Flow field characterization in a premixed, swirling annular flow

This paper presents measurements and large eddy simulations of the flowfield in an annular, swirling, reacting flowfield. Depending upon operating conditions, the flame can exhibit four different configurations, depending upon whether it is stabilized in the vortex breakdown bubble, inner shear layer, and/or outer shear layer. Flow field characteristics such as vortex breakdown bubble length, vortex breakdown zone topology, annular jet spreading angle, and outer recirculation zone topology vary substantially between these different configurations. For the most case, the LES captures these different topological flow features and flow bifurcations, although some quantitative differences exist for the reacting cases, principally in strength of the recirculation zone and jet spreading angle. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc

Simultaneous Flame, Spray, and Flow Imaging in a High Pressure Swirl Combustor

This paper presents measurements of the simultaneous flame position and flow velocity in a high pressure, liquid fueled combustor. Liquid fuels injected in swirling flows are commonly used in gas turbines, but data collection and analysis pose a challenge in the two-phase, reacting flow field, particularly when operating at high pressure. Measurements in a liquid fueled, swirl combustor were performed using simultaneous, high speed stereo-PIV, OH-PLIF and fuel-PLIF. The OH and fuel fluorescence were separated, and regions of liquid fuel, OH and liquid fuel+OH were identified during data reduction. The measurements were taken at elevated pressures to visualize the gaseous and liquid flow field, heat release region and fuel spray distribution. This paper extends work in a prior paper by analyzing the sensitivity of the physical locations of these regimes to the processing approach. Introduction Increased knowledge of the highly dynamic, reacting flow fields encountered in gas turbine combus-tors is important to the understanding of operational limits and emissions, and how improvements in one area affect the other. High speed (kHz), spatially resolved imaging techniques, such as particle image ve-locimetry (PIV) and planar laser-induced fluorescence (PLIF), contribute to the understanding of the dynamic combustion environment. The morphology of unsteady , three dimensional swirling flows is better understood thanks to high speed PIV measurements [1], [2], while high speed PLIF measurements, primarily using OH, have enabled understanding of the flame location [3-6]. This paper extends work on this topic described in Chterev et al. [12], and the rest of this section and the following summarize several key points described there. There are a number of challenges associated with simultaneous OH-PLIF and fuel-PLIF measurements in high pressure, liquid-fueled, swirling com-bustors. OH-PLIF measurements suffer from [7-10]: (1) reduction of fluorescence yield due to increased collisional quenching (mitigated somewhat by increase in number density); (2) collisional broadening and overlap of the excitation lines; (3) fluorescence trapping due to increased optical density at high pressures ; (4) laser energy absorption by liquid fuel and higher elevated gas concentrations; (5) interference from liquid fuel and unburnt hydrocarbon fluores-cence resulting from fuel decomposition [11]. Our prior study [12] obtained simultaneous high speed ste-reoscopic PIV (sPIV), OH-PLIF and fuel-PLIF measurements in a high pressure, liquid-fueled, swirling combustor. One of the challenges addressed was the difficulty of distinguishing fuel containing regions from OH containing regions using fluorescence measurements when burning complex fuels. A specialized detection method, utilizing both temporal and spectral filtering techniques, was demonstrated. In addition, a post-processing scheme using intensity histograms was developed to provide final separation of the signals. The objective of this paper is to further consider the sensitivity of the results to the thresholds used in the separation technique

Flame and flow topologies in an annular swirling flow

This article describes an investigation of flame shapes and flow configurations in a premixed, swirl-stabilized dump combustor. High swirl, annular nozzle flows of this nature enable a variety of different flame configurations and heat release distributions with their associated flow fields. These differences are significant, since each of these configurations, in turn, has different thermoacoustic sensitivities and influences on combustor emissions, nozzle lifetime, and liner heating. These different configurations arise because multiple flame stabilization locations are present, associated with the inner and outer shear layers of the annulus, and the stagnation point of the vortex breakdown region. We present results from high-speed luminosity imaging, particle image velocimetry (PIV), and OH-planar laser induced fluorescence (PLIF) to illustrate time-averaged and instantaneous flame shapes and flow fields associated with the different configuration families. Selected cases are compared with large eddy simulations (LES). Particular emphasis is given to the distinctly different flame and flow topologies that exist in these flows, and their sensitivity to geometric (such as centerbody size and shape, combustor diameter, exhaust contraction) and operational (e.g., bulkhead temperature, preheat temperature, fuel/air ratio) parameters. We particularly emphasize the importance of the centerbody shape, and its associated impact on the structure of the central recirculating flow, as differentiating between two different families of flame shapes. Copyright © 2014 Taylor & Francis Group, LLC