Effect of non-uniformity of flow on velocity and turbulence intensities over a cobble-bed
Article first published online: 3 NOV 2009
Copyright © 2009 John Wiley & Sons, Ltd.
Volume 24, Issue 3, pages 331–341, 30 January 2010
How to Cite
Afzalimehr, H. (2010), Effect of non-uniformity of flow on velocity and turbulence intensities over a cobble-bed. Hydrol. Process., 24: 331–341. doi: 10.1002/hyp.7495
- Issue published online: 18 JAN 2010
- Article first published online: 3 NOV 2009
- Manuscript Accepted: 15 SEP 2009
- Manuscript Received: 4 JAN 2009
- cobble bed;
- turbulence intensities;
- intermediate relative submergence;
- non-uniform flow
Non-uniform flows encompassing both accelerating and decelerating flows over a cobble-bed flume have been experimentally investigated in a flume at a scale of intermediate relative submergence. Measurements of mean longitudinal flow velocity u, and determinations of turbulence intensities u′, v′, w′, and Reynolds shear stress −ufwf have been made. The longitudinal velocity distribution was divided into the inner zone close to the bed and the outer zone far from the bed. In the inner zone of the boundary layer (near the bed) the velocity profile closely followed the ‘Log Law’; however, in the outer zone the velocity distribution deviated from the Log Law consistently for both accelerating and decelerating flows and the changes in bed slopes ranging from −2% to + 2% had no considerable effect on the outer zone. For a constant bed slope (S = ±0·015), the larger the flow rate, the smaller the turbulence intensities. However, no detectable pattern has been observed for u′, v′ and w′ distributions near the bed. Likewise, for a constant flow rate (Q = 0·040 m3/s), with variation in bed slope the longitudinal turbulent intensity profile in the longitudinal direction remained concave for both accelerating and decelerating flows; whereas vertical turbulent intensity (w′) profile presented no specific form. The results reveal that the positions of maximum values of turbulence intensities and the Reynolds shear stress depend not only on the flow structure (accelerating or decelerating) but also on the intermediate relative submergence scale. Copyright © 2009 John Wiley & Sons, Ltd.