Browsing by Subject "Turbulence--Measurement"

Now showing 1 - 2 of 2

Turbulence measurements in a meandering laboratory river channel
(1993) Syed, Owais Zahid, 1964-; Not available
Measurements of turbulence characteristics were performed in a laboratory meandering river channel. The measurements were performed using a single hot-film anemometer at five sections beginning from the apex of the first bend to the apex of the second bend. Measurements were made at different depths along the verticals at different positions across a cross section. The data gathered in this study included longitudinal velocity, relative turbulent intensity, auto-correlation functions, energy spectra, and normalized macroscale and microscale. The objectives of presenting and interpreting the data are to understand how the turbulence is affected by channel curvature and also how it changes with the depth. The average flow depth for the meandering channel was 0.40 ft. The average width of the channel was 5.42 ft. The average flow speed was 1.61 fps. The vertical profiles of the longitudinal velocity showed that the mean velocity profiles do not follow a logarithmic pattern in the upper part of the flow. For all the stations the relative turbulent intensity normalized with local mean velocity decreased with increasing distance from the bottom of the channel except near the water surface in the same location. The variation of the turbulent intensity with the relative depth was found to be non-logarithmic for all sections. The autocorrelation coefficients decreased from unity for no time lag to zero for a time lag on the order of 0.5 seconds. The energy spectra showed that most of the energy is concentrated in frequencies less than 10 Hz. The plots of normalized microscale show little depthwise variations. The plots of normalized macroscale show an S-shaped pattern in all the data
Turbulence measurements in open-channel flow with transverse bed slope
(1992) Lee, Ka Leung, 1963-; Holley, Edward R. (Edward Raymond)
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