M.S. Thesis Presentation by Justin A. Collins
Monday, September 25, 2000

(Dr. Minami Yoda, advisor)

"Velocity and Free Surface Measurements of Free Plane Jets"

Abstract

Protecting the first walls of inertial fusion energy power plant chambers is crucial for developing commercial fusion energy.   By absorbing the X-rays and ions, and attenuating the neutrons from the fusion event that may damage solid surfaces, thick liquid protection would decrease chamber size and increase the working lifetime of these power plants, thereby reducing capital costs. In all proposed liquid protection designs, the front and rear of the reactor chamber are shielded by a lattice of stationary liquid sheets with driver beams propagating through the lattice openings.  This design places stringent requirements upon the surface smoothness of the liquid sheets, since even moderate surface ripple can interfere with fuel targeting and ignition efficiency.  Minimizing ripple and its growth at the free surface of the liquid sheet is therefore a primary concern. The aim of this investigation is to quantify the effect of various design and operational parameters on the surface smoothness of vertical turbulent liquid sheets.

This experimental study used the Georgia Tech Oscillating Jet Facility and laser Doppler velocimetry (LDV) to study a vertical turbulent plane free sheet of water issuing into atmospheric pressure air. LDV was used to measure velocity profiles and turbulence intensities at various downstream locations. The nonintrusive laser-induced fluorescence (LIF) technique, which visualizes the free surface as the interface between fluorescing water and non-fluorescing air, was then used to determine the instantaneous free-surface geometry of the turbulent water sheet. The free-surface fluorescence images were recorded obliquely by a CCD camera onto videotape.  Individual videotape frames were digitized onto a PC and analyzed to identify the mean of the free-surface mean location and its standard deviation. The free surface location, which appears to be normally distributed about its mean, was found to have a standard deviation that grows logarithmically in the near field with downstream distance.  Both the maximum observed and statistically predicted maximum surface ripple were also found to grow logarithmically with distance downstream of the nozzle.  These results may lead to less stringent (and hence more feasible) design requirements for thick liquid protection.