A NEW LABORATORY TO STUDY HIGH-VELOCITY TWO-PHASE FLOWS

Oxygenation of water downstream hydroelectric turbines is of great importance for the preservation of the ecosystem following the dams. The admission of air into the low-pressure zones close to the turbine can be used to restore dissolved oxygen in poor quality water. In this context, a research program funded by NSERC and GE foster an Industrial Research Chair in two-phase flow based on experimental approach to characterize similar laws of aeration for the flow conditions encountered in hydroelectric power plants.

Experimental measures will focus on the quality and extent of bubbles populations. Indeed, it is the size of the bubbles and the extent of the cloud of bubbles which influence the effectiveness of an aerating system. A new laboratory named LEGH for Laboratory for Experiment with Great Height has been built to carry out this mission. Inside this laboratory, a high velocity water tunnel is being built that will be used to study flows similar to those that are found in hydroelectric turbines. It is important that the experiments be conducted by independently varying the pressure and velocity close to the typical operating conditions of a turbine. This will allow the results to be obtained over a wide range of conditions that will permit the validation of the laws of similitude that apply in such multi-phase flows. The experiments will result in the creation of a validation database for two-phase flow simulation programs and enrich the knowledge of the behavior of two-phase flows. This paper describes the design and operation of this new test loop.

A vacuum pump will allow to set the pressure level in the loop down to 0.2 bar, which is essential to develop the laws of similarity in Froude (flow velocity), Thoma (pressure level) and Reynolds ( viscosity) and thus to be able to vary these dimensionless numbers independently. Thanks to a 300 hp pump, the loop is able to reach a 2000 m³/h flow rate corresponding to a velocity of 20 m/s inside the test section. The loop operates with an air injection system. The injected air is removed by a bubble remover before the flow returns to the pump. The loop is built on three floors, to reach near cavitation pressures on the third floor (where the test section is located) and avoid cavitation pressure on the first floor where the pump is installed.