Development of Experimental Diagnostics for
Measurement of Velocity, Temperature and Void
Fraction in Cryogenic Simulant fluid
Kayla M. Kuzmich
Department of Mechanical and Aeronautical Engineering
Abstract
The United States Air Force is engaged in the advancement of fuel systems for its liquid rockets.
Fuel systems require liquid hydrogen and oxygen to be kept at temperatures less than -238 oF and at
pressures exceeding 500 psi. Previously these systems were developed by the fabrication and testing of
multiple designs. This method is inefficient and can be streamlined with the application of
Computational Fluid Dynamics (CFD). CFD employs numerical models of the fluid flow systems
however, these codes need to be validated for accuracy to ensure their viability. Complications arise in
performing validation experiments in liquid hydrogen and oxygen due to the high costs, extremely low
fluid temperatures, high pressures, and the presence of cavitation observed in these fuel systems. Simulant
fluids are used to mimic the behavior of liquid hydrogen and oxygen and ameliorate experimentation of
these systems. The purpose of this research is to develop experimental techniques to validate CFD codes
in cryogenic simulant fluids with the presence of cavitation.
Molecular Tagging Velocimetry (MTV) is a measurement technique that utlizes molecules
uniformly mixed throughout a fluid medium. The molecules are turned into long-lived tracers by
excitation of photons at a specific wavelength. Regions of interest are “tagged” by a pulsed UV laser; then
images of the tagged patterns are captured at two instances in their lifetime. The measurement of the
Lagrangian displacement vector obtained from the images provides an estimate of the velocity vector.
The first step of this work is to determine the optimal chemical
concentration for application of MTV. The chemicals used in this application
are cyclohexanol, cyclodextrin, and bromonaphthalene. Together they form
the phosphorescent complex used in the measurements. To determine the
optimal concentration levels a beaker containing 1.0 L of water, 0.04 mole of
cyclohexanol, bromonaphthalene to saturation is mixed. The fluid is pulsed
with a single beam Nd:YAG
laser from above. A series of
100 pair images are captured
with a CCD camera with a
delay of 3.5 milliseconds
between images in the pair.
Images are then analyzed and a relation of beam
intensity versus depth is determined. The concentration
of the cyclodextrin is increased in 0.00002 mole
increments to provide a map of intensity and attenuation
versus concentration.
In the second portion of this work an acrylic tank of dimensions 12”x12”x12” houses two,
6”x6”x1/4” quartz windows on opposing sides to allow the laser access to the fluid contained within. The
fluid is a mixture of water and phosphorescent complex that of which the concentration was determined in
the first portion of this work. Also contained in the tank is a Wedge-Lock ceramic plate air diffuser, this
device creates micron sized bubbles uniformly
distributed in a column. The bubbles produced
are used to simulate cavitation found in the fuel
systems of interest.
Measurements are first done in the tank
without bubbles and with minor fluid circulation.
Analysis is done by comparing the intersections
of the two beams and their displacement after
3.5 milliseconds. Using the distance the point of
interest travels in the time between images, a
velocity field can be determined. The same
measurements were repeated for five trials of
low bubble generation. When a high bubble
generation is used the overabundance of bubbles
prohibits the penetration of the laser through the
bubble cloud and disallows any measurements to
be made. During the generation of bubbles the
tank was stirred to provide fluid motion.
No Bubble Generation
Undelayed image
3.5 millisecond delayed image
Bubble Generation
Undelayed image
3.5 millisecond delayed image
This experiment verifies that MTV can be applied to a 2phase flow to measure velocity. The constraint on using this
process is the overabundance of bubbles due to the lack of
penetration with the laser.
High Bubble Flow
Class of 2009
Aeronautical and Mechanical Engineering B.S.
REU
Douglas Bohl, Ph.D.