Measurements and scaling of wall shear stress fluctuations |
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Authors: | Email author" target="_blank">K?J?ColellaEmail author W?L?Keith |
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Institution: | (1) Department of Engineering, US Coast Guard Academy, 06320 New London, CT, USA;(2) Submarine Sonar Department, Naval Undersea Warfare Center Division Newport, 02841 Newport, RI, USA |
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Abstract: | Measurements of velocity and wall shear stress fluctuations were made in an external turbulent boundary layer developed over
a towed surface-piercing flat plate. An array of eight flush-mounted wall shear stress sensors was used to compute the space-time
correlation function. A methodology for in situ calibration of the sensors for ship hydrodynamic applications is presented.
The intensity of the wall shear stress fluctuations, τ
rms/τ
avg was measured as 0.25 and 0.36 for R
θ
=3,150 and 2,160 respectively. The probability density is shown to exhibit positive skewness, and lack of flow reversals at
the wall. Correlations between velocity and wall shear stress fluctuations are shown to collapse with outer boundary layer
length and velocity scales, verifying the existence of large-scale coherent structures which convect and decay along the wall
at an angle of inclination varying from 10 to 13° over the range of Reynolds numbers investigated. The wall shear stress convection
velocity determined from narrow band correlation measurements is shown to scale with outer variables. The space-time correlation
of the wall shear is shown to exhibit a well-defined convective ridge, and to decay 80% over approximately 3δ for R
θ
=3,150.
Published online: 7 November 2002 |
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Keywords: | |
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