Scour around the single emergent cylinder due to subcritical and supercritical approach flow conditions

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ABSTRACT

Flume experiments with a uniform cohesionless sand with $d_{50}=0.9\mathrm{mm}$ were utilized in the current study to examine the local scour process around a single emergent cylinder under various geometrical circumstances and with a various flow characteristic that simulates an inundating tsunami flow. This single emergent cylinder represents a piloti-type column located over a movable bed material because piloti-type columns are used to elevate the building structures from the ground level. In the experiments, it was noted that the maximum scour depth probably occurs at the cylinder’s upstream face, resembling local scour around a scaled-down bridge pier in an open channel. Additionally, the scour hole around the cylinder is shallower the smaller they are, as are the horseshoe vortices that surround them. Furthermore, the effects of the surface bow-wave, hydraulic jump detachment and the wall-jet over the front face of the emerging cylinder were used to identify the relationship concerning the scouring pattern and selected flow characteristics over a piloti-type emergent column under tsunami flow. Empirical formulae have been finally developed to determine the maximum scour depth in front of the cylinder, which is beneficial to characterize the stability of the piloti-type columns, considering the specified Froude number conditions.

KEYWORDS:

• Single emergent cylinder
• scour depth
• bow-wave
• detachment hydraulic jump
• wall-jet

Acknowledgements

The author acknowledges the support of MEXT Scholarship (DISSANAYAKA) from Japanese Ministry of Education, Culture, Sports, Science and Technology. The authors also acknowledge the anonymous reviewers for their valuable comments to improve this manuscript. The author also acknowledges Dr. Junji Yagisawa, Dr. Yoshiya Igarashi, and Ms. Sai Suiriken for the given continuous support during the experimental activities.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research received no external funding.