Turbulence measurements in open-channel flow with transverse bed slope




Lee, Ka Leung, 1963-

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In a meandering river, both the bends and the transverse bed slopes influence the turbulence in the flow. As part of a research project to study the turbulence characteristics in a meandering laboratory river channel, turbulence measurements were made in a straight flume with a transversely sloping plane bed to evaluate the effect of the transverse bed slope. The flume was 30 in. wide and had a 10% transverse bed slope. The bottom of the flume was formed by sand of 2 mm nominal size coated with paint. The depths were 0.4 in. on the shallow side and 3.5 in. on the deep side. The average velocity was 1.3 ft/s. Constant temperature hot film anemometry was used and all measurements were made with single sensor probes. Some problems encountered in the application of hot film anemometry are discussed. A detailed account of the development of the techniques for data acquisition, processing and analysis is also given. The parameters used to characterize the turbulence include the mean velocity, turbulent intensity, autocorrelation coefficient, cross-correlation coefficient, spectrum, macroscale, Taylor microscale, energy dissipation rate, Kolmogorov microscale, and skewness and kurtosis of the probability distribution of the velocity fluctuations. Some of the variations of these parameters can be attributed to the depth variation and velocity variation across the flume. The mean velocities on a vertical normalized with respect to the depth-averaged velocity were found to vary in a similar way with the relative depth for different verticals. The same observation is obtained for the relative turbulent intensity, the energy dissipation rate and the Kolmogorov micro-length scale. For the other parameters, interesting patterns of variation can be identified. These findings will be compared with those of similar measurements in the meandering laboratory river channel so that the effect of transverse bed slope on the turbulence in natural river flow can be evaluated