Title: 5 kHz thermometry in a swirl-stabilized gas turbine model combustor using chirped probe pulse femtosecond CARS. Part 2. Analysis of swirl flame dynamics

Abstract

We have performed a detailed analysis of the temperature field in a turbulent swirl flame operating with a self-excited thermo-acoustic instability. The temperature field was measured using 5 kHz chirped-probe-pulse (CPP) femtosecond (fs) coherent anti-Stokes Raman scattering (CARS). The measurements are described in detail in the part 1 companion article. In this paper, part 2, a detailed analysis of the time-resolved temperature measurements and simultaneous pressure measurements is performed to provide insight into the dynamics and structure of the swirl-stabilized flame. Here this work is the first to capture the dynamics of the flame, flow, and coupled flow-flame processes using high-fidelity, spatially- and temporally-resolved thermometry in a flame of practical relevance. The time-averaged contour plot of the temperature field indicates that the flame is very flat and stabilizes approximately 10 mm downstream of the burner face. In this region, there are very significant temperature fluctuations indicating a very high level of unsteadiness. The temperature probability distribution functions (PDFs) are clearly bimodal in this region near the injector face. A Fourier analysis of the temperature time series revealed multiple coherent oscillatory modes. The strongest oscillation was found to be coherent and in-phase with an acoustic resonance at 314 Hz, as expectedmore » from the Rayleigh criteria for the unstable flame. An analysis of the phase-conditioned average temperature fields clearly shows an axial pumping of low-temperature reactants, which are consumed after a convective delay and result in a spike in the global heat-release rate. Continued analysis also revealed a 438 Hz oscillation that was found to correspond with the dynamics of convective transport by a helical precessing vortex core (PVC). The structure of the PVC, and its interaction with the flame, were studied based on the presence of this characteristic frequency in the power spectral densities computed throughout the flow. The precision and time-resolution of the CPP fsCARS measurements was also sufficient to enable computation of the integral time-scales as well as the PDFs of the temporal temperature gradients. A sample of state space trajectories were used to provide insight into the nature of coupling between the narrowband acoustic resonance and the broadband spectrum of turbulent flame processes.« less

Authors:

Slabaugh, Carson D. ^[1]; Dennis, Claresta N.  ^[1];

• Search DOE PAGES for author "Dennis, Claresta N."
• Search DOE PAGES for ORCID "0000-0001-5859-6343"

Boxx, Isaac ^[2]; Meier, Wolfgang ^[2]; Lucht, Robert P. ^[1]

---

+ Show Author Affiliations

1. Purdue University, West Lafayette, IN (United States)
2. German Aerospace Center (DLR), Stuttgart (Germany)

Publication Date:

Thu Jul 28 00:00:00 EDT 2016

Research Org.:

Purdue Univ., West Lafayette, IN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division (CSGB); King Abdullah University of Science and Technology; US Air Force Office of Scientific Research (AFOSR); USDOE

OSTI Identifier:

1533657

Alternate Identifier(s):

OSTI ID: 1396662

Grant/Contract Number:  

FG02-03ER15391; 1975–01; FA9550-09-1-0387

Resource Type:

Accepted Manuscript

Journal Name:

Combustion and Flame

Additional Journal Information:

Journal Volume: 173; Journal Issue: C; Journal ID: ISSN 0010-2180

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; 42 ENGINEERING; swirl flame; gas turbine; laser diagnostics; femtosecond CARS; thermometry