Initial Conditions and Near-Field Dynamics in Turbulent Liquid Sheets

Abstract

High-speed liquid "curtains" have been proposed to protect solid structures in fusion energy applications. Minimizing free-surface waves and spray formation in such flows is important for effective protection in this application. In this work, free-surface waves and turbulent breakup were studied experimentally in jets of water issuing from a rectangular nozzle into ambient air at a Reynolds number of 1.2×10 5 . Laser-Doppler anemometry was used to characterize the streamwise and transverse velocity components in the nozzle for two different flow calming section designs. Planar laser-induced fluorescence was used to measure the free-stream position in the near-field of the sheet. The results suggest that transverse velocity fluctuations in the nozzle are the primary factor in determining the amplitudes of free-surface waves. Removing a small amount of low-speed fluid immediately downstream of the nozzle exit ("boundary-layer cutting") is shown to both significantly reduce free-surface waves and the amount of spray due to turbulent breakup. Overall, boundary-layer cutting appears to have the greatest benefit when used on a "well-conditioned" turbulent liquid sheet.

Turbulent theory of velocity-profile-induced jet breakup

“…It also suggests that velocity profile relaxation is relatively weak in turbulent jets as the 1 term is always essentially much larger than δ 0 /d 0 . This conclusion is consistent with the experiments of Durbin et al [31], who found that having a thin boundary layer is less important than having low turbulence for reducing jet breakup. Additionally, the overall production-dissipation ratio is controlled by more than the boundary layer thickness (or equivalently, the velocity profile), as will be discussed in the next sections.…”

“…This has not been recognized in the turbulent jet breakup literature, but it is consistent with the experiments of Durbin et al [31]. Durbin et al compared the breakup of turbulent liquid (sheet) jets produced by nozzles with and without a screen placed immediately upstream.…”