Numerical modeling to investigate the effect of the presence or absence of a free surface on the flow around the cylindrical pier

Subject Areas : River engineering and sediment hydraulics

Mehdi Esmaeilzadeh Fereydani ¹ , Yasin Aghaee-Shalmani ^{2 *}

1 - Faculty of Civil Engineering, Department of Mechanical and Civil Engineering, Kho. C, Islamic Azad University, Khomeinishahr, Iran.
2 - Faculty of Civil Engineering, Department of Mechanical and Civil Engineering, Kho. C, Islamic Azad University, Khomeinishahr, Iran.

Received: 2025-04-04 Accepted : 2025-07-14 Published : 2025-07-21

Keywords: Turbulent flow, Three-Dimensional modeling, Free-surface, Rigid-lid, Froud number,

Abstract :

Due to their critical importance in hydraulic structures, bridge piers and the flow around them have always been a subject of special interest. In the present study, numerical modeling using the RNG turbulence model is employed to investigate turbulent flows around a cylindrical bridge pier under both free-surface and rigid-lid conditions. The primary objective is to numerically model the flow at subcritical Froude numbers of 0.10, 0.15, 0.20, 0.25, and 0.30 in both free-surface and rigid-lid scenarios. Based on the obtained results and their comparison, the differences between the free-surface and rigid-lid conditions become more pronounced at Froude numbers of 0.25 and 0.30. For instance, at a Froude number of 0.30, the difference in the downward flow velocity in front of the pier is 10% between the free-surface and rigid-lid cases. Additionally, the maximum horizontal velocity around the pier differs by 20% between the two models at the same Froude number. As the Froude number increases, the separation length upstream of the pier slightly increases. Furthermore, the separation length downstream differs between the free-surface and rigid-lid models across all Froude numbers, with an average difference of approximately 11% for the tested Froude numbers.

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