Experimental study of submerged hydraulic jumps generated downstream of rectangular plunging jets

This experimental study analyzes submerged hydraulic jumps generated in a 1.05-m wide stilling basin that receives overflow rectangular impinging jets, with the vertical distance between the sharp-crested weir and the bottom of the plunge pool being 2.20 m. Five submerged hydraulic jumps downstream of non-developed nappe jets were analyzed, with vertical falling distances to break-up length ratios between 0.76 and 0.78. The impingement velocity range was from 6.12 to 6.33 m/s, while the water depth / impingement jet thickness ratios were between 8.45 and 15.00. The velocity field and air entrapped were measured in several cross sections, with the farthest sections being located 1.0 m from the stagnation point. The entrapped air (void fraction and phase change detection) behavior measured with a phase-detection probe was classified as a function of the distance to the stagnation point / impingement jet thickness ratio and/or the mean void fraction of the vertical profiles. The maximum void fractions were observed near the free surface. However, the higher phase change detection frequencies (up to 130-140 Hz) were obtained near the bottom for local void fractions smaller than 0.15-0.20. The non-dimensional velocity distribution seems to be similar to previous published studies, extending their validity range. Furthermore, the free hydraulic jumps formula has been adapted to estimate the air rate in the shear stress layer and the growth of the characteristic length in the plunge pool.The researchers express their gratitude for the financial aid received from the "Ministerio de Ciencia, Innovación y Universidades" (MCIU), the "Agencia Estatal de Investigación" (AEI) and the (FEDER), through the Project “La aireación del flujo en el vertido en lámina libre por coronación de presas a nivel de prototipo y su efecto en cuencos de disipación de energía”, Ref: RTI2018-095199-B-I00. The work was partially funded by the "Comunidad Autónoma de la Región de Murcia" through the "Programa Regional de Fomento de la Investigación Científica y Técnica (Plan de Actuación 2018) de la Fundación Séneca-Agencia de Ciencia y Tecnología de la Región de Murcia”, Project “Análisis de la capacidad de descarga de vertederos tipo laberinto y de la disipación de energía aguas abajo de los mismos”, Ref: 20879/PI/18