An experimental study of a free surface impinged by a vertical water jet

VAUCHE, A.; BROCHARD, S.; GALLAUP, F.; BAYLLE, A.; PATERSON, A.; MARTINO, R.; AGUIRRE, M.; PIVA, M.

CABA

Encuentro; XV Reunión sobre Recientes Avances en Física de Fluidos y sus Aplicaciones; 2018

Asociación Física Argentina

We experimentally analyzed the dynamics of the free surface of a column of water impinged by a vertical jet of the same uid. As the ow rate of the jet is increased, the free surfacedevelops a bump around the impingement point by conversion of the jet kinetic energy into potential energy of the bump. A secondary instability develops when the bump breaks laterallyinducing a periodic global oscillation of the water cavity. By varying the jet ow rate (Q) and the water level (Hw), we determined the onset of a self-oscillating regime by observing thebump behavior with a fast video camera. Images are analyzed and the free surface prole is obtained and tted by a polynomial model. For given values of Q and Hw, the FFT of thesignal corresponding to the temporal evolution of the climax of the bump is obtained. As in previous works, the bump elevation was found to be proportional to the Froude number. Thethreshold where the self-sustaining oscillation begins is a straight line in the parameter plane (Q, Hw), which shows that the critical Froude number is approximately constant. Also, inorder to investigate the interaction of the jet self oscillation and the sloshing mechanism, experiments were also performed by reducing the spanwise connement length.