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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Increasing the Passive Scalar Mixing Quality of Jets in Crossflow With Fluidics Actuators

[+] Author and Article Information
Arnaud Lacarelle1

Institut für Strömungsmechanik und Technische Akustik Technische  Universität Berlin, Berlin, Germanyarnaud.lacarelle@tu-berlin.de

Christian O. Paschereit

Institut für Strömungsmechanik und Technische Akustik Technische  Universität Berlin, Berlin, Germany

1

Corresponding author.

J. Eng. Gas Turbines Power 134(2), 021503 (Dec 20, 2011) (7 pages) doi:10.1115/1.4004373 History: Received April 30, 2011; Revised May 11, 2011; Published December 20, 2011; Online December 20, 2011

Jets in crossflow are widely used in the industry for homogenization or cooling tasks. Recently, pulsating jets have been investigated as a mean to increase the scalar mixing efficiency of such configurations, whether for a single jet or for an array of jets. To avoid the disadvantages of mechanically actuated flows (costs, maintenance), a new injector based on a fluidics oscillator has been designed. Four injectors have been implemented in a generical jet in crossflow configuration and the mixing efficiency of the setup was compared with the one of the same setup equiped with standard non oscillating jets. With help of high-speed concentration measurement technique, the scalar mixing quality of both setups was measured at three positions downstream of the injection plane. In all the cases tested, the fluidics injectors present a better temporal homogenization, characterized by the Danckwerts unmixedness criterion, than the standard jets. For a defined mixing quality, a decrease of the mixing length by approximately 50% can be achieved with the fluidics injectors. Furthermore, the new injectors exhibit a mixing quality which is less sensitive to variations of the jet to crossflow momentum. The flapping motion of the fluidics injectors induces a wider azimuthal spreading of the fluidics jets immediately downstream of the injection location. This increases the macro- and micro-mixing phenomea which lead then to the high gains in mixing quality. It is thus demonstrated that fluidics oscillators present a strong potential to improve the passive scalar homogenization of jet in crossflow configurations.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Jet in crossflow configuration and illustration of the fluidics oscillation plane

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Figure 2

Simplified sketch of the fluidics injector

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Figure 3

One period of oscillation of the fluidics injector recorded at x/dh = 2.2

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Figure 4

Slice of the test channel and localization of the axial measurement planes downstream of the injection location

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Figure 5

Instantaneous snapshots of the concentration C* recorded at the measurement plane x/dh=67. (Left) standard injection, (right) fluidics injection. Re=72300, J=17.7.

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Figure 6

Fluidics Strouhal number (St = fdh/wj) depending on the jet Reynolds number of the fuel injection

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Figure 7

Average concentration pictures C¯*(i ) for the standard (left) and fluidics (right) injections, recorded at x/dh = 67, J = 17.7

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Figure 8

Comparison of the probability density functions of the time averaged concentration C¯*(i) for the standard and the fluidics injections, recorded at x/dh=67, J=17.7

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Figure 9

Pictures of the RMS value of the local concentration fluctuations CRMS'*(i ) for the standard (left) and fluidics (right) injections, recorded at x/dh = 67, J = 17.7

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Figure 10

Comparison of the probability density functions of the local RMS value of the concentration fluctuations CRMS'*(i ) for the standard and the fluidics injections, recorded at x/dh = 67, J = 17.7

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Figure 11

Temporal and spatial unmixedness criteria depending on the jet to crossflow momentum recorded at x/dh = 22

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Figure 12

Temporal and spatial unmixedness criteria depending on the jet to crossflow momentum recorded at x/dh=112

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Figure 13

Temporal and spatial unmixedness criteria depending on the streamwise location for J = 17.7

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Figure 14

Relative gain in spatial unmixedness Ux,fluidics/Ux,ref depending on the axial location x/dh and for different jet to crossflow momentums J

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Figure 15

Relative gain in temporal unmixedness Ut,fluidics/Ut,ref depending on the axial location x/dh and for different jet to crossflow momentums J

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