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

Experimental and Numerical Calculation of Turbulent Timescales at the Exit of an Engine Representative Combustor Simulator

[+] Author and Article Information
Charlie Koupper

Bordes 64510, France;
Toulouse 31057, France
e-mail: koupper@cerfacs.fr

Laurent Gicquel, Florent Duchaine

Toulouse 31057, France

Tommaso Bacci, Bruno Facchini, Alessio Picchi

Dipartimento di Ingegneria industriale,
University of Florence,
Florence 50139, Italy

Lorenzo Tarchi

Dipartimento di Ingegneria industriale,
University of Florence,
Florence 50139, Italy
e-mail: lorenzo.tarchi@htc.de.unifi.it

Guillaume Bonneau

Bordes 64510, France

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 15, 2015; final manuscript received July 21, 2015; published online September 1, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(2), 021503 (Sep 01, 2015) (10 pages) Paper No: GTP-15-1317; doi: 10.1115/1.4031262 History: Received July 15, 2015

To deepen the knowledge of the interaction between modern lean burn combustors and high pressure (HP) turbines, a nonreactive real scale annular trisector combustor simulator (CS) has been assembled at University of Florence (UNIFI), with the goal of investigating and characterizing the combustor aerothermal field as well as the hot streak transport toward the HP vanes. To generate hot streaks and simulate lean burn combustor behaviors, the rig is equipped with axial swirlers fed by a main air flow stream that is heated up to 531 K, while liners with effusion cooling holes are fed by air at ambient temperature. Detailed experimental investigations are then performed with the aim of characterizing the turbulence quantities at the exit of the combustion module, and specifically evaluating an integral scale of turbulence. To do so, an automatic traverse system is mounted at the exit of the CS and equipped to perform hot wire anemometry (HWA) measurements. In this paper, two-point correlations are computed from the time signal of the axial velocity giving access to an evaluation of the turbulence timescales at each measurement point. For assessment of the advanced numerical method that is large Eddy simulation (LES), the same methodology is applied to a LES prediction of the CS. Although comparisons seem relevant and easily accessible, both approaches and contexts have fundamental differences: mostly in terms of duration of the signals acquired experimentally and numerically but also with potentially different acquisition frequencies. In the exercise that aims at comparing high-order statistics and diagnostics, the specificity of comparing experimental and numerical results is comprehensively discussed. Attention is given to the importance of the acquisition frequency, intrinsic bias of having a short duration signal and influence of the investigating windows. For an adequate evaluation of the turbulent time scales, it is found that comparing experiments and numerics for high Reynolds number flows inferring small-scale phenomena requires to obey a set of rules, otherwise important errors can be made. If adequately processed, LES and HWA are found to agree well indicating the potential of LES for such problems.

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Fig. 1

Contour of the reverse flow zones predicted by LES (solid line) and PIV (dots) in the longitudinal plane of the CS (D00 case)

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Fig. 2

Mean and RMS values of axial momentum ρU¯ in the centerline of the CS exit plane (D00 case)

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Fig. 3

Schematic view of the CS: the multiperforated liner is shown by arrows, and the inner and outer feeding cavities are not shown

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Fig. 4

View of the trisector rig and detail of the swirlers and multiperforated liners

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Fig. 5

(a) R57 and (b) R56 split-fiber probes and (c) section of the quartz wire

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Fig. 6

281-points measurement mesh in plane 40

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Fig. 7

Typical autocorrelation coefficient of the axial velocity signal

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Fig. 8

Influence of the clipping value for Ruu on the evaluation of the mean turbulent timescale in plane 40

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Fig. 9

Turbulent timescales in plane 40 for D55 (looking downstream): acquisition frequency (a) f = 20 kHz, (b) f = 10 kHz, (c) f = 5 kHz, and (d) f = 2 kHz

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Fig. 10

Convergence of the calculation of tturb for all the HWA experimental signals in plane 40

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Fig. 11

tturb calculated over ΔtLES taken at different initial times of the HWA signal for an arbitrary point in plane 40

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Fig. 12

Maximum and minimum difference and standard deviation of the calculation of tturb performed on 138 windows of duration ΔtLES : (a) standard deviation σ/tturbf (%), (b) min(tturb), and (c) max(tturb)

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Fig. 13

Numerical domain of the LES of D55 configuration

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Fig. 14

Nondimensional turbulent timescale for the isothermal (a) and nonisothermal (b) LES of the D00 case

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Fig. 15

Comparison of the nondimensional turbulent timescale for HWA and LES with and without duct: (a) D55:HWA, (b) D55:LES, (c) D00:HWA, and (d) D00:LES

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Fig. 16

Nondimensional turbulent timescale at midspan in plane 40

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Fig. 17

LES prediction of the turbulent timescale tturb×Uref in the longitudinal plane of the CS (mm): (a) D55:nonisothermal LES and (b) D00:isothermal LES




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