Experimental study of gas entrainment from surface swirl

International audienceThis work addresses the general topic of the gas entrainment from a free surface by a swirl issued from the pumping of fluids below the free surface. This phenomenon is investigated through an analytical experiment in water. A shear flow is generated between a horizontal flow and a stagnant flow. At the bottom of the test section, a vertical pumping is added to produce gas entrainment. One particularity of these experiments is the possibility to change the shape of the channel generating the inlet conditions by adding obstacles so as to trigger different conditions for the turbulent shear flow. Depending on the flow conditions, a surface swirl can be created with a sufficient strength to entrain gas below the free surface to the vertical pumping outlet. The frequency of gas entrainment occurrence is measured using visualizations of the flow. Two entrained regimes are identified for low and high Reynolds number flows the surface swirl induced gas entrainment in its core reaching the suction nozzle and bubbles issued from the breaking of the gas core are pumped