Instantaneous Flow Structures in a Reacting Gas Turbine Combustor

Abstract

While many researchers have studied swirl-stabilized and other model gas turbine combustors, very few have investigated the flow field and combustion within a gas turbine combustor operated with realistic Jet-A fuel at elevated pressures and inlet temperatures. In this paper we present results from an investigation into the flow field and flame locations within a unique combustor furnished with an injector designed by GE Aircraft Engines. The combustor provides high optical access which has allowed the use of Particle Imaging Velocimetry to probe both instantaneous vortex and recirculation zone structures in the flow and obtain ensemble averaged profiles of pertinent turbulence quantities. Both non-reacting and reacting conditions were studied to assess the effects of a flame on the flow within the combustor. All reacting conditions were run with liquid Jet A as fuel. This too provides a more realistic configuration for it accurately captures the effects of droplet/spray combustion along with the correct heat release from a heavy hydrocarbon fuel. The location of the flame front was imaged using Planar Laser Induced Fluorescence (PLIF) of formaldehyde. This study is one of the first to apply PLIF to a gas turbine combustor running liquid Jet A. Important flow features present in the combustor have been identified and key differences between the reacting and non-reacting flow fields have been noted. With information about both the flow and flame front, structures that have not been highlighted in the past are shown to be important in the operation of the combustor. These results have indicated that the time-averaged flow field masks some very important details of the flow within a gas turbine combustor.

Unsteady Aspects of Lean Premixed Prevaporized Gas Turbine Combustors: Flame-Flame Interactions

“…For this LPP combustor an intense instability was observed at offdesign conditions, which is described in separate papers [1,2]. Movies indicate that flashback oscillations occur if the ratio of the pilot to main fuel flow rate is made sufficiently small.…”

“…1 General features of LPP combustion deduced from the measurements given next: a) flow and flame patterns, which appear to be complicated, but the relevant physics reduce to that of (b) and b) the shear layer that contains the premixed main flame, in which most of the fuel burns. [1,2] Yes No PLIF, PIV, 4.5 atm, Jet-A Seyfried et al [3] No Yes PLIF, 3.2 atm, kerosene, pilot only Meier et al [4] No Yes PLIF, 6 atm, kerosene LPP liquid fuel computations --------LP (i.e., gaseous fuel) flowfield measurements Stopper et al [9] Yes Yes PLIF, PIV, 6.0 atm, preheated Cheng et al [10], Johnson et al [11], and Littlejohn and Cheng [12] Yes No PIV, 8 atm, preheated…”

“…T HERE have been relatively few previous studies of lean premixed prevaporized (LPP) combustors that have provided images of the locations of flames, shear layers and recirculation zones [1][2][3][4]. Such measurements are needed to explain why LPP can to lead to significant reductions in NOx emissions [5][6][7][8] and to find ways to reduce the combustion instabilities that also can occur [5].…”

Experimental and computational investigations of flow dynamics in LPP combustor

“…To better quantify and qualify these instability problems, an in-depth understanding of the flow dynamics inside the combustor is of significant importance. Instantaneous vortex and shear layer vortex shedding in a LPP combustor were studied by using PIV, and both non-reacting and reacting conditions were investigated to assess the effects of the flame on the flow (13)(14)(15) . The structural characteristics in a lean premixed swirl-stabilised combustor, including the formation of recirculation zones and vortex interaction on the combustion instability, were experimentally investigated by using PIV and OH measurements (16)(17)(18) .…”

Unsteady Aspects of Lean Premixed-Prevaporized (LPP) Gas Turbine Combustors: Flame-Flame Interactions

“…There have been relatively few previous studies of lean premixed, prevaporized (LPP) combustors that have provided images of the locations of flames, shear layers and recirculation zones [1][2][3][4]. ________________________________________ operation most of the fuel is burned in a premixed flame (called the Main flame) that is anchored by a smaller non-premixed Pilot flame.…”