Turbulent Liquid Sheets for Protecting IFE Reactor Chamber First Walls

Turbulent liquid sheets have been proposed to protect solid structures in fusion power plants by absorbing damaging radiation. Establishing an experimental design database for this flow would therefore be valuable in various thick liquid protection schemes. The effect of initial conditions on the flow free-surface fluctuation was studied experimentally for vertical turbulent sheets of water issuing downwards from nozzles of thickness (small dimension) = 1 - 1.5 cm into ambient air. Sheets issuing from nozzles with both two- and three-dimensional fifth-order polynomial contractions with exit aspect ratios of 6.7 and 10 were investigated at Reynolds numbers ranging from 2 × 10⁴ to 1 × 10⁵. Mean velocity and turbulence intensity profiles were measured just upstream of the nozzle exit using laser-Doppler velocimetry to quantify initial conditions. Planar laser-induced fluorescence was used to visualize the free surface geometry of the liquid sheet in the near-field region up to 25 downstream of the nozzle exit. Fluctuations of the free surface, or surface ripple, are characterized by the standard deviation in the position of the gas/liquid interface.