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Research Papers: Gas Turbines: Turbomachinery

Methods for the Extraction and Analysis of the Global Mode in Swirling Jets Undergoing Vortex Breakdown

[+] Author and Article Information
Lothar Rukes

Hermann-Föttinger-Institut,
ISTA, TU Berlin,
Berlin, Germany
e-mail: lothar.rukes@tu-berlin.de

Moritz Sieber, C. Oliver Pashereit, Kilian Oberleithner

Hermann-Föttinger-Institut,
ISTA, TU Berlin,
Berlin, Germany

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 23, 2016; final manuscript received July 2, 2016; published online September 13, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(2), 022604 (Sep 13, 2016) (10 pages) Paper No: GTP-16-1271; doi: 10.1115/1.4034315 History: Received June 23, 2016; Revised July 02, 2016

Swirling jets undergoing vortex breakdown are widely used in combustion applications, due to their ability to provide aerodynamic flame stabilization. It is well known that vortex breakdown is accompanied by a dominant coherent structure, the so-called precessing vortex core (PVC). Reports on the impact of the PVC on the combustion process range from beneficial to detrimental. In any event, efficient methods for the analysis of the PVC help to increase the benefit or reduce the penalty resulting from it. This study uses particle image velocimetry (PIV) measurements of a generic nonisothermal swirling jet to demonstrate the use of advanced data analysis techniques. In particular, the finite time Lyapunov exponent (FTLE) and the local linear stability analysis (LSA) are shown to reveal deep insight into the physical mechanisms that drive the PVC. Particularly, it is demonstrated that the PVC amplitude is strongly reduced, if heating is applied at the wavemaker of the flow. These techniques are complemented by the traditionally used proper orthogonal decomposition (POD) and spatial correlation techniques. It is demonstrated how these methods complement each other and lead to a comprehensive understanding of the PVC that lays out the path to efficient control strategies.

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Figures

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Fig. 1

Experimental facility: all dimensions are in millimeters and not drawn to scale

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Fig. 2

The evolution of time-mean flow as heating is applied: (a) axial velocity at ρ* = 1 and (b) axial velocity at ρ* = 0.54

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Fig. 3

Time-mean temperature field at at ρ* = 0.54. The dashed line indicates the contour of zero axial velocity.

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Fig. 4

Radial distance between the inner shear layer and the temperature mixing layer versus streamwise distance for ρ* = 0.95, ρ* = 0.8, and ρ* = 0.54

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Fig. 5

Integrated coherent kinetic energy versus density ratio. The filled markers correspond to density ratios of ρ* = 1, ρ* = 0.95, ρ* = 0.8, and ρ* = 0.54.

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Fig. 6

The FTLE field at isothermal conditions ρ* = 1

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Fig. 7

The FTLE field at nonisothermal conditions ρ* = 0.54

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Fig. 8

The distribution of the spatial correlation coefficient for isothermal and heated conditions

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Fig. 9

The absolute growth rate for different density ratios

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Fig. 10

Spatial structure of the global mode: (a) without the presence of a heating element and (b) with the presence of the heating element and ρ* = 1

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Fig. 11

Frequency spectra obtained with a hotwire for the baseline case and with the heating element present

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