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

# Flame Response Mechanisms Due to Velocity Perturbations in a Lean Premixed Gas Turbine Combustor

[+] Author and Article Information
Brian Jones, Bryan D. Quay, Domenic A. Santavicca

Center for Advanced Power Generation, Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802

Jong Guen Lee1

Center for Advanced Power Generation, Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802jxl145@psu.edu

1

Corresponding author.

J. Eng. Gas Turbines Power 133(2), 021503 (Oct 27, 2010) (9 pages) doi:10.1115/1.4001996 History: Received April 12, 2010; Revised April 19, 2010; Published October 27, 2010; Online October 27, 2010

## Abstract

The response of turbulent premixed flames to inlet velocity fluctuations is studied experimentally in a lean premixed, swirl-stabilized, gas turbine combustor. Overall chemiluminescence intensity is used as a measure of the fluctuations in the flame’s global heat release rate, and hot wire anemometry is used to measure the inlet velocity fluctuations. Tests are conducted over a range of mean inlet velocities, equivalence ratios, and velocity fluctuation frequencies, while the normalized inlet velocity fluctuation $(V′/Vmean)$ is fixed at 5% to ensure linear flame response over the employed modulation frequency range. The measurements are used to calculate a flame transfer function relating the velocity fluctuation to the heat release fluctuation as a function of the velocity fluctuation frequency. At low frequency, the gain of the flame transfer function increases with increasing frequency to a peak value greater than 1. As the frequency is further increased, the gain decreases to a minimum value, followed by a second smaller peak. The frequencies at which the gain is minimum and achieves its second peak are found to depend on the convection time scale and the flame’s characteristic length scale. Phase-synchronized $CH∗$ chemiluminescence imaging is used to characterize the flame’s response to inlet velocity fluctuations. The observed flame response can be explained in terms of the interaction of two flame perturbation mechanisms, one originating at flame-anchoring point and propagating along the flame front and the other from vorticity field generated in the outer shear layer in the annular mixing section. An analysis of the phase-synchronized flame images show that when both perturbations arrive at the flame at the same time (or phase), they constructively interfere, producing the second peak observed in the gain curves. When the perturbations arrive at the flame 180 degrees out-of-phase, they destructively interfere, producing the observed minimum in the gain curve.

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## Figures

Figure 1

Schematic diagram of mixing section and combustor

Figure 2

Deconvoluted unforced flame images (CH∗ chemiluminescence) for Vmean=20 m/s, 25 m/s, and 30 m/s and ϕ=0.65,0.70,0.75,0.80

Figure 3

(a) LCOM versus equivalence ratio for various mean velocities, (b) flame’s surface area, (c) total CH∗ intensity over COM region versus mean flow velocity for various equivalence ratios, and (d) a deconvoluted image with the identified mean flame location and the COM region overlaid

Figure 4

Frequency dependence of flame length derived from forcing-period-averaged images for Vmean=25 m/s and ϕ=0.75

Figure 5

Fixed forcing V′/Vmean=5% FTF gain (top) and phase (bottom) versus frequency for Vmean=25 m/s, ϕ=0.65, 0.70, 0.75, and 0.80, and forcing frequency=80–340 Hz

Figure 6

Fixed forcing V′/Vmean=5% FTF gain (top) and phase (bottom) versus frequency for Vmean=20 m/s, 25 m/s, and 30 m/s, ϕ=0.70, and forcing frequency=80–340 Hz

Figure 7

(a) Phase-averaged chemiluminescence images during one period of inlet velocity fluctuation and (b) normalized fluctuation of flame area, COM length, total CH∗ intensity, and sum of CH∗ intensity over high intensity region (mean inlet velocity=25 m/s, mean equivalence ratio=0.75, and the forcing frequency=100 Hz)

Figure 8

(a) Phase-averaged chemiluminescence images during one period of inlet velocity fluctuation and (b) normalized fluctuation of flame area, COM length, total CH∗ intensity, and sum of CH∗ intensity over high intensity region (mean inlet velocity=25 m/s, mean equivalence ratio=0.75, and the forcing frequency=180 Hz)

Figure 9

Normalized fluctuation of flame area, COM length, total CH∗ intensity, and sum of CH∗ intensity over high intensity region (mean inlet velocity=25 m/s, mean equivalence ratio=0.75, and the forcing frequency=260 Hz)

Figure 10

fmin versus characteristic flame length (LCOM) for Vmean=20 m/s, 25 m/s, and 30 m/s, ϕ=0.65, 0.70, 0.75, and 0.80, and V′/Vmean=5%

Figure 11

Stdip versus characteristics flame length (LCOM) for Vmean=20 m/s, 25 m/s, and 30 m/s, ϕ=0.65, 0.70, 0.75, and 0.80, and V′/Vmean=5%

Figure 12

The frequency at which the second peak occurs versus fmin for Vmean=20 m/s, 25 m/s, and 30 m/s, ϕ=0.65, 0.70, 0.75, and 0.80, and V′/Vmean=5%

Figure 13

Gain of flame transfer function versus normalized frequency (f/fmin) for Vmean=20 m/s, 25 m/s, and 30 m/s, ϕ=0.65, 0.70, 0.75, and 0.80, and V′/Vmean=5%

Figure 14

Magnitude of second peak gain versus LCOM for Vmean=20 m/s, 25 m/s, and 30 m/s, ϕ=0.65, 0.70, 0.75, and 0.80, and V′/Vmean=5%

Figure 15

(a) τconv versus LCOM and (b) τconv versus τ (convection time based on LCOM and Vmean) for Vmean=20 m/s, 25 m/s, and 30 m/s, ϕ=0.65, 0.70, 0.75, and 0.80, and V′/Vmean=5%

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