceanogr. Div., Naval Res. Lab., Stennis Space Center, MS, USA
fYear :
2015
fDate :
2-6 March 2015
Firstpage :
1
Lastpage :
6
Abstract :
Small-scale variation in temperature and salinity can lead to localized changes in the index of refraction and can distort electro-optical (EO) signal transmission in ocean and atmosphere. This phenomenon is well-studied in the atmosphere and in this context is generally called “optical turbulence”. Less is known about how turbulent fluctuations in the ocean distort EO signal transmissions, an effect that can impact various underwater applications, from diver visibility to active and passive remote sensing. To provide a test bed for the study of the impacts from turbulent flows on EO signal transmission, as well as to examine and mitigate turbulence effects, we set up a laboratory turbulence environment allowing the variation of turbulence intensity. Convective turbulence is generated in a large Rayleigh-Bénard type tank (5m by 0.5m by 0.5m) and the turbulent flow is quantified using a suite of sensors that includes high-resolution Acoustic Doppler Velocimeter profilers (Vectrino Profiler) and fast thermistor probes (PME Conductivity- Temperature probe). These measurements allow the characterization of turbulent kinetic energy and temperature variance dissipation rates in the tank, for different convective strengths. Optical image degradation in the tank is then assessed in relation to turbulence intensity. The turbulence measurements are further complemented by very high-resolution computational fluid dynamics simulations of convective turbulence emulating the tank environment. These numerical simulations supplement the sparse laboratory measurements, providing full fields of temperature and velocity in the tank. The numerical data compared well to the laboratory data and both conformed to the Kolmogorov spectrum of turbulence and the Batchelor spectrum of temperature fluctuations. The numerical model was able to qualitatively reproduce the turbulence fields observed in the laboratory tank. Quantitatively, the numerical simulations are con- istent with the observed ε in the tank, but do not fully resolve the temperature gradients and thus underestimate Ξ. The unique approach of integrating optical techniques, turbulence measurements and numerical simulations can help advance our understanding of how to mitigate the effects of turbulence impacts on underwater optical signal transmission, as well as on the use of optical techniques to probe oceanic processes.
Keywords :
geophysical fluid dynamics; ocean temperature; remote sensing; salinity (geophysical); underwater optics; Batchelor spectrum; EO signal transmission; EO signal transmissions; active remote sensing; computational fluid dynamics simulations; convective turbulence; electro-optical signal transmission; fast thermistor probes; high-resolution Acoustic Doppler Velocimeter profilers; laboratory generated Rayleigh-Benard turbulence; laboratory turbulence environment; light distortion; oceanic processes; optical image degradation; optical techniques; passive remote sensing; refraction index; temperature fluctuations; temperature variance dissipation; temperature variance dissipation rates; turbulence Kolmogorov spectrum; turbulence intensity; turbulent fluctuations; turbulent kinetic energy; turbulent kinetic energy characterization; underwater applications; underwater microstructure fluctuations; underwater optical signal transmission; Ocean temperature; Optical distortion; Optical imaging; Optical refraction; Optical scattering; Optical sensors; Temperature measurement; ADV; Rayleigh-B??nard tank; optical turbulence; turbulence measurements; turbulent dissipation rate;
fLanguage :
English
Publisher :
ieee
Conference_Titel :
Current, Waves and Turbulence Measurement (CWTM), 2015 IEEE/OES Eleventh
Conference_Location :
St. Petersburg, FL
Print_ISBN :
978-1-4799-8418-3
Type :
conf
DOI :
10.1109/CWTM.2015.7098104
Filename :
7098104
Link To Document :
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