Dynamics and free-surface geometry of turbulent liquid sheets

Abstract

Turbulent liquid sheets have been proposed to protect solid structures in fusion power plants by attenuating damaging radiation. For the High-Yield Lithium-Injection Fusion Energy (HYLIFE-II) inertial fusion energy (IFE) power plant concept, arrays of molten-salt sheets form a sacrificial barrier between the fusion event and the chamber first wall while permitting target injection and ignition. Thick liquid protection can help make fusion energy commercially attractive by reducing chamber size and prolonging chamber lifetime. Establishing an experimental design database for this basic building block flow will provide valuable information about various thick liquid protection schemes and allow reactor designers to establish acceptable tolerances between chamber components. Turbulent water sheets issuing downwards into ambient air were studied experimentally at Reynolds numbers of 53,000 ??0,000 and Weber numbers of 2,900 ??,000 based on average velocity and the short dimension of the nozzle exit ( and delta). Initial conditions were quantified by the streamwise (x) and transverse (z) velocity components using laser-Doppler velocimetry just upstream of the nozzle exit. Characterization of the mean free-surface position and free-surface fluctuations, or surface ripple, and estimation of the amount of mass ejected as droplets from the free surface were quantified in the near-field (within 25 and delta of the nozzle exit). Surface ripple and mean sheet geometry were determined directly from planar laser-induced fluorescence visualizations of the free surface. The droplets due to the turbulent breakup of the jet, termed here the hydrodynamic source term, were measured using a simple collection technique to within 1 and delta of the nominal free surface of the jet. The influence of various passive flow control techniques such as removing low-momentum fluid at the free surface (boundary-layer cutting) on sheet geometry, surface ripple, and turbulent breakup were also quantified. The data obtained in this research will allow designers of inertial fusion energy systems to identify the parameter ranges necessary for successful implementation of the thick liquid wall protection system.