Velocity distribution in a V-shaped channel

摘要

To explore the hydraulic characteristics of a V-shaped channel, several series of experiments were conducted for measuring point velocity and boundary shear stress. Low & high-speed velocity propellers were used for measuring point velocities. In order to show the effect of cross sectional shape on the distribution of depth-averaged velocity in the experimental channel, some measurements of point velocities were undertaken for different flow cases. The contour plots of 2D isovels were drawn interpolating among averaged depths and velocities at a given position, obtained from superposing the various profile sections. It can be seen that the isovels are parallel to the channel boundary in a region close to the bed, and almost symmetric about the centerline, but not completely. A strong surface phenomenon is observable throughout the isovels plots. The variation of point velocities in each slice considered along spanwise direction in order to study the depthwise velocity profile distributions are plotted. Integrating the local velocities, u, over the flow depth, h, gives the depth-averaged velocity, U_d. The lateral variations of depth-averaged velocities are plotted. The results illustrate that the distributions are almost symmetrical about the cross sectional centerline, but they deviate for some flow cases; despite the flow condition was uniform for all cases. It may be found that the widely used log-law for vertical profile of velocity is not accurate and it is not applicable for any channel shape. At large flow depths the maximum velocity occurs at the centerline and reduces continuously towards the sidewalls indicating that the sidewalls exert a large influence on flow behavior. This leads to the view that the secondary current cells affect the flow behavior.