Experimental study on behavior of turbulence in a fully developed pipe flow.

概要

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To investigate the Lagrangian behavior of turbulent eddies in fully turbulent pipe flow, two point space-time correlations were measured by the electrochemical method; s-s correlation between the wall shear stresses spaced along the axial direction, s-u correlation between the wall shear stress and the local axial velocity in the same cross section, and u-u correlation between the local axial velocities in the same cross section. The correlation for time lag, defined as the delay time at which the correlation function becomes maximum, has been obtained for each cross correlation. The axial distribution of the time lags in the s-s correlation demonstrates that the axial velocity of turbulent eddies near the wall is 0.455 times the average velocity but is not proportional to the friction velocity as reported by Py. A model on transmission of turbulent disturbance is proposed here upon which the transmission velocities in the radial direction have been obtained from the s-u and u-u correlations respectively. The transmission velocity from the s-u correlation is proportional to (y/R)0.2, which corresponds to the radial velocity of an inrushing eddy. On the other hand, the transmission velocity in the bulk region obtained from the u-u correlation decreases towards the center.
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