Non-invasive and fast flow measurement techniques have had increasing importance
for the last decades. Scientists are looking for such quick techniques to be able to
monitor real velocities without disturbing flow itself. Ultrasound Doppler
velocimetry (UDV) being one of such techniques promising with advantages of
getting simultaneous velocity measurements from several points and of applicability
for opaque liquids as well. UDV is a technique which is still being developed for
new applications and analysis of complex flows.
In this study effect of sinusoidal oscillating, turbulent (random) and viscoelastic fluid
motions on UDV signals were investigated theoretically and experimentally.
Obtained mathematical relations for random and viscoelastic motions were utilized
to get statistics of flow and distribution of relaxation spectrum, respectively.
Analytical analysis and numerical simulation of sinusoidal oscillating flow depicted
that there is a critical value for the ratio of oscillation amplitude to oscillation
frequency for a specified set of measurement parameters of UDV. Above this critical
value UDV is not successful to determine mean flow velocity. Mathematical
relations between velocity probability density function (PDF) &ndash / velocity auto
correlation function (ACF) and UDV signal spectrum were obtained in the analysis
v
of flow with random velocity. Comparison of velocity ACFs from direct velocity
measurements and from raw in-phase (I) and quadrature (Q) signals through derived
relation, revealed that time resolution of UDV technique is not enough for getting a
good velocity ACF and thus turbulence spectrum. Using I and Q signals rather than
measured velocities to get velocity ACF, increased the time resolution in the order of
number of pulses used for getting one velocity value (Nprn).
Velocity PDF obtained from UDV spectrum was compared with the one obtained
from measured velocities with the assumption of Gaussian PDF. Both velocity PDFs
were consistent. Also some parameters of pipe turbulence from literature were
compared with the presented findings from velocity ACF obtained from I and Q
signals through derived relation. Results showed good compatibility.
In the last part of the study, complex viscosity of a linear viscoelastic fluid
mathematically related to spectrum of UDV for a pipe flow with small-amplitude
oscillating pressure field. Generalized Maxwell model was employed to express
complex viscosity terms. Zero frequency (mean flow) component of UDV spectrum
was used to obtain an equation for relaxation viscosities of generalized Maxwell
model. Results have revealed that UDV technique can also be used to probe some of
viscoelastic material functions.
In conclusion, UDV is relatively new but a promising technique for the measurement
and analysis of complex flows in a non-invasive manner.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12610727/index.pdf |
| Date | 01 July 2009 |
| Creators | Koseli, Volkan |
| Contributors | Uludag, Yusuf |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | Ph.D. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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