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Research Papers: Flows in Complex Systems

New Understanding of Mode Switching in the Fluidic Precessing Jet Flow

[+] Author and Article Information
Xiao Chen, Zhao F. Tian, Richard M. Kelso

School of Mechanical Engineering,
Centre for Energy Technology (CET),
The University of Adelaide,
Adelaide, SA 5005, Australia

Graham J. Nathan

School of Mechanical Engineering,
Centre for Energy Technology (CET),
The University of Adelaide,
Adelaide, SA 5005, Australia
e-mail: graham.nathan@adelaide.edu.au

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 15, 2016; final manuscript received February 1, 2017; published online April 24, 2017. Assoc. Editor: Kwang-Yong Kim.

J. Fluids Eng 139(7), 071102 (Apr 24, 2017) (10 pages) Paper No: FE-16-1516; doi: 10.1115/1.4036151 History: Received August 15, 2016; Revised February 01, 2017

We report the first systematic investigation of the phenomenon of “switching” between the two bistable axial jet (AJ) and precessing jet (PJ) flow modes in the fluidic precessing jet (FPJ) nozzle. While geometric configurations have been identified where the fractional time spent in the AJ mode is much less than that in the PJ mode, nevertheless, the phenomenon is undesirable and also remains of fundamental interest. This work was undertaken numerically using the unsteady shear stress transport (SST) model, the validation of which showed a good agreement with the experimental results. Three methods were employed in the current work to trigger the flow to switch from the AJ to the PJ modes. It is found that some asymmetry in either the inlet flow or the initial flow field is necessary to trigger the mode switching, with the time required to switch being dependent on the extent of the asymmetry. The direction and frequency of the precession were found to depend on the direction and intensity of the imposed inlet swirling, which will be conducive to the control of the FPJ flow for related industrial applications and academic research. The process with which the vortex skeleton changes within the chamber is also reported. Furthermore, both the rate of spreading and the maximum axial velocity decay of the jet within the nozzle are found to increase gradually during the switching process from the AJ to the PJ modes, consistent with the increased curvature within the local jet.

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References

Figures

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Fig. 1

Sketch of the flow through the FPJ nozzle in (a) the AJ and (b) the PJ flow modes. Adapted from Ref. [6].

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Fig. 2

Dimensions of the FPJ nozzles investigated here with (a) a contraction inlet and (b) a pipe inlet. Also shown (c) is the dimension of the computational fluid domain downstream from the FPJ nozzle.

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Fig. 3

Mesh employed to model the flow for the case in which the nozzle has smooth contraction inlet

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Fig. 4

Sketch of the alternative perturbation zones within the inflows at the pipe inlet (xi) that were used to initiate precession, i.e., Apz/Apipe = (a) 1/8, (b) 1/4, (c) 1/2, and (d) 1. Note that Apz is the area of the perturbation zone, and Apipe is the area of the pipe inlet. The magnitude of perturbation is shown in Table1.

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Fig. 5

Calculated normalized mean equivalent diameters of the precessing jet within the FPJ nozzle as a function of axial distance for three computational meshes. Refer to Fig. 2 for symbols and coordinates.

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Fig. 6

Calculated normalized mean equivalent diameters of the precessing jet within the FPJ nozzle as a function of axial distance for two time steps, i.e., 2 × 10−4 s and 2 × 10−5 s, respectively. Refer to Fig. 2 for symbols and coordinates.

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Fig. 7

Comparisons of the measured [10] and calculated normalized mean axial velocity profiles at x′/De=0.16 for the cases with (a) a pipe and (b) a contraction inlet

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Fig. 8

Cross-sectional contours of (a) the imposed axial velocity at the pipe inlet (xi) and (b) the predicted axial velocity at xo for the case Apz/Apipe = 1/2. The perturbation intensity in this example is 100%. Please note that all the cross-sectional views of data in this paper should be viewed looking upstream. (a) Nozzle inlet and (b) pipe inlet.

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Fig. 9

The predicted flow condition at xo for the case with an imposed tangential velocity component at the inlet flow to the contraction. Shown here are (a) the streamlines, (b) the profile of velocity u in x-direction, (c) the profile of velocity v in y-direction, and (d) theprofile of velocity w in z-direction at xo. The imposed tangential velocity at the inlet of the computational domain here is 30% of the axial velocity at xo.

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Fig. 10

The predicted cross-sectional axial velocity contours for the three asymmetric initial flow fields (tflow = 0.112 s, 0.180 s, and 0.223 s) chosen from the result for case B2 to trigger the mode switching for Approach C. Here tflow is the flow time after the start of the simulation. The velocity is normalized by the bulk mean axial velocity at the nozzle inlet (uo): (a) x/D = 0.175, (b) x/D = 0.6375, (c) x/D = 1.25, and (d) x/D = 2.125

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Fig. 11

The predicted cross-sectional axial vorticity contours for the three asymmetric initial flow fields (tflow = 0.112 s, 0.180 s, and 0.223 s) that were chosen from the result of case B2 to trigger the mode switching for Approach C: (a) x/D = 0.175, (b) x/D = 0.6375, (c) x/D = 1.25, and (d) x/D = 2.125

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Fig. 12

The simulated structure of the flow for case C3 at tflow = 0.023 s. (a) The streamlines within an axial-radial cross section through the flow, (b) the position of vortex core A shown with the calculated vorticity contours in cross-sectional planes, and (c) the deduced vortex skeleton.

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Fig. 13

The simulated structure of the flow for case C3 at tflow = 0.103 s. (a) The streamlines within an axial–radial cross section through the flow, (b) the positions of vortex cores A, A1, B, E1, and E2 shown with the calculated vorticity contours in cross-sectional planes, and (c) the deduced vortex skeleton.

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Fig. 14

The simulated structure of the flow for case C3 at tflow = 0.193 s. (a) The streamlines within an axial–radial cross section through the flow, (b) the positions of vortex cores A, B, E1, and E2 shown with the calculated vorticity contours in cross-sectional planes, and (c) the deduced vortex skeleton.

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Fig. 15

The simulated structure of the flow for case C3 at tflow = 0.308 s. (a) The streamlines within an axial–radial cross section through the flow, (b) the positions of vortex cores A, B, E1, E2, and F shown with the calculated vorticity contours in cross-sectional planes, and (c) the deduced vortex skeleton.

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Fig. 16

Predicted relative pressure contours on an internal cross-sectional plane (x/D = 1.375) for case C3 at tflow = 0.023 s, 0.103 s, 0.193 s, and 0.308 s. The dashed lines indicate the position of the jet, and the reference pressure is 1 atm.

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Fig. 17

Predicted axial evolution of the normalized equivalent diameter of the jet within the nozzle chamber during the transition from the AJ to the PJ modes for case C3. Refer to Fig. 2 for symbols and coordinates.

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Fig. 18

Predicted axial evolution of the inverse normalized maximum velocity of the jet within the nozzle chamber during the transition from the AJ to the PJ modes for case C3. Refer to Fig. 2 for symbols and coordinates.

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