Author(s): Rahil Ahmad; Hariom Gautam

Linked Author(s): Rahil Ahmad

Keywords: CFD; Tunnel Spillway; Discharge Capacity; Velocity Distribution; Hydraulic Modeling

Abstract: Tunnel spillways are critical hydraulic structures designed to safely convey excess reservoir water, particularly when existing diversion tunnels are repurposed to handle increased discharges. This study employs Computational Fluid Dynamics (CFD) to evaluate the hydraulic performance of two converted tunnel spillways, Tunnel Spillway-1 (TS-1) and Tunnel Spillway-2 (TS-2), at the Teesta-V Dam, Sikkim, India. A 1:40 scale model was developed using ANSYS ICEM, and simulations were conducted in ANSYS Fluent with a tetrahedral mesh of approximately 3.9 million elements, refined through mesh sensitivity analysis for numerical accuracy. The SST k-ω turbulence model was applied, with pressure boundary conditions at the inlet and outlet to simulate real-world hydraulic conditions. Discharge capacity analysis revealed that TS-1 and TS-2 can convey approximately 1834 [m3 s-1] and 1844 [m3 s-1] respectively, at maximum reservoir level. Results indicate that increasing tailwater levels reduce discharge efficiency due to decreased available head. Velocity profiles along the tunnel centerline showed peak velocities of 16 [m s-1] in the horseshoe section and 24 [m s-1] in the circular portion, with stable flow conditions and minimal velocity skewness. This study underscores the effectiveness of 3D CFD modeling as a cost-effective and reliable alternative to physical hydraulic models for tunnel spillway analysis. The findings contribute to the optimization of spillway design for improved flood management and dam safety.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1983-cd

Year: 2025