Experimental study of vortex-flame interaction in a gas turbine model combustor

Abstract

The interaction of a helical precessing vortex core (PVC) with turbulent swirl flames in a gas turbine model combustor is studied experimentally. The combustor is operated with air and methane at atmospheric pressure and thermal powers from 10 to 35 kW. The flow field is measured using particle image velocimetry (PIV), and the dominant unsteady vortex structures are determined using proper orthogonal decomposition. For all operating conditions, a PVC is detected in the shear layer of the inner recirculation zone (IRZ). In addition, a co-rotating helical vortex in the outer shear layer (OSL) and a central vortex originating in the exhaust tube are found. OH chemiluminescence (CL) images show that the flames are mainly stabilized in the inner shear layer (ISL), where also the PVC is located. Phase-averaged images of OH-CL show that for all conditions, a major part of heat release takes place in a helical zone that is coupled to the PVC. The mechanisms of the interaction between PVC and flame are then studied for the case P =10 kW using simultaneous PIV and OH-PLIF measurements with a repetition rate of 5 kHz. The measurements show that the PVC causes a regular sequence of flame roll-up, mixing of burned and unburned gas, and subsequent ignition of the mixture in the ISL. These effects are directly linked to the periodic vortex motions. A phase-averaged analysis of the flow field further shows that the PVC induces an unsteady lower stagnation point that is not present in the average flow field. The motion of the stagnation point is linked to the periodic precession of the PVC. Near this point burned and unburned gas collide frontally and a significant amount of heat release takes place. The flame dynamics near this point is also coupled to the PVC. In this way, a part of the reaction zone is periodically drawn from the stagnation point into the ISL, and thus serves as an ignition source for the reactions in this layer. In total, the effects in the ISL and at the stagnation point showed that the PVC plays an essential role in the stabilization mechanism of the turbulent swirl flames. In contrast to the PVC, the vortices in the OSL and near the exhaust tube have no direct effect on the flame since they are located outside the flame zone.

Imaging Flow Velocimetry with Laser Mie Scattering

“…Furthermore, Fischer et al reported time-resolved DGV measurements with a measurement rate of 100 kHz to investigate flow velocity oscillations and thermoacoustic phenomena [188,189]. High-speed PIV measurements with rates up to 10 kHz were achieved by Boxx et al [119,190], whereas volumetric, single shot PIV measurements in flames were for instance reported by Tokarev et al [191]. Flow measurements in flames are challenging due to the flame light, which disturbs the optical flow velocity measurement.…”

Prediction and control of combustion instabilities in real engines

“…Among all helical, shear later disturbances of swirled ows, the most well known is the PVC (precessing vortex core) and it plays a role in many CIs. Experiments [15,[151][152][153] as well as LES [12,14,154,155] showed that PVCs can trigger certain CI modes, disappear when the ame is ignited or appear only for certain ame positions. PVCs can even appear intermittently during CI.…”

“…Burner difference (15) where the reduced splitting strength S 0 depends only on K, called a splitting pattern factor and on ( Ŵ 1 − Ŵ 2 ), which is xed by the difference between the two burner types coupling factors. Eq.…”

Detached eddy simulation of non-reacting swirling flow in a vortex burner

“…Various studies have been conducted to investigate the effect of PVC on the stabilization of swirling flames. It was found that the PVC can enhance the fuel-air mixing [2] burned-unburned gases mixing [3] and it interacts with the thermo-acoustic oscillations of the flame [4]. PVCs are always encountered at isothermal conditions in gas turbine combustors [5][6][7][8].…”