Enhanced Physically Based Models for Pressure Characteristics at Plunge Pool Bottoms

Abstract

Predicting the characteristics of the dynamic pressures at plunge pool bottoms due to the impact of plunging jets is essential in designing and assessing the stability of lined or unlined plunge pool bottoms. In this article, by developing a large-scale physical model, the generated dynamic pressures at plunge pool bottoms are measured in different plunging jet conditions and pool water depths. The validity of the existing empirical formulations in predicting the dynamic pressure mean (CP) and pressure fluctuations (CP′) is assessed based on the experimental data. The comparison of the predicted results through existing empirical models with the observed experimental data indicates that the recently developed models have acceptable accuracy in predicting the CP coefficient, but not the CP′ coefficient. By running a parametric analysis through dimensional analysis, the dimensionless parameter of plunge pool Froude number [FrP=Vj/(gY)0.5, where, Vj = jet velocity at pool surface, g = acceleration due to gravity, and Y = plunge pool water depth] is introduced as an alternative to Y/Dj, (where, Dj is jet diameter at pool surface) to simultaneously consider the effects of pool water depth and jet velocity. The results indicate that at FrP≤2, the CP′ coefficient is negligible and = 0.10. At 2<FrP<4, increasing the FrP leads to an increase in the CP and CP′ coefficients, whereas at FrP≥4, plunging jet acts on the pool bottom in the form of a core jet; the CP and CP′ coefficients are independent of the FrP parameter. In this circumstance, these coefficients are constant of 0.86 and 0.31, respectively. The nonlinear regression analysis is applied to develop empirical models of the CP and CP′ coefficients based on the FrP parameter in the effective ranges of FrP. The results indicate that the FrP by considering two effective variables of jet velocity and pool water depth is more effective than the Y/Dj ratio in describing the characteristics of dynamic pressure generated at the pool bottom. The extent to which the results are applied in practice is addressed. © 2023 American Society of Civil Engineers.