Jet Impinging in Plunging Dropshafts of Medium Height

Abstract

A physical model study was conducted on jet impingement in a plunging dropshaft with different drop heights of 3.38 and 1.88 m. Experimental observations show that an upward splash, annular flow, and downward bounced jet could be formed when the approaching jet hits the opposite shaft wall. The impinging pressure on the shaft wall was mainly dominated by the incoming flow velocity, and the mean pressure on the shaft wall can be reasonably well-predicted when considering the bounced flow. The pulsation of the impinging pressure on the shaft wall was significant, with the maximum pressure being approximately 1.4–3.8 times the mean value. The impinging pressure at the shaft bottom was primarily determined by the velocity at which the falling jet reached the pool. The mean value can be well estimated using the annular flow and bounced jet assumption. The pulsation intensity increased with an increase in drop height or flow rate, which could be alleviated by a plunging pool with a larger depth. However, for flows in dropshafts under study, the impinging pressure and the hydrostatic pressure of the cushion layer were within the same order of magnitude; thus, the increase of the pool depth leads to a reduction of the energy-dissipation rate.