Two free-surface water tables are available, and both use the hydraulic analogy to simulate a two-dimensional internal or external gas flow by a free-surface waterflow. The first table was specially designed to simulate transonic and supersonic flows by operating in the sub- and supercritical regimes, at Froude numbers up to 7.
This table has a 1.4 m long, 0.9 m wide glass bottom, and provides a maximum flow rate of 26 m3/h. Optimum water depth for supercritical operation is 5 mm. Expansion waves and shocks are simulated by surface waves and hydraulic jumps. Addition of accessories makes possible the simulation of supersonic nozzle and intake flows. In case of subcritical operation, water depth can be varied in a wide range, up to about 100 mm, usual values being in the range 20 to 50 mm for the simulation of low speed internal flows. In this regime, it can also be used for surface flow visualization using soap bubbles.
The second water table is specially designed to simulate subsonic internal flows by operating in the subcritical regime, at Froude numbers lower than one. It has a 3 m long and 0.8 m wide glass bottom, and a maximum water depth of 50 mm, controlled by the position of the outlet weir. Water is supplied by a recirculating pump through six independently regulated lines. Maximum flow rate is 3 m3/h. Flows are visualized by injection of coloured dyes. Addition of accessories makes possible the study of three-dimensional water flows without a free surface.