A new measurement technique called fiber optic reflectometer (FOR) was
developed to investigate multiphase flows. The principle and setup of the FOR technique
were introduced and applied to various experiments. Based on the coherently mixed
signal between the Fresnel reflection off the fiber-liquid interface and the scattered
signal off the object, such as a gas bubble, and a solid particle, this single probe
technique is capable of simultaneously measuring the velocity of the object with a high
accuracy and the phase of the fluid. In addition, bubble diameter, velocity, and void
fraction were measured directly.
By means of a simple modification of the FOR technique, solute concentration and
refractive index change were measured with a greatly improved accuracy. This modified
technique was used for measuring of a NaCl concentration in deionized water to validate
a new normalization technique.
In the second part of this thesis, a plunging breaking wave in deep water has been
studied. Using the wave focusing method, a strong plunging breaker was generated with
accuracy in the deep water condition in a two-dimensional wave tank. It was possible to
describe the breaking process in detail using a high speed camera with a frame rate of 500 or 1000 fps.
Four kinds of experimental techniques were employed or developed to investigate
the plunging breaker. Bubble image velocimetry (BIV) and particle image velocimetry
(PIV) were used to measure the velocity fields. The velocity fields of the highly aerated
region were obtained from the BIV measurements. In addition, the modified PIV
technique is capable of measuring the velocities in the entire flow field including the
aerated region. Mean and turbulent properties were obtained by the ensemble average.
The mean velocity, mean vorticity, and mean kinetic energy were examined over the
entire flow field. In addition, the Reynolds stresses and turbulent kinetic energy were
calculated with high temporal and spatial resolutions. Free surface elevation was
obtained from wave gauge measurements. BIV and PIV images were also used to obtain
the free surface elevation and the boundary of the aerated region for more accurate
results.
The FOR technique was used to obtain the void ratio at each splash-up region.
Compressibility of the plunging breaker was considered. Mass flux, momentum flux,
kinetic energy, and Reynolds stresses at each FOR station were recalculated using the
void ratio obtained from the FOR measurements. All terms at the first splash-up region
were highly overestimated more than 100 percent unless the void ratio was applied to the
calculation of fluxes and energies. Compared with the fully developed first splash-up
region, the overestimation at the second and third splash-up was less significant.
However, most terms were overestimated by 20~30 percent when the void ratio was not
considered.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-08-8501 |
| Date | 2010 August 1900 |
| Creators | Lim, Ho Joon |
| Contributors | Chang, Kuang-An |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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