Assessment and Control of Primary Turbulent Breakup of Thick Liquid Sheets in IFE Reactor Cavities: The “Hydrodynamic Source Term”

Abstract

The “hydrodynamic source term” has been identified as a possible issue for thick liquid protection schemes in inertial fusion energy reactor cavities. The hydrodynamic source term refers to the ejected droplets due to the primary turbulent breakup of the jets themselves. Droplets are continuously ejected from the surface of the jets and spread about the chamber, possibly interfering with driver propagation and target injection. Published correlations are examined in order to estimate upper limits for the hydrodynamic source term in the case of the robust point design (RPD-2002), an update to the High-Yield Lithium Injection Fusion Energy II (HYLIFE-II) design. Experimental data for vertical turbulent sheets of water issuing into ambient air downward from nozzles of thickness (small dimension) δ = 1 cm and aspect ratio of 10 are compared with the empirical correlations at near-prototypical Reynolds numbers of 1.3 × 10⁵. A simple mass collection technique was developed to estimate the amount of ejected droplets from the jet surface. Boundary layer cutting is examined as a means of reducing the source term and improving surface smoothness. Alternate flow conditioning schemes are also explored to establish the relative importance of “traditional” flow straightening elements. Planar laser-induced fluorescence was used to visualize the free-surface geometry of the liquid sheet in the near-field region up to 25δ downstream of the nozzle exit. These results indicate that boundary layer cutting can suppress the hydrodynamic source term for a well-conditioned jet but is not a substitute for proper flow conditioning.