ADV MEASUREMENTS OF TURBULENCE OVER SMOOTH AND ROUGH BEDS

Abstract

In our present context of work, emphasis is given on validation of earlier obtained results on smooth and rough beds, and earlier work done in literature on obstruction effect on gravel bed channel on various turbulence parameters. On smooth bed data was seen to follow the log-law with a great accuracy. The turbulent intensity decayed exponentially along the depth with value of D, Dv, D, and Ck to be 1.5, 0.44, 0.40and 0.98, less than the values provided in literature. Also the turbulent kinetic energy dissipated exponentially along the depth with value of constant and exponent to be 1.32 and 2.10. Reynolds stress varied linearly on smooth bed. On rough bed the data again followed log-law with lc and B as 0.4 and 8.61. Also the correlation coefficient found was 0.75 greater than the theoretical equilibrium value of 0.4-0.5 and value of u'w72k was 0.1599 very close to the theoretically acclaimed value of 0.15. Again turbulent intensity decayed exponentially with coefficients Du, Dv, DW, Cku, Ckv and Ck, as 1.28, 0.51, 0.26, 1.67, 1.79 and -1.29, the negative value of Ck, implied increasing vertical turbulence along the depth due to the presence of roughness. The Reynolds stress distribution was scattered and uncorrelated. Turbulent kinetic energy again decayed with values of coefficient and exponent respectively as 1.2 and 2.7. In obstructed flow all the laws that are followed by unobstructed flow became irrelevant. Large wake and separation was seen around the obstruction with eddies flowing in sheet. Stress plane swapping was seen near the bed with high turbulent energy in obstructed flow and also a sudden increasing pattern was seen in Reynolds stress distribution while sinusoidal variation in vertical turbulent component.