Vorticity fields around a pier on rigid and mobile bed channels

ABSTRACT

Experimental investigation with reference to vorticity fields around circular bridge pier having diameter, d = 8.8 cm, at different angles, namely, θ = 0°, 90°, and 180° with respect to center of pier diameter, on rigid and mobile beds, is compared for identical flow conditions. The instantaneous velocity measurements were carried out using 16 MHz down looking micro-Acoustic Doppler Velocimeter (ADV) at different grids along the flow depths. The sediments having mean size, d₅₀ = 0.75 mm, and geometric standard deviation, σ_g = 1.29, are used in experimentation. The results reveal that, on both rigid and mobile bed, with increasing the angle, the strength of primary vortex is decreased. On the other hand, the strength of secondary vortex has been found to increase with the angle, that is, the primary vortex is found to be strong in front of the pier, whereas the secondary vortex is predominant behind the pier. Further, the strengths of primary and secondary vortices are found to be ≈30% more on rigid bed than mobile bed for same flow condition.

KEYWORDS:

• Primary vortex
• Secondary vortex
• Acoustic Doppler Velocimeter
• Rigid bed and Mobile bed

Acknowledgments

Authors are thankful to the Center of Excellence (CoE) on “Water Resources and Flood Management” of SVNIT Surat funded under TEQIP-II, Ministry of Human Resources Development (MHRD), Government of India, necessary infrastructure support for conducting the experiments. The authors are thankful to the anonymous reviewers for their constructive comments and suggestions in improving the quality of the manuscript.

Disclosure of potential conflicts of interest

No potential conflict of interest was reported by the author(s).