IWRA Proceedings

This paper presents the study of the hydraulic operation of the Netzahualcoyotl dam emergency spillway, in the state of Chiapas, Mexico, by Computational Fluid Dynamics (CFD). The numerical model solves the Reynolds Averaged Navier-Stokes equations(RANS) in three-dimensional cartesian coordinates using the finite volume method on structured meshes. The free surface is determined by the VOF (Volume Of Fluid) method.

 

The reason to modify the executive project of the emergency spillway was to correct the hydraulic deficiency of the original geometry. The prototype discharge capacity was lower than the expected by design (Qdes = 10,650 m3/s). This analysis sought to ensure a capacity of 9,400 m3/s associated with a return period (Tr) of 10,000 years, at least.

 

The computational domain consisted in interconnected mesh blocks with cell sizes of four, two and one meter. Respectively results were validated with a physical model (scale 1:65) built at the Federal Electricity Commission Hydraulics Laboratory. Numerical tests matched remarkable well the flow velocities along the emergency spillway at the physical model. The correlation coefficients between the computed and measured velocities were 95.6% and 97.3% for the right and left channels, respectively.

 

The versatility of the numerical model allowed to consider scenarios and compare different design proposals. The flow discharge was uniformly distributed along the channel, avoiding the flow concentration over the left margin and reducing the effects of inadmissible scour at the riverbed. The similarity between the numerical and physical models, given by the correlation coefficients, confirm the reliability of using three-dimensional numerical models design, review and improve hydraulic structures, supported by the validation of data from a physical model.