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Fundamental Issues and Canonical Flows

Behavior of Unsteady Turbulent Starting Round Jets

[+] Author and Article Information
Neerav Abani

Achates Power, Inc., 400 Sorrento Valley Boulevard, San Diego, CA 92121neerav.abani@gmail.com

Jaal B. Ghandhi

Department of Mechanical Engineering,Engine Research Center,  University of Wisconsin-Madison, 125 Engineering Research Building, 1500 Engineering Drive, Madison, WI 53706ghandhi@engr.wisc.edu

J. Fluids Eng 134(6), 061202 (Jun 11, 2012) (8 pages) doi:10.1115/1.4006385 History: Received July 05, 2011; Revised March 09, 2012; Published June 11, 2012; Online June 11, 2012

Turbulent starting jets with time-varying injection velocities were investigated using high-speed schlieren imaging. Two solenoid-controlled injectors fed a common plenum upstream of an orifice; using different upstream pressures and actuation times, injection-rate profiles with a step increase or decrease in injection velocity were tested. The behavior of the jet was found to be different depending on the direction of the injection-velocity change. A step increase in injection velocity resulted in an increased rate of penetration relative to the steady-injection case, and a larger increase in injection velocity resulted in an earlier change in the tip-penetration rate. The step-increase data were found to be collapsed by scaling the time by a convective time scale based on the tip location at the time of the injection-velocity change and the difference in the injection velocities. A sudden decrease in injection velocity to zero was found to cause a deviation from the corresponding steady-pressure case at a time that was independent of the initial jet velocity, i.e., it was independent of the magnitude of the injection-velocity change. Two models for unsteady injection from the literature were tested and some deficiencies in the models were identified.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental setup to produce variable-rate injection profiles. Helium from the tank is provided to injectors Inj1 and Inj2 through regulators R1 and R2 . The sac volume pressure was measured with the pressure transducer Px .

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Figure 2

Schematic of typical injection profiles obtained using the experimental setup

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Figure 3

Measured sac pressure for (a) case A, and (b) case B

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Figure 4

Instantaneous images of (by column) Cases A2 , A, and A5 ; each row corresponds to the time given referenced to the start of injection

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Figure 5

Jet-tip-penetration data for (a) case A, (b) case B

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Figure 6

Dimensionless jet-tip-penetration data for (a) case A, (b) case B. Color scale is the same as Fig. 5.

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Figure 7

Dimensionless jet-tip deviation data for (a) case A, (b) case B

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Figure 8

(a) Jet-tip penetration data for case C, (b) measured sac pressure data for case C

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Figure 9

(a) Dimensionless jet-tip deviation data for case C, (b) dimensionless jet-tip deviation data for case C

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Figure 10

Dimensionless jet-tip deviation data for cases A and B plotted against (a) the jet diameter-based dimensionless time, and (b) the jet tip-based dimensionless time

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Figure 11

Dimensionless jet-tip-deviation data for cases A and B plotted against the jet tip-based dimensionless time for (a) the 1D model, and (b) the effective velocity model

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Figure 12

Dimensionless jet-tip deviation data plotted against time for Case C

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