Abstract
A high-resolution particle image velocitmetry system is used to investigate the relationship between secondary flow and aspect ratio in a straight channel. Considering the symmetry of open channel flow, the flow parameters in half of the flume are measured. Since the variation of the aspect ratio has a direct impact on the intensity and structure of secondary flows, this study was conducted in a smooth open channel to study the influence of aspect ratio on the structure and strength of secondary flows with aspect ratio change from 3 to 7.5 under supercritical flow condition. Profiles and contour-maps of time-averaged stream-wise and vertical velocities were acquired using precise measuring instruments. The results show that there are several secondary flow cells in the cross section, and their structure affects the velocity distribution and energy distribution, which makes the velocity distribution deviate from the traditional logarithmic distribution, and the maximum velocity occur below the surface. The flow intensity of secondary flows is different under different aspect ratios. Results show great agreement with classical theory.
Highlights
Turbulent flow is a relatively common phenomenon in the engineering field, and studies on turbulence have been conducted in the field of hydraulic, shipping, and aeronautical engineering.A turbulent channel flow is always accompanied by transverse circulating currents, which are called secondary flow
The present study aims to investigate the characteristics of secondary flow in an open channel, the influence of aspect ratio on the flow field
Considering that symmetry is a characteristic of open channel flow in the rectangular flume, Results this3.study only investigates half of the flume region
Summary
Turbulent flow is a relatively common phenomenon in the engineering field, and studies on turbulence have been conducted in the field of hydraulic, shipping, and aeronautical engineering. Nezu and Nakagawa [2] indicated that two vortices exist in the cross section: free surface vortex and bottom vortex These two counter rotating vortices change the shear stress and velocity distributions in the flow field. 1 shows the brief structure of secondary currents, which changes simple open channel flow pattern. An open channel flow cannot be regarded a simple flow when secondary currents exist. Given the simple boundary condition and wide application of open-channel flow infield, pertinent studiesfield, relating to water supply, sediment transportation, and pollutant dispersion the engineering pertinent studies relating to water supply, sediment transportation, andare of importance. The present study uses a measurement technique called particle image velocimetry (PIV) to acquire the flow parameters in open channel with B/H (aspect particle image velocimetry (PIV) to acquire the flow parameters in open channel with B/H (aspect ratio) changes from 3 to 7.5. (b) Typical isotach patterns for flow along a corner [9]
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