Author(s): Reza Fatahi-Alkouhi; Ahmad Shanehsazzadeh; Mahmud Hashemi

Linked Author(s): Reza Fatahi-alkouhi

Keywords: Energy dissipation; Plunge pool; Impinging jets; Physical modeling; Nonlinear regression

Abstract: Predicting the efficiency of plunge pools in dissipating the dynamic energy of impinging high-velocity jets of free spillways is essential for assessing the stability of the bed and subsequent scour depth. In this study, a large-scale physical model is developed to assess the energy dissipation of the plunge pools at the bottom. A wide range of hydraulic conditions including impinging jet velocity and plunge pool water depth is considered, resulting in plunge pool Froude number FrP up to 8 which is in the prototype range (FrP=Vj/(gY)0.5, where, Vj is jet velocity at impact on pool surface, g and Y are acceleration due to gravity and water depth, respectively). The hydrodynamic pressures mean and fluctuation at plunge pool bottom are measured at the impinging jet centerline (stagnation point, SP). Buckingham theorem is applied to introduce non-dimensional parameters, among them is the plunge pool efficient parameter (η) which relates the mean hydrodynamic pressure head at the bottom and the kinetic head due to jet velocity at the plunge pool water surface. Results indicate that η varies between 0.1 and 0.95 depending on the magnitude of Y/Dj (Dj is jet diameter at water surface) and FrP. The multiple nonlinear regression-derived model (MNLR) are developed to predict the efficient parameter of plunge pool (η). Statistical analysis of empirical model indicates that the energy dissipation is accurately predicted by the model, the average values of RMSE and R2 are 0.04 and 0.95, respectively. The model can be applied in practice for the preliminary design purposes.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221452

Year: 2022