Hydraulic response and turbulence-model sensitivity of a circular culvert under discharge escalation: a CFD and HY-8 comparative study

Thi Noi Doan; Tong Anh Tuan; Quang-Thai Nguyen

doi:10.7409/rabdim.026.015

Received: 2026-07-27
Accepted: 2026-09-29
Published: 2026-10-16

Vol. 25 No. 3 (2026)

Hydraulic response and turbulence-model sensitivity of a circular culvert under discharge escalation: a CFD and HY-8 comparative study

Thi Noi Doan

, Tong Anh Tuan

, Quang-Thai Nguyen

Section: Articles

https://doi.org/10.7409/rabdim.026.015

Abstract

The article presents a systematic analysis of the hydraulic response of a circular culvert under discharge escalation scenarios using three-dimensional computational fluid dynamics (CFD) modeling and comparison with conventional HY-8 design-level predictions. Three discharge conditions were considered: the design flow Q₁ = 6.70 m³/s and escalated flows Q₂ = 10.05 m³/s = 1.5Q₁ and Q₃ = 13.40 m³/s = 2.0Q₁. Turbulence-model sensitivity (SST k–ω, Realizable k–ε, and RNG k–ε) was examined to quantify model-induced uncertainty in outlet-velocity prediction. Results indicate that outlet velocity increases approximately linearly with discharge, reaching 7.42-7.51 m/s under the highest flow condition, while deviations among the turbulence models remain below approximately 1.5%. Headwater depth increased from 1.94 m at Q₁ to 3.68 m at Q₃. CFD and HY-8 headwater depths agreed closely across all three scenarios: 1.94 versus 1.93 m at Q₁, 2.68 versus 2.67 m at Q₂, and 3.68 versus 3.69 m at Q₃, corresponding to relative CFD-HY-8 differences of +0.52%, +0.37%, and −0.27%, respectively. HY-8 is therefore used here as a design-level benchmark rather than as independent validation of local CFD fields. Non-dimensional analysis based on HW/D, a diameter-based velocity scaling parameter V / √gD, and Reynolds number indicates that discharge escalation primarily amplifies upstream headwater submergence. Although conveyance capacity remains hydraulically adequate, elevated outlet velocities substantially increase downstream scour potential. The findings support hydraulic safety assessment and outlet-protection design under intensified discharge conditions.

Keywords:

circular culvert, CFD, extreme discharge, grid independence, HY-8 benchmarking, inlet-controlled flow

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Doan, T. N., Tuan, T. A., & Nguyen, Q.-T. (2026). Hydraulic response and turbulence-model sensitivity of a circular culvert under discharge escalation: a CFD and HY-8 comparative study. Roads and Bridges – Drogi I Mosty, 25(3), 225–246. https://doi.org/10.7409/rabdim.026.015

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Thi Noi Doan

dtnoi@utc.edu.vn
https://orcid.org/0009-0007-4624-0316

Affiliation:

University of Transport and Communications, 3 Cau Giay St., 11528 Lang Ward, Hanoi Viet Nam

Tong Anh Tuan

https://orcid.org/0009-0008-4185-4594

Affiliation:

University of Transport and Communications, 3 Cau Giay St., 11528 Lang Ward, Hanoi Viet Nam

Quang-Thai Nguyen

https://orcid.org/0000-0001-9109-9509

Affiliation:

Vietnam Academy of Science and Technology, Institute of Mechanics, 264 Doi Can St., 11119 Ngoc Ha Ward, Hanoi Viet Nam

Hydraulic response and turbulence-model sensitivity of a circular culvert under discharge escalation: a CFD and HY-8 comparative study

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Thi Noi Doan

Tong Anh Tuan

Quang-Thai Nguyen