Turbulent Mixing: Optimizing Downstream Development of a Passive Scalar

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Turbulent Mixing Optimizing Downstream
Development of a Passive Scalar
Angelina Padilla Jesus Ruiz-Plancarte John
LaRue Department of Mechanical and
Aeronautical Engineering, University of
California, Davis Department of Mechanical and
Aerospace Engineering, University of California,
Irvine
Abstract Premixers with fuel injection help burn
fuel cleanly and efficiently in gas turbine
combustors. However, currently there isnt a
guide indicating the optimal diameter of the
injection ports and the spacing between them. By
systematically measuring different variations of
these two, the optimal combination that minimizes
the horizontal mixing distance can be discovered,
improving the devices efficiency. The premixer
is modeled by a wire mesh grid with heated
segments downstream of a turbulence grid in a
low-speed wind tunnel. The goal of the study is
to determine the effect of the size of the heated
segment and the separation between them on the
mixing of the heated and unheated air as a
function of downstream distance. The approach
consists of measuring the time resolved velocity
and temperature using hot wire anemometry and
small diameter resistance thermometry. However,
this part of the study focuses on ensuring the
wires are passive scalars.

• Introduction
• Model grid as a passive scalar
• Turbulence increases mixing
• Modeling premixers with fuel injection
• Heated wires Diameter of holes
• Spacing between heated wires Space
  between holes
• Grid turbulence fluid dynamics in
  premixer

• Conclusion
• Tighten wires
• Rearrange Instruments
• Use different CTA

• Preliminary Results
• Single wire with turbulence grid Noisy!

• Calibration
• Analog to Digital
• Velocity

Figure 3 Power spectra with turbulence grid.

• Experimental Design Setup
• Closed return wind tunnel
• Pitot tube Reference velocity
• Thermal Couple Reference Temperature
• Preliminary test grid 1 block

Figure 5 Modified signal of the wires with the
turbulence grid in place.
Figure 2 This setup converted digitized units to
velocities.
CTA Comparison

• Future Research
• Use grid with 52 blocks
• Heat different combinations of wires
• Velocity, length and temperature measurements

• Data Analysis
• Vortex Shedding
• Instrumentation Order
• Constant Temperature Anemometer (CTA)

Figure 4 Comparison of two different CTA signals.
Acknowledgements I would like to thank the UC
LEADS Program, Ilona Pak, Lisa Gauf and everyone
in Graduate Studies. I would especially like to
thank all of the people in the Wind Tunnel Lab,
and HP Roseville.
Figure 1 Technical drawing of grid.